PH YSICS AND TE CHNOLOGY TREATMENT TECHNIQUES , MODALITIES AND NEW TECHNOLOGIES S 543

proton beams, the coarse resolution of beam modelling leads to systematicdeviations of the calculated dose in the presence of lateral density inhomo­geneities.The computing performance of the TPS for carbon ion biologicaldose optimization is remarkably good. For simple cases, the time from defin­ing the PTV to obtaining an acceptable treatment plan can be as short as onehour.For almost all treatment plans, the generated particle number distribu­tions do not yet yield optimal irradiation times.Conclusions: The TPS syngo PT Planning allows efficient generation of clin­ical treatment plans at HIT. Improvements e.g. more precise proton dose cal­culation algorithm, generation of plans of faster beam application, simplifieddata handling, straightened worldlow are currently implemented in the nextTPS version 10 be released in fall 2010.

CT ...............- ....

Physics and Technology : Treat­ment techniques, modalities andnew technologies1581 poster

A COMPARI SON OF THE DOSIMETRY AND VISIBILITY OF 1251ONCOSEED MODEL 90 11 AND 671 1 PROSTATE BRA CHYTHERA PYSOURCESG. Roberts ' , B. Al-Oaisieh " , P. Bownes '

, ST JAMES INSTITUTE OF ONCOLOGY THE LEEDS TEACHING HOSPITALSNHS TRUST, Leeds, United Kingdom

Purpose: The ' '''' I source currently used fcr prostate brachytherapy at St.James's Institute of Oncclogy is the Oncura Oncoseed model 6711 (Rapid­Strand). A new, thinner, version of this source has been developed (model9011 - ThinSeed). ThinSeeds are implanted using narrower needles, whichcould potentially reduce oedema, keeping the dose distribution closer to thatplanned. Trauma 10the urethra may also be reduced by using the narrowerneedles. The aim of this study is to assess i) how differences in dosimetrybetween the two sources would affect treatment planning and ii) what impactthe smaller size 01 the ThinSeed source would have on imaging.Mater ials: To investigate dosimetry, ten sample patients planned on theVariSeed v8.0 treatment planning system using 0.458U RapidStrand seedswere selected and anonymised. Dosimetry data for the 9011 source wastaken from Rivard (Med. Phys. 36(2) 2009). The RapidStrand sources werereplaced with ThinSeed sources of the same strength, with the source posi­tions unchanged. The plans were compared using dose-volume indices forthe prostate, urethra and rectum. The source strength was then adjusted untilthe prostate dose indices closely matched those of the original RapidStrandplans. The patients were re-planned by an experienced dosimeuist usingThinSeeds and compared to the plans in terms of dosimetry and number ofseeds and needles. To investigate visibility, images of dummy seeds of bothtypes were taken using ultrasound, fluoroscopy, CT and MRI. The ultrasound,fluoroscopy and CT images were acquired with the seeds inserted into Per­spex or tissue equivalent phantoms, which were positioned in a water tank.The MR images were acquired using tissue equivalent phantoms containings'ngle seeds. The images were analysed visually and by taking line profilesand distance measurements. The resolution of closely spaced seeds on CTimages was investigated using a purpose buill jig.Results: The ideal source strength to be used with ThinSeed sources is0.488U.This allows a similar dcse disfriouticn to 0.458U RapidStrand scurcesto be obtained. Applying the current 0.458U source strength used withRapidStrand requires extra seeds and needles, potentially increasing costand trauma. The closest available strength, 0.496U, gave acceptable clinicalplans with no change in the number of needles required. The visibility of bothseeds was similar on ultrasound, fluoroscopy and MR images. On CT imagesthe thinner seeds give reduced artefacts and better resolution. Further studyinto the vis,bility of multiple seeds on MR images would required il MR imagesare to be used for post treatment dosimetry.

Conclusions: ThinSeeds of O.496U could replace 0.458U RapidStrandseeds with no major changes in treatment planning . The use of ThinSeedswould have minimal effect on ultrasound and fluoroscopy imaging duringtreatment. However, ThinSeeds may improve seed identification on CT im­ages for post treatment dosimetry.

1582 poster

A FEA SIBILITY STUDY OF VMAT FOR THE TREATMENT OF HEADAND NECK CANCER WITH A SYNER GYS LINEAR ACCE LERATORJ. Alvarez Moret' , O. Koelbl ' , B. Dobler '

, UNIV.- KUNIKUM REGEN58URG. Depa-t rnent of Radiotherapy, Regens­burg, Germany

Purpose : VMAT is a complex treatment technique lor IMRT that may pro­vide OAR-shielding ccmparable to IMRT with better treatment efficiency. Thistechnique has been recently clinically established at our departmen t. Thepresent Sludy compares the plan quality quality and absolute dosimetr icalyand verification of VMAT (volumetric modulated arc therapy) with step-and ­shoot IMRT for head-and-neck carcinomas. The parameters gantry spacing(gs), beam-en time and number of arcs that are required to obtain an accept­ableclinically acceptable plans have been compared.Materials: Radiation therapy plansCT datasets of four patients who under­went IMRT for tumors of oral cavity, oropharynx and hypopharynx were werereplanned using VMAT. The last clinical version 3.3 of the treatment planningsystem Oncentra MasterPlan v3.3, which supports VMAT planning with onesingle are, dual arcs or multiple individual arcs for our and an Elelda Syn­ergyS linear accelerator with 6 MV photons and Beam Modulator, wereasused in the study. Calculated doses to PTV, parotids, spinal cord and brainstem were compared between IMRT and VMAT plans with single arc anddual arc with regard to plan quality and treatment efficiency. Plan quality wasassessed by calculating 099 %, 01%, and homogeneity of the PTV, andforthe parotids, 050% for the parotidswas evaluated. For spinal cord and brainstem D50% and 'he maximum doses expressed as D2% were reported . Toevaluate the plan eff iciency, the beam-on time and number 01monitor unitsBwaserc considered. For the study,T the dose prescription was set to 70 Gyinat 2 Gy daily fractions to the average of the PTV, including primary tumorand boost. The clinical IMRT plans were individually optimized using seven7 coplanar equidistant fields. For VMAT, six 6 different plans were calculatedwith following set up: one arc with gs of 40 and a maximum beam-on timeof t 50 seconds; three sets of dual arc with 20

, 40 and 60 gs respectively byallowing a maximum of 150 s per arc , two dual arc with 40 gs and a maximumof 200 sand 400 s respectively. For both tochniques the same dose-volumeobjectives were used. The VMAT plans with variable gantry spacing weredosimetrically verified using the 2D-Arrays MatriXX (IBA) to Investigate thelnnuence of increasing the gs en the ag~eement of the dose distribution toprove that by in:;reasing the GS, Ihe aqrsernent at the calculated dose withthe measured dose decreasesResults : Dosimetric results areResults of the plan comparison are givenshown for one example in !Table. 1 for one typical case. Target coverageand homogeneity as well as OAR sparing results of IMRT and all dual arcVMAT plans improved for IMRT and all dual arc VMAT plans as compared tosingle arc VMAT. The same behavior was observed in the fulfillment of thedose objectives to the OARs: dual arc and IMRT could fulfill these objectives ,while single arc was considerable inferior. In general, Iincreasing the beam­on time does not increase the plan quality. The dose verification of the IMRTand dual arc VMAT with 2°,4" and 6° GS shows that increasing the GS inthe optimization step degrades the agreement of the measurement and thecalculation using the gamma index with dose tolerances of 4% and a di~­

tance to agreement of 3mm (Pixels with < 1: IMRT: 99.89%, VMAT GS 2° :98.88%, VMAT GS 4° :98.19%, VMAT GS 6° : 92.93%). Decreasing the gsincreases the calculation time considerably and does not increase the planquality, but a belle rthe result of the dosirnetrical verification agreement hasbeen obtained(Pixels with 1 < t for 4% dose tolerance and 3mm distance of

S 544 PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

agreement: IMRT: 99.9%, VMAT gs 2°: 98.9%, VMAT gs 40:98.2%, VMATgs 6°: 92.9%).Tab. 1. Summary of the results for PTV, parotid glands, spinalcord, brain stem and normal tissue (All tissue included in the CT without thePTV). H=(D95%-D105%/Daverage)*100, V1r4g150s= VMAT with 1 rotation4° and 150 seconds, V2r4g300s= VMAT with 2 rotations 40 and 300 sec­onds, etc.

I MRT V1r:JQ V2':J Q

~=V.l.J~Q i=V2f,IQ

I SOs lOOs lOOs oIOOs

P TV

I::> ( r 1 65 .6 60.9 65 .3 65.2 63.7 65 .4 65 .6IJ,f J 72 .6 74 .2 73 .1 72 .6 73 .7 73 .3 75 .1I' 5 .4 10.4 6 .2 5 .7 8. 1 6 .1 7 .8P lSro lidIt:nI::> 'CO r) 27 .4 27.1 25 .0 24 .3 23 .5 24 .3 20 .0P lSrolidrl h io' (CO,,) 26 .5 23 .3 23 .6 23.2 24 .8 22 .4 20 .1S plnlS l

o rd.:>A v I 5 1.9 58.4 50 .0 50 .4 52 .1 49 .8 49 .7Or41n~ I

J (Gr) 49 .5 50.2 49 .6 50 .3 49 .6 50 .0 49 .2No rnwlTls sue.. ( ; 14.5 14.4 14 .5 14.5 14.7 14 .5 14.8l ( -.) 4 .9 4 .2 4 .0 4 .0 4 .3 4 .0 4 .3

Conclusions: The comparison plan comparison of the DVHs and dose distri­butions of the six plans in the four patients shows that applying only one singlearc does not achieve sufficien1 plan quality, When us;ng dual arc VMAT tl1esame or slightly better plan quality as by compared to IMRT can be achieved.It has been demonstrated, that allowing the optimizer to increase the beam­on time above 150s per arc does not improve the quality, using between 100and 150 per arc seems to be enough. The agreement of the verification in­creases when reducing the gs of the dose calculation. However, decreasingthe gs increases the calculation time considerably.

1583 poster

ACCELERATED PARTIAL BREAST IRRADIATION WITH MAM­MOSITE BRACHYTHERAPY APPLICATORJ. Garcia Ruiz-Zorrilla' , F. Clemente Gu1ierrez' ,M. A. De la Casa de Julian', L. C. Martinez Gornez ", E. Cabello

Murill0 2, R. Diaz Fuentes", A. Ferrando sanchez", J. Castro Novals '

1 HOSPITAL 12 DE OCTUBRE, Radiofisica, Madrid, Spain2 HOSPITAL 12 DEOCTUBRE, Oncologia Hadtoterapica, Madrid, Spain

Purpose: Mammosite is a HDR brachytherapy applicator specially designedfor partial breast irradiation. This work shows the description of the tech­nique, i1sImplementation in our hospital and the medical resutts In the pa­tients treated so far.Materials: The device consists of a catheter with a silicone balloon and ashaft Which is 15 cm in leng1h and 6 mm in diameter. The shaft has a mainchannel for the conduction of the source of Ir-192 and a secondary channelwith a separate exit for filling purposes. The applicator is connected to Nu­cletrons HDR Classic Microselectron through an adapter. The applicator isplaced into the lumpectomy cavity either during the surgery or several daysafter. It is inflated with saline solution and iodized contrast until the cavityis completely filled and the applicator is correctly adapted. The PTV is de­fined in the CT images as a 1 cm thick shell of breast tissue surrounding theballoon, excluding air, skin and chest wall. The treatment is delivered in 10fractions of 3.4 Gy/fraction, twice daily, with a minimum of 6 h between frac­tions. For dose prescription, six points are defined in the PTV at a distance of1 cm from the balloon surface: 4 placed on a plane, perpendicular to the axis,and 2 along the axis of the catheter. A multiple dwell position technique isused to improve the dose coverage of the PTV, compensating the decreaseddose caused by the source anisotropy.Verification and checking of the bal­loon diameter and the correct adjustment to the cavity were done along thetreatment with ultrasound scan before each session.Results: Tolerances and evaluation results for .rnplants:

v.... ~H 01 the'&.Ioon (an) ~~ry(fN'I"I) VPfVN..,(~)e.Iooft -.u._~.. (mm)

YoIr"l'lCe 1'4 ,0 SlO 'SlOG »0...... .. O · ~ I 00 .. I 00 ·26 !>6 ·}70

.....- ., 10 01 110.........O' 01 01 80

_....

The dosimetric parameters evaluated from DVHs were: percentage of volumereceiving 90% of the prescription dose (090 ), percentage of volume receiv­ing 100%, 150%, 200% of the prescription dose (V100%, VI50%, V200%respectively). The mean values of lhese parameters were: 090=99.4% (s:5.2%), V100%,=90.0% (s: 5.2%), V150%,=30.7% (s: 4.9%), V200% =5.8%(s: 2.5%), These results were compared to those of other authors and alsowith interstitial.Conclusions: This applicator provides an excellent tissue-ballon conforma­tion, making the technique easy to Implement and reproducible, achievingresults comparable to interstitial. Mammosite simplifies the implementationprocess and the treatment planning, which could improve the availability ofthe partial breast irradiation with brachytherapy.

1584 poster

ANALYSIS OF THE INTERNAL MARGINS FOR RESPIRATORY­GATED RADIOTHERAPY BY USING END-EXPIRATORY PHASEASSESSMENTS WITH A MOTION PHANTOM: INFLUENCE OF THE4-DIMENSIONAL-CT SCAN TIMEY. Yaeqashi", K. Tateoka", K. Fujimoto', K. Shima 1, J. Suzuki', T.

Nakazawa' , M. Hareyarna!1 GRADUATE SCHOOL OF MEDICINE ,SAPPORO MEDICAL UNIVERSITY,Sapporo, Japan2 KUSHIRO CITY GENERAL HOSPITAL, Kushiro, Japan

Purpose: The purpose of this study was to analyze the internal margin (1M)for respiratory-gated radiotherapy performed using 4-dimensional- CT (40­CT) imaging in the end-expiratory phase.Materials: The 4D-CT data were acquired on a GE Lightspeed RT CT scan­ner in a cine mode with a 0.7-s gantry-rotation cycle, and a 0.25-s Image­reconstruction period. Respiratory motion was recorded by a Varian respira­tory gating system with a phantom for simulating sinusoidal motion. A spherewith diameter of 25.4 mm was inserted in the sinusoidal-motion phantom.The displacement of the cranial-caudal motion ranged from 5.0 mm to 30.0mm, and the respiratory period ranged from 2_0-sto 6.0-s. After 4D-CT scan­ning, all the CT images were sorted into images for 10 respiratory phases; theend-expiration was considered as 50%; the end-inspiration was consideredas 0%; and the maximum intensity projection (MIP) image was calculated at4060% on a GE Advantage 40 application. For evaluation of the IMs during4D-CT data acquisition and the MIP imaging, we measured the differencesin the diameter of the sphere on the static images and the 50% phase imageby using the Varian Eclipse measurement tool with the same display scale.Further, the MIP image was compared with the 1M calculated from the sineperiodic function during the 4060% phases.Results: The difference between the sphere diameters in the static and 50%phase images ranged from 0.37 to 4.6 mm. The difference value increasedwith an increase in the velocity of the respiratory period. Since the phantommotion was according to a sine cycle, 1he sphere diameters under both con­di1ions should be equal in theory, but the actual values were different. Thisdifference was observed because the 1Mof the sphere appears as motion ar­tifact in the image during the scanning period of 4D-CT. We defined this 1M asIMscan. The difference between the 1Mmeasured from the MIP image andthe theoretical value calculated from tile sine function was 1.126.23 mm. Dueto the influence of IMsacn, the MIP image was overestimated with referenceto the actual displacement of the sphere.Conclusions: When the end-expiratory phase is used in respiratory gated­radiotherapy, the 1Mis already contained in the image. Therefore, if IMscanis not subtracted from the internal target volume, the internal target volumemay be overestimated.

1585 poster

ASSESSMENT OF NON-SMALL-CELL LUNG CANCER TUMORMOTION, DOSIMETRIC COVERAGE AND REGRESSION USINGFOUR-DIMENSIONAL COMPUTED TOMOGRAPHYA. Houle', C. Martel', D. Blais', P. Despres", K. Boudam', M. P

Campeau", E. Filion!, 1. T. Thuc Vu!1 CENTRE HOSPITALIER DE l.'UNIVERSITE DE MONTREAL, Department ofRadiation Oncology, Montreal, Canada

Purpose: To evaluate motion, dosimetric coverage and volumetric changesof lung cancer tumor during radiotherapy, using four-dimensional computedtomography (4DCT),Materials: Twenty-five cases were prospectively analyzed by comparingplanning 4DCT to mid-treatment 4DCT. The tumor was delineated on at least3 respiration phases representing the whole tumor motion. The second 4DCTwas registered to the first one in order to analyze dosimetric coverage of theplanning target volume (PTV), using the initial plan. The tumor motion, dosi­metric coverage and volumetric changes were compared on both scans usinga paired samples t-test.Results: Initial tumor motion ranged from 0 to 23 mm (mean ± 1a : 5 :L 5mm) in the cranial-caudal direction, 0 to 3 mm (1 ± 1 mm) in the lateral dirsction and 0 \0 8 mm (2 ± 2 mm) in the anterior-posterior oirection. No signif-

PHYSICS AND TECHNOLOG Y TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 545

icant difference in motion was observed between the first and second 4DCT.Mean cranial-eaudal motion was significantly greater (p~O.O l g ) lor lower thanfor upper lobe tumors (9 mm vs 3 mm). No significant change of the 95%isodose coverage was found betwee n the first and second scan (mean -0.6%-+- 3%), with a maximal coverage reduction of 8%. No significant variationsof mean, maximal or minimal doses in the PTV were reported. Changes ingross tumor volumes (GTVs) ranged from +11% to 71%, with a mean of -27%.GTV volumes were significantly lower (p=0.028) at the mid-treatment 4DCT.A GTV volume reduction of more than 25% was observe d in 48% of patients.Mean volume reduction was significantly greater (p=0.001) for the 10 patientswho received concomitant chemothe rapy compared to the 12 patients whodid not receive chemotherapy (44% vs 15%).Conclusions: Treatment planning using 4DCT allows internal targel vol­ume (lTV) individualization which differs from one patient to another. A mid­treatment 4DCT allows evaluation of tumor regress ion and quality assess ­ment. Globally, dosimetr ic coverage remained appropriate during treatmen t.A proportion of patients exper ienced a significant regression of tumor volume,but further studies are needed to evaluate the possibi lity of dose escalationto this volume.

1586 poster

ASSESSMENT OF REPEATABILITY OF IRRADIATION OF PATIENTSIN IMRT TECHNIQUE BA SED ON CHANG ES OF ANALYSED DOSEDISTR IBU TIONS OBTA INED US ING AN EPID SYS TEMM. kruszyna" , M. Litoborski" , S. Adamczyk!

i GREATER POLAND CANCER CENTRE, Medical Physics Department.Poznan, Pdand

Purpose: The aim of this work was to investigate changes of the dose dis­tributions which were measu red using an electronic portal imaging device(EPID) during daily treatment.Materials: Varian system was used: Clinac 2300 C/O with EPID aSSaD,Eclipse 8.2.24, OBI. In the first part of the study the dose distributions ofthe homogeneous stat ic field were collected by the EPID system for the an­thropcmorphic phantom. A region of the phantom was cnosen with a largegradie nt 01tissue den sity. Images were assembled for gantry angles a and90 degrees and the phantom was shilled in lateral, longitUdinal and verti­cal directions. In position 0 mm for all directions thereference fluency mapwas measured. Next,S patients (62 subfields) treated by IMRT techniquefor cancer of the pelvis region were chosen and fluency maps were collected(SDD 140 em) daily. Before the treatme nt session patien ts were positionedusing the OBI system: kV images were performed daily and in several daysadditionally CBCT. Shifts of displacement were applied using CBCT or kV ifCBCT was not performed. The dose dist ributions measured during the firstsession using only kV imaging were accepted as reference fluency maps foreach subfield. All measured fluency maps were compared to proper refer­ence maps using the gamma evaluation method (criteria DTA 3 mrn, DD3%, score > 95%). Score results were analysed in respect of variability ofsubfields and repeatability of irradiation of patients.Results : Results show a correlation between score and posit ion of the phan­tom. It depends on gantry angles, gradie nt of density and region of the phan­tom. The number of measured fluency maps for patients was a mean of 19for each subfield (1178 collec ted fluency maps). There is a correlation be­tween median score for each subfield and time of radiatio n and results of pre­treatment IMRT ver~ icat ion. There are some correlations between score re­suits and vertical positions because the biggest shifts of patients were lor thisdirection , For each patient there was determined the number of fluency mapswhich passed the study criteria: 98.92%, 100%, 94.26%, 89.63%, 100%. Thevariability process was analysed in graphs (Fig. 1).

Conclusions: The results confirm that positioning is very important in re­peatab ility of irradiation (phantom case) and physiological motion can havea significant influence on variabi lity of dose distributions (patient case). Thismethod is non-invasive and can be used additiona lly to check daily precisiontreatment of patients.

1587 poster

CAN 120 -M LC IMR T PL ANS BE TREATED ON AN 80-M LC LI NEARACC ELER ATOR?O. Calvo " . W. Xudong' , C. Esquivel ' , S. Stathakis " , N. Paoanlkolaou'

1 CT RC @ UT HSC AT SAN ANTONIO, Radiation Or.eology Department.San Antonio, USA

Purpose : In a clinic with multiple linear acce lerators, it may be possible todeli ver a treatment plan genenated for a planned linear accelerator on an­other accelerator with matching beam characteristics. Th is is true for mostconventional radiation therapy plans. However, an IMRT plan is optimized fora specific machine having a unique number and size of MLCs. This studyinvestigates the dosimetry and dose delivery of IMRT plans originally gener­ated for a 120-MLC linear acce lerator but tnansferred to an 80-MLC Varianlinear accele rator.Materials: Nine head-and-neck IMRT plans created on a Philips Pinnacle3

Treatment Planning System for a Varian 2100C/D 120-Millenium MLC lin­ear acce lerator are being analyzed . Each field was reconfigured for an 80­Millenium MLC Varian machine using the Varian MLC Shaper software. Thereconfigured fields were exported to the RadCalc software used for treatmentplanning dose calculation verifica tion. Once each lield was replaced with thenew MLC configurations, it was expor led to the Pinnacte" treatment planningsystem . Each plan was recalculated to deliver the same dcse 10 the sametarget volume using the same number of monitor units for the same numberof fractions. The isodose distribution and dose volume histogram (DVH) forboth plans were comp ared. In addition, the MatriXX™ 2D ion chamber arrayfrom IBA was used for absolute dose verification of each plan delivered onthe 120·MLC Varian 21OOC/D and on the 80-MLC Varian 2300 EX. Isodosedistributions, histogram and the gamma nuence were compared.Results: The MLC shaper applicator takes the average length of 1>'<0 adjacentMLCs. When two adjacent leaves greatly differ in length. gross adjustmentsare made to create an equivalent leaf for the 80-MLC plan. In addition, minorfield size adjustments are made by the Shaper program. t.ow isodose linesare comparable for both modes of delivery with adequate sparing of normaltissues and other surrounding structures. Structures close to or adjacent tothe targe l region receive higher doses. Higher isodose lines and hotspotswere larger for the 80-MLC plan as can be seen in the planning and dosevalidation (See Figure 1). Plan A is a representation of the majori ty of plansdelive red on both machines (see Figures a-c). Plan B represents a plan withsigniflcam dosimetric differen ces between delivery on a 120-MLC machineand 80-MLC machine (See Figures d-I),

[J

1= 12 " l ' III 2a n :u

U"'mb. ro . . . .. tO n

:0

10

Conclusions: The results indicated that delivery of a 120-MLC IMRT head­and-neck plan after undergo ing MLC shaping can be deli vered on an 80­MLC linac. In cases were a patient is transferred from a 120-MLC maohineto an 80-MLC linac for a small number of fractions of the total dose regime,changes in dose distribution may be insignificant. However, investigation ofeach individual plan must be evaluated, either through the TPS or IMRT dosevalidatio n before an extended or permanent transfer of a patient is made.

1588 poster

CLIN ICAL IMPLEMENTATION O F INTENSITY MODULATED AR CTHERAPY FOR HEAD AND NEC K CANCER AT A UK INSTITUTIONH. James " C. D. scrase", L. Bumstead I

I THE IPSWICH HOSPITAL NH S TRUST, Radiotherapy Physics , Ipswich ,United Kingdom2 THE IpSWICH HOSPITAL NH S TRUST, Clinical Oncology, Ipswich, UnitedKingdom

S546 PHYSICS AND TECHNOLOGY: TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

1590 poster

Physics support time savings of around 40% may be achieved with Co-60 incomparison to Ir-192.

1.0000

0],

0.1000VI0

§"X X )< "0..<:Q.lL".,"0 ""

0.0100 "0010],

.!:! ee-;;; ...JE ~

0.0010 0z

010],

1.0VI

c 0.1000 0"0

.Q ~~0 0.-=c 0], 01

.~ <> "00.8 0.0100 "0 ee

0], + 0], ...JVI .!:! ~0"0 -;;;-;;;

0.6 0.0010E

'6 0..,Za:

(a)1.2

S--lL 1.0c

.Q0c:

0.8.~="0.

2-0

0.13VI'20:(

0.4 0.0001

0 5 10 15 20Distance from source,

(b) alongsource axis(cm)

1.2 1.0000

Fig '1. Affect of anisotropy and radial dosefunction on dose curves in (a) distance

along source axis and (b) perpendicular tosource axrs

0.4 0.0001

o 5 10 m ~

Distancefrom source,perpendicular to sourceaxis(cm)

-(> Radialdose function Ir-192Radial doss function co-eoAnisotropy function co-eo

o Anisotropy function Ir-192---- Co-60 total dose- - - - - - - - Ir-192 total dose

COMMISSIONING OF FLATTENING FILTER FREE BEAMS OF ANEW LINEAR ACCELERATOR AND THE ACCURACY OF THEIRMODELLING IN ECLIPSE TREATMENT PLANNING SYSTEMS. Lang', J. Hrbacek ", J. Bocanek", S. Klock'

, UNIVERSITY HOSPITAL ZURICH,Zurich, Switzerland2 VARIAN MEDICAL SYSTEMS INTLAG, Zug, Switzerland

Conclusions: The economic and practical advantages of Co-60 over Ir-192have been demonstrated. A clinical treatment planning study has showedno significant difference in achievable dose distributions; and a theoreticalbenefit to OARs with Co-60 is dependent on the dose planning and prescrib­ing method. Over 40 treatments have now been performed using the HDRMultisource at Portsmouth.

Purpose: To provide an overview of dosimetric properties of two photonbeams and their flattening filter free (FFF) modalities of the new linear accel­erator Trilogy MX (Varian Medical Systems). To evaluate FFF beam modelling

Purpose: For the past decade a phased process of implementing new tech­nology has been used althis institution. The Varian RapidArc™intensity mod­ulated arc therapy planning and delivery systems were installed and commis­sioned in 12/2009. This study describes the planning, quality assurance (QA)and delivery of the first patient treatment in comparison with a standard fixedfield IMRT plan following pre-clinical evaluation.Materials: A 66 year old male diagnosed with T3N2b SCC of the tongue basewas selected as the first clinical IMRT arc patient. Treatment plans were cre­ated for RapidArc™and fixed field IMRT to synchronously deliver 65Gy to thetumour and affected nodes, 60Gy to the high risk elective nodes and 54Gy tothe remaining elective neck nodes in 30 fractions. The fixed field IMRT planwas intended to be used as a back up on days when the arc enabled linac wasunavailable due to routine maintenance and quality assurance (QA) or break­down. Pre-treatment QA checks were undertaken on both plans followingdepartment protocols and an estimate of whole body effective dose (WBED)to the patient from each delivery was made by irradiating thermoluminescentdosimeters (TLD) in an anthropomorphic phantom.Results: A clinically acceptable plan was produced comprising two 320 ro­tating arcs delivering 230 and 218 monitor units (MU) respectively. A 9 fixedfield IMRT treatment was planned to deliver the equivalent doses with a totalof 1417 MU's. Analysis of dose volume histogram data and the 3D dose distri­butions showed good agreement between plans for PTV coverage. Dose con­straints to organs at risk were met in both cases. Pre-treatment QA checksshowed measured point doses to be within 2% of those planned for the arctreatment and 2.5% for the 9 field IMRT treatment, within departmental toler­ances. The in-phantom TLD measurements showed a reduction in scattereddose outside the treatment volume and consequently a reduction in estimatedWBED for the arc treatment (0.37Gy vs. 0.56Gy in 30 fractions). 24 of 30 frac­tions were delivered with the arc plan and the remaining 6 fractions with the 9field IMRT. Delivery time for the arc treatment totalled 2.5 minutes comparedto 10 minutes for the IMRT. Both treatments were tolerated by the patienthowever he did appreciate the significant reduction in treatment time with thearc plan.Conclusions: This first patient treatment has demonstrated the use of a twoarc IMRT delivery to treat a highly complex volume in the head and neckterritory. Doses achieved are equivalent to those delivered with a 9 fixedfield IMRT plan. The more efficient form of delivery has resulted in a signif­icant reduction of MU's delivered per fraction and a reduction in estimatedWBED. The reduced treatment time improves the patient experience and pa­tient throughput. This clinical case has endorsed our policy to adopt IMRTarc treatments as routine for head and neck cancers.

C060 OR IR192 FOR HDR BRACHYTHERAPY? EVALUATINGSOURCE PARAMETERS, CTV & OAR DOSES, OPTIMAL PRESCRIB­ING & ECONOMICSA. Palmer', B. Mzenda'

i QUEEN ALEXANDRA HOSPITAL, Medical Physics, Portsmouth, UnitedKingdom

1589 poster

Purpose: A rigorous analysis is presented of the various clinical, physicaland economic factors to be considered when choosing between a new high­specific activity Co-50 source and the more common Ir-192 source for highdose rate (HDR) brachytherapy treatments. A study of clinical treatment plansand an evaluation of the physical and practical differences in using the twosources are undertaken.Materials: The IBt-Bebig HDR MultiSource<!3J brachytherapy unit, using Ir­192 or Co-60, was recently installed at Portsmouth, UK. Following a full sys­tem characterisation, a combination of direct measurements, simulations andclinical studies were used to compare the two available isotopes. The physi­cal properties of the sources, affecting dose distribution, were compared us­ing mathematical modelling. A 3D-image based treatment planning studycompared Co-60 and Ir-192 dose distributions and GEC-ESTRO reportingparameters for 20 gynaecological cancer patients, analysing differences incoverage of the high-risk CTV and minimising dose to organs at risk (OAR).The capital and ongoing support costs were evaluated for the two sources,for a contextual background to the clinical results.Results: Two important aspects of transit dose and dwell positioning wereidentified during commissioning of the HDR system, and re-evaluated follow­ing corrective software update. Fig. 1 shows the radial dose function differ­ence between the two sources is highly suppressed by the inverse squarelaw. The remaining deviation, apparent past 5cm from the source, 1-2%lower from Co-60, only leads to reduced OAR doses if careful considera­tion is given to dose prescribing methodology. The results obtained indicatethat the anisotropy function and efficacy of intra-applicator shielding do leadto differentiation between the two sources' dose distributions. While the dosedistribution around Co-60 and Ir-192 sources differ, the treatment planningcomparison showed clinically insignificant changes to high-risk CTV cover­age or OAR doses, when plan dwells were optimised via inverse planningtechniques. Even for identical dwell patterns, small differences in D2cc forOARs is affected more by the prescribing method, to CTV or Point A, than bythe choice of isotope. Significant cost savings may be achieved with Co-60source replacements every 4-5 years compared to Ir-192 every 3-4 months,but the capital costs of equipment and room shielding are greater for Co-60.

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 547

1592 poster

5' 05~ill.e: 04~

'0illiii 0.3~<ii0 0.2i50ill 0.11i5o

-5 0 5 10Field size [em]

Figure: Dynamic gantry vs. doserate. Different arc segment sizes

with different doserates to produce the same relat ive output ~

COMPARING ADJUVANT HEMITHORACIC RADIATION USING3D CONFORMAL (3DCRT) VS. INTENSITY MODULATED RA­DIOTHERAPY (IMRT) TECHNIQUES IN MALIGNANT PLEURALMESOTHELIOMA (MPM) PATIENTS TREATED WITH EXTRA­PLEURAL PNEUMONECTOMY (EPP)J. Chol, R. Dinniwell", M. de Perror'

1 PRINCESS MARGARET HOSPITAL, Radiation Oncology, Toronto, Canada2 TORONTO GENERAL HOSPITAL, Thoracic surgery, Toronto, Canada

in Eclipse treatment pianning system. To compare beams with Triiogy linearaccelerator.Materials: Fundamental dosimetric characteristics (depth dose curves, pro­files, output factors, surface dose, transmission and dosimetric leaf gapof high definition multileaf collimator (HDMLC)) were measured for photonbeams of nominal energy 6 MV and 10 MV (X6, X10) and their FFF modal­ity (X6FFF, X10FFF). Using the measured data, dose calculation algorithm(AAA 8.9.08) has been configured. Modelled profiles and depth dose curveswere compared with measured dataset using gamma analysis with 1 % dosedifference (DD) and 1 mm distance to agreement (DTA). In the same fash­ion, measured profiles and depth dose curves were compared for X6 beamof Trilogy MX and Trilogy.Results: Removing the flattening filter has several implications on the beamproperties: non-flatness of profiles, lowering of mean energy (TPR20/1 0: X60.667, X6FFF 0.631, Xl0 0.738, X10FFF 0.692), higher dose at the refer­ence point per current on the target (X6FFF/X6: 2.26 times, X10FFF/X10:4.03 times), higher maximal dose rate (X6 & X10 600 MUlmin, X6FFF 1400MU/min, X10FFF 2400 MU/min), higher surface dose (%dd@0.075mm: X618.9%, X6FFF 24.3%, X10 14.0%, X10FFF 19.1%), depth of maximal dosecloser to the surface (X6 14.3, X6FFF 12.1, X10 22.3. X10FFF 210 mm).sharper penumbra (up to 0.5 mm at drnax), lower out-ol-field dose. lowervariation of the output with field size (output factor for 2x2 cm2 140x40 cm2X6 0.792/1.185, X6FFF 0.802/1.137, X10 0.796/1.139, X1OFFF0.836/1.077),lower MLC transmission (X6 1.2%, X6FFF 1.0%, X10 1.4%, X10FFF 1.2%).Dosimetric leaf gap of HDMLC is 1 mm.Eclipse modelling of the 4 beamsis comparable percentage of points passing the gamma criteria of 1 mmDTA & 1% DO tor depth dose curves: X6 99.2%, X6FFF 99.5%, X10 98.3%,X10FFF 99.7%, for profiles: X6 96.9%, X6FFF 98.1%, X10 95.3%, X10FFF95.1%. Similar results were obtained for the X6 beam comparison of Trilogyand Trilogy MX. Output factors of the two machines differ with in +1- 1%.Conclusions: Basic dosimetric properties of X6, X6FFF, X10, and Xl0FFFbeam of Trilogy MX linear accelerator are summarized. Modelling of flattenedand FFF beams in Eclipse is comparable. The X6 beam of Trilogy and TrilogyMX is clinically interchangeable.

1591 poster

COMMISSIONING OF SIX VARIAN 2300 IX FOR ROTATIONAL IMRT(RAPIDARC): CHARACTERISTICS OF MACHINE AND PATIENTSPECIFIC QAU. Bjelkengren' , D. Sjostrom 1, M. Sjolin I

1 COPENHAGEN UNIVERSITY HOSP ITAL" Department of Oncology, Herlev,Denmark

Purpose: Rotational IMRT (R-IMRT) is a beam delivery technique that in­corporates the simultaneous modulation of gantry rotation, dose rate and dy­namic MLC. The objective is to deliver a complete treatment in one or twoarcs. This technique has two major advantages; dose conformity and shortover all treatment time. Having severallinacs commissioned to the same dosi­metric properties for the R-IMRT technique will lead to an increased flexibilityin the clinic since the patient is not limited for treatment on one linac. The aimof this study was to investigate the similarity in R-IMRT relevant dosimetricproperties for six linacs.Materials: Six Varian 2300 iX linacs with RapidArc capabilities were includedin the study. The linacs were evaluated using a series of tests proposed byLing et.al. for RapidArc comm issioning. These tests include positional ac­curacy of the MLC, accuracy in modulation of dose rate and gantry speed.MLC leaf speed tests are also included. Dosimetric images of these testswere acquired on the linac EPIDs and on gafchromic film. Further, clinicalcases were measured on each linac using a Delta4 diode array (Scandidos,Uppsala): one prostate plan containing a single arc and an H&N plan of twoarcs were measured on each linac. For the EPID measurements represen­tative profiles of the test were compared to an open field measurement andalso compared relative between the linacs. For the clinical cases a gammacriterion of 2% dose deviation and 2 mm DTA was used and compared totreatment planning data. Dose profiles were also compared for the clinicalcases.Results: For the EPID measurements, output for four of the linacs were within4,0 % of the open beam pro1lle. Two accelerators indicated a large devia­tion on the EPID (figure). The same test acquired with gafchromic 111m didnot show any deviation compared to an open beam profile. For the clinicalprostate case the following results passed the gamma criterion [96.3 ; 99.1],mean 98.0 % and for the H&N case; [85.8 ; 97.6], mean 92.8 %.Conclusions: The concept of having several dosirnetrically identical or nearlyidentical linacs for RapidArc delivery is possible. All but two accelerators meta criterion g<1 for 90 % of the measurement points. All accelerators passedg<1 for 90 %, with a 3 % dose deviation and 2 mm criterion. However pa­tient specific QA is very time consuming. The idea of using a general nnacperformance QA is much more time efficient. especially when using EPIDs.As the behaviour of an EPID is not always easy to interpret the use of dosi­metric film as a backup is essential. The results showed two linacs deviat­ing significantly on the dosimetric EPID image and not on the subsequentfilm measurement. This issue has not at this point been resolved and trou­bleshooting is in progress. The issue may be attributed to the EPID since filmmeasurements and the clinical test plans is wilhin what can be accepted.

Purpose: To quantify the differences between 3DCRT and IMRT in MPMpatients treated with adjuvant hemithoracic RT after EPP.Materials: A retrospective cohort review of 21 left-sided MPM patientstreated from November 2005 to February 2010 was performed (3DCRT=5and IMRT=16). Relevant dosimetric parameters for the clinical target vol­umes (CTV), and organs at risk were compared. All statistical tests were2-tailed with a significanl p-value of 0.05. The prescribed dose to the targetranged from 50 Gy (n=5), 54 Gy (n=7), and 60 Gy (n=9).Results: With respect to CTV coverage, the IMRT (compared to the 3DCRT)technique was able to achieve more homogeneous target coverage with asmaller standard deviation of the target dose (p=0.04), larger 092 (rela­tive volume receiving more than 92% prescribed target dose, p=0.01), andsmaller D108 (relative volume receiving more than 108% prescribed targetdose, p=0.006). With respect to organs at risk, both techniques providedsimilar right lung sparing. IMRT provided slightly better heart and left kidneyspar ing. 3DCRT provideo slightly better cord, liver and right kidney sparing.Conclusions: The 3DCRT technique, because it relies on boney landmarks,can sometimes result in serious geographical misses of the target. IMRTprovides significantly better target coverage with less under- and over-dosagecompared to 3DCRT but at the cost of slightly more dose to cord, liver andright kidney.

1593 poster

COMPARISON OF TREATMENT PLANS USING PHOTON BEAMSWITH AND WITHOUT FLATTENING FILTERS. Viziblova I, V. Vondracek", K. Badraoui Cuprova ", J. Vilirnovsky '

1 FAKULTNI NEMOCNICE BULOVKA, Department of Radiation Physics, Praha,Czech Republic

Purpose: The characteristics of the flattening filter free photon beams of­fer new possibilities in application in certain radiotherapy techniques (IMRT,stereotactic radiotherapy). This paper compares various lrealment plans us­ing flattened and unflattened photon beams.Materials: The calculations were made for 6 MV and 18 MV Varian Clinac2100 C/D photon beams. The Eclipse treatment planning system (using pen­cil beam convolution algorithm) was used for plan calculation. Several treat­ment plans were created for various diagnosis (prostate cancer, head andneck malignities, breast cancer, lung coin lessions). A pair of plans werecreated for each patient - one with flattened beams and one with unflattenedbeams. The results comparison was realized by DVH (PTV, OAR). Further­more lhe minimum and max imum doses in PTV and the number of usedMU were compared. The Monte Carlo treatment head model and geometricphantom model were created for independent TPS results verification. Forsimulation the EGSnrc/BEAMnrc Monte Carlo system was used. Real patientplans were converted to geometric phantom and then compared with MonteCarlo simulation.Results: Flattening filter free plans for both energies were clinically accept­able, namely for IMRT and small stereotactic fields. For larger fields there

S 548 PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

was observed less uniform PTV coverage for unflattened beams comparedto beams with flattening filter. The number of MU was much lower for unflat­tened beams. The Monte Carlo simulation results were in good agreementwith Eclipse plans.Conclusions: Flattening filter free radiotherapy can be an interesting possi­bility thanks to its lower irradiation time and dose reduction outside the treat­ment volume. The calculated treatment plans with flattened beams can berealized with unflattened beams as well. MC simulations confirmed the sameTPS accuracy for beams with and without flattening filter.

1594 poster

COMPARISON OF FOUR STEREOTACTIC PHOTON RADIO­SURGERY METHODS IN THE TREATMENT OF BRAIN TUMORSN. Khaledy", A. Arbabi", D. Sardari", M. Ghalibaftan", M. Dabaghi 2

i MAHAK HOSPITAL, Radiotherapy, Aqdasieh, Tehran, Iran Islamic Republicof2 ISLAMIC AZAD UNIVERSITY [SCIENCE AND RESEARCH BRANCH], MedicalRadiation, Tehran, Iran Islamic Republic of

Purpose: The four conventional stereotactic methods are used for treat­ment of intracranial tumors: IMRT, ARCS(SRSfT), GammaKnife(GK), Cy­berKnife(CK). Depending on the shapes and tumor sizes, the use of eachof these methods may be superior or omissions to another. Heretofore dif­ferent researches has been conducted to compare each of these differenttechniques, but these researches were the next single (only on a shape, sizeor location specific tumor, has been done) and the four methods reviewed inthis article did not reviewed together before. Following research is SummaryResults of recent twelve researches in the world.Materials: The tumor reviewed shapes include: oval, sphere, Hemisphereand irregular shape. The size of these tumors is split into three maximumdiameter of: 1-smaller than 1.5cm (small) and 2- 1.5cm-2.5cm (average) and3-bigger than 2.5cm (large). With review the dose volume histogram (DVH)and isodose and by using the treatment planning system with three dimen­sional CT image the necessary comparisons has been done. The dose uni­tormity and dose coverage in and around the tumor, as well as percentagedepth dose (PDD) in outside the tumor (healthy tissue) were investigated. Thefigure.1 indicate DVH for some stereotactic methods and some tissues

Conclusions: For small tumors (especially acoustic tumors) GK and CK,for medium tumors ARCS and IMRT and for larger tumors IMRT, overall, actbetter than other methods.

1595 poster

COMPARISON OF RAPIDARC-SUPINE AND 3D CONFORMAL­BELLY BOARD RADIATION TECHNIQUES FOR RECTAL CANCERL. Nyvang" J. B. Petersen" A. R. Jenserr'

1 AARHUS UNIVERSITY HOSPITAL, Department of Medical Physics, AarhusC, Denmark2 AARHUS UNIVERSITY HOSPITAL, Department of Oncology, Aarhus C,Denmark

Purpose: We compare the dose distribution from a 3D-conformal plan for thepatient in the prone position using a belly board, and a dynamic arc treatmentplan for the patient in the supine position. Traditionally patients in our clinichave been treated in the prone position in a belly board using the 3-field boxtechnique to minimize the dose to the small intestine. New conformal tech­niques like volumetric modulated arc techniques might give a similar sparingof the small intestines and normal tissues in general.Materials: Ten patients scheduled to receive preoperative radiotherapy with52 Gy to the CTV and 46 Gy to the internal elective lymph nodes using asimultaneously integrated boost had a therapy CT scan in prone (belly board)as well as in supine position. A conventional 3D-conformal treatment planbased on two lateral opposing fields and a posterior field was made on theprone CT-scan and a RaipdArc treatment plan was made on the supine CT­scan. The small intestine and the bladder were delineated by a senior physi­cian on both scans.Results: In the table below we summarize the mean values of the followingdescriptors: For the small intestine the V5Gy,intestine, V15Gy,intestine andV30Gy,intestine are shown. For the bladder V40Gy,bladder, V45Gy,bladderand V50Gy,bladder have been chosen. The doses given to the hottest ern"and 1 crrr' of the femur heads are named D1/2cm3,femur and D1cm3,femurrespectively. Finally we calculated the conformity index, CI95% expressingthe conformity to the 95% isodose. Except for the V5Gy,intestine and theCI95% a paired t-test show no significant difference of the means.

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Dec rip to r Prone ( 3D Supine p- valu econform al ) ( Ra pidArc)

v.; 679 em' 411 em] 0.00 1V 246 em' 32 5 em] 0 .207V 132 em' 107 em] 0. 44 5V 83 em] 102 em] 0 .3 10V 69 em] 69 em] 0 .99 1V 8 em ' 19 em] 0.0690 ", ..... , ..... .. 45 Gv 4 2 Gv 0 .0790, ....., ........ 44 Gv 41 Gv 0 .148CI9 5% 1.7 1. 3 0 .00 1

Conclusions: It seems to be possible to have similar sparing of the nor­mal tissues when the treatment technique is changed from the belly board totreatment in the supine position. One should also notice the difference in con­formal index, which is in favour of the intensity modulated plan as expected.

1596 poster

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COMPARISON OF THE PERFORMANCE AMONG TREATMENTPLANNING SYSTEMS FOR PROSTATE CANCER WITH ELEKTAVMATK. Shiraishi', A. Haga 2

, A. Sakurni", K. Nakaqawa", K. Ohtomo ", K. vooa'

1 UNIVERSITY OF TOKYO, Department of Radiology, Tokyo, Japan2 UNIVERSITY OF TOKYO, Medical Physics in Radiation Oncology, Tokyo,Japan3 KAMEDA MEDICAL CENTER, Medical Physics in Radiation Oncology,Chiba, Japan

Results: For large targets: the dose uniformity and target coverage in IMRTfor all of discussed shapes was better than another three methods. Also, thelower dose was given to healthy tissue (sensitive tissue around the tumor,such as salivary glands, nerves and cochlea, ...). For medium targets: IMRTcoverage was better than ARCS but the isodoses below 50% in CK and IMRTwere irregular compared with ARCS. That means no dose uniformity andreceiving additional doses by the healthy tissue, GK in this case was not havea good coverage. For small targets (like most acoustic and pituitary tumors):The uniformity and coverage by GK were good, and uniformity of CK wasalmost good. CK , GK and ARCS were delivered lesser dose healthy tissuecompared to with the IMRT.

Purpose: To compare the performance of treatment planning systems(TPSs) for prostate cancer with Elekta VMAT.Materials: Data set for this study consists of five prostate cancer patients atlow risk and two prostate cancer patients at high risk.Single-arc VMAT planswith D95 prescription (dose to 95% of target volume) of 76Gy in 38 frac­tions have been created using three commercial TPSs; Monaco v2.03beta(Elekta CMS), ERGO++ v1.7.2, (Elekta CMS), and Pinnacle v9.0 SmartArc(Philips). Effort was made to maintain the rectum dose volume histograms(DVHs) almost identical among the three plans. The resulting plans werecompared in terms of total monitor units (MUs), the dose homogeneity de­fined by Dmax/76Gy, the dose conformity defined by area> 2GyIPTV and

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 549

dose in organs at risk (OAR). All plans were delivered three times on EleklaSynergy. The dynamic parameters of dose rates, gantry angles, multi-leafcollimator (MLC) positions and jaw positions have been recorded with 0.25sec interval in the controller.Results: All rectum DVHs for low risk patients were similar for doses morethan 40Gy, while for high risk patients, ERGO++ provided somewhat higherdoses in rectum and also cold spots in seminal vesicles. The averaged MUswere 595, 411 and 430, and the averaged dose homogeneitys in target vol­ume were 1.08, 1.07 and 1.05 for Monaco, ERGO++ and SmartArc, respec­tively. Dose conformity for Monaco seemed to be better than those of othersystems. Delivery times were less than 3 minutes for all plans. Monaco andERGO++ needed longer delivery times, main Iy due to the creation of move­only segments. Observed errors in the gantry angle, MLC position, and jawposition were small and reproducible. They did not impact the dose distribu­tion significantly.Conclusions: All TPSs used in this study provideo satisfactory VMAT plansfor prostate cancer. The dynamic parameters were also well controlled.

1597 poster

COMPARISON OF THREE RADIOTHERAPY TECHNIQUES: RAPIDARC, IMRT, 3DRT IN BILATERAL BREAST CANCER PATIENTSK. Trela!, D. Gabrys], R. Kulik2, L. Michalecki '. G. Glowacki], L. Misztal 2

] MARIA SKLODOWSKA-CURIE MEMORIALCANCER CENTER AND INSTITUTEOF ONCOLOGY, GLiWICE BRANCH, Radiotherapy, G1iwice, Poland2 MARIA SKLODOWSKA-CURIE MEMORIALCANCER CENTER AND INSTITUTEOF ONCOLOGY, GLiWICE BRANCH,Physics and Medical Technology, Gliwice,Poland

Purpose: Radiotherapy in bilateral breast cancer patients is an challenge forclinicians during treatment planning. This difficult irradiation may be improvedwith new modern techniques of radiotherapy such as IMRT or RapidArc. Esti­mation of usefulness of RapidArc irradiation technique in comparison to IMRTand 3DRT in patients with bilateral breast cancer after breast conserving ther­apy.Materials: In our analysis we included ten bilateral breast cancer women, af­ter breast conserving surgery dedicated for the lurther elective irradiation onlyto the both breasts. Supraclavicular and axilla region were not irradiated. Allpatients were irradiated to the total dose of 50 Gy in 2 Gy per fraction, tivetimes per week. For each patients three plans were prepared: IMRT, 3DRT ­classical th ree dimensionallangential field radiotherapy, and RapidArc (Volu­metric Modulated Arc Therapy). a novel version of IMRT. We analyzed dosevolume distribution for target volume as well as for normal tissue (lung andheart), we also calculated Conformality Index (CI).Results: Mean CI for RapidArc was 0.92 (range 0.86-0.96), for IMRT 09(range 0.8-0.97) and for 3DRT 0.8 (range 0.84-0.92). Mean volume of thelung Irradiated wlth the dose 0140 Gy for RapidArc, IMRT and 3DRT were:tl.2% (range 4.5% - t3%); 5.8% (range 3.0% - 7.4%); 6% (range 4.1%­9.4%) respectively. Mean volume of both lungs irradiated with 220Gy forRapidArc, IMRT and 3DRT were: 47% (range 20% - 67%), 10.8% (range9% - 12.5%); 12.1% (range 9.t% - 15.t%) respectively. Mean volume of theheart irradiated with the dose 240Gy for RapidArc, IMRT and 3DRT weret .9% (0% - 4.7%); 0.6% (0% - 0.9%); 0.8% (O% - 1,5%) respectively.Conclusions: Independently from the applied technique, in all comparedirradiation plans for the bilateral cancer of the breast high conformality indexwere achieved. In all cases estimated volume of heart being irradiated tothe high dose,s for every technique. was low. In our analysis the essentiallimitation for RapidArc standard use in all bilateral breast cancer patients islarge volume of the lung irradiated with the dose 220Gy. Further evaluationis carried out for proper patients selection for such a treatment.

t598 poster

COMPRASION OF THREE DIMENSIONAL CONFORMAL RADIOTHERAPY AND INTENSITY MODULATED RADIOTHERAPYTECHNIQUES FOR GLIOBLASTOMA MULTIFORME TREATMENTD. Ayse'. A. Haydaroqlu '. N. Olacak", tLEre!:!'

, EGE UNIVERSITY FACULTY OF MEDICINf, Radiation Oncology, Izmir,Turkey

Purpose: The aim of this study is to compare Three Dimensional ConformalRadiotherapy (3DCRT) to use as standard technique in Glioblastoma Multi·form (GBM) treatment with Intensity Modulated Radiotherapy (IMRT) Tech­niques in terms of target coverage and dose to critical organs.Materials: t 4 patient with GBM diagnosis were treated with 3DCRT thentreatment plans were replanned with IMRT for same target volumes and criti­cal structures. 3 field in 3DCRT technique and 5 field in IMRT technique wereused. Dose constraints is determined as of 54 Gy for brain stem, optic chi­asm, optic nerves and 2,5 Gy for lens. The prescribed dose was 50 Gy to thePTV(50 Gy}, 10 Gy to the PTV(60 Gy), with a total cumulative dose of 60 Gy10the (PTV 60 Gy) both at 2 Gy per daily fraction. Dosimetric measurementswere made for quality assurance for IMRT plans.Results: When compared with the 3DCRT plans, maximum dose (Dmax)

was decreased by 14% and mean dose (Dmean) by 20.4% for brain stem,Dmax by t8% and Dmean by 39% for optic chiasm, Dmax by 30,4% andDmean by 48% for right optic nerve, Dmax by 43,5% and Dmean by 51,3%for left optic nerve, Dmax by t2,5% and Dmean 38,3% for right lens, Dmaxby 9,5 % and Dmean by 2 % for left lens in IMRT plans. When the dose tonormal brain tissue outside of the target was analyzed, Dmean is decreasedby t4,1% for Brain-GTV and 20% for Brain-PTV. However, inhomogeneitycoefficient tCll was increased by 21,2% for PTV (50 Gy) and no differencewas detected between inhomogeneity coefficient value for PTV (60 Gy).Conclusions: It is determined that the analysis of measurement values arenot statistically meaningful difference between 3DCRT and IMRT in termsof target coverage, however IMRT has better sparing of critical organs andnormal brain tissue outside of the tumor.

f599 poster

CREATING AND EDITING 3D STRUCTURE SHAPES USING IM­PLICIT SURFACESL. Hibbard', G. van der Wielen 2

, H. de Boer", T. Mutanga2, B. Heijmen2

I ELEKTACMS, Research and Development. Maryland Heights, USA2 ERASMUS MC - DANIEL DEN HOED CANCER CENTER, Radiotherapy,Rotterdam, Netherlands

Purpose: Accurate anatomy delineation in 3D requires user-drawn contoursfrom 2D cross sections. In our approach, anatomic shapes drawn in 2D viewsthat display the anatomy most clearly are joined into a 3D implicit surfacerepresentation. That shape can be modified by re-drawing the surface profilein any intersecting plane.Materials: Mixtures of interactively-drawn transverse (T), sagittal (S), andcoronal (C) plane contours are used for organ surface creation. A surfaceis taken as the O-th level set of an implicit function f(x,y,z) =0 defined by aweighted sum of radial basis functions (RBFs) centered on constraint pointsthat lie on or close to the structure surface. Weights are obtained by factoringa linear system involving the constraints alone. Surface points between theconstraints are computed by interpolating the implicit function. The resultingimplicit surfaces are smooth , continuous, and can represent complex (evendis-oint) shapes. These surfaces are insensitive to input contours' non-exactIntersections Changing constraint points' locations and/or numbers changesthe shape of the surface. Meshing the implicit surface enables it to be viewedand re-shaped. Surface creation and edit ing are implemented in a develop­ment version of a commercial interactive contouring program, CMS Foca14D.Results: Reconstruction accuracy is measured by comparing implicit sur­faces with surfaces built from expert-drawn contours. In two sets of prostatepatients-one set drawn with a strict protocol, the second a mixture of pa­tients from several clinics-bladders reconstructed with Single T,S,C contour­sets traced in tile central aspect of the organ agreed with the expert-drawntully contoured bladders w.th average Dice ooefficients 01 >0.9 and averagemean distance between nearest points in the two structures of <1.7 mm. like­wise, prostates reconstructed the same way had average Dice coefficients of>0.89 and average mean distance of <1,6 mm. These values approach thosereported for inter-observer variances.Conclusions: We have demonstrated a method to efficiently create and mod­ify 3D structures based on implicit surfaces created from a small number of2D contours in arbitrary planes. Ongoing work aims to find minimal sets ofconstraints sufficient to represent the shape and to increase the computa­tional speed.

1600 poster

CT BASED TREATMENT PLANNING OPTIMIZATION FOR PALLIA­TIVE RADIOTHERAPY IN PATIENTS WITH SPINAL METASTASES;REDUCE TOXICITY AND OPTIMIZE DOSE DISTRIBUTIONSY. van der Linden I, W.Tamminga], M. Sibma I, R. Kaatee '

I RADIOTHERAPEUTIC INSTITUTE FRIESLAND, Leeuwarden, Netherlands

Purpose: In the randomized Dutch Bone Metastasis Study on the effective­ness of palliative radiotherapy for painful bone metastases (8 Gy single frac­tion vs. 24 Gy in six fractions), 26% and 16% in a subgroup of 342 patientswith spinal metastases reported considerable nausea and vomiting, respec­tively. Depending on the expected depth of the vertebra in relation to therequired dose distribution, 27% of the patients were treated with two parallelequally weighted opposed fields with the prescribed dose in the mid plane.The remaining received a single dorsal field with the prescribed dose at afixed depth of 5 to 7 ern, resulting in higher doses to the subcutaneous tissue.Choice for a certain treatment technique was mostly institution dependent. In183 patients with lumbar metastases, even 32% were treated with two op­posed fields, and hence a relatively large volume of normal tissue receiveda high dose. In an attempt to reduce toxicity and improve dose distributionsin patients with spinal metastases, a protocol lor CT based treatment planoptimization was developed at our institution.Materials: Palliative radiotherapy for painful bone metastases is preferablydelivered at a 'one stop' visit at our institution. CT based planning is per­formed on all patients. Time between CT, planning and actual treatment is as

S 550 PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

short as possible. For the development of the treatment plan optimization pro­tocol, 12 CT scans were collected on four different vertical localizations in thespine (cervical, upper thoracic, thoracolumbar, lumbar) and three body sizes(considerable body mass, normal, slender). The minimal target dose con­straint was set at 80% of the prescribed dose. The maximum acceptable dosein the normal tissue was 115% of the prescribed dose. Using these objectivesa straightforward planning protocol was developed and tested prospectivelyin the clinic.Results: The optimal standard setting was: the isocentre and normalizationpoint fixed at the dorsal border of the vertebral body, and virtual simulationusing a initial single 10 MV dorsal field. In 75% of the CT scans, the optimaldose settings were reached. In the remaining. an anterior field was added toenhance the 80% isodose to the ventral vertebral border. Possible modifica­tions of the protocol were: if the distance of the dorsal border of the spinousprocess was < 2 cm, a 6 MV dorsal field was applied. If the maximum dose> 115%, the normalization point was changed to 4 or 3 em. Compared tothe old techniques the new treatment planning protocol resulted in straight­forward planning and better dose distributions to both the treatment target(=vertebra) and the normal tissues (=ventrally the bowel, dorsally the skinand subcutaneous tissues).Conclusions: Development and implementation of a CT based optimizationprotocol for the treatment of patients with spinal metastases is realistic, im­proves dose distributions and promotes treatment planning consistency.

1601 poster

CYBERKNIFE 'HDR-L1KE' PROSTATE CANCER TREATMENT:DOSIMETRIC CONSEQUENCES OF AN ENDO-RECTAL BALLOONR. Zinkstok", S. Aluwini", I. K. Kolkrnan-Deurloo", M. Hooqeman", E. de

Klerck' , B. Heijmen 1

i ERASMUS MEDICALCENTER ROTTERDAM, Rotterdam, Netherlands

Purpose: In our institute, 'HDR-like', hypofractionated CyberKnife (CK) treat­ment is used as an alternative tor HDR brachytherapy for low-risk prostatecancer patients. As the fraction time is relatively long compared to conven­tional EBRT and applied CTV-PTV margins are only 3 mm, it is importantto account for intra-fraction positional instability of the prostate. Due to thesometimes large and rapid (rotational) motion, the tumor tracking capabilitiesof the robotic CK cannot always fully compensate for intra-fraction motion.The additional use of an endo-rectal balloon (ERB) may improve the target­ing accuracy. Although the dosimetric impact of an ERB has been studiedextensively in the context of IMRT, the decidedly non-homogeneous HDR-likedose distribution that is employed in CK treatments requires a separate study,which is the purpose of this work.Materials: For 10 patients, CK treatment plans were developed based on CTscans with and without an air-filled ERB. A dose of 4 x 9.5 Gy was prescribedto an isodose of around 60% of Dmax, while aiming at delivery of the pre­scribed dose to at least 95% of the PTV. OAR constraints included a rectumDmax of 100%, a rectal mucosa Dmax of 75%, a bladder Dlcc of 100%,and urethra D5%, Dl0%, and D50% of 120%, of 110% and 105%, respec­tively. DVHs were generated to compare the plans without and with an ERB.Furthermore, two-dimensional dose maps of the rectum inner and outer wallwere generated to assess differences in surface dose distributions.Results: From the DVHs, no significant differences were found between thenon-ERB and ERB plans for the most important clinical parameters (PTVcoverage, rectum Dmax, bladder Dl cc and urethra D5%, Dl0% and D50%).Dose map analysis for the outer rectal wall showed that insertion of an ERBcaused the wall area receiving 20-30 Gy to decrease significantly from 12%to 6%, while it caused the area receiving 0-5 Gy to increase significantly from18% to 29%. At the same time, the maximum dose to the posterior half ofthe rectal outer and inner walls decreased significantly by (10.0±6.7) Gy and(6.3:t5.7) Gy, respectively.Conclusions: The presence of an ERB did not compromise our ability tomake HDR-like treatment plans that fulfill the tolerances for target and OARs.Moreover, the ERB plans showed a more favorable surface dose distributionfor the Inner and outer rectal walls.

1602 poster

DAILY UNCERTAINTIES IN TUMOR GEOMETRY AND POSITION:IMPACT ON LUNG SBRT ALIGNMENTJ. Tanyi', P.Gagnon" M. Fuss'

, OREGON HEALTH & SCIENCE UNIVERSITY, Portland, USA

Purpose: To investigate interfraction variations in volume and motion rangeof the GTV in stereotactic body radiotherapy (SBRT) for lung cancer usingfour-dimensional computed tomography.Materials: A simulation 4DCT scan plus 5 pretreatment 4DCTs, correspond­ing to each treatment fraction, were performed on a 16-slice CT scanner(using a Brilliance Big Bore spiral CT simulator; Philips, mc.) on each ofour SBRT patients. Each patient was immobilized in a whole-body vacuumsystem (BodyFIX, Medical Intelligence, Schwabmuenchen, Germany). Eachvacuum bag was affixed with three fiducial markers for in-room laser-based

alignment. GTVs were automatically delineated using an independent con­touring/deformable imag registration platform (MIMvista, Cleveland, OH) us­ing preset CT density thresholds on each of the 10 phases of the respiratory­correlated CTs. Interfraction variations in GTVs and excursions, defined bythe motion of the GTV centroid between full inhale and full exhale, were eval­uated. Internal target volumes {lTV} were subsequently generated from cor­responding GTVs and used to assess the geometric implications of the inter­fraction variation of target volume as a function of external marker alignmentand bony anatomy registration using the Dice similarity coefficient.Results: Mean GTV excursions at simulation in left-right (LR), anterior­posterior lAP}, and superior-inferior (SI}, directions, with a 95% confidencelevel, were 2.54, 4.96 and 9.17 mm, respectively. During treatment, the ex­cursions were 3.71, 4.86 and 9.73 mm, respectively. For the ten patientsassessed in the current study, the random variations in the GTV were 0.08ern" at full inhale and 0.13 ern" at full exchale. The systematic variationswere 3.25 em" and 3.17 ern", respectively. The mean Dice similarity coef­ficient index for current cohort was 0.49±0.19 based on fiducial alignment,and improved to 0.59±0.18 as a result of bony anatomy registration.Conclusions: While interfraction variations in GTV and target motion ex­cursion appeared to be small, interfraction tumor motion must be assessedon an individual basis to account for tumor-specific motion and deformation.Furthermore, neither fiducial marker alignment nor bony anatomy alignmentadequately predicted interfraction target motion and deformation.

1603 poster

DELIVERY OF TWO-DIMENSIONAL SPATIALLY-SLOWLY-VARYINGINTENSITY-MODULATED BEAMS BY JAWS ONLY (JO) IN ROTATE­TRANSLATE MODES. Webb', G. Poludniowski '

, ROYAL MARSDEN HOSPITAL TRUST & INSTITUTE Of CANCER RESEARCH,Joint Department of Physics, London, United Kingdom

Purpose: IMRT can be delivered by Jaws-only (JO) provided some compro­mises are accepted. It is shown how the use of a rotate-translate methodol­ogy (ROTJO), also employing only jaws, can lead to a del ivery of a prescribedtwo-dimensional intensity-modulated beam (2D 1MB)wherein the modulationis spatially slowly varying.Materials: The proposed method of IMRT delivery is by translating a long, butnarrow, JO-created slit of radiation and varying the fluence delivered alongthe path of translation. This is repeated for a number of collimator rotationangles in the range 0 - 1800

, the delivered 2D 1MBbeing the sum of such"rotate-translate" contributions. We call this 'rotate-translate jaw-only IMRT"or ROTJO IMRT. The line integrals of the prescribed 2D fluence (201MB)at each jaw-orientation constitute a Radon transform of the prescribed 2D1MB. A central-slice theorem and convolution - back projection (CBP) formulafollow in direct analogy to computed tomography (CT). Capitalising on theanalogy between rotate-translate CT, the required intensities for the compo­nent slit contributions are obtained via a CBP. In ROTJO, the measured ray­projections of Hay CT are replaced by line integrals through a prescribed 2D1MB. Further, in ROTJO, the mathematical process of the back projection of aconvolved x-ray projection in x-ray CT is replaced by the physical laying downof fluence by a slit of radiation. There is a crucial difference, namely that someconvolved projections of x-ray linear attenuation coefficient in x-ray CT haveto be negative in order to reconstruct a CT scan. However, of course, fluencecannot be negative and these contributions are set to zero here. This wouldresult in discrepancies between the delivered and prescribed 2D 1MBand afurther iterative stage is required. Planning proceeded as follows. To obtainthe required fluences of the translating slit: (i) Projections of the 2D bixel flu­ences (2D 1MB) were formed for a set of "head-twist" orientations in 0-180°(ii) The projections were convolved with a Ram-Lak filter to create convolvedprojections. (iii) Negative terms in the convolved projections were set to zero.(iv) The zero-adjusted convolved projections were further iteratively adjustedby adding and subtracting "grains" of (convolved) projected fluence until thedelivered 2D 1MBmatched the prescribed 2D 1MBIn a least-squares sense.Positivity of (convolved) adjusted projections was maintained throughout.

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES , MODALITIES AND NEW TECHNOLOGIES S 551

Results : II was found that with just 6 orientations a smoothly-varying pre­scribed 2D 1MB could be delivered with high accuracy and typically with amonitor-unit efficiency of about 5%.Conclusions: For prescribed 2D IMBs with few high-frequency componentsthis method could complement the traditional JO method for highly variableprescribed 20 IMBs.

1604 poster

DOSE ESCALATION USING SIMULTANEOUS INTEGRATE D BOOSTFOR GLIOBLASTOMA MULTIFORME : A COMPARATIVE PLANNIN GSTUDY OF VOLUMETRIC MODULATED ARC RADIOTHERAPY WITHFIXED FIELD INTENSITY MODULATED RADIOTHERAPYT. V. Ajithkuma r" , S. Grayd on", T. Roques' . A. Williams2

, A. Vinall2 , J .

Tomes''1 NOR FOLK AND NORWICH UNIVERSITY HOSPITAL NHS TRUST, Departmentof Oncology, Norwich, United Kingdom2 NORFOLK AND NORWICH UNIVERSITY HOSPITAL NHS TRUST, Departmentof Medical Physics, Norwich, United Kingdom3 NORFOLK AND NORWICH UNIVERSITY HOSPITAL NHS TRUST. Departmentof Radiotherapy. Norwich. United Kingdom

Purpose: The recently reported RTOG study 98-03 has shown a clinical ben­efit with dose escalation in Glioblastoma multitorrne (GBM). Simultaneousinlegrated boost (SIB) using intensity modulated radiotherapy (IMRT) is anattractive option to delivery dose escalation in GBM without increasing treat­ment time. In this study, we compared conventional 7-field IMRT with singleand two-arc volumetric arc therapy (VMAT) to evaluate the optimal method todeliver dose escalation in GBM.Mater ials: Image data sets of 7 previously treated patiems were used. Theplanning treatment volumes (PTVs) were outlined using the definition as inthe RTOG 98-03 study. The PTV receiving a total dose of 84 Gy equivalent at2 Gy per fraction (PTV 84 Gy2) was defined as the contrast enhancing resid­ual tumour with 3 mm margin, and the PTV 72 Gy2 as the contrast enhancingresidual tumour and the resection cavity with 3 mm margin. A 1.5 em marginwas added to the contrast enhancing residual tumour and the resection cavityto define CTV60 and a further 3mm margin was added to the edited CTV60to define the PTV60. The organs at risk (OAR) oullined included optic appa­ratus, brain stem, eyes, lens. pituitary and normal Drain minus PTV3. Planswere compared in terms of PTV coverage. OAR dose and number of monitorunits to deliver 2 Gy to PTV60Results : The conformity index of PTV60, PTV 72 Gy2 and PTV 84 Gy2 werecomparable in all the plans. There was no relative advantage with any plansin terms of OAR sparing (table.1). Both the VMAT plans resulted in reducednumber of MU compared with IMRT plan. Single Arc plan resulted in 17%less (p; 0.58) and two-arc plan 21% less (p;O.OOl) MU compared with IMRTplan.

'I;p~Parameters IMRT 1- Ar c 2 Arc

( Avera ge value of 7 cases) VMA.T VMII.T

Conformit y inde x I IFT\ I E4 G~':< 1 O.?? C.9'j 0 :3I-' r~" 72 G~·;: 1 0 78

IPW 60

~.0. 96 0. 98 0 .97

!O,.~ans at ri'ik; B"Sln sfem

ll,ll~X t . ,) 45 .':. .,; , +6 .;- C:;.Eo Nean (!:iY) 22 .3 232 23 0. 99

Optic ct:!i~~

Om.... (W) 34 . 1 36.6 36 0 .9 7D Me a.l"'l (~ 28 .4 30 .S 30 0.'38

RIght cp tJr. nerveOIU..-(G, ) 25 .5 ~' 7 7 26 .7 0 .9 7C' M~ il r l ( Ci~ 17 .3 ] 8.3 11::. ,:- ).913

Left or:,tJ <: '~ r, e

OW..,,(!W 3 1 30.b ) 1. 7 0 .99O Me Lln (~ 2» .2 19 15 .2 0.75

Right eyeQJ1lt3~(~L : 5 ~ 15.2 4- ) .C:JJo t!lear ~G1) r.« 7 2 ; (I . ~::'

Left ey~

Qro~! C\.iV 19.8 l E- .2 14 .7 0.5 3o Me.n CGY) 9.2 7.S 7.3 0. 64

P1tultitrt

Pm!' (W ) 33 .3 34 . 1 33 .6 0 .99o Nean mll. ) 28. 6- 29 Z 28 .8 0 .9 9

F.Il2t"t e -rsQl!m CGV) 6.3 5 4. 9 0 .53o Mean (~¥) s.i 44 4 .4 0 .7 1

Lefttens~::;(\jiJ .:.. : '0. 1 C.72j veen ~G:l ) 4 ,9 .:.;: ...t,7 c.ss

Who le brain minus PT\/W0Jl1R!(!W 63.9 64 .9 (13,7 0 ,74D Metll l (~y) 17 .1 17 l7 0, 99

MU to d.~\ive r 2 .fu: ~. 540 513 0. 17

Conclusio ns: Compared with 7 field IMfl T, two-arc VMAT achieved equalPTV and OAR sparing using fewer monitor units, suggesting two-arc VMATis the optimal technique to deliver dose escalation with SIB in GBM. Furtherstudies are being planning with the addition of more image data. to confirm

the optimal radiotherapy technique for a proposed study of dose escalationwith SIB using IMRT in GBM.

1605 poster

DOSES OUTSIDE THERAPEUTIC VOLUME FOR IMRT AND STATICFIELDS - STUDY FOR HEAD AND NECK CANCER SM. Peszynskai J. Malicki2

1 M. KOPERNIK MEMORIAL REGIONAL SPECIALIZED HOSPITAL, Locz,Poland2 GREAT POLANDCANCER CENTRE, Poznan, Poland

Purpose: In recent years for head and neck tumours treatment techniqueshave changed from static fields to IMRT. This is due to better uniformity ofdose in PTV and better sparing of organs at risk (OARs). However, there arestiIJ not sufficient data on doses in regions distant from the PTV if using IMRTin place oi static fields. We compared tho doses in OARs distant from thePTV for IMRT and 3DCRT (static fields).Malerial s: For 12 consecutive patients who underwent IMRT/SIB with headand neck cancers the alternative treatment plans were retrospectively elabo­rated for 3DCRT. Calculations were done using Eclipse and AAA algorithm.Techniques were: for IMRT/SIB with 6 MV photons: cT3-4NO-2: ptv154 Gy.ptv260 Gy in 30 fractions; cTI -2NO: ptv154 Gy, ptv269.96 Gy in 33 fractionsor ptv154 Gy, ptv267.5 Gy in 30 fractions. For static fields 3D-CRT with 6 and15 MV: cT3-4NO-2: t st phase: ptv150 Gy. 2nd phase: ptv260 Gy at 2 Gy:cTl-2NO: tst phase: ptv150 Gy at2 Gy, 2nd phase: ptv270 Gy at 2 Gy. Twosituations were considered for dose points outside the PTV: (1) which lay out­side but near the beam border (inside the calculation range of the algorithm)and (2) points located outside the range of the algorithm.Tocompare doses anew index was elaborated which accoonted fer the large dose gradient withinthe checked OAR For each OAR 9 sub-volumes were derived representing90% to 10% of OAR, in steps of 10%. For each sub-volume mean dose wascalculated and the index value for the OAR was the average of an 9 means.Doses were statistically evaluated for: cerebellum, brain-stem, mandible andthyroid gland.Results : For all OARs no significant dillerences in doses were detected asassociated with the choice of IMRT or 3DCRT. The obtained indices in brain­stem for all patients showed a similar distribution regardless of techniqueused. For thyroid gland for 5:12 cases using IMRT the index was reducedby 0.4-6.5 Gy in comparison to 3DCRT. For mandible data fell into 2 oppositesubgroups 01 similar sizes: lor the 1st the average index was by 6.7 Gy lowerfer IMRT than 3DCRT and for the 2nd by 8.7 Gy higher. For cerebellum for12/12 cases the index for IMRTwas higher than for 3DCRTby 2.57-14.00 Gy,which indicated a consis tent trend.Conclusions: The group at 12 patients was too small to detect differencesat the required level of significance. However. a tendency has been observedfor cerebellum showing that slightly higher doses were absorbed using IMRTthan 3DCRT.

1606 poster

DOSIMETRIC COMPARISON BETW EEN 2 CLASS SOLUTIONS FORHEAD AND NECK CANCER IRRADIATIONL.Dim GOmez' . J. M. Richarte Reina2

• J . Lupiani Casteltancs" , E.

Gonzalez Calvo' , I. Castro Ramirez2 , L. Gutierrez Bayard1 , D. De lasPcnas" C. Salas Buzon ! , V. Diaz Dlaz I , I. Villanego Beltran' , E. AlonsoRedondo '1 HOSPITAL UNIVERSITARIO PUERTA DEL MAR, Servicio de OncologiaRadioterapica, Cadiz, Spain2 HOSPITAL UNIVERSITARI O PUERTA DEI MAR, Servicio de Radiofisica yProtecci6n Hadiolcqica, Cadiz, Spain

Purpose : For the treatment of head and neck ( H&N) tumours is requiredhigh doses of radiation to planning target volume (PTV). In locally advancedcarcinoma. this volume can reaches from the skull-base to supraclavicularchains. We know that to achieve eradication of microscopic disease is due toa dose of at least 50Gy increasing in tumour and areas of subclinical diseaseto 72·74Gy lor total control. In these cases, they have raised 2 main problems.First, the different densities of the anatomical structures make very difficult toobtain a homogeneous dose plan. Second. 1heproximity of multiple organsat risk (OAR) with high variability of morbidities if they exceed their tolerancelevels. To overcome these difficulties, we have used different techniques andthe comparison between 2 of them in our centre is the aim of our study.Mater ials Eight patients were selected diagnosed of locally advanced H&Ncarcinoma with and without involvement of supraclavicular chains. We useda multileaf linear accelerator model Primus and a system of treatment plan­ning PCRT 3D. In the first plan, we use an anteroposterior (AP) beam forsupraclawcular chains with matching in the first phase and photons and elec­trons beams in spinal cord reduction. The other plan covers the volume withphotons beams in 6 directions: AP, laterals and posterior oblique (PO). (APand PO do not include spinal cord) Dose prescription: 50Gy, 2Gy/ f, 5 daysa week. Our condition for comparison and acceptance of treatment was seta hmlt dose of 45 Gy to the spinal cord in any point. We also studied other

S 552 P HYSICS AND TECHNOLOGY : TREATMENT TECHNIQUES , MODALITIES AND NEW TECHNOLOGIES

OAR, with special interest in parotids.Results: With the 6 fields plan. we use only one isocenter, and then theposi tioning is more accurate and reproducible. We get better coverage withthe techn ique that avoids use of electrons, with 4 to 10 % of improvement ,and more homogeneous treatment plans. There are not differences in OAReffects .Conclus ions : We believe that the 6-fields technique is better for Clinical prac­lise due to the greater coverage of PTVs althoug h dose in OAR is not affected ,and the positioning is more reliable in every treatment day.

1607 poster

DOS IMETRIC EVALUATION OF A 3D DOSIMETER FOR HELICALTOMOTHERAPYM. Paiuscc " , V. DErrico !, E. Cagni ' , A. Bolli ' , D. Larnoert ini" , L. Scotti'' ,

A. Gianlornbard o" , M. lori ', AZIENDA OSPEDALIERA S. MARIA NOVA, Medical Physics, Reggio Emilia,Italy2 AZIENDAOSPEDALIERA S. MARIA NOVA, Radioterap ia, Reggio Emilia , Italy3 TECNOLOGIE AVANZATE TA, Torino, Italy

Pur pose: The aim of this work is to assess the performance of the 3D diodedosimet er compared to a 2D dosim eter for helical tomot herapy pre-treatmentverification.Materials : The 3D dos imeter ArcCHEC K (Sun Nuclear, Melbourne, FL) hasbeen developed for an efficient quality assurance of IMRT especially for ro­tationa l therapy. It has a cylindrical detector geometry with 1386 diodes at aphysical dept h of 2.9 cm. The basic characteristics : linearity, reproducibility ,dose rate dependence and absolute calibration accuracy were tested at theaccelerator with a 6 MV photon beam. The dosimeter 's sensitivity to gantryrotation offse t as well as setup errors was evaluated for clinical plans withdifferent modul ation factor , pitch and leaf open time. The measu red doseswere compared in term of percentage dose difference(DD%). To investigateif the three dimensionality is a valuable addition in the QA procedure, differ­ent sinograms were created to del iver the same dose in a small inner part ofthe phanto m with different doses per projection s. Data were collected withthe ion chamber in the central holder of the arcCHECK. The same plans andleaves patterns were measured with the 2D array Seven29 and the OCtaviusphantom, the method conventionally used in our institution.Result s : The dosime ter were found to be satisfactor y in terms of reprod ucibil­ity (0.2%),linearity « 0.1%), dose rate dependence (0.5%), and absolu te cal­ibration accurac y (0.3% ). The system offered sufficient sensitivity to errorsinduced by setup deviations . With a gantry rotation offset of 2 degrees and anapplied threshold of 10%, more than 40% of points has DD% > 2%. The samemeasur ements performed with a 2D array have shown quite similar sensitiv­ity. Measurem ents of different planned sinograms have shown as, thank s tothe geometry, the dosimeter is able to capture dif ferences on the dose pro­jections.: with the IC measurements withi n 1% the diode 00% is higher than3Conclusions :

1608 poster

DOSIMETRIC EVA LUATION OF LEFT BREAST IRRADIATIONUSING A DEEP INSPIRATI ON BREATH HOLD TECHNIQUE WITHFORWARD PLANNED IMRTC. Burke ' , A. M. Kennedy 1 , L. Rock ' , P. Thirion 1 , A. Mihai ' , J. Armstrong 1

i UP MC CANCER CENTERS IRELAND, BEACON HOSPITAL, Radiotherapy,Dublin , Ireland Republi c of

Purp ose : The use of whol e breast irradiation for cancer of the breast is awell establ ished therapeutic modality. For left breast cancer patients, cardiactoxicity still remains the most significant side effect particularly for youngerpatients . One method to reduce this toxicity is to use a deep inspirationbreath hold (DIBH) technique for treatment of Ihese patients. This investi­gation will evaluate this treatment technique when used in conjun ction withforward planned IMRT.Materi als : This work will compare the use of DIBH using the Varian RPM sys­tem with stand ard non-breath hold CT images for the treatment planning ofleft breast cancer using both forward planned IMRT and conventional wedgecompensated techniques. Dose -volume histograms will be used to compa rethe level 01 radiation dose to the heart for each technique. In addition, theeffect of DIBH on the irradiated volume of breast , heart and lung will be anal ­ysed. The use of complex treatment planning technique s will be analysed forefficacy when used in conjunction with the breath hold technique.Results : For forward planned IMRT treatment s, a significant reduction inheart dose was observed for all patients when comparing breath-hold treat­ments With free breathing treatments. The average reduction seen for thesepatients was approximately 30%. The analys is was performed on 15 pa­tients. A corresponding increase in lung volume of approximately 60% wasobserved for the breath hold patients although the mean lung dose remainedunchanged between the brea th hold and the free breathing. Small reductionswere noted for the lung volume receiving 20Gy for the breath hold technique.

Conclusions: The use of the breath hold technique for the irradiation of leftbreast demon strates clear dosim etric advantag es when compared with freebreathing techniques . A large reduct ion in heart dose is observed for allpatients . When used in conjunction with a forward planned IMRT approach,the reduct ion in heart dose is enhanced by the preferential shielding of thehear t. The effect of increased lung volume in the treatmen t field does notlead to an increase in mean lung dose and in fact yielded a small reduct ion involume at lung receiving 20Gy.

1609 poster

DOSIME TRIC EVAL UATION OF VM AT WITH MONTE CARLO DOSECALC ULATION FOR HEA D AND NECK TUMOURSF. Stieler l , V. Steil I , R. Boggula1 , F. Wenz' , F. tonr', UNIVERSITY MEDICAL CENTER MANNHEIM, Departmen t of Radiotherapyand Radiation Oncology, Mannheim , Germany

Pu rpose: Volumetric modulated arc therapy (VMAT) has the potential to re­duce treatment time and to increase MU-efficiency in comparison to estab ­lished static-gantry intensity modulated radiotherapy (IMRT). VMAT was firstclinically estab lished in the department of radiatio n oncology of the UniversityMedical Center Mannheim in January 2009. The combination of this efficientirradiation technique with a treatment planning system (TPS) which uses aMonte-Carlo dose-calculation algorithm further improved the overall processThis evaluation was accomplished to verify dosimetrically this technique be­fore the clinical introduction of MC-planned VMAT for head and neck cancer.Materials: This study was based on 10 patients with head and neck tumors.The planning target volume (PTVj encompassed the prima ry tumor and thecervical lymph nodes with sparing of one parotid and the spinal cord . VMATplans were created using Monaco 2.03 (Elekta CMS Softwar e, SI. Louis,USA) with a single rotat ion. The DICOM export over Mosaiq 2.0 (ElektaSoftware, UK) to the linear accelerator Synergy 6MV (Elekta Oncology, UK)was evaluated . The irradiated plans were verified using water equivalentphantoms with ionisation chamber and radio sensitive films and also witha 2D-array (MatriXX Evolut ion, ISA Dosimetry, Schwarzenbruck, Germany ).Measu rements with the 2D array were performed both with the array placedstatically in a homogeneous phantom on the treatment table and irradiatedwith the actual bam geometry with and without a angle -dependent correct ionlookup-table for lateral beam directions and then attached to the linac with adedicated gantry holder, accumulating all beams at a perpendicular incidence("collapsed beam setup").Results : All DICOM plan files were export ed without problems from the TPSto the accelerator. The mean treatment time was 6.09 minutes ± 59 seconds.The mean deviation for the absolute dosimetric measurements between thecalculated and the measured dose using the ion chamb er was -2.69%±0.87.The gamma index analyse of film dosimetry showed for the criter ia 3%/4mman agreement of 89.53%±3.13 and for 5%/5mm 97.06%±1 .50. For the mea­surements with the 2D-array in the phantom without correct ion the agreementfor 3%/4mm was 92.55%±3A6 and for 5%/5mm 99.76%±OAO, with lateralcorrect ion the agreement was for 3%/4mm 95.38% ± 1.64 and for 5%/5mm99.91%± 0.17. The 2D-array measurements with the gantry holder showedan agreement of 99.43%± 0.23 and for 5%/5mm of 99.94%±0.06.Conclusions: After prior commissioning of VMAT and the mult iple tests per ­formed in this evaluation , MC calculated VMAT plans for large and complextarget volumes such as head and neck tumors can be treated reliable andefficient.

1610 poster

DOSIMETRIC EVALUATIONS OF 2D TUMOR MOTION IN RESPIRA­TORY GAT ED IMRTA. Seeha se I, C. Grohrnann " , R. Werner 2

, M. Todorovic", C. Petersen " , F.Cremers'i UNIVERSITY MEDICAL CENTER HAMBURG - EpPENDORF (UKE, Depart ­ment of Radiotherapy and Radio-Oncology, Hamburg , Germany2 UNIVERSITY MEDICAL CENTER HAMBURG - EpPENDORF (UKE, Depar t­ment of Medical Informatics, Hamburg, Germany

Purpose : Tumor motion caused by respiration is a major problem in radio­therapy of bronchia l carcinoma. Hence, both inter- and intrafractio nal patien tmovements have to be included into the planning process in increasing thesafety margins. However, this also leads to increased dose deposi tion inhealthy tissue. Respiration gated radiotherapy aims to reduce the normaltissue complication probability while giving the prescribed dose to the tumor.Mater ials: In this study a motion phantom and a pressure sensitive respira ­tory gating system (AZ-773V, Anzai Medical) were used to analyze the clinicalsuitability of the gating techn ique . A sinusoida l respiration pattern with 2D tu­mor motion was simulated with the motion phantom . Ionization chambers orradiochrom ic films (GafChromic EBT2 films) embedd ed in water equivalentRW3 slices were used for dose verification . Simple geometric target volumesas well as model pat ient cases were investigated for different gat ing parame ­ters. Therefore, intens ity modulated treatment plans (2 Gy dose per fract ion)have been created. After performing dynamic and gated treatments with vary-

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 553

ing gating parameters (gating levels, respiration frequencies) and influence offractionation, the results have been compared to static dose distributions.Results: The major effect of tumor motion is dose blurring at the border ofthe tumor volume leading to decreased dose gradients. By non gated treat­ment the penumbra is 2.5 times as wide as the penumbra of the static irra­diation. Through gated therapy nearly static penumbra width were achieved.Although gating on intensity modulated plans also revealed underdosages,the achieved dose distributions were superior to non-gated dynam ic irradia­tions. No influence of respiratory rates on gated therapy can be obtained aslong as the motion pattern is regular. Measurements of non-gated dynamicirradiations tend to underdosages, with the possibility of emerging cold spots.Due to fractionation, small dose variations sum up to significant dose errors,30% of the PTV area showed underdosages up to 72% at the goal dose.Such underdosage effects can be avoided with the use of gating techniques.Conclusions: Gated therapy enables steeper dose gradients and a bettersparing of organs at risk. While dynamic non-gated IMRT treatments tendto underdosages, gated therapy rectifies the dose blurring. Therefore safetymargins can be reduced.

16tt poster

EFFECT OF HEART AND RESPIRATORY MOVEMENTS TO RADIA­TION THERAPY DOSESS. Peltola", P.K61hi 1

, 1. Tuunane", P Hyyrnin". H. Eskola''

1 TAMPERE UNIVERSITY HOSPITAL, Department of Oncology, Tampere,Finland2 TAMPERE UNIVERSITY OFTECHNOLOGY (TUT), Department of BiomedicalEngineering, Tampere, Finland

Purpose: Novel technology enables in principle very accurate targeting asa function of respiratory and cardiac cycles. Gati ng can be used to com­pensate involuntary motion to increase the quality of diagnostic images or totarget the radiotherapy treatment accurately. Gating cuts the radiation beamon and off during diagnostic imaging or radiotherapy treatments, and that waythe radiation is delivered only in the predetermined phases of motion cycles.Respiratory gating takes into account an organ motion due to breathing andgates the radiation beam so that the radiation is on only when the organ is ina quite stable state. Cardiac gating takes into account the movement of heartand surrounding organs due to cardiac contraction. Dual gating combinesthe respiratory gating and the cardiac gating. However, respiratory gating,or at least a breath hold, is a prerequisite for cardiac gating. An extent ofrespiratory motion is so much bigger than motion due to cardiac contraction.that there is no use for only cardiac gating without some kind of respiratorycontrol. The purpose of this study was to study theoretical background of res­piratory, cardiac and dual gating, to evaluate the movement of heart and leftcoronary arteries due to cardiac contraction and to evaluate the possible ef­fects of cardiac gating on cardiac doses in radiotherapy treatments, becauseradiation doses that heart receives during radiotherapy need to be kept assmall as possible to avoid radiation induced heart diseases.Malerials: Respiratory gating in radiotherapy is nowadays a standard pro­cedure in many oncology clinics, but cardiac gating in radiotherapy has onlybeen investigated by few research groups. In diagnostic imaging, cardiacgating is a routine procedure in computed tomography (CT) and magneticresonance imaging (MRI), and dual gating is under development in positronemission tomography (PET) imagingThe movement of heart and coronary ar­teries due to cardiac contraction was evaluated by segmenting and studyingcardiac gated CT images of one female and one male patient. The effects oncardiac doses in cancer treatments near the heart (breast cancer, lung tumorand oesophageal cancer) were evaluated by treatment planning software.Results: Differences found in the dose volume histogram analysis of treat­ment plans for breast. lung and oesophageal cancer can be explained by thedeformation and orientation changes in the heart's internal structures. Thedetected structures were the aortic and mitral valves, the left anterior de­scending coronary artery, the left circumflex coronary artery, the total heartvolume, and the planning target volume. Their movement was detected inbeam eye views of treatment plans. Differences in the structure movementsof different patients were observed. The gating window could be chosenbased on the dose volume histograms and CT images. This fact suggeststhat patient selection plays an important role in the benefits of cardiac gating.Conclusions: Results suggest that the effects of cardiac gated radiotherapyin cardiac doses are quite small. The doses of the whole heart volume insystole and diastole vary only in the case of maximum doses but not in meanor total doses. The differences of doses can be seen more clearly in leftcoronary arteries. Due to the limited patient material, this study can be con­sidered a preliminary study. The preliminary results presented in this thesisdemonstrate that cardiac gating, in addition to respiratory gating in radio­therapy treatments near the heart, could be beneficial for carefully selectedpatient groups. More analysis with larger patient data would benecessary toobtain more reliable results. Based on our results, further investigation canbeconsidered feasible and worth studying.

1612 poster

EVALUATION OF THE EFFICACY OF MODULATED ELECTRONRADIATION THERAPY IN COMBINATION WITH IMRT FOR THEPLANNING OF NOVEL BREAST CANCER TREATMENTSB. Palma I, A. Ureba', R. Arrans tara", F. Salquero", A. Leal'

1 UNIVERSIDAD DESEVILLA, Fisiologia Medica y Biofislca, Seville, Spain2 HOSPITAL VIRGEN DE LA MACARENA, radiation of physics, Sevilla, Spain:3 UNIVFRSIDAD SEVILLA - FACULDAD MEDICINA, Fisiologia Medica yBiofisica, Sevilla, Spain

Purpose: To evaluate the potential efficacy of modulated electron radiationtherapy (MERT) in combination with IMRT, both to be delivered by the samephoton multileaf collimator (xMLC), for the application of novel breast can­cer treatment techniques in terms of tumor control probability (TCP), normaltissue complication probability (NTCP) and equivalent uniform dose (EUD).Materials: Four accelerated partial breast irradiation (APBI) and four simulta­neously integrated boost (SIB) cases were planned using an in-house MonteCarlo treatment planning system (CARMEN). APBI cases were planned us­ing MERT and MERT+IMRT depending on PTV position in depth. SIBcases were all planned with MERT+IMRT. Detailed xMlC simulations wereincluded in the optimization process implemented in CARMEN. Dose-volumehistograms (DVHs) were obtained for all the plans. Doses were then con­verted to conventional fractionation doses using the biologically equivalentdose (BED) equation with a/j'J=3. EUD, NTCP and TCP were calculatedfollowing Niemierko et al. (phys Med 23; 2007) proposed parameterizationusing radiobiological parameters from different references.Resulls: Average EUD for APBI cases was 56.2 Gy, with Tep values over97% and NTCP of 0% for pneumonitis, pericarditis, and ipsilateral-breast fi­brosis for all the evaluated cases. TCP values for SIB plans were over 95%and over 99% for breast PTV and boost PTV, respectively and NTCP for pneu­monitis was 0%. EUD values were of the same order of those obtained forthe sequential boost irradiation technique.Conclusions: The TCP/NTCP values obtained for both breast treatmenttechniques, together with the technical advantage of using the xMLC, turnsthe MERT+IMRT approach into a real alternative for the clinical implementa­tion.

1613 poster

EXPERIMENTAL VERIFICATION OF SOFT-DOCKING SYSTEMPRECISION IN INTRAOPERATIVE RADIATION THERAPYS. Adamczyk \ M. l.itoborski '

1 GREATER POLAND CANCER CENTRE, Medical Physics Department,Poznan, Poland

Purpose: The purpose of this study was to investigate the impact of an im­precise soft-docking system set up on dosimetric parameters of high energyelectron beam and to determine the dod<,ing tolerance for clinical use.Materials: In order to test possible eftects of applicator misalignment onbeam characteristics, several dosimetric parameters in different applicatorsettings were studied. In this study the electron accelerator Mobetron (In­traOp Medical Inc., Santa Clara, CAl was used. The ionization chamber ar­ray 2D-Array seven29 (PTW. Freiburg, Germany) was placed perpendicularto the central axis of the beam, in direct contact with the end of the applica­tor, and irradiated with 6 MeV electron beam energy.Dose distributions obtained tor different applicator settings were analyzed using MultiCheck (PTW,Freiburg, Germany) software. Comparison between beam characteristics' re­sultant of translational and rotational (tilt and rotation of gantry) misalignmentof the beam's central axis with that of the applicator was made. The impactof changes in distance between the appl icator upper surface and the gantrywas also verified. Several electron beam parameters, such as beam sym­metry, absorbed dose at a certain depth in the central axis, and central axisdeviation, were examined.Results: This study showed that even when a Mobetron soft-docking systemindicates that the gantry is properly docked, changes in beam characteristicscan play an important role. Measurements revealed that shifting the gantryin the horizontal plane longitudinally and laterally produces a change in CAXdeviation between 5.7% and 7.3% with respect to the set-up in which thecentral axis of the beam aligns perfectly with the axis of the applicator. Thisproved that the limit values of translational shifts allowed by the system shouldbe narrowed. It was demonstrated that changing the tilt or rotation angle ofthe gantry produces no significant change in beam symmetry (below 2%).Finally, the absorbed dose measured in the central axis at approximately 2cm depth differs significantly when changing the height of the gantry withrespect to the surface of the applicator. When increasing and decreasingthe space between the gantry and the upper surface of the applicator, dosechanges 01 5.3% and 7.1% respectively were found.Conclusions: Imperfect docking can have a significant influence on dosedistribution. There should be no allowance for misalignment In soft-docking,especially when considering height or translational shifts of the gantry in thehorizontal plane.

S554 PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

1614 poster

PTV DVHComplrison for Three RlpidArc PatienlS

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FEASIBILITY OF DOSE PAINTING USING VOLUMETRIC MODU­LATED ARC (RAPIDARC) OPTIMIZATIONS. Korreman', S. Ulrich", S. Bowen", M. Deveau", R. Jeraj"

t COPENHAGEN UNIVERSITY HOSPITAL, RIGSHOSPITALET, Department ofRadiation Oncology, Copenhagen, Denmark2 UNIVERSITY Of WISCONSIN SCHOOL OF MEDICINE AND PUBLICHEALTH,Departmen1 of Human Oncology, Madison, USA3 NIELS BOHR INSTITUTE, FACULTY OF SCIENCES. UNIVERSITY OFCOPENHAGEN, Copenhagen, Denmark4 UNIVERSITY OF WISCONSIN SCHOOL OF MEDICINE AND PUBLICHEALTH.Department of Medical Physics, Madison, USAfi JOZEF STEFAN INSTITUTE, Ljubljana, Slovenia6 UNIVERSITY OF WISCONSIN SCHOOL OF MEDICINE AND PUBLICHEALTH,Departmen1 of Medical Physics and Department of Human Oncology,Madison, USA

Purpose: Dose painting strategies are limited in practice by the optimizationalgorithms in treatment planning systems and the physical constraints of thebeam delivery equipment This study aims to investigate the planned doseconformity to a dose painting prescription using the RapidArc optimizer andbeam delivery technique.Materials: A head & neck cancer patient underwent a [61 Cu]Cu-ATSM (surro­gate of hypoxia) PETICT scan, and uptake data were extracted for treatmentplanni ng. PET SUVs at every voxel were converted to prescribed doses witha base dose of 60Gy (in 2Gy fractions), and an overaiI target mean dose of90Gy. The voxel-based prescription was subsequently converted into discretelevels, and the target was segmented into substructures according to theselevels. The patient structure set was imported info Eclipse 8.6. Optimizationwas performed using the Eclipse inverse arc optimizer, and varying the follow­ing parameters one at a time: MLC leaf width (5 mm and 2.5 rnrn), number ofarcs (1 and 2) and collimator rotation (O,15, 30 and 45 degrees). No normaltissue constraints were applied. Conformity of planned doses to prescribeddoses was evaluated using quality volume histograms (QVHs). and relativevolumes receiving planned doses within 5% of the prescribed dose.Results: The best conformity was obtained using the MLC with 2.5 mm leafwidth, two arcs, and collimators in 45/315 degrees, with 80.5% of the volumereceiving a dose within 5% of the prescription. Using only one arc (2.5 mmleaf width, collimator 45 degrees) had only a small deteriorating effect (77.2%vs. 80.5% within 5% of planned dose) on conformity. The effect of increasedMLC leaf width (two arcs, collimator angles 45/315) was also small (77.2%vs, 80.5% within 5% of planned dose). The collimator angle had the largestinfluence on plan conformity; for angles of 30, 15 and 0 degrees (one arc, 2.5mm leaf width), the relative volumes receiving within 5% of the planned dosedecreased to 76.0%, 72.5% and 64.3%. Number of monitor units ranged from74510 1123 per fraction, and the general trend was that plans with higherconformity had higher number of monitor units.Conclusions: Results demonstrate that planning of prescription doses withmultiple leveis for dose painting is feasible using RapidArc. Small depen­dence was observed on MLC width and number of arcs, whiie the collimatorrotation was most important for plan conformity.

1615 poster

FEASIBILITY OF USING COARSE MLC LEAVES TO OBTAINDOSIMETRICALLY SIMILAR RESULTS AS THINNER LEAVES FORRAPIDARC PLANSC. Buckey', S. Stathakis! , N. Papanikolaou'

, UNIVERSITY OF TEXASHEALTH SCIENCE CENTER/CANCER THERAPY ANDRESEARCH CENTER,San Antonio, USA

Purpose: To determine the feasibility of using a multileaf collimator (MLC)with leaf widths of 1.0 ern, to obtain dosimetrically similar results to an MLCwith 0.5 cm leaf widths, for RapidArc treatments.Materials: The CT data of 10 patients, who had recently completed treatmentat our clinic, were loaded into the Eclipse treatment planning system. Twoplans were generated for each patient: a single-arc plan using a 0.5 cm MLCleaf widlh, and a two-arc plan using a 1.0 cm MLC leat width, with the isocen­ter of one field shifted by 0.5 cm in the direction perpendicular to leaf travel.The optimization parameters used were the same as those employed duringthe original patient treatment plan. Both pians were optimized by Eclipse's arcoptimization algorithm, without any manipulation of constraints or other out­side Intervention once the process was underway. All plans were normalizedsuch that 95% of the target volume received 100% of the prescribed dose.Results: For all 10 patients, the two-arc 1.0 cm MLC plans were able toreturn at least equivalent results for PTV coverage; in all but one instancethe two arcs had superior PTV coverage and homogeniety as compared tothe single-arc 0.5 cm MLC plan. Dose to organs at risk (OARs) were notidentical, but no trend for higher OAR doses for a particular leaf width can beestablished. On average, the number of monitor units used for the two-arc1.0 cm MLC plans increased by 15%, when compared to the single-arc 0.5cm MLC plans.

Absolute Dolt'l c6y

Conclusions: By using two arcs, with an isocenter shift of half a leaf-width. itis possible for centers using a 1.0 cm MLC leaf-width to plan RapidArc casesthat are dosimetrically similar to those planned with a 0.5 cm leaf width.

1616 poster

FEASIBILITY STUDY OF THE USE OF RAPIDARC IN STEREOTAC­TIC RADIOTHERAPYJ. Puxeu vaque '. i. Modolell i Farre', E. Zardoya', M. C. l.lzuain", M.

Macia 2, A. Lucas2

i INSTITUT CATALA D'ONCOLOGIA, Medical Physics Department, L.:Hospitaletde L1obregat,Spain2 INSTITUT CATALA D'ONCOLOGIA, Radiation Oncoiogy Department,L.:Hospitalet de L1obregat,Spain

Purpose: Radiosurgery treatments were set up in our hospital in 1994. Un­til 2006 Conical collimators from Brain iab ranging from 1cm to 4cm at theisocentre were used tor the beam conformation. In 2007, after the installationof a new Linear accelerator(Linac) model Trilogy (VARIAN MEDICAL SYS­TEMS) with a multileave collimator (MLC) of 0,5cm in the twentieth centralcentimeters, most of the radiosurgery treatments were performed with theabove machine. After a study realized In our centre that analysed dosimetricdistributions, it was concluded that better conformation [conformity index) withcollimator cones was obtained for volumes smaller lhan 2,5 cm. In Decem­ber 2009 the necessary equipment for the RapidArc technique (Varian) wasinstalled in our hospital.The purpose of this study is to evaluate the Viabilityof the use of the RapidArc Technique for three different cases representativeof stereotactic treatments in our institution.Materials: New treatment plans using the new technique have been createdand compared with lhe original plans(dynamic arcs), evaluating the advan­tages/disadvantages of both techniques. The first case was an only volumeto be treated, the second with three lesions 10be treated simultaneously andthe third was a volume treated in fractionated methodology.In all cases, TPSfrom Brainlab (Iplan 3.0.2) was used for the treated pians (dynamic arc) andEclpse (Varian) with an inverse atqonthrn was used for the RapidArc plans.Results: The first results suggest a better conformation of the volumes withRapidArc techn ique. For example, in the case of three volumes (total vo ume3,7cm3

) is 1.86 for RapidArc and 3.4 for Oinamic Arc. On the other hand,the volume that received low doses (""3Gy) was much bigger in RapidArcTechnique.Figure 1_ An example of dose distribution for two of the threePTV's using RapidArc(left) and Brainlab dynamic arcs (right) are presented.Better conformity for high doses using RapidArc can be observed. Sagitalplane

Conclusions: The RapidArc technique achieved a diminution on the treat­ment time without a considerable increase in the planni ng time and accept­able dose distributions. On the other hand, the increase in low dose volumesmay not be critical in a fractionated treatment but must be considered in singletreatment sessions

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 555

1617 poster

FIXED VS MOVING GANTRY IMRT VS TOMOTHERAPY - A PLANCOMPARISON FOR HEAD AND NECK1. Wiezorek', K. Brachwitz ", E. Blank'. D. Georg3

, K. Schubert", 1. Wendt1

1 UH JENA,Jena, Germany2 RUPPINER KUNIKEN GMBH, Neuruppin, Germany3 MEDICAL UNIVERSITY OF VIENNA, Vienna, Austria4 UH HEIDELBERG, Heidelberg, Germany

Purpose: This multicentre planning study compares static gantry and mov­ing gantry IMAT vs Tomotherapy for a parotid gland sparing head-and-necktechnique with a simultaneous integrated boost (SIB).Materials: Treatment plans for 10 patients with head and neck tumours (Or­pharynx, Hypopharynx, Larynx) were created for helical Tomotherapy usingthe treatment planning system (TPS) HiArt, for VMAT using Monaco (Elekta),for step&shoot IMRT using the KonRad (Siemens), and for dynamic IMRTusing Eclipse (Varian). The aim of the planning study was to achieve simi­lar doses to the PTV with median dose of 52.2Gy I 55.8Gy and to the boostvolume with a median dose of 60.9Gy I 65.t Gy), while fulfilling as good aspossible OAR constraints for the parotid glands (Dmedian<20Gy), the spinalcord (Dmax<43Gy), and the mandibles (Dmedian<45Gy). The evaluation wasbased on PTV coverage, conformity index (CI=Volume93%/PTV), homogene­ity index (HI=ID5%-D95%]/Dmean), DVHs of OARs, healthy tissue volumereceiving more than 5Gy (V5Gy) and monitor units (MU) or treatment time.Results: Depending on IMRT technique and TPS, mean CI values rangedfrom 0.96 for the step& shoot plans to 0.97 for both VMAT and HiArt plans.and to 0.98 for sliding window plans The HI for the boost volume varied from0.05 for the HiArt plans to 0.10 for the Konrad step&shoot plans. Mean valuesof the median doses of the parotids were 14.1Gy for Tomotherapy, 18.6Gyfor sliding window, 21Gy for step&shoot and 23Gy for VMA1. The mean val­ues of the maximal dose of the myelon incl. 7mm margin varied belween34.2Gy (HiArt), 40.6Gy (VMAT), 42.9Gy (Konrad with step&shoot) to 449Gy(Eclipse with sliding window) V5Gy values were lowest for the dynamic IMRTtechnique with fixed gantry angles (3499ccm) and largest for the Tomother­apy (5122ccm). On the other hand. lowest mean MU values of 500 wereachieved for VMAT, compared to 1275 for dynamic IMRT based on Eclipse.Mean treatment times ranged from 8min (HiArt) over 9min (VMAT) and 12min(step&shoot) to about 24min (dynamic IMRT).Conclusions: Depending on IMRT technique and TPS, mean CI valuesranged from 0.96 for the step& shoot plans to 0.97 for both VMAT and HiArtplans. and to 0.98 for sliding window plans The HI for the boost volume var­ied from 0.05 for the HiArt plans to 0.10 for the Konrad step&shoot plans.Mean values of the median doses of the parotids were 14.1Gy for Tomother­apy, 18.6Gy for sliding window, 21Gy tor step&shoot and 23Gy for VMA1.Themean values of the maximal dose of the rnyelon incl. 7mm margin variedbetween 34.2Gy (HiArt), 40.6Gy (VMAT), 42.9Gy (Konrad with step&shoot)to 44.9Gy (Eclipse with sliding window). V5Gy values were lowest for thedynamic IMRT technique with fixed gantry angles (3499ccm) and largest forthe Tomotherapy (5122ccm). On the other hand, lowest mean MU values of500 were achieved for VMAT, compared to 1275 for dynamic IMRT based onEclipse. Mean treatment times ranged from 8min (HiArt) over 9min (VMAT)and 12min (step&shoot) to about 24min (dynamic IMRT).

16t8 poster

FLUOROSCOPIC BLOCK-MATCHING BASED MEAN POSITIONTRACKING OF RESPIRATORY MOTION FOR LUNG CANCERRADIOTHERAPYL. Grezes-Besset ', S. Joel', P.Clarvsse", D. Sarrut 1

1 CENTRE LEON-BERARD - CREATIS LRMN CNRS UMR5220 - INSERMU630, Lyon, France" CREATIS-LRMN CNRS UMR5220 - INSERM U630. UNIVERSITE OELVON, Lyon, France

Purpose: Tracking tumor motion during radiotherapy treatment of lung can­cer is challenging due to temporal variations in breathing patterns. Sometreatment, such as gating or tracking with multi-leaf collimators, may requirean instantaneous precise position of the tumor together with the evaluation ofthe trend of the motion, in particular mean position drifting or abrupt shift. Thepurpose of this study is to evaluate the leasability of block-matching basedmean position tracking of tumor respiratory motion from fluoroscopic se­quence acquired with a Cone-Beam, using an elliptical model fitting adaptedtrom [Ruan st ai, Med Phys, 2008J.Materials: Apparent motion acquisition:Data was acquired on the Synergysystem from Elekta. Three patients underwent a fluoroscopic session (150two-dimensional Images covering approximately 30s, i.e 7 respiratory cycles)prior to conventional radiation treatment. The angle of projection betweenthe vertical position and the kV source was 90° (viewing point in front of thepatient face). In previous work [Grezes-Besset et ai, ICCR, 2010j, we explainhow to extract individual point trajectories in a region of interest using anadapted block-matching algorithm on fluoroscopic sequences (Figure a) andthen how to obtain a reliable apparent motion using the k-rnsans-» clusteringalgorithm. Mean position tracking:To track the mean position. we form a state

vector at each instant from the current apparent motion value and the valuefrom K previous samples. We then used the ellipse fitting method from IRuanjto obtain the mean position at each corresponding instant. The few degreesof freedom of the ellipse provides robustness to noise.Results: We tested the mean position tracking algorithm. As reference, wecalculated the mean value apparent motion per cycle. Figure b) presents anexample of result for one patient. The apparent motion appears in red, themean position tracked is in blue and the reference mean position per cycle isin green

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Conclusions: We show that apparent tumor motion in fluoroscopic imagecan be tracked with a block-matching and mean position approach. Thismean position tracking method has the advantage to be calculated at eachinstant, whereas our reference mean position can be computed only per cy­cle. Once extended to the tracking of other regions, it could provide helpfuldynamic information during treatment.

1619 poster

FURTHER DOSIMETRIC SPECIFICATION AND MONTE CARLOMODELLING OF A NEW ELEKTA RADIATION HEAD WITH INTE­GRATED 160-LEAF MLCC. Thompson], D. Christofides", C. Evans", S. Weston!, V. Cosgrove', D. I.

Thwaites ' , G. Thompson". K. Brown"1 ST JAMES'S INSTITUTE OFONCOLOGY, THE LEEDS TEACHING HOSPITALSNHS TRUST, Medical Physics Engineering, Leeds, United Kingdom2 ELEKTA UK LIMITED, Crawley, West Sussex, United Kingdom

Purpose: Following initial evaluation measurements of a new 160-leaf ElektaMLC and linac head design, further measurements were made to completeover-all specification and to compare with Monte Carlo calculations.MaterialS: All the measurements were obtained in a water phantom using aPTW p-type SI diode. Monte Carlo modelling was performed in Leeds usingthe BEAMnrc code, using a core model validated against previous MLC de­siqns. Penumbra measurements were confirmed for 6MV photons, at Scmdeep in water, with leaves in the A-B (col. 0°) and G-T (col. 90°) direc­tions using a 1Oxl Ocm2 field off-set from the central axis. Analysis of leaftransmission and inter-tip leakage were made, with opposing leaves sepa­rated absolutely by 1mm (set by feeler gauge), positioned 10cm and 15cmoff-axis. Collimator scatter (Sc) and the potential effect of the dynamic leafguide (DLG) on output were also measured.Results: 80%-20% penumbra varied from 3.9-4.5mm, with leaves positionedfrom zoen to -l5cm over the central axis. Monte Carlo calculations were onavsraqe within 0.2mm of measurements. Larger penumbrae were observedwith leaves in the A-S dlrecticn compared to the G-T,believed to be due to thesource-spot being elliptically shaped. Maximum leaf transmission for a 6 MVbeam was 0.44% with an average of 0.35%. accurately predicted by MonteCarlo. Inter-tip leakage for a 1mm gap was found to be a maximum of 4.7%and 2.2%, 10cm and 15cm away from the central axis, respectively. Theseagreed with the model to within 0.25%. Sc factors were almost identical tothose measured on MLCi and MLCi2 machines, (range -0.97-1.04 from 5cmto 40cm wide square fields, 6MV and 1OMV)and were not found to be affectedby the position of the DLG (i.e. location of the leal-tip from the edge of theDLG).Conclusions: The Monte Carlo model has been shown to be able to accu­rately predict the dosimetric characteristics of the new head design and MLC.The consistency of the Sc factors with the previous MLCilMLCi2 head de­signs would indicate that minimal changes would be expected to be made indosimetric models of the new head in treatment planning systems.

1620 poster

HIGH DOSE HYPOFRACTIONATED RADIOTHERAPY UNDERRESPIRATORY GATING FOR LUNG AND LIVER METASTASES.M. Almaghrabi', E. Rio!, M. Mahe', E. Bardet'

1 CENTRE RENE GAUOUCHEAU, Saint-Herblain, France

S 556 PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

Purpose: In this study we retrospectively assessed toxicity and local controlafter high dose hypofractionated radiotherapy (HDRT) for patients ineligiblefor surgery or chemotherapy.Materials: Study accrual period: from November 2005 to April 2009, weincluded 21 metastasic lesions from12 patients (18 in lung and 3 in liver). Forall patients, number of metastases did not exceed 3. Median age was 63years (46-79). Performance status (KPS) was> 60 with acceptable lung, liver& renal functions. Primary sites were: colorectal, breast, ENT, oesophagusand thyroid (n~6, 2, 2, 1, 1) respectively. Treatment planning was made by CTscan using detecting system, that gives slices measuring 1 mm allowing real­time 3D reconstruction and connected with special equipment for respiratorygating (Dyn'R systemuring "breath hold" in inspiratory phase (8-15 seconds),CT slices were reconstructed with iodine injection. Planning target volume(PTV) was obtained by addinga 3D margin 10·15 mm to clinical target volume(CTV), respecting protocol applied in our centre for organ at risk. Medianprescribed dose at isocenter was 33 Gy (25Gy-42Gy) in 4-6 fractions for 2weeks maximum (2-3 F/week) with conformational equally spaced coplanar,10 to 25 MV beams, on Elektanac.Results: Median CTV volume was 18 cm3 (range 2-120). Median PTV vol­ume was 57 cm3 ( range 18-191). Media n percent 01 CTV covered by theprescription isodose line was 98% (range 85 to 100%). Median percent ofPTV covered by the prescription isodose line was 95% (range 88 to 99%).To predict acute and late toxicity after (HDRT) comparatively to the equiva­lent of standard dose (2 Gy/fraction, 5 fractions/week), we employed LinearQuadratic Model; with a1b~1 0 for acute toxicity and a1b~3 for late toxicity.Acute and late toxicity were eva luated by CTC.NCI toxicity scale. Three pa­tients with lung metastases experienced esophag itis grade 2, 1 patient ex­perienced couqh grade 2 and 1 patient with liver metastasis experienced agrade 1 cholestasis syndrome. There was no radiation induced liver disease.After median follow up of 15 months, 1 patient died in the first month due toprogressive disease. Median survival was 19 months. The estimated sur­vival rates at 12, 18, 24 months were 66%, 42%, 33% respectively. Tenpatients (83%) had sustained tumour response according to RECIST criteria(1 complete response, 2 partial responses, and stable disease for 7 patients).The median time to maximal response was 3,4 months (3-6 months), Only1 patient had local relapse at 12 months and 4 patients developed distantmetastases. Progression-free survival was 9 months (5-18).Conclusions: HDRT with respi ratory gati ng is safe and feasible with goodloca l control. Treatment tolerance was favourable without grade 3 or 4 toxicity.Based on this data we suggest this technique for oligometastatic (lung or liver)patients who are not eligible for surgery or chemotherapy.

1621 poster

IMPACT OF RAPIDARC TECHNOLOGY IN A BUSY CLINICALDEPARTMENT: COMPARISON OF TREATMENT TIME & MONITORUNITS WITH IMRT TECHNIQUES. Subramanian", T. S. Shanumugam', A. Gandhi", K. Muruqesan", K.

Subramanian 1, S. Chilukuri 2

1 YASHODA CANCER INSTITUTE, radiation oncology medical Physics,Hyderabad, India2 YASHODA CANCER INSTITUTE,Radiation Oncology, Hyderabad, India

Purpose: Rapid Arc (RA) technology was successfully implemented at ourcentre since February 2009 and more than 350 patients have been treatedtill March 2010. In this study we compared the total MUs and the treatmentdelivery time for 75 RA patients treated in the month of Jan-Feb 2010 withthe respective sliding window dynamic multi-leaf collimator (SW-DMLC) IMRTplans.Materials: The site of irradtation with RA was brai n in 15, head and neck(H&N) in 20, thorax in 13, abdomen in 10 and abdominopelvic/pelvic in 17patients. A majority of Rapid Arc plans consisted of single arc for brain, tho­racic and abdominal tumors, two or more arcs for H&N and abdominopelvictumors. All cases were re-planned with SW-DMLC IMRT using Eclipse [Ver­sion 8.9] TPS achieving the same treatment goals. Dynamic IMRT plansconsisted of 4-9 beams depending upon the complexity of targets. The beam"ON" time was defined as the time elapsed between the beam 'ON' of the firstArc/Field and the beam "OFF" of the last Arc/Field of the treatment [with sin­gle isocenter]. The beam "ON" time for Rapid Arc treatment was measuredon the first day of treatment whereas for IMRT, treatment was simulated ona phantom with planned parameters. The total treatment time was computedby summing patient pos itioning time [mean-3min], alignment time [mean forbrain- 3minutes (min), for H&N- 4 min, for abdominopelvic/pelvic, abdominaland thoracic- 5min], KV Imaging & analysis time [mean-5min] and the beam"ON" time. The total treatment time was analysed for IMRT & RA assumingtime other than beam "ON" time to be identical.Results: The average MUs & Beam ON times for IMRT & RA are presentedin Table 1. The average Beam ON time and MU was lesser with RapidArccompared to IMRT. The total treatment time gain in treating 75 patients perday with RA instead of IMRT was 5.9 hrs with reduction of 5t,658 MU's.Assuming same proportion of cases (sitewise distribution), only 55 patientscould have been treated on IMRT per day as opposed to 75 patients beingtreated on RapidArc (machine working for 18 hrs/day).

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no,,, t-M..::l -'U,8 1..u ..... '.2.1

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1.-- 447.1 UOoIU: lU.! '.11 4.117S7IMU I .0.:31'-

·:t....../~_k 1M- ..., Nt.' .... .... ...iliNG NU I MO.J "*'

TGb4 ....11i~~4ay 51~.u I-..,Itllllft'l5-9MtsJ

Conclusions: The results of this study show an advantage with Rapid Arcover dynamic IMRT with a several hours gain of treatment time on the ma­chine with reduced MU's without compromising the treatment qoals, RapidArc is an efficient technology with a significant impact in busy centres with alarge load of patients being treated on high precision techniques.

1622 poster

IMRT WITH DAILY INTRA-FRACTIONALLY MODULATED JUNC­TION(S) FOR CRANIO-SPINAL IRRADIATION.M. Kusters". R. Louwe I, P.van Kollenburq", M. Kunze-Busch", C. Gidding 2

,

E. van l.i~dere, J. Kaanders 1, G. O. Janssens1

1 RADBOUD UNIVERSITY NIJMEGEN MEDICAL CENTER, Department ofRadiation Oncology, Nijmegen, Netherlands2 RADBOUD UNIVERSITY NIJMEGEN MEDICAL CENTER, Department ofPaediatric Oncology, Nijmegen, Netherlands3 RADBOUD UNIVERSITY NIJMEGEN MEDICAL CENTER, Department ofNeurosurgery, Nijmegen, Nether lands

Purpose: To develop a treatment technique for cranio-spinal irradiation usingintensity-modulated radiotherapy (IMRT) with improved dose homogeneity atthe field junction(s), increased target volume conformity and minimized doseto the organs at risk (OARs).Materials: Five patients with high-risk meduIloblastoma. underwent CT sim­ulation in supine poslnon. For each patient, an IMRT plan with daily intra­fractionally modulated junction(s) was generated as well as a treatment planbased on conventional 3D planning (3DCRT). A dose ot 39.6 Gy in 22 dailyfractions of 1.8 Gy was prescribed. Dose-volume parameters for target vol­umes and OARs were comparee for the two techniques.Results: The maximum dose with IMRT was <107% in all patients. V<95and V>107 were <1 ern" for IMRT compared to 3-9 ern" for the cranio-spinaland 26-43 crrr'for the spinal-spinal junction with 3DCRT. These observationscorresponded with a lower homogeneity index and a higher conformity indexfor the spinal PTV with IMRT compared to 3DCRT: 8% vs. 21% and 0.6 vs.0.3. respectively. !MRT provided considerable sparing ot acute and late react­ing tissues. V75 for the esophagus, qastro-esophaqeal junction and intestinewas 81%,81% and 22% with 3DCRT versus 5%,0% and 1% with IMRT re­spectively. With IMRT dose reduction to the larynx and proximal esophaguswas Independent of the shoulder position. For late reacting tissues like theheart and thyroid, a significant reduction of the exit dose was observed withIMRT. V50 and V75 for the heart was 7t% and 42% versus 0% with IMRT.V50 and V75tDr the thyroid was 72% and 32% versus 6% and 0% with IMRT.Conclusions: IMRT With dai ly intra-fractionally modulated junction results ina superior target coverage and junction homogeneity compared to 3DCRT. Asignificant dose reduction can be obtained for acute as well as late reactingtissues.

t623 poster

INCLUSION OF MLC LEAKAGE IN TREATMENT PLANS TO REDUCEMONITOR UNITS AND TREATMENT TIMEJ. Stenbsck", H. Alkhat.o" , B. Y Tsanq", W. Gebrearnlak", D. Tedeschi '

1 SOUTH CAROLINAONCOLOGYASSOCIATES, Columbia, USA2 UNIVERSITYOF SOUTH CAROLINA,Coiumbia, USA

Purpose: The efficiency of a treatment plan is extremely important to re­duce a patient's time on the table. Decreasing the amount of monitor units toachieve a prescribed dose will directly decrease this time. In this regard, twotechniques ot IMRT treatment delivery were tested and compared.Materials: The variable technique, which is the standard method of IMRTtor Flekta, allows the secondary collimator to vary for each segment mini­mizing the MLC leakage. In the static technique, the secondary collimatorremains fixed at the largest MLC segment for that particular beam. An an­thropomorphic phantom was treated for two types ot cancer to analyze eachtechnique. A typical head and neck PTV was placed on the phantom's CT as

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 557

well as a typical cervical cancer. Each plan was optimized using static andvariable techniques to either account for or minimize the MLC leakage. TLDswere placed throughout the treatment regions to confirm the treatment plans.Additionally, a case study is presented for patients being treated for bilaterallungs in which static and variable plans were created and analyzed.Results: The static and variable techniques provide similar dose coverage forall the regions of interest in the phantom. The difference comes when the totalmonitor units are computed for each technique. For the cervical treatment,the monitor units are decreased from 938 to 751. The head and neck casehad a much more dramatic decrease from 1685 to 743 monitor units for thevariable and static techniques, respectively. The bilateral lung cases will bepresented to show when and why a static treatment cannot reproduce theDVH of a variable treatment.

~ DIIIlIIJ;-~ I ........... Ia' I~-... I ........... Ia. I~-...

-- .. - - . ""'" ~

..... ... A7 ... .7 """ -""'" ." 72 ... ... :!!ill -".... ... ... ..~ 7 .".. ..... .,. • :12 .... s 074 ....... " 1M "" • 8 2.. ...- ... - ... .. - ~7

..... U lI!I .... " .... ......

..... . OR ... S ..... ...701." ..- .- .....

Conclusions: A method is presented here in which monitor units can be min­imized while maintaining the integrity of the treatment. There are limitations tothis technique and an example is shown to demonstrate the need to carefullyanalyze treatment planning for each patient.

1624 poster

INITIAL CLINICAL EXPERIENCE WITH NON-MELANOMA SKINCANCER TREATMENT USING XOFT ELECTRONIC BRACHYTHER­APYY. Honq", B. Paliwal", J. Welsh!

! UNIVERSITY OF WISCONSIN, MADISON, Human Oncology, Madison WI,USA2 UNIVERSITY OF WISCONSIN CANCER CENTER, Radiation Oncology,Wisconsin Rapids, USA

Purpose: The Xoft Axxent@X-ray source has been used for treating non­melanoma skin cancer since the surface applicators became clinically avail­able in 2009. The current study presents the initial clinical experience of thisnovel electronic Brachytherapy (eBx) source with surface applicators for pa­tients with non-melanoma skin cancer.Materials: Ten cases for a total of nine patients with basal cell carci­noma or squamous cell carcinoma were treated with eBx using the XoftAxxent@system and low-energy x-ray source (50-kVp), and/or with concur­rent Chemotherapy using Efudex Fluorouracil (5-FU). The new surface appli­cators available with this device have four available sizes of 10mm, 20mm,35mm, and 50mm in diameter. Pre-treatment calibration includes dose-ratemeasurement, air-gap factor, energy verification, beam flatness and symme­try, and treatment planning with patient specific cutout factors. Treatmentregimen includes 45 Gy in 15 fractions of 3 Gy each (3 fractions per week), or40 Gy in 8 fractions of 5 Gy each (2-3 fractions per week). Physician ioenti­fied the PTV with a 2-1 Ommexpended margin to the lesion and a prescriptiondepth of 2-6 mm, depending on the diagnosis. Patients were scheduled forfollow-up re-evaluations after completion of therapy.Results: The average nominal dose-rate output at the skin surface for the35mm applicator is 1.35 Gy/min with ±5% variation for fifteen sources. Forthe same source, the output variation is within 2%. The effective SSD wasalso calculated based on the air-gap measurements for four applicator sizes.The field flatness and symmetry are well within 5%. Treatment duration iscalculated based on the nominal dose-rate, the prescription fraction size, thedepth dose percentage, and the cutout factor. Follow up rechecks show slowtumor response after the completion of treatment, with the representation ofscab forming and new skin developing. Regression of nodules and decreaseddischarge were seen in all patients about two weeks following the treatment.Cosmesis was subjectively improved. The most common side effects Includemild erythema, drainage, and dry desquamation. Side effects were mild tomoderate, and well tolerated. No data was collected yet for analyzing long­term toxicity.

, . I

• <0 ',.1

Conclusions: The Xoft eBx with surface applicator performed well clinicallyfor non-melanoma skin cancer. All eligible patients completed treatment. Tu­mor response was shown 1-2 weeks after the treatment, and then improveslowing over the following months .

1625 poster

INTEGRAL DOSE EVALUATION IN CONFORMAL RADIOTHERAPY,INTENSITY MODULATED RADIOTHERAPY AND TOMOTHERAPYFOR LUNG CANCER TREATMENTSM. C. Pressello ', D. Araqno ', M. Betti", C. Caruso". P GRIMALDI!, A.

Monaco", R. Rauco ', M. Pacilio", E. SANTINI!! AZIENDA OSPEDALIERA SAN CAMILLO - FORLANINI, Medical PhysicsDepartment, Roma, Italy2 AZIENDA OSPEDALIERA SAN CAMILLO - FORLANINI, Radiotherapy, Roma,Italy

Purpose: To compare Conformal Radiotherapy (3DCRT), Intensity Modu­lated Radiotherapy (IMRT) and Tomotherapy (TIHA) plans for lung cancertreatments highlighting the variation of Integral Dose (ID) related to treatmenttechnique complexity.Materials: Ten patients with non operable NSCLC (stage IIIB) were treatedwith TTHA and re-planned tor IMRT and 3DCRT. Prescribed dose to PTV of64.5 Gy was delivered in 30 fractions. The target volume was considered theprimary tumour and the metastatic lymph node area, ranging from 100 to 300cc. Both 3DCRT and IMRT treatment plans were optimized with Pinnacle3(cc convolution algorithm) for a 6MV Siemens Primus. TTHA plans character­istics: pitch of 0.25 or 0.287, beam width 2.5cm, MA from 1.2 to 2.68.3DCRTplans characteristics: five coplanar wedged tields.IMRTplans characteristics:five coplanar beam, DMPO optimization, Step&Shoot delivery.Dosimetriccomparison on PTV coverage was carried out calculating conformal indexCOIN (Baltas 1998), homogeneity S-index (Yoon 2007). OAR sparing wasevaluated reporting Dmean and V20 for lung, V50 and V30 for esophagus,V30 for heart and Dmax for spine. Dosimetric evaluation on dose distributionand DVH were performed with an in-house software.Quantitative radiobiolog ­ical considerations on DVHs were performed with BIOPLAN (Sanchez-Nieto2000).To evaluate in-field 10 (D'Souza 2003) to normal tissue (NT), a ROIwas created with standardized criteria for all patients, including all body tis­sue from 2.5 cm above PTV to 2.5 cm below it, avoiding PTV. To evaluateout-ot-field NT exposure the volumes of isodoses below 5 Gy were calculatedfor all the patients and planning techniques.Results: Despite of PTV coverage was between 95% and 105% of pre­scribed dose for all techniques, a more conformal and uniform dose distri­bution was achieved with IMRT and TTHA with higher TCP values calculatedfor TTHA plans.A reduction of doses to OARs was observed with the increaseof technique complexity, either for dose-volume indicators as for Dmean andDmax. TTHA and IMRT plans in-field ID has decreased of about 10% re­spect to 3DCRT. Concerning to out-of-field NT exposure, technique complex­ity leads to low doses irradiation of larger volumes as the increase of 5Gyisodose volume showed.Conclusions: A reduction of in-field ID related to the increasing techniquecomplexity for lung cancer treatments was observed as showed by other au­thors for pelvis (Ayoama 2006). For TIHA out of field dose for NT increasesaccording to previous results (Tao 2006).

S 558 PHYSICS AND TECHNOLOGY: TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

1626 poster 1627 poster

INTER-INSTITUTIONAL COLLABORATION FOR THE CLINICALINTRODUCTION OF VMAT FOR HEAD-AND-NECK CANCERA. Holt! , D. Van Gestel 2

, M. Arends", E. Korevaar" , D. SchuringO, M.

Kunze-Busch 6 , R. Louwe6, E. tamers", C. van Vllet-Vroeqlndew]!

1 THE NETHERLANDS CANCER INSTITUTE - ANTONI VAN LEEUWENHOEKHOSPITAL, Department of Radiotherapy, Amsterdam, Netherlands2 UNIVERSITY RADIOTHERAPIE DEPARTMENT ANTWERP, Antwerp, Belgium3 RADIOTHERAPEUTIC INSTITUTE FRIESLAND, leeuwarden, Neiherlands4 UNIVERSITY MEDICAL CENTER GRONINGEN, Department of RadiationOncology, Groningen, Netherlands5 CATHARINA ZIEKENHUIS, Department of Radiotherapy. Eindhoven,Netherlands6 RAOBOUO UNIVERSITY NIJMEGEN MEDICAL CENTER, Department ofRadiolherapy. Nijmegen, Netherlands

INTRAOPERATIVE RADIOTHERAPY SIMULATION USING RADI­ANCE: INITIAL EVALUATION BY RADIATION ONCOLOGISTSJ. Pascau", J. A. Santos Miranda2

, A. Bouche". V. Morill03, J. Lopez", C.

Gonzalez-San Segund0 2 , F.Carlos", M. Desco ': F.Calvo"1 HOSPITAL GENERAL UNIVERSITARIO GREGORIO MARAf>iON, Unidad deMedicina y Cirugia Experimental, Madrid, Spain2 HOSPITAL GENERAL UNIVERSITARIO GREGORIO MARANON, OncoloqiaBadioterapica, Madrid, Spain, HOSPITAL PROVINCIAL DE CASTELLON, Oncologia Hadoterapica,Castellon, Spain4 HOSPITAL PROVINCIAL DECASTELLON, Radiotisica, Castellon, Spain5 HOSPITAL GENERAL UNIVERSITARIO GREGORIO MARANON, Oncologia,Madrid, Spain

1628 poster

Conclusions: The results show that radiance tool can be used to simu­late IOERT cases of different locations. The three ORs provided completelyequivalent results for 65% of the cases evaluated. The results demonstralethat agreement in segmentation protocol, and information from the surgicalprocedure, are necessary to obtain equivalent simulations. This tool allowscomparing the approaches from several users, and can be used to exchangeexperience between ORs with more and less experience, and also to o.s­cuss the surgical procedure with the surgeons. This work was supported byprojects PI08i90473 and PI09f90568.

Purpose: Intraoperative External Radiotherapy (IOERT) is a challengingtreatment since it involves radiation therapy and surgery. Patient specific plan­ning systems for this technique have not been previously available. Radiancevirtual simulator has solved this limitation. This tool simulates the treatment inseveral steps: segmentation, by which the user can select regions to irradiateand regions to protect; applicator positioning using the CT image and 3D ren­dering to guide the process; parameter selection (applicator diameter, bevelangle and electron beam energy) by optimizing the Dose Volume Histograms(DVHs) on the different regions. The result of the process can be stored In asingle file, allowing the comparison of different procedures. The purpose ofthis work Is to evaluate the tool in clinical cases by several radiation oncclo­gists (RO).Maferials: 14 cases, with a CT previous to IORT, were used for the evalua­tion. They Included the following locations: breast (3), rectal (6), rectal relapse(1), ovary relapse (1), pancreas (1), retroperitoneal (1) and Ewing sarcomas(f). All were simulated by three different ROs: R01 was an specialist withiong experienoe on IOERT procedures, and his simulations were used as areference. R02 and R03 were less experienced users. CIInical history of thepatient was provided with every case. Each evaluator segmented the regionsof interest, placed the applicator and selected the treatment parameters inorder to obtain the best dose coverage on the target volume. Concordancebetween users was evaluated for the following aspects: segmentation regions(qualitatively), treatment parameters (considering agreement when parame­ters were the same or within one step difference) and applicator position.Results: High agreement was found in the following cases: 3 breast and 3rectal cancer, retroperitoneal sarcoma, rectal and ovary relapses. All ORsperformed similar tumor and high risk areas segmentation. Parameter agree­ment was above 83%, and average applicator position difference was 1.26 em(0.6-2.19). However, the remaining locations showed higher deviations in theresults because of two main reasons: different criteria for segmenting highrisk areas (1 rectal and 1 pancreas) and different surgical access simulated(2 rectal and 1 Ewing).

I~ oPllk."1*_" _ eJO' and _gy 12 V

Rod ..... _

em

Average difference ± SD p-value(VHAT - IHRT) (paired t-test)

PTV- elective Cl95 - 0.16 ± 0.08 .009

PTV - boost e[95 o ± 0.2 n.s.

Omax (Gy) -1.3 ±3.1 n.s.Brainstem

Omean (Gy) . 1.0 ± 5.2 n.s.

Omax (Gy) - 2.5 ± 3.8 n.s.Spinal cord

Dmean (Gy) -2.1±1.9 n.s.

V25 (%J - 6.9 ± 4.1 .020left parotid

Omean (Gy) - 2.1 ± 1.2 .014

V25 (%] - 6.2 ± 3.3 .014Right percttd

Omean (Gy) - 1.9 ± 1.5 .045

V25 (%) - 13.2 ± 9.8 .D4DOral cavity

Dmean (Gy) - 2.5 ± 1.1 007

V45 (%J - 8.3 ± 4.8 .018Larynx

Dmean (Gy) -1.7 ± 1.5 n.s

Pharyngeal V45 (%) 0.5 ± 14.7 ns.constrictors

Dmean (Gyj o ± 2.0 n.s

Conclusions: Collaboration between institutes on the clinical introductionof a new treatment modality can help to accelerate the learning curve and,resulting from exchange and discussion within the group, to achieve a highquality ot treatment planning within a short time. VMAT plans for SIB treat­ments of HNC were found to be comparable or better than IMRT plans, whiledelivery time can be Significantly shortened.

Purpose: The main advantage of VMAT is a decreased treatment time, lead­ing to improved patient comfort and smaller intra-fraction variations. In theNetherlands, five institutes established a workgroup to aid a fast and secureclinical introduction of VMAT for treatment of head-and-neck cancer (HNC)and to assure a high quality of VMAT treatment planning in all participatinginstitutes. At the same time, this collaboration allows a more objective evalua­tion of the potential of VMAT for HNC as a replacement for IMRT techniques.Malerials: For treatment planning, CT datasets of five patients including de­lineated structu res were shared between the participating institutes Four In­stitutes used Pinnacle ' (Philips Medical Systems) and one institute OncentraMasterplan (Nucletron) to produce treatment plans to be delivered on Elektalinear accelerators equipped wilh a standard MLC or alternatively a beammodulator. Both trealment planning systems make use of VMAT optimizationmodules developed by RaySearch Laboratories. According to a treatmentprotocol agreed on beforehand by all participating institutes, which included aguideline for dose prescription and plan acceptance criteria, VMAT and IMRTplans were generated for a simultaneous inlegrated boost (SIB) treatment ofHNC. All institutes used their locally developed treatment planning techniqueand inverse planning objectives as starting point.Results: All institutes rapidly succeeded in producing clinically acceptableVMAT plans for SIB treatments of HNC with only small changes to the inverseplanning objectives used for IMRT. Differences between both IMRT and VMATplans of different lnstltutes tended 10 be small, and may be due to the plan­ner's preferences, guided by each institute's clinical practice. Discussion oflhe results and exchange of information regarding VMAT treatment planningparameters and objectives resulted immediately in further improvement of theVMAT plans. Preliminary results from comparison of VMAT and IMRT plansof the same Institute for a single patient showed significantly better sparingfor most OAR's (see table). In this case, the mean dose to parotids and oralcavity was reduced to on average 23 Gy and 33 Gy for VMAT, respectively, ascompared to 25 Gy and 35.5 Gy for IMRT. VMAT plans were found to have anoverall better conformity for the elective PTV. All institutes reported for VMATa reduction in delivery times by about 50% as compared to IMRT.

IS IT POSSIBLE TO IMPROVE FORWARD PLANNED MULTISEG-

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 559

MENT LUNG PLANS USING XIO OR MONACO IMRT?M. Essers", S. Ho12

, G. D'Olleslaqer". M. van de Pol2

1 INSTITUTE VERBEETEN, Medical Physics,Tilburg, Netherlands2 INSTITUTE VERBEETEN, RadiationOncology,Tilburg, Netherlands

Purpose: Toinvestigatewhether the radiationtreatment of stage III lung can­cer patients, treated to a dose of 66 Gy, can be improved using the IMRToptions of XiO or Monaco (CMS).Materials: A retrospectiveplanning study hasbeen performed tor 10patientswith stage III lung cancer. The prescribed dose was 66 Gy in 24 fractions.The treatment criteria tor lung cancer patients were as follows: 100% of thePTV must obtain at least 90%, and 100% of the CTV at least 95% of theprescribed dose .The lung volume receiving 20 Gy or more, V20Gy, mustbe smaller than 25%, while V5Gy < 60%. and the mean lung dose (MLD)must be <;: 16Gy. For the oesophagus,V45Gy < 25%. The maximumspinaicord dose is 50 Gy. Standard forward planned multisegment plans (3 to 5beam directions, and up to 3 segments per beam) were compared (usingthe abovedescribed dose criteria) with IMRT plans calculated using X,OandMonaco. The difference between the two CMS products is that XiO usesdose(-value)objectives,whereas Monaco (in addition also based on a MonteCarlo dose calculation algorithm) applies dose{-value) as well as biologicalobjectives AND constraints. A class solution using more or less standardbeam directions and prescription values was developedand used.Results: The IMRTclass-solutionconsists of 5 coplanarbeams, more or lessequally spaced over 200 degrees. The XiO plan consists of 41 to 82 (aver­age 60) segments, while the Monaco plan consists of 35 to 57 (average46)segments. Using XiO, no substantial improvementwith respect to the stan­dard treatmentplans was found tor all studied dose(-volume)values (Tabie1).The MLD could be slightly improved for 4 patients, whereas for the other 6.the MLDwasequal or even higher,comparedto the conventionalplans.UsingMonaco,the lung and oesophagusdose could substan1ially be improved (Ta­ble t}, In addition. for 2 patients. routinely and using XiO IMRT, a PTV doseof only 60 Gy was possible, while using Monaco IMRT, a PTV dose ot 66 Gywas achievable.

V:;COOI.I,",~g V:5G~'iu~~ MLD (Gy) V4~G~'L'~~

Conventional 22% 54% 16_1 32%

XiO1J'.~RT 23% 53% t58 30%

~onaco IMRT 18% 41)% 13.8 21%

Table i: Comparison ofaverage tUfJg V;:x,. VSG(, Ml.D and Ot?S~hagu"5 V"5GY for CGnveiific ,v3,'

hmg plans in XiO.. lMRT plans m XiD and lMRT plans in Monaco,

Conclusions: Using Monaco it is possible to improve the target coveragewhile reducing lung and oesophagusdose, comparedto standard plans. Us­ing XiO. no substantial improvement in the dose coverage or dose sparingcan be achieved.

40%,4% to 60%for 010 and 00.1em. respectively. For rectumthe differencewas 25% to 70%, 1% to 57% for 010 and DO.1 em, respectively.Conclusions: Different patient position during the real-time procedure andCT acquisition results in diHerences in geometry of the analyzed structures(prostate gland and organs at risk). Statistically significant differences wereobserved between dose distribution parameters for rea-time intraoperativeUS-baseddosimetry and post-implant CT-based dosimetry. For the CT post­dosimetry high dose area parameters lor the prostate (Vt50, V200) weremore conservative. The doses for the urethra were higher and lhe doses forthe rectum were lower than for US-baseddosimetry.

1630 poster

LEAF INTERDiGITATION AND SMALLER LEAFS HAVE NO EFFECTON THE QUALITY OF VMAT TREATMENT PLANSZ. Kesterenvan, E. Darnen", C. van Vllet-Vrceqindewi] 'I THE NETHERLANDS CANCER INSTITUTE - ANTONI VAN LEEUWENHOEKHOSPITAL, Radiotherapy, Amsterdam. Netherlands

PurpGse: Varioustypes of MLCs are available on the market, allowing leafinterdigitationand with various leaf widths. The purposeof this study is to de­termine the effect of interdigitationand leafwidth of Elekta MlCs on volumet­ric modulated arc therapy (VMAT) treatment planning in Pinnacle'' (PhillipsMedicai Systems).Materials: Three types of MlCs were modelled in Pinnacle. First. an ElektaMLC with 1 em ieats without interdigitation (regular MLC) was Implemented.From this machine, two interdigitating MLCs were modelled: one with 1 cmleaf width (interdigit MLC) and one with 0.5 cm leaf width (thin MLC). AllMLCs have a field of view of 40 by 40 ern", The eHect of interdigitationandleaf Width is expected to be more pronounced for irregular tumour shapes.Different tumoursshapes were studied;prostate and early-stage lung canceras an example of more spherical PTVs. rectum and head-and-necktumoursfor more concave and irregular PTVs. Five patients were randomlyselectedper tumour site. Treatmentplans were generated with the SmartArc modulein Pinnacle version 9. Healthy tissue integral dose (10), dose conformity(CI) and dose homogeneity(DH) in the PTV were compared, where DH wasdefined as (Drnax Dmin)iDmean. For the various tumour sites, the mean andmaximumdoses in OARswere evaluated.Results: The three MLCs had statistically significant different performance,although the differences were small. The performance of the interdigit andthin MLC relative to the regular MLC is summarized in the table; an asterixdenotes degradation in performancewith respect to the regular MLC.The IDincreased for both types of MLC whereas the CI improved. The DH becameworse for the interdigit MLC and improved for the thin MLC. Stratifying pertumour site pointedout that these differenceswere most prominentfor rectumand prostate tumours. No statistically significant differences in mean andmaximumdoses in OARswere observed.

1629 poster

+ 2.02 Ow"; - 10.81 %

+ 1.08 6/0 :&:: + 0.14 %)0;-0.36% -2.34%

PTV Dose Homogeneity <DH)

Healthy tissue [ntegral Dose (,,,,lD~)L--'"-}-E;;;."-------'~'E;;;."-~Conformity Index V95% rcn

Conclusions: Although statistically significant differences in 10, CI and DHwere observed, the clinical relevance of the increase in 10 and decrease inCI IS debatable. No tumour shape dependent improvementswere observed.In the case of 10 and DH, the interdigit MLC yields poorer results than theregular MLC. in contrast to expectations.

Relative difference to regu'.r NLCrn~l'djgJt HLC Thin /tft.CIS THE DOSE DISTRIBUTION BASED ON TOMOGRAPHY IN

THE LONG TERM AFTER IMPLANTATION COMPARABLE WITHINTRAOPERATIVE TRUS-BASED PLANNING, FOR REAL-TIMEPERMANENT 1-125 PROSTATE BRACHYTHERAPY?G. Zwierzchowski", B. Blas.ak", J. Skowronek.'

i GREATER POLAND CANCER CENTRE, Medical Physics Department,Poznan. Poland2 MEDICAL UNIVERSITY, Electroradiology, Poznan,Poland;3 GREATER POLAND CANCER CENTRE, Brachytherapy Department.Poznan,Poland

Purpose: The advantageof low-dose rate prostatebrachy1herapy is the qual­ity of life after treatment, good clinical results and short, one-time hospitaliza­tion. CT/MR-basedpost-dosimetry is the mandatory procedure after implan­tation. The structures' geometry during the implantation is different from thegeometry during the dose delivery.The aim ot this study was to compare thedose distributions for real-time intraoperative US-baseddosimetry and post­implant CT-based dosimetry.Materials: The dosimetry resuits tor 20 patients implanted with linked 1-125seeds were analyzed. A real-time intraoperative procedure was performedunder general anaesthesia. The treatment plan containing information aboutseeds' positions and dosimetry parameters for prostate and critical organs(urethra, rectum) was prepared, and 1hen1-125 seeds were introduced intothe prostate gland. CT scanning on the next day after implantationwas per­formed to evaluate the positions of the seeds. The study was based on twogroups of patients: with CT scans one day after implantation (11 patients)and with CT scans after one day and one month (9 patients). For both imag­ing modalities (TRUSand CT images) the dosimetry parameters for prostate(090.00.1 cem,V100, Vt50. V200), urethraandrectum (010, DO.1ccm) wererecalculated for each patient. .Resulls: US and CT based analysis showed difterences for 010, 090,DO.1cm, V100, V150 and V200. For prostate the differencewas 4% to 40%,1% to 17% for 090 and DO.1 em and 7% to 32%, 2% to 36% and 4% to 42%for V100, V150 and V200, respectively. For urethra the difference was 5% to

1631 poster

LOCAL EXPERIENCE IN KIDNEY DOSE REDUCTION USING AMULTIPLE-FIELD CONFORMAL RADIOTHERAPY TECHNIQUE FORGASTRIC CANCER TREATMENTSR. TortosaOliver', C. Andres Rodriguez', del Castillo Belmonte'. D.Aionso HernandezI , R. Barquero1

, HOSPITAL CLiNICO UNrvERSITARro, Department of Radiophysics,Valladot, Spain

Purpose: Gastric tumors are usually very difficult to be treated with stan­dard radiotherapytechniques due to delivered doses in kidneys. We presentour experienceusing a multiple-fieldconformal radiotherapytechnique whichsignificantly reduces dose delivered In kidneys. This technique is comparedto the more commonly used, four-field box around the target (0-90-180-270orentations).Malerials: 20 patients with gastric tumors are analyzed. In all cases, 45 Gyare prescribed to 1.8 Gy!session fractionation. Twotreatment techniquesareplanned. using 15 MV photons: - Box: Four-field arrangementwith standardquidelines (0-180-270-90).- Multiple-field conformal technique: Four-fieldar­rangement distributed around the upper right quadrant, consisting of these

S 560 PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

fields: Antero-posterior (0), left-lateral (90), right-anterior (-325) and left­anterior (35-45). These fields can be complemented with segments to im­prove dose distributions. In addition, enhanced dynamic wedges of 60 areused in fields RA and LLBoth techniques were planned to give similar targetcoverage, and delivered dose to normal tissues is compared using parame­ters as V20 (percentage of volume receiving 20 Gy) in kidneys or maximumdose in spinal chord.Results: The conformal technique provides much higher dose conformationaround target volume with non-significant differences in doses to target vol­umes (variations less than 0.3%), as seen in Figure 1. The irradiation ofhealthy tissue has considerably diminished with this technique. In the caseof the sum of both kidneys, V20 parameter decreases almost 30%, beingmore important in the right kidney (56%) than in the left kidney (10%). Non­significant variations are found in doses to other organs at risk, being belowtolerances for both techniques in every case.

Fig 1. Dose distribution using two techniques: box (left) versus conformedtechnique (right).Conclusions: The conformal technique reduces up to 30% the volume ofboth kidneys that receive inadequate dose level. These improvements arefurther complemented by a higher conformation to the target volume withouta reduction in the dose levels received by the tumor.

1632 poster

MODELING OF THE TREATMENT HEAD OF A NEW MOBILEELECTRON ACCELERATOR FOR IORTP.Adrlch", A. Nieciecka', A. Wasilewski', A. Wysocka-Rabin'

i THE A. SOLTAN INSTITUTE FOR NUCLEAR STUDIES, Accelerator Physics~nd Technology Dpt, Otwock-Swierk, Poland

WARSAW UNIVERSITY OFTECHNOLOGY, Warsaw, Poland

Purpose: Intraoperative radiation therapy (IORT) enables a high dose ofelectron radiation to be delivered in a single fraction directly to an exposedlocation, after tumor ablation during oncological surgery. First, highly-mobileelectron accelerators, dedicated for IORT, have been developed in the lastdecade. Construction of such machines differs considerably from the con­struction of linear electron accelerators for teleradiotherapy. The purpose ofthis work is to find an optimal solution of a treatment head assembly and appli­cators for a new mobile electron accelerator for IORT that is being prototypedat our institute.Materials: Two variants of the treatment head assembly and applicators weremodeled. For the first variant, the overall mass was minimized while for thesecond model, the compactness (SSD) was subject of minimization. Bothmodels incorporated circular applicator tubes of diameters ranging from 4 to10 em. For each model the scallering and flallening foils were first found fol­lowing prescription given by K.K. Kainz et al., Phys. Med. BioI. 50 (2005)755-767. Then, using Monte Carlo codes BEAMnrc and DOSxyznrc, a colli­mation system was modeled and its influence on therapeutic beam propertieswas calculated. The calculations were carried out for initial beam energiesranging from 4 to 12 MeV. An iterative procedure of consecutive adjustmentsof the scallering foil(s) and collimation system was carried on until the model,in the same time, (i) resulted in desired properties of therapeutic beams forall beam energies and field sizes (i.e. good depth-dose profile, good flatnessof the off-axis dose profiles) and (ii) assured fulfillment of the radiation pro­tection requirements as specified by state and international requlations andrecommendations.Results: For the first model, the optimization procedure resulted in a lightweight, simplified construction, lacking of heavy, metallic collimators andequipped with a single scattering foil and plastic applicator tubes. For thesecond model, the procedure allowed to minimize the SSD by means of em­ploying metallic applicators and a system of scallering-flallening foils filledinto a relatively heavy, metal collimator. In each case the scallering foil(s)Is(are) universal for every beam energy and every field diameter.Conclusions: Two different models of the treatment head and applicatorsfor a newly prototyped electron accelerator for IORT have been designed,verified and optimized based on Monte Carlo calculations. Prototype modelswill be constructed and tested in the laboratory. Final selection of the modelto be incorporated in the accelerator prototype will be based on the results ofthe laboratory tests and mechanical considerations concerning constructionof entire accelerator. This work was funded by the polish Ministry of Science

and Higher Education and the European Union in frame of the OperationalProgramme Innovative Economy, project no. POIG 1.1-21.

1633 poster

MONITORING OF MAINTAINABILITY OF DEEP INSPIRATIONPHASE VIA CINE ACQUISITION, IN PATIENTS WITH BREASTCARCINOMA RECEIVING RADIOTHERAPYE. Goksel", E. Malcok", M. Garipaqaoqlu", Senkesen', H. Kucucuk", E.

Tezcanli", M. Seng6z2, I. S. Aslay'

, ACIBADEM KOZYATAGI HOSPITAL, Department of Radiation Oncology,Kozyatagi - Istanbul, Turkey2 ACIBADEM UNIVERSITY, Department of Radiation Oncology, Istanbul,Turkey3 ISTANBUL UNIVERSITY ONCOLOGY INSTITUTE, Department of RadiationOncology, Istanbul, Turkey

Purpose: Radiotherapy (RT) in deep inspiration (DI) phase is recommendedbecause of reducing exposed heart dose for patients with left breast cancer.This prospective study evaluates whether deep inspiration phase was main­tained by patients receiving radiotherapy during this phase.Materials: Twenty-one patients receiving adjuvant radiotherapy were in­cluded. All patients were positioned supine on breast board. Computer­ize Tomography images were taken in the treatment position for 3 differentseries: during free breathing (FB), DI and end of expiration (EE). By thismeans, whether patients could keep different respiration phases such as EEand DI were tested. Targets and organ at risk (OAR) were delineated onFB and DI series. For each patient, three dimensional conformal plans weredone on FB and DI series using planning system (Varian Medical Systems,Eclipse, Version 8.6). Qualities of both plans were evaluated based on ourin-house protocol considering target dose homogeneity and lower OAR (lungand heart) doses. For all patients DI plans were found better than FB plans.Therefore DI plans were chosen for treatment. In order to reduce the treat­ment time, 600MU/min dose rate was chosen. Then breath control educa­tion was given to patients, their compliance of DI phase was double checkedin simulator. Maintaining DI phase during treatment was monitored usingcine acquisition mode (CAM) of Linear accelerator (Varian Medical Systems,Clinac DHX-OBI) for the period of treatment in every fraction. CAM capturesseveral images of treatment fields during treatment which is useful to testcontrol breath holding. In this study, intratraction breath holding maintain­ing (BHM) was quantified as displacement of chest wall among first capturedimage and subsequent images. Moreover, magnitude of breath holding dif­ferences (BHD) were determined as measuring chest wall position variationbetween planning and captured images at the beginning of treatment. Fur­thermore, relation of treatment time and patient compliance was studied.Results: Two of 21 patients were excluded because they could not havebreath control after evaluating planning CT series. Three of remaining 19patients were excluded since they could not maintain breathing in DI phasesin simulation. Sixteen patients received treatment during DJwhile excluded5 patient received their treatment without breath control. Treatment plan pa­rameters of DI and FB were different in all patients. Median treatment timesfor fields were 11,97 (26,98-6,65) seconds. Median BHD and BHM displace­ments were found 0,245 (0-0,86)cm and 0,07 (0-0,31)cm respectively. BHDdifferences were <OAcm in all but 2 patients. Treatment time did not effectpatient compliance.Conclusions: Although treatment in DI phase is successful to reduce expo­sured heart and lung dose, some patients could not keep breath holding inDI phase. Radiotherapy during DI monitored via CAM could safely used in aselected patient.

1634 poster

NEW RADIATION THERAPY TECHNIQUE FOR CRANIOSPINALIRRADIATION WITHOUT JUNCTION MOVEMENTJ. M. Lee', S. K. Ann", K. Jeong', J. W. voon', J. H. Cho", C. O. Suh ', YONSEI CANCER CENTER, YONSEI UNIVERSITY HEALTH SYSTEM,Department of Radiation Oncology, Seoul, Korea Republic of

Purpose: To introduce a treatment method to maintain the homogeneity ofdoses to tumors without any movement of field junctions in patients receivingcraniospinal irradiation (CSI) divided into three treatment sites.Materials: The subjects of this study were 5 supine patients and 5 pronepatients with medulloblastoma being treated in three separate fields, rangingfrom the brain to the sacrum spinal canal. For cranial field, half beams wereused, and the Y2 field was opened to 20 em. The isocenter was set at the2 level of C-spine with SAD 100 em, and then the collimator was rotated.The isocenter of the upper spinal field was set to be the same as the cranialisocenter, and half beams were used to make the Y1 field 20 em. the couchwas rotated by 2700

, and the gantry was rotated to obtain the same angleas the cranial collimator angle. To match the divergence of the lower spinalfield WIth that of the inferior border of the upper spinal field, the couch wasrotated by 2700

, and the gantry was rotated toward the head of the patientWIth the thick side of the wedge facing the head of the patient. The depth of

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 561

the isocenter of the lower spinal field was set to be the same as that of theisocenter of the cranial field. All the treatment plans were made using theradiation therapy plan system (Pinnacle3F

\ Philips, Netherlands).

Fig. 1. Sagittal geometry of new technique for CSI without jonction movementA: Cranial field (halt beam, collimator angle 5_7° , gantry ang Ie 90°)B: Upper spinal field (half beam, couch rotation 270°, gantry angle 5-7°)C: Lower spinal field (couch rotation 270 c

, gantry angle 10-15 e, wedge angle

10-15°)0: Isocenter of cranial field and upper spinal fieldE: lsocenter of lower spinal fieldF: Junction of upper spinal field and lower spinal fieldResulls: Determining the collimator angle of the cranial field as 5_70 is effec­tive in preventing the upper spinal field from falling on the chin. Determiningthe gantry anqle of the lower spinal field as 10-15 C and adjusting the notpoint occurring to the wedge angle (10-15°) are effective In preventing anyhot point area from occurring on the spinal cord. It is important to make tothe lower spinal superior field 10 cm or smaller in order to reduce the gantryangle. Close attention must be paid to superior size of lower spinal field Asthe lower spinal superior field increases by 2.5 cm, the qantrv angle increasesby 2" and the hot points in the spinal cord increase. Since half beams wereused on the cranial field and the upper spinal field, junction movements werenot necessary for these fields. The junction of spinal field could be identifiedvisually in the case of prone patients. In the case of supine patients, the di­vergence of the beams on the body of the patient was the same as that onthe bottom surface of the couch, and thus the junction could be identified vi­sually without moving the junction by attaching a piece of paper to the bottomsurtace of the couch While treating the patient.Conclusions: With this treatment method, CSI can be conducted while main­taining the homogeneity of doses without any junction movement However,this treatment method can not be used on patients with a length between theC-spine 2 level and the sacrum spinal canal exceeding 55 cm since wedgeshould be used to prevent the hot point depending on gantry angle.

1635 poster

OPTIMIZATION OF RADIOTHERAPY TECHNIQUE IN APICALLUNG TUMOUR: A COMPARATIVE STUDY OF 3D CONFORMALRADIOTHERAPY (3D CRT) WITH INTENSITY MODULATED RADIO­THERAPY (IMRT) AND VOLUMETRIC MODULATED ARC THERAPY(VMAT)C. MartinI J. Harrowven", R. Fitchett ", T V Ajithkurnar '1 NORFOLKAND NORWICH UNIVERSITYHOSPITAL NHS TRUST. Departmentof Oncology, Norwich, United Kingdom

Purpose: Apical lung tumours frequently present with localised disease. Thestandard management of these tu rnours is concu rrent chemoradiation fol­lowed by resection, but many patients with inoperable tumours will receiveradical radiotherapy or chemoradiotherapy. Because ot proximity to crrticalstructures, 3D CRT seldom results in inadequate tumour coverage. IMRThas the capacity to produce steep dose gradients and thus can deliver highdoses of radiotherapy to lhe tumour volume with conformal avoidance of crit­ical structures. VMAT can deliver IMRT in a short 1reatment time. This studywas done to determine the optimal radiotherapy technique in apical lung tu­mours.Materials: CT data sets of 5 previously treated patients With apical lung tu­mours were used. For each data set 3 plans were generated: a two-phase3D CRT an IMRT and a single arc VMAT using RapldArc. The prescriptiondose was 66Gy in 33 fractions whilst dose to the spinal cord with a margin of5mm was limited to 46Gy, dose to the oesophageal V50 below 32% and thebrachial plexus dose below 60Gy. Plans were compared using PTV coverageand the volume of lung minus PTV receiving 5% (V5i, 20% (V20) and 40 %(V40) ot the prescribed dose.Results: Even with IMRT and VMAT it was difticult to achieve PTV coverageas recommended by ICRU 50/62. With 3DCRT, the mean PTV covered by95% isodose was 66.2% (range 54.6 80.1) compared With81.7% (range 76.287.3) with IMRT and 81.3% (62.7- 92.7) with VMAT (p~0032J Similarly IMRTand VMAT resulted in more PTV volume covered oy the 90% 01 prescribeddose than with 3D-CRT An average of 91.6% of PTV was covered with IMRT

(range 85.6- 96.6). 92.7% with VMAT (range 86.2-99.2) and 78% with 3D CRT(range 60.3-861) (p~O.024). This improvement in PTV coverage with IMRTand VMAT was achieved without significant difference in V5 {p~0.87}, V20(p~0.81) and V40 of lung (p=0.18) compared with 3D CRT. However, bothIMRT (mean 722; range 651- 767) and VMAT (mean 487; range 393-581)resulted in higher monitor units compared with 3D CRT (mean 240; range227-270). A comparison of IMRT with VMAT has shown that VMAT resultsin equivalent PTV coverage by both 90% (p~O.I) and 95% (p=0.46) of pre­scribed dose, Similar V20 (p~0.07) and a smaller V5 (p=0.014). VMAT alsoresults in an average 32% reduction in monitor units compared with IMRT(p~0.0048).

Conclusions: This study shows thal both IMRT and VMAT can improve PTVcoverage of apical lung tumours compared with 3DCRT. without increasingdose to lung and within tolerance doses of the organs at risk. Even with IMRTand single arc VMAT a dose distribution as recommended by ICRU 50/62cannot be achieved and hence, radical radiotherapy of apical lung tumoursremains a major challenge due to proximity to neurological structures. VMAToffers the best possible PTV coverage with fewer monitor units than IMRT.Further studies are needed to find a class solution for radical radiotherapytechnique in apical lung tumours.

1636 poster

OUTCOME OF 72 PATIENTS TREATED WITH HYPOFRACTIONATEDSTEREOTACTIC RADIATION THERAPY (SBRT) FOR LIVER METAS­TASES: REPORT OF A SINGLE INSTITUTION'S EXPERIENCEN. Andratschke 1, M. Molls 1

, F. Heppt", S. Schillt, H. Geinitz'

I KUNIKUM RECHTS DER ISAR. TU MUENCI-iEN. Academic RadiationOncology Department, Muenchen, Germany

Purpose: To report on the outcome and toxicity in treatment of liver metas­tases by hypofractionated stereotactic body radiation therapy (SBRT) in pa­tients not eligible lor surgical treatment.Materials: From 2000 to 2009, 72 patients with 84 metastatic lesions in theliver not eligible for surgical resection have been treated with SBRT at our in­stitution. lrnmnbilisation for image acquisition and treatment was carried outin a vacuum couch with a low-pressure foil. Additionally, patients receivedoxygen during CT scanning and treatment to reduce breathing motion. Plan­ning target volumes ranged from 43-1074 ccm. Treatment consisted of 3-5fraction with 5-12.5 Gyl fx prescribed to the surrounding 60-95% isodose.Minimum dose to the plann ing target volume was prescribed depending onthe given dose constraints for the small bowel (maximal total dose < 5x5.4or 3x7.0 Gy). Follow-up 6 weeks after completion of SBRT and every 3-4months thereaHer included blood count, serum liver parameters and CT and/or MRI scans until tumour progression.Results: Initial follow-up data from 67 patients indicated a high local con­trol rate of 80% at 3 years for lesion treated with 3x12.5 Gy or <10OCcmand40% at 3 years for lesion treated with 5x7Gy or > 100ccm with discouragingprogression-free and overall survival due to systemic progression. Overallsurvival at 24/48/72 months was 44%, 321% and 20%. Treatment was tol­erated very well with only minor side effects like grade loll taligue, nausea,dermatitis, gastritis (n~1) and cholezystitis (n=1; antibiofic therapy). Long­term complications included 1 skin ulcer (local surgery) and 2 rip fractures(analgesics1 due to radiafion necrosis in areas within the 60%-isodose. Inthis analysis we will present long-term follow-up data after 9 years of experi­ence in SBRT of liver tumours.Conclusions: SBRT proved as a highly eHective local treatment option forliver metastases without major side effects observed so far. Local contro l wasmainly influenced by lesion size and radiation dose, while overall survival waspredominantly affected by lesion size. Unfortunately, systemic progressionstill inhibits long term survival in this poor prognostic group wilh very few longterm survicors.

1637 poster

PARAMETERIZE BREATHING CURVES AND THE CORRELATIONOF BREAHTING CHARACTERISTICS WITH PATIENT PARAMETERSB. Guo", L Vazquez.", X. G. Xu", C. Shi 'I UNIVERSITYOF TEXAS HEALTHSCIENCE CENTER/CANCER THERAPY ANDRESEARCH CENTER,Radiat ion Oncology, San Antonio, USA2 RENSSELAER POLYTECHNIC INSTITUTE, Nuclear Engineering Department,Troy. New York, USA

Purpose: Breathing curve of lung patient is an important parameter fermotion management in radiation therapy. The characteristics of breathingcurves, such as amplitude, period, baseline and brealhing 'irregUlarity" arecritical factors in a 40 treatment planning/delivery. Generally, these charac­teristics are considered as patient specrtic however few studies to analyzethe relat ionsh ip of patient features with them exist. In this study, we proposeda simple yet accurate method for analyzing the characteristics of breath ingcurves and study the correlation of them with patient features.Materials: Piecewise cosine functions are used to fit breathing curves anddetermine Ihe characteristics. The equation below describes the piecewise

S 562 PHYSICS AND TECHNOLOGY: TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

cosine function in which lp(i) and tl(i) are the peak and lrough of i-th cycle.A1 and A2 correspond to Amplitude, wI and w2 correspond 10 lhe angularfrequency, and B1 and B2 correspond to the baseline of cycles. For a patientwith irregular breathing pattern, piecewise cosine fitting yield a mean error of0.04 mm. Statistical analysis is performed to correlate mean and standarddeviation of amplitude, period and baseline over breathing cycles with pa­tient parameters including age, gender and tumor site, base on a total of 305breathing curves from 158 patients acquired using Real-time Position Man­agement (RPM) system. Pearson correlation method is used to determinethe correlation of age with breathing characteristics. Two-sided unpaired t­test is used to study whether gender or presence of tumor in lung affect thebreathing characteristics significantly.yfitted It)=A 1(i}cos{wt (i)[Hp(i)]}+B 1(i);tp(i):S;kl1(i)y1itted(t)=A2(i)oos{w2(i)[I-tt(i}uIl+82(i); tt(l] :S;ktp(i+ 1)Results: Age has no correlation with breathing characteristics studied. Pear­son correlation analysis yields a correlation factor of only 0.083 (p = 0.185).Gender affects both the mean (p = 0.971) and standard deviation (p = 0.425)of breathing period. The effect of gender on breathing amplitude or baselinevariation is insignificant. Presence of lung tumor affects the mean amplitude(p = 0.317) and period (p = 0.384). The baseline variation is also affectedslightly (p = 0.860). Tumor location is irrelevant 10 the variance of amplitudeor period. Table 1 lists the raw data and results of the t-tests.

, . , . , , ,' ... ,t: "' ... 'lJ ,,,

"' It. '" ." .lJ- • ..., • J< .. 1111 .., .... I". II.' ...to .... • ))1 Ill' .- .... . .- .- • I .."_.

- c...• ..· ) ..1..····1 ' f... ·" 1 ., ( .,-of "'1 " •• • ....1. ........11 I": "' '" ,.. '" ,.. '" '" '".... ..., .... 111t .... "" lilt 'PI .. IIU II.'

to .." • IU lUI '"' 1 4.' .- , • • .." It')_.l' f..··ul .. I.....' . ) ' f"." " . .. C. · ....I . c... ....

Conclusions: Statistical analysis of large number of breathing curves revealsthat patient parameters may affect the breathing curve statistics thus affectingthe management of tumor motion in radiation therapy.

1638 poster

PERFORMANCE CHARACTERIZATION OF A HIGH-RESOLUTIONIMAGING SYSTEM FOR SMALL ANIMAL RADIATION RESEARCHA. Gasparini 1, R. Clarkson", P. Lindsay", J. J. Sonke'

i THE NETHERLANDS CANCER INSTITUTE - ANTONI VAN LEEUWENHOEKHOSPITAL, Radiation Oncology, Amsterdam, Netherlands2 PRINCESS MARGARET HOSPITAL, Radiation Oncology, Toronto, Canada

Purpose: j.dGRT systems bridge the technology gap between pre-clinicalradiation research and clinical radiation therapy. The purpose of this researchwas to quantify the CBCT image quality improvements of a new flat panelimager (FPI).Materials: The small animal image guided Irradiator XRad 225Cx (PrecisionInc X-rays, North Branford, USA) is a system that combines a high accu­racy CBCT imaging system and a high dose therapeutic X-ray source on thesame platform. We evaluated lwo units with differenl a-Si FPI. Unil1 con­tains a XRD 512-400 (Perkin Elmer, Waltham, USA) with Gd203 scintillator,a sensitive area of 20.48x20.48 cm2 and a pixel pitch of 400 j.lm (512x512pixels). Unit 2 contains a XRD 0820 AN with a Csi scintillator and a 200j.lm pixel pitch (1024x1024 pixels). The focal spot size on both units was 1mm and the focus-detector distance was 64.5 cm with a magnification M-2.Images were reconstructed using in-house developed software based on theFDK algorithm. Image uniformity, system spatial resolution and contrast tonoise ratio (CNR) were studied on a j.lCT image quality phantom. Three setsof about 580 projections were acquired over a 3600 gantry rotation: 40kV­50mA 40kV-250mA and 100kV-20mA. Images were reconstructed at 200 j.lmvoxel size for unit 1, and 100 /l.m and 200 I,·m for unit 2.

Axial slice of the spatial resolutionplane In the ~ICT image qualityphantom for unit 1 (top) and unit 2(bottom). The wire thickness of thecolis Is indicated. The images weretaken at 40 kV and 250 mA for bothunits.

Results: The x-ray detector XRD 0820 AN (unit 2) achieved a considerablyhigher spatial resolution compared to XRD 512-400 (unil1). The calculatedFWHM of the MTF increased from 0.7 rnrn' of unit 110 2.1 mrn' for 100 lim

voxel size in unit 2 (40kV-250mA). The MTF value at 10% of the maximumindicates that structures of 200 j.lm can be resolved (see figure). CNR wasabout 30% lower in unit 2 for the same voxel size. Image uniformity wassimilar between the two units with variations of about 4%.Conclusions: The X-ray detector XRD 0820 AN was successfully tested forthe small animal Irradiator XRad 225Cx. A higher resolution, fundamental forimaging of small animals, was achieved despite the relatively large focal spotsize. CNR however was reduced despite the Csi scintillator for all exposuresettings evaluated.

1639 poster

PERFORMANCE EVALUATION OF CYBERKNIFE TUMOR TRACK-

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 563

ING TREATMENTM. S. AI Khawaja1 , V. Marchesi", D. WOLF1, A. Noel3

! CRAN - CENTRE A. VAUTRIN, Academic Physics, Vandoeuvre-les-NancyCedex, France2 CRAN - CENTRE A. VAUTRIN, Vandoeuvre-les-Nancy Cedex, France3 CRAN - CENTRE A. VAUTRIN, Physics, Vandoeuvre-Ies-Nancy Cedex,France

Purpose: The CyberKnifeis a robotizedradiotherapysystem which, allowstotreat soft tissues tumors moving according to the respiratory motion, with thepossibilityof real time tumor trackingby means of its subsystem "Synchrony".This work tries to assess the submillmetricprecisionof this type of treatment.Materials: The collected data of 32 log files of synchrony treatments (for 10patients: 8 with three fractions, 2 with 4 fractions) were usee to simulate therespiratory motion of the tumors in dilferent locations (Liver, Lungs ...), byusing a dedicated platform. A ACCURAY plastic cubic phantom, which canreceive two radiochromic films in two central orthogonal plans (axial, frontal)was used to evaluate the geometric precision with the E2E ACCURAY soft­ware. A Shapiro-Wilk statistical test was used to verify the normality of thegeometric precision measurements.Gafchromic EBT films were used to per­form a Gamma index analysis with RIT113 software (v5.1) and to calculatethe differencebetweendeliveredand prescribeddose distributionsto the PTV(480 cGy @80% isodose) in the central axial plan. A Perfection V7001V750Epson Scannerwas used to digitize the films.Results: The geometric precision of tumor-tracking treatment with Syn­chrony, whichcan also be called the total targetingerror and which representsthe offset betweenthe centers of the delivered and the planed treatments, isalways inferior to the accepted limit of 1.5 mm with a maximum value of 1.42mm and minimum of 0.25 mm. The Shapiro-Wilk test shows that the mea­surements follow a normal distribution with p=0.74 mm and ",2=0.1. TheGamma index results, with a dose tolerance of 3% and DTA=1.5 mm, showan high agreement degree between the prescribeG and the delivered dose,with a good matching for the dose profiles in the vertical and the horizontalaxis. The number of pixels with a gamma value larger than 1 is always lessthan 5%. The difference between the delivered and prescribed dose calcu­lated over the entire PTV- is always inferior to 2%, with maximum of 1.41%,minimumof -0.5% and the mean =0.34% (1 SD=0.74%).Conclusions: The performance analysis of cyberknife tumor tracking treat­ment with synchrony shows that the system is capable to treat respiratorymoving tumors in different body locations,with a high precision for the differ­ent complexitypattern of respiratory cycle.

1640 poster

QUALITY ASSURANCE PROCEDURES DURING COMMISSIONINGOF A TREATMENT PLANNING SYSTEM AS A TOOL TO ESTABLISHNEW STANDARDS BEFORE MIGRATIONG. Bieleda", G. Zwierzchowski", B. Blasiak'~ GREATER POLAND CANCER CENTRE, Medical Physics, Poznan,Poland

MEDICAL UNIVERSITY, Electroradiology, Poznan, Poland

Purpose: Treatmentplanning system commissioning is one of the most im­portant parts of the quality assurance system in a working brachytherapyde­partment. Migrationto a more sophisticated system is always a step forwardfor the planning team but careful verification of the workflow and obtained re­sults is mandatory. The question is not only whether the quality and safetyof the previous standards can be preserved, but also about the pOSSibility ofreaching a higher level. The general objective of this study was to compareand verify calculation algorithms implemented in the treatment planning sys­tems Plato Brachytherapy v.14.3.7 and Oncentra Masterplan (Brachy) V.3.1SP 3.Materials: In order to revise the optimization algorithms implemented in thecomparee treatment systems, a series of 20 interstitial breast cancer appli­cations and 13 intracavitary gynaecological applications were used. Treat­ment plans were optimized using geometric optimizationwith distance optionand IPSA. The parameters V, D90, Dl00, Vl00, V150, V200 and DNR weregained for target volume and V, DO,I, Dl and D2 for the critical organs forthe GYN cases. On the basis of the value of Student's t-test parameters (O!= 0.05) plans prepared using optimizationalgorithms implemented in the twotreatment planning systems were compared.Results: For the treatment plans prepared using Oncentra Masterplan alower value of DNR (p = 0.018) was obtained. Uniformity of the dose distribu­tion does not collide with comparable D90 values for both treatment planningsystems (p = 0.109). Dose throughout the target volume (Dl00) was alsoprovedto be higher in plans preparedusing Oncentra Masterplan (p = 0.012).It was observed that the plans prepared for GYN intracavitarybrachytherapyby Plato Brachytherapy were characterized by a higher dose (D90) in a vol­ume of HRCTV (p = 0.006). On the other hand. dose distributions in theplans optimized using algorithms implemented in Masterplan Oncentraweremore homogeneous (p = 0.010). At the same time doses deposited in thecritical organs in the treatment plans calculated using Oncentra Masterplanwere lower.Conclusions: For interstitial applications (breast cancer) Oncentra Master­plan planning system enables one to prepare a more homogeneous dose

distribution. For intracavitary applications Plato Brachytherapy system en­sures better coverageof the target area but the dose is more heterogeneousand doses are higher in critical organs.

1641 poster

RADIOSURGICAL TREATMENT PLANNING OF AVM FOLLOWINGEMBOLIZATION WITH ONYX: POSSIBLE DOSAGE ERROR INTREATMENT PLANNING CAN BE AVERTEDN. Shtraus", S. Alanl", D. Schitter ", S. Mimon2 , B. Corn", A. Kanner2

.', TEL AVIV MEDICAL CENTER, Radiotherapy, Tel Aviv, Israel- TEL AVIV MEDICAL CENTER, Neurosurgery, TelAviv, Israel

Purpose: Treatment of arteno venous malformations (AVM) of the brain ischallengingdue to the size and location of the nidus-properand its proximityto the cerebrovascularcirculation, Recent advances in catheter techniquesand new immobilizationmaterialssuch as Onyx (a liquid agent that is lessad­hesive and slowly polymerizing) have increased the probability of achievingobliteration. When planning radiosurgical cases following such immobiliza­tion, however, one must be cognizant of the distortions introduced by thisnovel substanceon imaging studiesMaterials: A sample of Onyx was irradiated to define the attenuation permm thickness. The difference in attenuation compared to water was deter­mined. Dosecalculationswere performedusing 3 methods of inhomogeneitycorrections. Homogeneouscalculationswere comparedto "standard"hetero­geneity corrections and to "modified" heterogeneitycorrections by assigningindividual electron densities to the normal brain and the OnyxResults: The difference between the attenuation of water in comparison tothe Onyx was approximately3% for beam energy of 6 MV. Best calculationresults were achieved when using the mcoitiad inhomogeneity correctionswhich were based on the actual attenuationof the OnyxConclusions: The use of Onyx caused significant image artifact on MR andespecially CT. As such, a correction must be manually introduced into theplanning system to account for this potential error. Otherwise, dose calcula­tion may be unreliableand could havedire consequencesfor patients receiv­ing high doses of radiotherapy

1642 poster

RAPID ARC TECHNIQUES FOR PROSTATE CANCER TREATMENTL. Tsvang1 , S. Dubinski1, D. AlezraI , Z. Symon'

1 INSTITUTE OF ONCOLOGY, CHAIM SHEBA MEDICAL CENTER, RadiationTherapy

Purpose: The use of new radiotherapy treatment technique, such as RapidARC allows the achievementof good therapeutic results for the prostatecan­cer treatment and the optimal use of treatment delivery device. Therapeuticand treatment delivery parameters were compared using the Eclipse treat­ment planning system for the routine IMRT planning technique and differentRapid ARC techniques to identify the optimal planning.Materials: CT scans of 15 a low and median risk prostate cancer patientswith the gold seeds implanted to the prostate treated with Rapid Arc tech­nique were utilized for this study. Patients were immobilized in the supineposition with a knee rest. The followingstructures were contoured: proslateexpanded 0.6 em for PTV2; CTV including prostate and part ot seminal vesi­cles, expanded by 0.8 cm for PTVI and 1 emfor PTV;bladder; rectum; penilebulb and femurs.The additional structures were contoured for the use in thetreatmentplanning constraints. Prescriptiondose was 78-82 Gy.AII treatmentplans were plannedby two physicists.Three treatment techniqueswere com­pared: 7- fields IMRT plan and two various Rapid Arc plans (RA planl with2 arcs: 130°-230° and 250°-110°; R.A. plan2 with 2 arcs: 150°-210°). Themean dose for each structure and specific volume dose for critical organsnormalized to the prescription dose were calculated and compared for eachtechnique. Conformity index and dose deliver parameters also were com­pared.Results: The Rapid Arc plans allow to receive a desired dose interval forprostate,PTVI and PTV2structures. The dose to critical organs is somewhathigher for RapidArc plans in comparisonwith IMRTplan, but it is significantlylower than accepted in medical practice dose limitations. One of Rapid Arcplans can significantly reduce the dose to penile bulb and reduce to 50% theoperation time of the delivery device. Table 1 shows an average value ofmean dose for investigatedstructures and critical organs.

S 564 PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

Table 1. Average value of mean dose the IMRT plan and the Rapid Arcplanl for structures and critical organs (% of prescription dose).

Structures sort and IMRT plan Rapid Arc plan!critical organs

Prostate 100.85 101.1

95% PTVI vel. 96.87 96.97

95% PTV2 vol. 98.6 99.37

Rectum 33.9 35.17

Bladder 33,38 38

Femur head 22,9 31.4

Penile Bulb 50,7 39,6

Monitor Units 1349 693

Conclusions: The Rapid Arc technique with two arcs allows to achieve ahomogeneous and controllable dose to given structures, significantly reducethe daily patient treatment time and enhance the use of treatment equipment.

1643 poster

RAPID ON-LINE SOLUTION FOR SPINAL SBRT WITH ELiCALTOMOTHERAPY.S, Vagge!, M, Zeverino", A. Bacigalupo 1 , S, Aqostinelli", F. Cavaqnetto",

M. Guenzi", S, Barra 1 , F, Ricchetti!, R, Corvo 1

1 ISTITUTO NAZIONALE PER LA RICERCA SUL CANCRO, Department of~adiation Oncology, Genova, Italy

ISTITUTO NAZIONALE PER LA RICERCA SUL CANCRO, Department of~edical Physics, Genova, Italy

ISTITUTONAZIONALE PERLA RICERCA SUL CANCRO, Genova, Italy

Purpose: To develop a technique that allows for on-line acquiring images,planning and delivery of highly conformal dose distributions SBRT for verte­bral metastasis by the use of MVCT image guidance and StatRT (work-stationintegrated module for planning calculation),Materials: Three different smart protocols were elaborated, for the IMRTplanning optimization with StatRT for the cervical, dorsal and iumbar seg­ments of spinal column lesions, The principal intent was to obtain good targetcoverage and a fine cord sparing in the minimum calculation time as possi­ble. PTV was the entire vertebral body plus a margin of 1,5 mm, on the basisof our institutional experience and the cord was contoured as the vertebralcanal minus 3 mm. At first StatRT was compared versus Tomoplan than wesimulate the planning of 7 different clinical cases, Fractionation schedule was30 Gy in 3 consecutive fractions, based on a BED (assuming Oilf3= 2Gy) cal­culated as a median of the wide used schedules for spinal SBRT. DifferentOARs for different districts were taken into account during the developmentof our protocols,Results: In spite of equivalent good target coverage and OAR's sparing theStatRT calculation module in 5 minutes could obtain a 05 less than 64 % andof the PTV prescribed dose to the spinal cord. The median dose coverage tothe PTV was 93% for 095 and 103% for 05, We obtained a median beam ontime around 10 minutes, Tomotherapy MVCT scan could take 4 minutes toacquire simulation scan of more than 30 centimeters length in coarse mode,and the IGRT set-up usually doesn't take more than 5 minutes,Conclusions: Without taking into account the subjective variability of timeneeded to contour, we can say that approximately twenty-five minutes areneeded to pertorm a high quality treatment, with remarkable gain for patientsboth in terms of time consumption and in terms of high conformation of thedose delivered,

1644 poster

RAPIDARC VERSUS INTENSITY-MODULATED RADIATION THER­APY FOR HEPATOCELLULAR CARCINOMA: A COMPARATIVEPLANNING STUDYK, Kim", J, M. Park1

, E, K. Chie ", S, J, Yel, S, W.Hal

1 SEOUL NATIONAL UNIVERSITY COLLEGE OF MEDICINE, Department ofRadiation Oncology, Seoul, Korea Republic of2 INSTITUTE OF RADIATION MEDICINE, MEDICAL RESEARCH CENTER,SEOUL NATIONAL UNIVERSITY, Seoul, Korea Republic of

Purpose: To compare the dose-volumetric results of RapidArc (RA) withintensity-modulated radiation therapy (IMRT) in patients with hepatocellularcarcinoma,Materials: Twenty previously treated patients with hepatocellular carcinomawere the subjects of this planning study. Ten patients were treated for por­tal vein tumor thrombosis (Group A), and 10 patients for primary liver tumor(Group B), Prescription dose to the planning target volume was 54 Gy in 30fractions and the planning goal was to deliver more than 95% of prescribeddose to the 95% of planning target volume,Results: In Group A, mean doses to the liver and non-target liver were in­creased with RA vs. IMRT (22,9 Gy vs, 22.2 Gy and 18,7 Gy vs, 18,0 Gy, P= 0,0275 and 0.0307, respectively), However, V30 of the liver and non-target

liver was lower in RA vs, IMRT (31,1% vs, 32,1% and 21.4% vs, 22.6%, P =0,0283 and 0,0351, respectively), In Group B, however, neither mean dosesnor V30 of the liver and non-target liver significantly differ between the twoplans, V35 of duodenum and V20 of kidney was lower with RA in GroupsA and B, respectively (p = 0,0058 and 0,0124, respectively). Both maximaldoses to the spinal cord and monitor unit were significantly lower in the RAplan, regardless of the group,Conclusions: The dose-volumetric results of RA vs, IMRT were different bythe different target location within the liver. In general, however, RA tended tobe more effective in the sparing of non-liver organs at risk such as duodenum,kidney, andlor spinal cord, Moreover, RA was more efficient in the treatmentdelivery compared with IMRT in terms of total monitor unit used.

1645 poster

ROLE OF TC-RM IN THE DEFINITION OF PROSTATE CANCERVOLUMES FOR THE RADIOTHERAPY PLANNING,F, Locatelli", G, Beltrarno ", L.C. Bianchi", A. Berqantirr'

1 CENTRODIAGNOSTICO ITALIANO, CyberKnife Center, Milan, Italy

Purpose: Following advances in conformal radiotherapy, a key probiem nowfacing radiation oncologists, is target and organ at risk definition.This studywas performed to evaluate the suitabilityof MR (T1w and T2w sequences)with CT to provide improved definition of pelvic treatment volumes for Cy­berknife prostate radiotherapy,Materials: Twelve patients with low and selected intermediate risk prostatecancer treated with Cyberknife stereotactic radiosurgery at our institutionwere analyzed, Anatomic contouring of the prostate and organ at risk (rec­tum, bladder, urethra, penile bulb, femoral heads) were done with image tu­sion of CT and MR T1wand T2w sequences,Four treatments planning weregenerated for each patients: a plan based on CT-delineated GTV, one basedon T1w-TC-delineated GTV (case 2), one based on T2w -TC-delineated GTV(case 3) and one based on all image- delineated GTV (case 4).oose wasprescribed to the planning target volume (PTV) that consisted of a volumetricexpansion the prostate 5 mm, reduced to 3 mm in the posterior direction.Thetreatment regimen consists of a total dose of 38 Gy delivered at 9,5 Gy perfraction, with> 95% of the PTV encompassed within the prescription isodosevolume with bladder and urethra maximum dose <120% of prescribed dose,rectum maximum dose < 100% prescribed dose and rectum V85< 2cm3,We

analyzed bladder and urethra 010 and urethra D50,Other organ at risk wereonly used for dose evaluation, Wilcoxon signed rank test was used for analysisof the different target volumes and doses distributions to OAR,Results: For each patients targets were compared with CT-delineated GTV(reference imaging), GTV volumes were smaller when MR was used for de­lineation (case 2: -15.2%±9,1; case 3: -18.1%±11 ,6; case 4: -9,26%±7.3,for all p=0,005), We decided to compare treatment plans prepared using allMR sequences with CT because T1w and T2w informationare complemen­tary and so both useful.We could not always respect rectum dose limit inparticular in case 1.Mean of rectum maximum doses was significantly higher(p=0,004) in case 1 than in case 4 (40,27Gy vs 38.64Gy; -4,23% with a max­imum of -21%),Mean rectum V85 was 4,04 cm3± 2.2 in case 1 and 2,21cm3±0.8 in case 4,Bladder and urethra 010 were 2,77% and 3.35% higherin case 1, respectively; urethra 050 was 2.4% higher.Conclusions: Using MRI to delineate the prostate results in more accuratetarget definition and a smaller target volume compared with CT, allowing forImproved target coverage and decreased doses to critical normal structures.

1646 poster

SHIELDING ASSESSMENT OF A NEW MOBILE ELECTRON ACCEL­ERATOR FOR INTRA OPERATIVE RADIATION THERAPY (IORT)A, Wysocka-Rabin', P Adrich", A, Nieciecka 2 , A, Wasilewski'

I THE A, SOLTAN INSTITUTE FOR NUCLEAR STUDIES, Accelerator Physicsand Technology Opt, Otwock-Swierk, Poland2 WARSAW UNIVERSITY OF TECHNOLOGY, Warsaw, Poland

Purpose: IORT permits delivery of a high dose of ionising radiation to cancertissue as a single fraction, following tumor ablation during oncological surgery.However, the presence of an accelerator in the operating room raises ques­tions concerning protection of personnel and the need for some degree ofshielding, The aim of this work was to study leakage and scatter radiationfrom two different models of a prototype electron accelerator that was de­signed in our institute, This shielding study will help inform decisions aboutthe choice of an accelerator treatment head and applicators for the new ac­celerator,Materials: The Monte Carlo code, BEAMnrc/EGSnrc, was used to build twomodels of a treatment head and applicators, and to calculate the amount ofdose delivered outside the treatment field, FLUKA code was used for beam­stopper and shielding calculation. Two different treatment head assembliesand applicators were modelled, The first model was characterized by a sim­ple light-weight treatment head, with a single scattering foil, without heavycollimators, and with plastic applicators, The second model Incorporated amore complex system of scattering, flattening foils filted into a set of heavy

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 565

collimators, and metallic applicators.Results: Calculations of dose delivered outside the treatment field, X-rayand neutron contamination in the surface of patient were performed for initialbeam energies ranging from 4 to 12 MeV and for circular applicators with di­ameters ranging from 3 to 10 cm. Two-D distribution of dose equivalents andneutron leakage in and outside operating room were calculated specificallyfor a maximum energy of 12 MeV and a 10 ern diameter applicator. The doseequivalent value around the treatment head, at a distance of 1 m from thebeam axes, was calculated for the same energy and applicator size.Conclusions: Based on these calculations, it was determined that dose dis­tribution in the plane of the patient fulfilled the radiation protection require­ments for both accelerator models. An analysis was also performed to deter­mine shielding requirements for personnel, or alternatively to introduce somelimit to the number of 10RT procedures performed weekly in operating room.Assuming three patients per week (with a cumulative dose of 3x20 Gy) anddaily measurements, the accelerator model that uses plastic applicators willrequire slightly more shielding than the second model with metal applica­tors.This work was funded by the Polish Ministry of Science and Higher Edu­cation and the EU in frame of Operational Programme Innovative Economy,project no. POIG 1.1-21

1647 poster

SIMPLE IMRT TECHNIQUE FOR RADIOTHERAPY IN BREASTCANCER INCLUDING LOCO-REGIONAL NODESJ. Casals Farran1, J. F. Calvo Ortega', S. San Jose 1, M. Pozo1 S.

Moragues'J HOSPITAL QUIRON BARCELONA, Radiation Oncology, Barcelona, Spain

Purpose: To compare the classical 3DCRT technique to a simple IMRT de­livery for irradiation of breast pius supraclavicular fossa with or without axilla.Materials: 3DCRT plans for breast cancer including supraclavicular and ax­illar nodes are classically performed by using a monoisocentric technique,consisting of 2 tangential half-fields on the breast site matched to 2 obliqueopposing halt-tields on the node area. Enhanced dynamic wedges and MLCcollimation are used on the 3DCRT planning. The same beam arrangementcan be converted into an IMRT plan, by removing wedges and allowing anoverlap between tangential and oblique fields. Inverse optimization calcu­lation and dynamic (Sliding Windows) delivery is considered for the IMRTapproach. Twenty patients were planned with 3DCRT and their respectiveplans were converted into IMRT plans. Calculations were made on Eclipsetreatment planning system (v 8.0) with AAA model and comparison betweentechniques was assessed by analysing the PTV homogeneity (HI) and con­formity indices (CI), heart V30, V20 and average dose to ipsilateral lung, andmean doses to surrounding structures. All plans were normalized so thatmean dose at PTV was 50Gy and 99.5% of PTV volume was covered at leastby the 90% of the prescribed dose. A two-tailed Student t-test (0: of 0.05) wasdoneResults: The average ipsilateral lung receiving> 20 Gy for 3DCRT and IMRTwere 25.6% and 19.8% (p< 0.001), respectively, and the average heart vol­umes receiving> 30 Gy for 3DCRT and IMRTwere 5.3% and 3.7% (p» 0.05),respectively. The average mean dose to the contralateral breast was 0.5 Gyfor 3DCRT and 0.6 Gy for IMRT (p>0.05). The healthy tissue mean dose wascomparable with both techniques (5.1 Gy for 3DCRT vs 4.7 Gy for IMRT, p-­0.05). Similar dose coverage of PTV was reached with both techniques: av­erage minimum dose at the 99.5% of PTV was 90.8% for 3DCRT and 90.9%for IMRT. Average maximal dose for PTV was 110.6% for 3DCRT and 108.3%for IMRT. Worse HI (12% vs 8.6%, p-c0.0001) and CI (2.7 vs 2.3, p-: 0.0001)values were reached with 3DCRT than IMRT.Conclusions: IMRT plans were significantly superior to 3DCRT ones interms of PTV homogeneity and conformity, as well as sparing of the ipsi­lateral lung. No significant differences were found on the remaining normalstructures analysed. IMRT described on this work is not a complex techniqueand doesnt involve the use of multiple beams that generally increase the ra­diation doses on normal tissue (contralateral breast and lung).

1648 poster

STATIC AND ROTATIONAL IMRT VERSUS IMPT FOR ADVANCEDPROSTATE CANCER: A TREATMENT PLANNING STUDYG. Kragl J

, I. Fotina', B. Knaus!", G. Goldner', P. Georg', M. Stock', D.

Georg'i MEDICAL UNIVERSITY OF VIENNA, Department of Radiotherapy, MedicalRadiation Physics, Vienna, Austria

Purpose: Dosimetric evaluation of rotational 1M RT bench marked to staticIMRT and intensity modulated proton therapy (IMPT) for the treatment ofprostate cancer with pelvic node involvement.Materials: CT data sets of 10 prostate cancer patients with a rectal balloonfor internal organ immobilization were randomly selected. 50.4 Gy were pre­scribed to the pelvic lymph node area (PTV1, 1 cm CTV-PTV margin) witha simultaneous integrated boost of 56 Gy to the prostate (PTV2, I cm CTV­PTV margin) (28 fractions), followed by subsequent 22Gy-boost (single dose

2 Gy) to the prostate with the dorsal margin reduced to 5 mm (PTV3). Foreach patient treatment plans were generated using three different treatmentmodalities: static IMRT, single arc VMAT, and IMPT. Photon plans were cal­culated with Monaco 2.01; proton plans with XiO 4.41 (both Elekta-CMS). Forpelvic and boost plans a 9 equidistant field setup was chosen for static pho­ton IMRT. For IMPT, APPA-fields were used for pelvic plans and two opposedlateral beams for the boost plans. All treatment plans were evaluated withrespect to target dose conformity, homogeneity, DVH parameters, and MUefficiency.Results: The treatment plan acceptance criterion of 95% PTV coverage with95% of the prescri bed dose was met by all plans. For the whole treatmentcourse, the average maximum dose was 110, 111, and 105% for IMRT,VMAT,and IMPT, respectively. The average relative rectum volumes receiving 50 Gy(V50Gy) were 39.8, 46.9, and 30.9% for IMRT, VMAT, and IMPT; and V70Gywas 10.5, 12.3 and 11.4%. V50Gy values for the bladder were 34.0, 39.4 and35.6%, while V70Gy was 13.0. 14.4 and 14.2%. For doses smaller than 50 Gysuperior sparing of rectum and bladder was achieved with IMPT. Mean bowelvolumes receiving more than 45 Gy were 164, 157 and 146 cern. Comparedto IMRT, the average number of required MU with VMAT was similar for pelvicplans and 7% lower for boost plans. Pelvic plans required an average numberof segments of 85 and 109 for IMRT and VMAT. Respective values for theboost plans were 73 and 76.Conclusions: DVH parameters of all considered organs at risk achieved withthe investigated RT techniques complied with recent QUANTEC recommen­dations. Similar dose distributions were observed with IMRT and VMAT. Atlow doses, best sparing of organs at risk was achieved with IMPT. The deliv­ery efficiency of VMAT improved compared to static gantry IMRT.

1649 poster

STATIC IMRT VERSUS HELICAL TOMOTHERAPY IN THE POSTOP­ERATIVE TREATMENT OF NASAL CAVITY AND PARANASAL SINUSCANCERD. Van Gestal ' , A. Coelmont' , B. De Ost' , D. Van den Weyngaert]

I UNIVERSITY RADIOTHERAPIE DEPARTMENT ANTWERP, Antwerp, Belgium

Purpose: To compare non-coplanar step-and-shoot (SS) fMRT and HT inthe postoperative treatment of malignant tumours of the nasal cavity andparanasal sinuses (NC/PS) in patients with overlap between PTV (planningtarget volume) and PRY (planning risk volume).Materials: For eight patients treated postoperatively on HT with a field widthof 2,5 em for NC/PS we also made a 6 MV non-coplanar inversed planned7 field step-and-shoot IMRT plan as described by Claus et al. (Int J RadiatOncol Bioi Phys 2001; 51,318-331). This is done on a Pinnacle 8.0m plan­ning system for an Elekta SL Beam Modulator (4 mm leave width). AI patientshave an overlap zone (PTV overlap) between their PTV and the PRY of opti­cal nerves, optic chiasm and/or brainstem. The prescribed dose to the PTVis 60 Gy in 30 fractions; the recommended dose to PTV overlap is 56 Gy withan absolule maximum of 59 Gy. The plans are normalised to the D2 of thePTV overlap. We compared 2 uniformily indices (D5-D95 and D2-D98) andthe dose near max (D2) of the PTVs as well as the treatment times. For 26OARs the mean dose and specific critical doses and volumes were analysed.Results: Uniformity indices of the PTV are belter for HT than for SS with anaverage difference in D5-D95 and D2-D98 of 48,6% and 42,3% respectively.For the PTV overlap, with a mean volume of only 4cc, the uniformity indicesare worse for HT (19.5% and 16.7% respectively). The underdosage of thePTV due to the gradient towards the PTV overlap is smaller for HT (V57 of98.2% vs 96.1%).For the optic structures SS is equivalent to HT but for mostof the other structures HT does better. The dose to the lacrymal glands (­25% and -52%). oral mucosa (-58%), salt palate (-29%), homolateral parotid(-42%). swallowing structures. the homolateral submandibular gland and thenon specified normal tissue is clearly reduced by the use of HT (clr Table).Only the inner ears are better spared with S5 (-28.6% homolateral and ­58.6% heterolateral). The median treatment time of HT is 6.1 min. comparedto 12 to 15 min for SS.

S 566 PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

SYSTEMATIC CHARACTERIZATION OF MLC LEAF DYNAMICSWITH MILLISECOND RESOLUTIONK. Hojbjerre 1 , P. Keall2 , B. Ch02

, A. Sawant", D. Huarr', P. R. Poulsen"

1 AARHUS UNIVERSITY HOSPITAL, Department of Oncology, Aarhus C,Denmark2 STANFORD CANCERCENTER, Stanford, USA3 AARHUSUNIVERSITY HOSPITAL, Aarhus C, Denmark

1652 poster

Figure 1: Fitted leaf position as function of time fordifferent step sizes. For steps smaller than 2 mm,the leaf acceleration is not maximal, resulting innearly constant step durations of about 60 ms.

Conclusions: The dynamics of individual leaves was determined for simplestep motions. However, these simple steps could be pieced together to sim­ulate a complex IMRT/IMAT plan. This may provide valuable insight into thecorrespondence between planned and actual leaf-motion, and thus delivereddose, in highly modulated IMRT/IMAT plans. Furthermore, the Widespreaduse of IMRT/IMAT requires an extensive QA system of leaf performances.The presented method is suitable as a monthly QA test of the individual leaf­motors. For dynamic MLC tracking, a detailed knowledge of the leaf dynamicsallows simulations of different real-time MLC refitting procedures and test ofplan-robustness with respect to tracking.

200150100Time [ms]

50

6

..... 5EE

4c:0:w 3'iii0Q.

2...IIIGI...I 1

Purpose: The dynamic capabilities of the individual leaves of a multileaf colli­mator (MLC) directly impacts how well the intended dose distribution of highlymodulated IMRT/IMAT plans is delivered. The prospect of tracking tumourmotion due to e.g. respiration place even higher demands on the dynamicproperties. In this study, the acceleration and maximum velocity of the indi­vidual leaves in a Varian Millennium 120-leaf collimator was determined withhigh temporal resolution.Materials: A prototype dynamic MLC tracking system was programmed tomove the MLC leaves step-Wise back and forth at well-determined times.Synchronization between these times and the 50ms updated MLC log out­puts of the actual leaf positions allow us to reconstruct the actual leaf motionon a millisecond timescale, under the assumption of reproducible leaf dynam­ics within an experiment. This assumption was verified by the measurements.The motion was reconstructed for both thin and thick leaves with steps rang­ing from ±0.1 mm to ±40 mm. Furthermore, the influence of initial leafvelocity was investigated.Results: The acceleration of the leaves depended on the step size, withaccelerations linearly increasing from 5 to ""11 Ocm/s2 as the step size in­creased from 0.1 to 2mm. Consequently, all steps smaller than 2mm took",,60ms to complete (Figure 1). For large steps, the leaf reached a maximumacceleration which varied from 100 to 115cm/s 2 for thin leaves and from 62to 68cm/s 2 for thick leaves. The maximum leaf velocity ranged from 3.7 to4.1crn/s for thin leaves and from 3.2 to 3.3cm/s for thick leaves. It was sys­tematically 0.1cm/s larger for inward motion than for outward. Preliminaryresults on initial leaf velocity show that leaves asked to continue their motionwill do so without an intermediate halt.

1650 poster

Conclusions: The tens of thousands of beamlets of HT compensate largelythe lack of non-coplanar irradiation in the treatment of NC/PS. HT performsa more homogeneous irradiation of the PTV with a steeper gradient towardsthe PTV overlap while better sparing the OARs. Moreover, the use of non­coplanar beams in SS-IMRT causes a higher integral dose to the normaltissue of the neck and makes the SS treatment time significantly longer.

Purpose: The treatment of the breast bed tumour using a simultaneous pho­ton boost is a good alternative to the classical use of electrons. This tech­nique is widely used and provides similar clinic results than the treatment ofthe bed tumour in a second phase with electrons. The purpose of this studyis to evaluate the robustness of this technique studying the uncertainties in­herent to the positioning of the patient.Materials: In our institution the classical irradiation using tangential beams isused but using segments instead of wedges. The homogenization of the dosedistributions of the entire breast is accomplished using segments selectedfollowing an IMRT forward approach. With the use of 8-12 segments dosehomogeneity between 95% and 106% is usually accomplished. To give theboost to the tumour bed 5 to 8 fields equiespaced 30° are added followingthe bed tumour contour. 200 and 214 cGy per fraction are prescribed tothe breast and to the tumour bed respectively. The total dose to the breastis 50 Gy and 60 Gy to the tumour bed. The patient is positioned with thetwo arms elevated using the breast board from MED-TEC. To evaluate therobustness of the technique a new CT to the patient is done by the end ofthe second week of treatment. The new CT is fused with the planning CT.The original structures and irradiation plan are associated to the new CT anda new calculation is done using the second CT as base. The dosimetricdiscrepancies between both plans and the possible movement of structuresare then evaluated. This procedure has been repeated in t 5 patients.Results: The comparison of contours between the planning CT and the veri­fication CT shows good agreement in most cases. In some of them the devi­ations were significant but they were inside the margins of PTV. The recalcu­lation of the original irradiation plan in the verification CT shows no significantdifferences with the original planning, the homogeneity in the CTVs continuesbeing good, the covering of the CTVs is similar for both CTs and the OAR donot show significant increases.Conclusions: In this study the robustness of the technique used in our insti­tution to treat the bed tumour of the breast with an integrated photon boosthas been evaluated. The results show that this technique is low dependentof small movements of the patient between fractions and that the clinical po­sitioning protocol used allows a good reproducibility of the patient positiontaking into account the margins considered.

STUDY OF THE ROBUSTNESS OF THE INTEGRATED PHOTONBOOST IRRADIATION TECHNIQUE FOR THE TREATMENT OF THETUMOUR BED FOR BREAST PATIENTSDGranero", L. Brualla", A. Gonzalez", J. C. Gordo", A. Vicedo", M. T.

Garcia 1 , R. Joan 1

1 ERESA, HOSPITAL GENERAL UNIVERSITARIO, Department of MedicalPhysics, Valencia, Spain2 ERESA, HOSPITAL GENERAL UNIVERSITARIO, Department of RadiationOncology, Valencia, Spain

1651 posterTECHNICAL AND CLINICAL BENCHMARKING OF VOLUMETRICMODULATED ARC THERAPY FOR PROSTATE CANCERR. Ruchaud 1

, G. Faure", R. de Crevoisier", C. Rodriques", L. Georges! , J.

Bravetti", E. Barthelrne", P. Fau", A. Methlin", M. Nabet!1 CENTREPRIVE DE RADIOTHERAPIE DE METZ, Metz, France2 CENTREEUGENE MARQUIS, Rennes, France

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 567

Purpose: To provide technical and clinical data on Volumetric ModulatedArc Therapy (VMAT) for prostate cancer patients and to compare this noveltechnique with conventional Intensity Modulated Radiation Therapy (cIMRT).Materials: 80 prostate cancer patients treated with VMAT were re-plannedwith clMRT at the same total dose of 74 Gy. Dose delivered to PTV andcritical structures, monitor units (MU) delivered, radiation delivery time andpre-treatment QA time were used as benchmarking metrics to compare thetwo delivery technique. Acute toxicities and individual pre-treatment QualityAssurance (QA) were evaluated on an inter-patient study, involving the same80 patients and an equivalent cohort of 80 patients (same dose and sameinstitution) treated with clMRTResults: Compared to cIMRT, VMAT reduced mean MU from 388 MU to 291MU, mean radiation delivery time from 6 min to 1.2 min, treatment planningfrom 14,5 min to 13 min and dose QA time from 13 min to 2.2 min. c1MRTdisplayed a sharper dose gradient than VMAT, a reduced integral dose (ratioof 1,18), with various differences in other dosimetric parameters dependingon the organs. The inter-patient QA study indicated that clMRT and VMATmeasurement points median pass rate was respectively 100% and 97%.Uri­nary grade 2 and 3 toxicities were respectively: 18% (cIMRT) versus 23%(VMAT) and 0% (cIMRT) versus 3% (VMAT). Lower gastrointestinal grade 2and 3 toxicities were respectively: 6% (cIMRT) versus 5% (VMAT), withoutany grade 3 toxicitiesConclusions: VMAT in localized prostate cancer provides low acute urinaryand rectal toxicity rates, comparable to those observed after c1MRT at thesame total dose, while providing a substantial gain in efficiency

1653 poster

TESTING THE ELEKTA INTEGRITY CONTROL SYSTEM FACILI­TATING CONTINUOUSLY VARIABLE DOSE RATE IN RELATION TOVOLUMETRIC MODULATED ARC THERAPYE. L. Lorenzen', A. Bertelsen', C. Brink 1

i ODENSEUNIVERSITY HOSPITAL, Laboratory of Radiation Physics, Odense,Denmark2 UNIVERSITY OF SOUTHERN DENMARK, Faculty of Health Sciences,Odense, Denmark

Purpose: Currently binned variable dose rate (BVDR) is used on Elekta ac­celerators during Volumetric Modulated Arc Therapy (VMAT) deliveries. Thenext version of the accelerator control system (Integrity) supports continu­ously variable dose rate (CVDR). Using CVDR rather than BVDR for VMAThas the potential of shortening treatment time but may lead to lower dosimet­ric accuracy due to faster moving accelerator parts. Using a beta version 01Integrity and the current clinically used accelerator controlling system, Desk­top 7.01, differences in treatment times and dosimetric accuracy of the twosystems were investigated.Materials: The study included measurements on clinically used VMAT plans(head and neck, prostate and lung, so far 8 patients). The treatment timewas measured from beam on to beam oft and the accuracy of the dose de­livery was determined by comparing measurement with the Delta4 phantomto expected dose using gamma evaluation. Additional tests where designedwere either the jaws, MLC's or gantry moved at constant speed under largevariations in dose rate. Running both Integrity and Desktop 7.01 with BVDRthese tests were meant to show if there are any differences in the way the twosystems control the movements of the accelerator. The positions and doserate were recorded using the control systems with a sampling time of 0.125s.Results: Using the Integrity control system with continuously variable doserate gave a significant reduction in treatment time ranging from 24% to 35%averaging at 30% or approximately one minute. The gamma evaluation of theDelta4 measurements showed equally good agreement for both systems with94% to 100% (on average 98%) of the detectors passing the gamma criterion(2% of 2Gy and 2mm). The tests showed no significant differences in thecontrol of either MLC's or jaws. However, Integrity had a signiticantly bettercontrol of gantry movement with a standard deviation of the gantry error of0,22 degrees versus 0,60 degrees for Desktop 7.01Conclusions: Using CVDR for VMAT with the Integrity desktop results in asignificant reduction in treatment time compared to BVDR with an averagereduction of 30%. This time reduction could in theory result in higher inaccu­racy due to faster moving MLC's, jaws and gantry, but dose measurementsshowed that the Integrity desktop using CVDR resulted in the same accu­racy. This finding might be related to the improved gantry control with Integritycompared to Desktop 7 and also to the use of CVDR resulting in less abruptchanges in dose rate and accelerator movements during treatment comparedto BVDR.

1654 poster

THE APPLICATION OF BRAIN GLIOMA CT PERFUSION IMAGEINGIN RADIOTHERAPY TREATMENT PLANNINGJ. Chen', Y. Yln", J. Lu I, J. Zhu'

, SHANDONG TUMOR HOSPITAL AND INSTITUTE, Radiation Physics, Jinan,China

Purpose: This manuscript aimed to investigate the value and feasibility of CTperfusion imaging in brain glioma radiotherapy treatment planning primarily.Materials: 7 casese with brain glioma were selected into the research andunderwent the localization and immobility by CT simulation (Siemens Sensa­tion 32). Next to the routine scannings (CT-r) without enhancement, perfusionwere underwent at once. In several series of perfusion scanning images, weselected one as the CT-p, in which the tumor sectional area was the biggest.And then the two series images were transfer to the Treatment Planning Sys­tem (Pinnacle 8,Om). The MR scannings were underwent in the same bodylocalization system, according to the CT scanning. And the images weretransferred, too. After reconstruction, registrations of CTs and MR were un­derwent: a) MR vs. CT-r: b) CT-p vs. CT-r. Tumors were confirmed andcontou red by a diagnostic radiologist and a radiation oncologist together re·ferring to the registration images. Then GTV-p, referring to perfusion images(mainly to the information of bloodflow of brain), and GTV-MR, referring to MRimages were obtained. The volume of the GTVs were calculated and com­pared using the SPSS 13.0 software, Paired, two-tails Student's t-test wasapplied to the comparison. Secondly. volume-I, both containing GTV-p andGTV-MR, was obtained; volume-2, covering not only GTV-p but also GTV-MRwas abtained, too.Results: GTV-p was a little, but significantly bigger than GTV-MR. GTV-pwas 26.77±4.52 rrr', a 2.92% increase on average compared to GTV-MR,26.01 ±4.65 m3 And then, the difference of volume-l and volume-2 wasmerely 0.83±0.11 m3

.

Conclusions: Confirmation and contour GTV of the brain glioma referringto brain CT perfusion images is as effective and reliable as referring to MRimages. Additionally, CT perfusion can offer the information of tumor localbloodflow. With the help, the specialized and individual treatment plans couldbe generated. The feature that CT routine scanning and perfusion could becarried out in same machine synchronously, without body position movement,is ideal to image registration.

1655 poster

THE COMPARISON OF THE CONFORMAL RADIOTHERAPY TWOOPPOSING FIELDS AND DYNAMIC RAPIDARC RADIOTHERAPYIN ADJUVANT TREATMENT FOR PATIENTS WITH TESTICLESEMINOMAS.G. Glowacki I , I Wesolowska2

1 MSC Mf,MORIAL CANCER CENTER AND INSTITUTE OF ONCOLOGYGLIWICE BRANCH, Department of Radiotherapy, Gliwice, Poland2 MSC MEMORIAL CANCER CENTER AND INSTITUTE OF ONCOLOGY Gu­WICE BRANCH, Department of Radiotherapy and Brachytherapy Planning,Gliwice, Poland

Purpose: To compare CFRT two opposing fields and dynamic RapidArc ra­diotherapy in planning of adiuvant radiotherapy in patients with pTi and clini­cally negative nodes seminomas.Materials: A treatment planning study was performed to compare CFRT twoopposing fields (2F) with dynamic therapy RapiArc for ten patients with early­stage postoperational seminomas. For each patient from this group two treat­ment plans were performed to irradiate paraaortic Iymphnodes including leftkidney hillus in the case of left testicle seminoma: first - two opposing fieldsAP/PA and second using RapidArc. The treatment plans were performed toachieve the minimum dose for PTV no lower than 95% of total dose. Treat­ment plans were compared using dose-volume histograms and plots of me­dian doses lor left and right Kidney (K) V20, VIS, Vi O. Liver (L) V30. D maxfor Spinal Cord (SC) and D max for Intestines (IN). For the evaluation of sta­tistical significance the nonparametric Wilcoxon's test was performed.Results: - Minimum dose in PTV (PTV min) for 2F plan was 29,1 Gyandthe same for the RapidArc technique The median dose for both techniqueswas 31,0 Gy. - D max for SC was 32,6 Gy in AP/PA plans and 31 Gy usingRapidArc (p~ 0,005) - The median volumes of left kidney V20, V15 and Vi 0were 25%, 30%, 35% for 2F technique and 4%, 8%, 15% respectively usingRapid Arc for planning radiotherapy of the patients with left testicle cancerIp~0,04). -The median volumes of right kidney V20, Vi5 and Vl0 were 5%,7%, 10% for 2F technique and 0%, 0%, 3% respectively using Rapid Arc forplanning radiotherapy of the patients with left testicle cancer (p~0,04, p~0,06,

p~0,13). -The median volumes of left kidney V20, V15 and Vl0 were 4%,5%, 7% for 2F technique and 0%, 2%, 5% respectively using Rapid Arc forplanning radiotherapy of the patients with right testicle cancer (p~0,04. p~

0,07, p~0,34). The median volumes of right kidney V20, V15 and Vl0 were8%, 10%, 13% for 2F technique and 0%, 2%, 4% respectively using RapidArc for planning radiotherapy of the patients with right testicle cancer (p~0,04,p=0,04, p~O,08). - Liver V30 was very low and comparable for all performedplans:2F- 3%, RapidArc 0% (p~O,OI) The median dose for whole liver was0,5 Gy and 4,5 Gy respectively (p~0,005). - D max for intestines was accept­able in all plans 2F- 33 Gy, RapidArc - 32 Gy (p=0,03).Conclusions: 1 - All plans fulfill ICRU 50 recommendation for PTV min2 ­DVH demonstrated better protection of the kidneys in RapidArc technique ascompared to AP/PA plans.3 - Similar and acceptable protection of liver, spinalcord and intestines in all performed plans

S568 PHYSICS AND TECHNOLOGY: TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

1656 poster

THE FIRST EXPERIENCE WITH RAPID ARC DURING PROSTATECANCER PATIENTS IRRADIATION.H. Urbanczyk' , R. Kulik', J. Ciechowicz 3

, L. Miszczyk'

1 MSC MEMORIAL CANCER CENTER AND INSTITUTE OF ONCOLOGYGLIWICE BRANCH, Radiotherapy, Gliwice, Poland, MSC MEMORIAL CANCER CENTER AND INSTITUTE OF ONCOLOGYGLiWICE BRANCH, Radiotherapy Planning, Gliwice, Poland3 MEDICALUNIVERSITY OF LODZ, Computer Laboratory, Lodz, Poland

Purpose: Rapid Arc (RA) is modern dynamic radiotherapy technique. Radi­ation oncologists are hope this 1echnique will increase possibilities of treat­ment. In our department we started to irradiate patients using RA last year.We want to evaluate the safety of prostate cancer (PCal patients (pts) irract­ated with RA.Materials: 20 pts aged between 54 and 80 years (median 66) were irradiatedwith RA between May 2009 and October 2009. All pts have favorable Pca.CTV was prostate, PTV was prostate with 5 mm margin. Intraprostatic an­chors were used for everyday evaluations of prostate position. EORTCfRTOGscales were used for evaluation rectal and bladder acute toxicities. Studentand U Mann Whitney tests were used for statistical analysis.Results: Dose 60 Gy includes between 9 and 33% of rectum {median 22.75)and dose 70 Gy includes 3 and 17% of rectum (median 10.4). Dose 60Gy includes between 4 and 35% of bladder (median 15.5) and dose 70 Gyincludes 2 and 20% of bladder (median 8.45). We observed acute rectaltoxicities level 1 al 3 pts. We observed acute bladder toxicities at 6 pts, level1 at 5 pts. and level at the other one. Both toxicities do not depend on age orirradiated doses.Conclusions: Using of Rapid Arc seems to be well-tolerated and safe thera­peutic option for prostate cancer patients, free from unacceptable rectum andbladder acute toxicity, Organs of risk, like rectum and bladder were irradiatediow dose and this dose does not influence on acute toxicity.

1657 poster

THE USE OF PROBABILITY VOLUME HISTOGRAMS (PVH) ANDISO-PROBABILITY OF RESPONSE CHARTS IN TREATMENT PLANEVALUATIONP.Mavroidis', B. C. Ferreira", A. Tzikas", M. D. C. topes"1 KAROLINSKA INSTITUTET AND STOCKHOLM UNIVERSITY, Departmentof Oncology-Pathology, Division of Medical Radiation Physics, Stockholm,Sweden2 LARISSA UNIVERSITY HOSPITAL, Department of Medicai Physics, Larissa,Greece3 UNIVERSITY OF AVEIRO, 13NPhysics Department, Aveiro, Portugal4 KAROLINSKA INSTITUTET AND STOCKHOLM UNIVERSITY, Department ofMedical Radiation Physics, Stockholm, Sweden5 INSTITUTO PORTUGUES DE ONCOLOGIA COIMBRA . FRANCISCO GENTlL,EPE, Department 01Medical Physics, Coimbra, Portugai

Purpose: This study aims at demonstrating new methods of treatment planevaluation and comparison. This was performed by applying them on threedifferent cancer types and treatment plans of different conformalities in eachcase. Furthermore, their usefulness is examined in conjunc1ionwith tradlton­ally applied radiobiological and dosi metric treatment plan evaluation criteria.Materials: Three different cancer types (head and neck, breast and proslate)were selected to quantify the benefits of the proposed treatment plan eval·ualion method. In each case, conventional conforma l radiotherapy (CRT)and IMRT treatment configurations were planned. The probabilities of targeland normal tissue responses were calculated using the Poisson and the rei­alive seriality models. The different dose distributions were compared usingthe complicatton-ftae tumour control probability (p+), the bioiogically effec­tive uniform dose, BEUD and common dosimetric criteria. Furthermore, thedifferent treatment plans were evaluated based on the dose distribution con­verted to D2Gy, iso-probaoilty and iso·BED dose charts and correspondingprobability volume histograms.Results: For the head & neck cancer case, at the prescribec dose level ofthe CRT and IMRT dose distribu1ions, the P+ values are 0.0% and 24.9% fora BEUD to the target of 54.6 Gy and 63.5%, respectively. The respective totalcontrol probabilities, PB are 30.7% and 87.0%, whereas the correspondingtotal complication probabilities, PI are 96.9% and 62.1%. Similarly, for thebreast cancer case. the P+ values are 88.0% and 89.1% for a BEUD of 61.6Gy and 61.4%, respectively. The PB values are 90.0% and 89.6%, whereasthe PI values are 2.0% and 0.5%. Finally, for the prostate cancer case, lhe P+values are 28.7% and 51.3% for a BEUD of 69.3 Gy and 70.7%, respectively.The PB values are 54.5% and 62.9%, whereas the PI values are 25.8% and11.6%. The use of local iso-probabilitv charts is very useful for plan evaluationsince, by considsrinq the radiosensitivity of each tissue, the visual informationfocuses on the doses that may cause an effec1in that particu lar organ. In thisway, the focus is on the radialion therapy effect in each organ independentlyof the prescription dose. For example, when different doses are prescribedto different volumes of the PTV, what it is examined is if 100% cure in eachof such volumes can be obtained. Also, the dosimetric information provided

by low doses in the normal tissues is reduced eliminating some visual noisesince fhese low doses may not have an actual clinical effect. On the contrary,in the target volumes cold spots are immediately visualized just as hot spotsin the normal tissues (see figure).Conclusions: It was shown that in all the cancer cases examined, the IMRTtreatment plans are more effective than the CRT plans by increasing the prob­ability of tumour control while improving the sparing of the organs at risk. Theproposed converted to D2Gy, iso-probabi'ty and iso-BED dose charts andhistograms illustrated better the difference in the effectiveness of the differ­ent treatment plans providing a very helpful evaluation tool in the processof treatment plann ing.fectiveness of the different treatment plans providing avery helpful evaluation tool in the process of treatment planning.lt was shownthat in all the cancer cases examined, the 1M RT treatment plans are moreeffective than the CRT plans by increasing the probability of tumour controlwhile improving the sparing of the organs at risk. The proposed converted toD2Gy, iso-prohabilty and iso-BED dose charts and histograms illustrated bet­ter the difference in the effec1ivenessof the different treatment plans providinga very helpful evaluation tool in the process of lreatment planning.

)

1658 poster

THE VERO SYSTEM, A NOVEllGRT DEVICE FOR STEREOTACTICBODY RADIATION THERAPY: COMMISSIONING AND FIRST EXPE­RIENCED. verellerr , T Depuydt', N. Christian !, M. De Ridder', G. Storme 1

i UZ-BRUSSEL,Radiation Oncology, Brussel, Belgium

Purpose: Due to the recent introduction of the VERO system in the field,very little detailed information is available. An overview will be given of theexperimental data aoquired during commissioning.Materials: The VERO system, a novel radiation therapy platform developedfor image guided stereotactic body radiotherapy (SBRT), has been installedand commissioned in our hospital {Fig. t). This device is a Joint product ofBrainLAB (BrainLAB AG, Feldkirchen, Germany) and MHi (Mitsubishi HeavyIndustries, Tokyo, Japan). A newly developed small 6 MV linac with attachedMLC is mounted on an O·ring gantry. The MLC consists of 60 5-mm·leafsand produces a maximum field size of 150x150mm. The gantry rotates 360 0

about the horizontal axis, similar to a C-arm linac platform, but additionallyallows rotafion about the vertical axis, a so caiied "skew" of +/. 60°. Orthog­onal gimbals hold the linac, which allows pan and tilt motions of the iinacand the therapeutic beam. This mechanism offers the possibi iity to activelycompensate for mechanical distortions during gantry rotation and to performreal-time tracking of moving tumors. Beside an EPID for MV portal imaging,the system is equipped with a dual orthogonal kV Imaging systems attachedto lhe O-ring at 45° from the MV beam. This imaging system allows Simul­taneous acquisition of orthogonal X-rays images and fluoroscopy. Also kVcone-beam CT imaging is available. An automated infra-red marker basedpatlent-positioninq device is integrated. The treatment couch provides 50 po­sitional correction (X,Y,Z,pitch,roll). The 6th degree of freedom, the yaw anglecorrection, is handled by the O-ring skew. We have conducted full commis­sioning of this novel SBRT platform, including full mechanical, dosimetric andbeam characterization, and report on the performance of this device installedin a clinical environment.

PHYSICS AND TECHNOLOGY TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES S 569

Results: The linac produces a beam with 6MV nominal energy withTPR20,10 beam quality index of 0.671. The output reproducibility was ver­ified and the largest deviation of 0.03% was found for a dose rate of 500MU/min. Gantry angle dependence of linac output was smaller then 0.26%.The largest deviation of proportionality of the output with the MU setting was2.0% for the 1 MU delivery. The MLC leakage measurements showed intra­leaf leakage of below 0.5% and intra-leaf leakage of below 1.8%. A beampenumbra was seen of 4.4mm in X direction and 4.5mm in Y direction. Thebeam flatness and symmetry were respectively 103.6% and 101.1% in X, and103.3% and 100.7% in Y direction. A radiation isocenter radius was found of0.23 mm, 0.01 mm and 0.06 mm for gantry rotation, O-ring rotation and gantrywobble respectively. Data on image guided patient positioning accuracy willbe available at the time of the conference.Conclusions: Based on the experimental results, the systems characteristicswere considered adequate for SBRT treatments.

1659 poster

TOTAL SKIN ELECTRON BEAM THERAPY: EVALUATION OF MODI­FIED ELECTRON FLUENCE DISTRIBUTION FROM THE ENERGYDEGRADER.W. H. Choi l

, Y. Chunq'', C. O. Suh 2, K. Jeong 2

1 GANGNAM SEVERANCE HOSPITAL, YONSEI UNIVERSITY, Department ofRadiation Oncology, Seoul, Korea Republic of2 YONSEI CANCER CENTER, YONSEI UNIVERSITY, Seoul, Korea Republic of

Purpose: The purpose of this research is to estimate the correlation betweenthe spatial fluence distribution and the size of the energy degrader for the totalskin electron beam therapy (TSEBT) using linear accelerator with electronbeam energy of 6 MeV.Materials: The spatial distribution of electron f1uence for treatment area (30cm behind the energy degrader) was measured using ionization chamber andGafchromic EBT2 film. The TSEBT treatment used high dose rate of 6 MeVelectron beam from Elekta Synergy linear accelerator. The 90 cm (width) x180 cm (height) x 1 cm (thickness) acrylic energy degrader was positionedat a source-to-surface distance (SSD) of 320 cm while treatment position ofpatient was at a SSD of 350 cm. In-vivo dosimetry on a patient was performedusing EBT2 film patches.Results: From the measured percent depth dose, the estimated electron en­ergy was 2.7 MeV at the treatment distance. While skin doses were enhanceddue to scattering from the energy degrader, the spatial uniformity in the treat­ment space was reduced. The fluence difference between SSD 350 cm and360 cm was about 10% which was larger than 6% in the setting without theenergy degrader. The EBT2 profile results revealed that the effective treat­ment area was much smaller than the size of the energy degrader. At thetreatment distance, the effective treatment area determined by 90% (80%)isofluence line was reduced to 50 cm x 150 cm (60cm x 170 cm). This resultwas confirmed by in-vivo measurement at patient treatment. Especially, thedose delivered to elbow where positioned at the edge of the treatment spacewas considerably low and unstable. The measured doses at left and rightelbows were 55% and 62% of prescribed dose, respectively. Also, the dosevariation was about 20% due to daily set-up.Conclusions: For the verification of patient positioning and set-up, theshadow of patient is usually checked whether it is in the frame projectedby light field. However, since the actual effective treatment space is muchsmaller than the light field projection, close attention must be paid when de­termining the size of energy degrader. In-vivo dosimetry should be performedto determine the dose actually delivered, especially at the edge part of the ef­fective treatment space

1660 poster

TREATMENT OF HEPATIC METASTASES WITH STEREOTAXICRADIOTHERAPY AND EXACTRAC RESPIRATORY CONTROLSYSTEMO. Miranda", E. Rio' , S. Gaudaire", M. Mahe '

1 CENTRERENE GAUDUCHEAU, Radiotherapy, Saint-Herblain, France2 CENTRERENE GAUDUCHEAU, Physics, Sainf-Herblain, France

Purpose: Stereotactic Radiotherapy (RST) for the treatment of liver metas­tases is a technique which become more and more used because of resultsand good tolerance. Exactrac Gating System allows a better control andadaptation of the treatment to every session, with one margin of error in theorder of 0,3 mmMaterials: Patients with a unique liver metastasis treated in the Service ofRadiotherapy of the Centre Renuducheau in Nantes by RTS. RST was issuedby the apparatus Novalis by using the system of respiratory control ExactracGating. A radio-opaque marker near the tumour was performed for all pa­tients.. Dose delivered was 40Gy in 4 fractions, lOGy each at 01, 03, 08and 010.Results: Between 2007 and 2009, 9 treatments have been made in 8 patients(1 patient treated for 2 locations). Median age was 69,3 years old (64-75).Thedose delivered at the is centre was 40Gy for all. Four treatments were asso­ciated with chemotherapy with Irinotecan. The margins for the CTV and PTVwere 3 and 5 mm for 5 treatments and 5 and 8 mm for 4 patients. Mediantreatment time calculated in UM was 1768UM (t412-2168UM). The organsat risk receiving the largest dose were liver, stomach and kidney.Conclusions: The treatment of liver metastases with Stereotactic Radiother­apy associated with the respiratory control system Exactrac Gating is feasible,well tolerated and provides benefits in terms of accuracy and reproducibilityof sessions with a decrease in dose to organs at risk.

1661 poster

VAGINAL MOULD APPLICATOR VERSUS OVOIDS: A 3D-MRIGUIDED BRACHYTHERAPY STUDY COMPARISON IN PATIENTSWITH LOCALLY ADVANCED CERVICAL CANCER.R. Mazeron '. I. Dumas " G. Francois", L. Monnier", S. Vieillot 2

, C.

Haie-Meder!, INSTITUT GUSTAVE Roussy, Villejuif, France2 CRLC VAL IJ'AURELLE/PAUL LAMARQUE, Montpellier Cedex 5, France

Purpose: To compare two MRI compatible vaginal applicators designed for3D guided brachytherapy in locally advanced cervical cancer: the personal­ized vaginal mould and the Fletcher's applicator.Materials: Patients (pts) with locally advanced cervix cancer (FIGO stagedfrom t B2) were included in a prospective cross over study. All pts weretreated with pelvic +1- para-aortic concomitant chemoradiotherapy (45 Gywith weekly platin 40 mg/m) followed by MRI guided PDR utero-vaginalbrachytherapy (BT), delivered in two fractions for all patients, either with themould or the ovoids. Intervals between fractions were short enough to avoidsignificant tumour volume modifications. 50% of the pts had the first appli­cation with the mould, and the remaining 50% with the ovoids. The volumesof interest (HR-CTV, IR-CTV, bladder, rectum and sigmoid) were delineatedaccording to the GEC-ESTRO recommendations on MRI acquired the day ofimplantation. A dose of at least 7.5 per fraction was prescribed to the IR-CTV.A systematic optimization was performed to achieve the best CTVs coverage(IR-CTV> 15 Gy and HR-CTV > 37.5 Gy), tacking into account organs at risk(OAR) constraints (EqD2: bladder 2cc <:: 80 Gy, rectum 2cc <:: 75 Gy andtotal TRAK <:: 2.0 cGy). Dosimetric studies were performed with OncentraGYN software. BT was followed by an EBRT boost to a total dose of 60 Gyin case of macroscopic pelvic or para-aortic nodes, tacking into account theBT contribution. Moreover, a quality of life study was conducted to determinethe tolerance of the two diHerent applicators, with a question naire given to thepatients at each 8T fractionResults: From February 09, 20 patients were included. Full data are availablefor the t1 first patients. OAR volumes and CTV volumes were comparable,except for vagina, as there was no vaginal packing when the mould was used:67.8 ern" (23-137) with the mould applicator and 78.2 crrr' (47-135) with theovoids. Moreover, mean uterine active lengths were not different betweenboth applicators: 56.8 mm with the mould (45-70) and 60 mm with the ovoids(40-70). Vagina l active lengths were also quite similar: 32.0 mm (25-45)and 29.5 mm (25-45) respectively. Dosimetric data showed comparable CTVcoverage. IR-CTV: Vl 00 =96.2% vs 95.6, 090 =10.8 Gy vs 10.0 and 0100:6.4 Gy vs 6.2. HR-CTV: V250 = 74.2% vs 70.5,090 = 15.6 Gy VS 15.3 and0100 = 10.3 Gy vs 10.0, for the mould and the ovoids respectively. Therewere no differences within OAR DVH: D2cc bladder (11.78 Gy vs 12.9), D2ccrectum (9 Gy vs 7.7) and D2cc sigmoid (8.3 Gy vs 7.6), for the mould and theovoids respectively. The questionnaire showed an advantage for the mould interms of tolerance at the time of the applicators withdrawal significantly lesspainful with the mould.Conclusions: Preliminary results showed comparable dosimetric perfor­mances between both applicators. The tolerance at the mould applicator wasbetter than the Fletcher appl icator. Complete data on the 20 patients will be

S 570 PHYSICS AND TECHNOLOGY: TREATMENT TECHNIQUES, MODALITIES AND NEW TECHNOLOGIES

presented at the meeting.

1662 poster

VALIDATION OF TWIN RAPIDARC TM MACHINES IN A SINGLEINSTITUTION.P. Fenoglietto [, N. Ailleres 2

, J. B. Dubois ", D. Azria"

1 CRLC VAL D'AURELLE/PAUL LAMARQUE, Radiation Oncology, MontpellierCedex 5, France2 CRLC VAL D'AURELLE/PAUL LAMARQUE, Montpellier Cedex 5, France3 CENTRE VAL D'AuRELLE,Montpellier, France

Purpose: IMRT was implemented since many years in our institution thathad treated more than 1100 patients with this technique. To achieve a goodflexibility concerning the patients treatments we installed three equivalent ma­chines who are energy matched. All these accelerators were equipped with120 leaves MLC tuned by the physicist team to be equivalent for sliding win­dow technique delivery. In 2008 we installed a Hapldarc! machine and startto treat our first patients. Since end of 2009, a second machine was upgradewith this new technology. Many tests were realised to check if a patient couldbe optimised and calculate for a specific machine and treat on another one.Materials: Twenty patients with prostate and H&N cancers previously treatedwith Rapidarc™ and 6 MV photons were selected for this analysis. Opti­mization and calculation were done on an Eclipse treatment planning system(Varian, Palo Alto, USA) with the 8.5 version allowing just one arc. Half of thepatients were planed for the linear accelerator A and the rest on the machineB. Verification was done for all patients on both linear accelerator, with theelectronic portal imager of the machines using amorphous siliciurn (AS1000)and the analyse was realised with the EpiQa software.( Epidos, bratislavia,Slovakia). Rotational treatment plan was deliver and the portal imager mea­sured a collapse plan in 2D who was compare to one compute in the Eclipseworkstation. The gamma index formalism was used with threshold of 3% and3 mm and the algorithm allow absolute dose comparison. As the AAA calcu­lation grid was 2.5 mm and the measurement resolution was 0.39 mm 1pixel,we adopt a smoothing analyse too, resulting on an acquisition matrix around2.5 mm . All the plans were controlled on the machines A and B.Results: If we look at the comparison between measure and compute dose,global results were 97.32 ± 1.69% of points passing the gamma criteria forthe A machine and 95.65 ± 2.40% for the B. For the smooth analysis, wereach 98.78 ± 1.14% and 98.39 ± 1.62% for A and B respectively. Con­cerning the 10 H&N patients, the percentage are 95.63 ± 1.09% and 93.32± 2.10% for analysis on the machine A and B and a measurement grid of0.39 mm. Again, a smooth analyze provide excellent results where 97.78 ±1.00% (A) and 96.94 ± 1.69% (B) of points obtain a gamma <1 for 3% or3mm. Prostate cases, more simple in modulation give the best values with99.00 ± 0.48% for the linac A and 97.98 ± 0.59% for the linac B withoutsmoothing.The difference between the 2 dose matrix acquired on the portalare very small, 99.92 ± 0.06% of points passing the criteria.Conclusions: In an institution with twins Rapidarc™ machine, patients couldshift during treatment from one to the other with no need of new dosimetry.

1663 poster

VMAT, IMRT AND 3D-RT DOSIMETRIC COMPARISON IN LYMPHOMATREATMENTD. Gabrys 1 , K. Trela! , R. Kulik2

1 MARIASKLODOWSKA-CURIE MEMORIAL CANCER CENTER ANDINSTITUTEOF ONCOLOGY, GliWICE BRANCH, Department of Radiotherapy, Gliwice,Poland2 MARIA SKLODOWSKA-CURIE MEMORIAL CANCER CENTER ANDINSTITUTEOF ONCOLOGY, GliWICE BRANCH, Department of Radiotherapy andBrachytherapy Planning, Gliwice, Poland

Purpose: Late radiotherapy effects seen in lymphoma patients may be re­duced by decreasing volume and delivered dose to nontargeted tissue. Thismay be done with improved treatment techniques such as 3DRT, IMRT or Vol­umetric Modulated Arc Therapy (VMAT). The last one involve simultaneouschanges in dose rate, gantry angle, gantry rotation speed as well as accurateand fast dynamic multileaf motion while radiation is on.Materials: Based on treatment planning CT's of 20 patients, we compareddose distribution of VMAT with a sliding window IMRT and 3D conformal ra­diotherapy using Varian Eclipse Medical System. Results were comparedusing Wilcoxon test.Results: IMRT and VMAT showed better dose distribution within the targetvolume in comparison to conformal 3DRT. Both conformality index (CI) andhomogeneity index (HI) were the best in VMAT 0.98 and 0.07 in comparisonto IMRT and 3DRT both CI 0.94 (p<0.005), and HI 0.08 and 0.09. Lowermaximum dose was achieved with IMRT, and only higher minimum dose wasachieved with 3DRT. Dose delivered to 95% of target volume was the highestwith VMAT 98.5% vs 95.5% IMRT and 95.7% 3DRT. Both IMRT and VMATresults in similar (lower) level of dose distribution in the lung. V20Gy were8.1%,8.3% and 14.8% for VMAT, IMRT and 3DRT respectively (p<0.003),also lung mean dose was significantly lower for VMAT and IMRT 16.6 Gy in

comparison to 3DRT 19.3 Gy. VMAT was the best in heart sparing in bothhigh and low dose regions, mean dose was 8.6 Gy, 8.9 Gy and 12.8 Gyfor VMAT, IMRT and 3DRT (p=0.02), and V20 Gy were 4.5%,5.1% and 9.5% respectively. IMRT showed lower dose distribution within salivary glands,thyroid , larynx and spinal cord. The volume of non-target tissue (body volumeminus PTV), which was irradiated with 5 Gy was the lowest with 3DRT thanfor other techniques, but the volumes irradiated with doses lOGy and morewere significantly lower with VMAT and IMRT.The smallest number of monitorunits was needed to deliver 3DRT (mean 179), VMAT (mean 460), and thehighest in IMRT (mean 1222), p-, 0.003, but time needed to deliver radiationwas the shortest for VMAT and the longest for IMRT.Conclusions: IMRT and VMAT showed better dose distribution within thetarget volume and organ at risk in comparison to conformal 3DRT. Additionalfollow-up is necessary to determine whether improvements in dose deliveryaffect long-term morbidity and disease control. Larger low-dose regions mightlead to a higher incidence of second cancers.

1664 poster

VOLUMETRIC MODULATED ARC THERAPY (VMAT) USING NUCLE­TRON ONCENTRA MASTERPLAN: COMPARISON WITH STANDARDIMRTC. Andres Rodriguez l

, del Castillo Belmonte", D. Alonso Hernandez', R.

Tortosa Oliveri, R. Barquero?1 HOSPITAL UNIVERSITARIO DE VALLADOLlD, Department of Radiophysics,Valladolid, Spain2 HOSPITAL UNIVERSITARIO DE VALLADOLlD, radiation protection, Valladolid,Spain

Purpose: The purpose of this paper is to analyze the Volumetric ModulatedArc Therapy (VMAT) module from Oncentra MasterPlan treatment planningsystem, comparing results with those obtained by the Step&Shoot IMRT tech­nique of this planning system.Materials: A Varian 21iX linac with 120-MLC is chosen. Different locationsof target volumes were selected for the study: ORL, prostate, lung, gastricor endometrium. Dose and fractionation prescription used are the typical forIMRT treatments.Two treatment plans for every case were generated in Nu­c1etron Oncentra Master Plan, the first plan using five-field Step&Shoot IMRTbeams and the second plan using single VMAT dynamic arc. Dose calcu­lations were performed using 6-MV photon beams, with identical planningobjectives in both cases. Treatment plans were compared using two param­eters: Conformity Index (CI) for 95% of reference isodose and HomogeneityIndex (D5/D95). Other plans features, as normal tissue doses, number ofmonitor units or calculation times are also tested.Results: Dose distributions obtained were highly optimized and doses to tar­get volumes were increased using VMAT module. In all cases, ConformityIndex was better for VMAT plan (closest to 1). While analyzing Homogene­ity Index, it can be seen that dose homogeneity around the target volumewas generally better using VMAT. Results for two concrete patients (ORL andprostate cases) are shown in table 1. Both plans maintain delivered doses tonormal tissues below tolerance dose levels.

Cases ORL PROSTATE

Technique STEPII.SHOOT VMAT STEP&SHOOT VMAT

CL" 1.198 1.011 1.028 1.021

HI (I>,/o.,l 1.130 1.058 1.044 1.028

Table 1. CI and HI parameters for two example patients

An observed improvement using VMAT module is that curves of dose-volumehistogram are barely degraded in the final calculation, once optimization andsegmentation have been made, using VMAT module. In Step&Shoot, degra­dation can produce changes up to 2 Gy to target volumes doses and evenvariations of 10% in VOlume receiving a particular dose level when final cal­culation is performed.Conclusions: A satisfactory behavior of VMAT planning module of OncentraMasterPlan is obtained. The comparison made using different parametersbetween both treatment modalities leads to better dose distributions with re­spect to the Step&Shoot IMRT module.

1665 poster

VOLUMETRIC MODULATED ARC THERAPY VS. CONVENTIONALSTEREOTACTIC TECHNIQUES FOR BENIGN INTRACRANIALTUMORSC. Srinivas", T. Swarny", A. Gandhi 1 ,A. Jotwanl", S. Subramanian 1

1 YASHODA CANCER INSTITUTE, radiation oncology medical Physics,Hyderabad, India

RADIATION TECHNOLOGISTS S 571

Purpose: To compare dosimetry of various conventional Stereotactic radio­therapy techniques with Intensity Modulated Stereotactic radiotherapy (IM­SRT) and Volumetric Modulated Arc Therapy (VMAT-RapidArc) in benignbrain tumors at various locations.Materials: Ten patients diagnosed with benign brain tumors of various sizesat different locations were planned with non-coplanar (NC) static conformalbeams (SCB) with 3 mm micro MUltileaf collimator (mMLC), NC DynamicConformal arc (DCA) with 3 mm mMLC, NC DCA with 5mm MLC, NC IMSRTwith 3 mm mMLC, Co-planar VMAT- RapidArc with 5 mm MLC and HybridCoVMAT-RapidArc + DCA. For each of the patients, the target was definedon CT-MR fused images. All the 6 plans for each patient were planned onEclipse Treatment Planning Software (TPS) version 8.5. Beam shaping wasdone either by 3mm Brainlab mMLC or by Varian's millennium MLC. Targetobjective was to encompass atleast 99% of PTV with > 95% of prescribeddose. All Organs at Risk (OAR) were prescribed standard dose constraints.Patients were treated with the best available plan after complete plan eval­uation with respect to PTV coverage, modified Conformity Index [Paddick. JNeurosurg 2000:93(219-222)}, Gradient Index and dose to OAR.Results: In all the plans, the target objectives were met and the maximumdose did not exceed 107%. Results are summarized in table 1. Dose to OARwas within standard dose constraints for all the plans.

IITawe 1Technique Mean PTV Mean Mean

Coverage Conformity Gradient, Index IndexStatic Conformal Beams 99.2% ± 0 .54 0.86 ± 0.02 3.6 ± 0.28with 3mm mMlC.DCA with 3mm mMlC 99.1%±. 0.82 ± 0.03 3.48 ± 0.25

0.52-

DCA with S mm MlC 99.0% ± 0.58 0.82 ± 0.04 3.48 ± 0.14

IMSRT 99.2% ± 0.55 0.87 ± 0.02 336 ± 0.21

Co-VMAT-RapidArc 992% + 0 43 0.86 ± 0.03 3.36±0.19-Hybrid (Co-VMAT-RapidArc 99.6% ±0.28 0.91 ± 0.02 3.11 ±O.lt+ DCA)

Hybrid plan was superior to other plans in all the patients with respect to everyparameter used for plan evaluation and hence was chosen for treatment in allpatients.Conclusions: Various conventional techniques of Stereotactic Radiotherapywere dosimetrically comparable, Hybrid plans consisting of Co-planar VMAT­RapidArc and Non Co-planar Dynamic ConformalArcs was dosimetrically su­perior to conventional SRT techniques and IMSRTfor a variety of intracranialtargets at different locations.

1666 poster

VOLUMETRIC MODULATED ARC THERAPY WITH UNFLATTENEDPHOTON BEAMSJ. Cashmore1

1 HALL-EDWARDS RADIOTHERAPY RESEARCH GROUP, RadiotherapyPhysics, Birmingham, United Kingdom

Purpose: The flattening filter has been shown to be unnecessary for deliveryof intensity modulated beams, producing treatment plans of almost identicalquality, but with reduced leakage radiation and some improvements in calcu­lation accuracy. The beam is also seen to be more stable as the flattener actsas an amplifier to any changes in steering. With the move towards intensitymodulated arc techniques filter removal may offer faster, more reliable andmore stable beam delivery.Materials: A standard Elekta precise linear accelerator has been com­missioned to operate in both conventional and unflattened modes at 6MV,and beam data measured to commission a test platform of the Elekta/CMSMonaco treatment planning system. Tests for beam flatness and symmetryat variable dose rates required for VMAT have been investigated for each de­livery method. Treatmentplans havebeen created to test the synchronisationof gantry, leaf position and overall dosimetric accuracy of IMRT and VMATdelivery.Results: The modellingof untlatteoec beams is nowpossible within the mod­ified Monaco system, as are plan optimisation and dose calculation. Deliveryof IMRT plans for standard head and neck cases has shown that the beammodel is accuratewith 98-99% of points passing gamma analysis at 3%/3mm.Measurements also show that beam flatness and symmetry are more stablefor unflattened delivery making rotational delivery more consistent.The VMAToption within Monaco is in clinical use at some clinics and soon to be imple­mented at this clinic. Full measurements for standard cases will be performedand presented.Conclusions: It has been demonstrated that the flattening filter is not neces­sary for modulated radiotherapyand that the Monaco TPS is capable of accu­rately modelIing and planning these treatments. These beams are also more

stable during rotational delivery and less susceptible to changes in beamsteering at the different gantry angles required for VMATdelivery. This couldpotentially lead to faster, more accurate delivery compared to standard accel­erator configurations with lower whole-body radiation doses to the patient.

1667 poster

WATER-BATH PHOTON IRRADIATION TECHNIQUE FOR KAPOSISARCOMA OF THE LIMBSS. Perez1

, J. A. MolinaI, C. VillarI, F. TorresI , L. CerezoI

1 HOSPITAL DE LA PRINCESA, Radiation Oncology, Madrid, Spain

Purpose: Classic and AIDS-related Kaposi's sarcoma (KS) is a radiosen­sitive disease that can be successfully treated with different radiation tech­niques. This vascular neoplasm has a predilection for the lower limbs in95% of the cases. When the lesions are extensive and affect the interdig­ital spaces, they are difficult to treat with electrons fields, The aim of thisstudy is to present a practical radiation thechnique, used at our institution forthe treatment of KS.Materials: We report a radiation technique, placing both legs and feet ina plastic recipient and covering the whole extent of the lesions with water.Two parallel high energy (15 MV) photon portals were used, calculating themaximum dose at mid plane. Tendaily fractions of 3 Gy were generally usedto a total dose of 30 Gy. A boost to the nodular lesions was given after thistreatment in some patients. using small electron fields, administering 8 Gy ina single dose. Eight patients have been treated with this technique in the last10 years in our department.

Results: Long-term results show a high tumour response-rate, in excessof 90%, and local tumour control rate in approximately 70% at the cases.Moderate or severe limb oedema has not been observed In these patients.Conclusions: The water-bath technique is simple to perform and is very suc­cessful in terms of response and local tumour control in patients with KaposiSarcoma of the limbs.

Radiation Technologists1668 poster

3D VIRTUAL TRAINING FACILITYL0sterholm l

, I. Nordentott", H. Frarnholt'

I HERLEV HOSPITAL, Radiotherapy, Herlev,Denmark

Purpose: Off-line training on how to handle a modern linac is essential in abusy radiotherapy department. This work will demonstrate how Herlev Hos­pital optimize a 3D virtual trainIng facility.Materials: In 2007 8 new accelerators had to be taken into use while in­creasing the patient intake. This created an exceptionally large demand fornew RTI's. A more centralized training method. which ensured a both highlyprofessional and technical level but at the same time only required few hu­man resources, had to be implemented. The solution proved to be a 3Dvirtual training facility. The System consists of a 3D virtual model of a linac.An authentic hand pendant is used to control the motions of the machine,adding both sound and light makes the experience very realistic. Training ofstudents in the 3D training facility provides a calm and focused learning envi­ronment It increases skills in handling the equipment, as it lets the studentget acquainted through "hands on" exercises, in a stress free anvironment