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Hit or Miss: Is there a role for CT/MRI fusion in Sarcoma radiotherapy planning?
Paris-Ann Gfeller
B.C. Cancer Agency, Vancouver, Canada Musculoskeletal Tumour Group
C. Candish, K. Goddard, C. Grafton, L. Weir
Outline
o Background
o Study Design
o Results
o Conclusions
BackgroundSarcoma Radiotherapy Planning
o The delineation of tumor from normal tissues is critical to the radiotherapy planning process
o In Sarcoma treatment planning, improper delineation of tumour can lead to:
Over-treatment of normal tissues o Severe late effects of
treatment(fibrosis, fracture, edema)
Under-treatment of tumouro Tumour recurrence
BackgroundSarcoma Radiotherapy Planning
o Appropriate imaging is essential to properly delineate tumour volumes
o Majority of current radiotherapy planning systems are CT based
o With CT images alone it can be difficult to differentiate between tumor and normal tissue
o Sarcomas are routinely imaged using MRIo MRI correlates with tumour extent and invasion into local structureso MRI shows peritumoral edema, which is included as part of target
volume
BackgroundCT vs. MRI
CT MRI
Tumour is better defined by MRI compared to CT
BackgroundHow Can We Combine CT and MRI?
By co-registering (fusing) CT and MRI images, Radiation Oncologists can contour on CT and MRI simultaneously, using imaging information from both modalities
CT MRI
BackgroundHow is Fusion Done?
CT MRI-Fusion
BackgroundCT/MRI Fusion for Sarcomas?
There are no published studies describing the use of CT/MRIFusion for sarcoma treatment
o CT/MRI Fusion studies in other tumor sites have shown:
o Improved tumor delineation with fusion o More accurate representation of gross disease
o Decreased interobserver, intraobserver variation with fusion o More reproducible
o Is there a benefit for CT/MRI fusion in sarcoma radiotherapy planning?
Study Questions?
1. Is CT-MRI Fusion useful in sarcoma planning?o Does Fusion alter the tumour volumes? o Does Fusion improve consistency between observers
(interobserver variation)? o Does Fusion improve consistency within observers
(intraobserver variation)?
2. Is CT/MRI fusion felt to be valuable to the planning process? o Radiation Oncologists opiniono Radiation Therapists opinion
Study Design
In 2004 a BCCA protocol was developed for fusion
sarcoma patientso Coordination of planning CT and MRI on the same
day, in treatment position, with an immobilization device
o “Best” MRI image series selected in consult with radiology and fused with a planning CT
Study Design
o 19 patients were planned and treated from May 2004 to February 2005 at Vancouver Cancer Centre (BCCA) with the CT-MRI fusion protocol
o Identified all patients who had been treated according to protocol
o Excluded patients who had received chemotherapy or surgery prior to radiation planning
o Excluded tumours located in the thorax or head and neck
o 9 patients met study criteriao 6 patients treated preoperatively, 3 patients had
radiotherapy as definitive treatmento 5 MFH, 3 Fibromatosis, 1 Liposarcoma
Study Design
o Original non-contrast planning CT images and MRI images retrieved and then co-registered to produce CT/MRI fusion images
o 2 image sets for each patient createdo CT image seto CT/MRI fusion image set
Study Design
3 Radiation Oncologists (RO’s)
9 CT Image Sets9 Patient Summaries
Contour tumour volumesComplete Survey
9 Fusion Image Sets, 9 Patient Summaries
Contour tumour volumesComplete Survey
54 Image Sets
Volumes Analyzed for:
Difference in Mean Volumes
Max/Min Ratio, X/Y/Z
Observers repeated contours on CT and Fusion for Intraobserver Δ
Minimum 2 week delay between contouring on image sets
RESULTS
ResultsMean Contoured Tumour Volume By Patient
0200400600800
100012001400160018002000
1 2 3 4 5 6 7 8 9
Patient Number
Mean Volume (cc)
CT Fusion
CT volumes were 20% larger then fusion volumes
ResultsContoured Tumour Volumes
Oncologists included more NORMAL TISSUE if unsureof volume on CT vs. MRI
o This accounted for larger overall CT volumes
CT Fusion
ResultsContoured Tumour Volumes
CT contours not always inclusive of MRI signal changes
oGROSS TUMOUR EXCLUDED
CT Fusion
Interobserver VariationMaximum Variation Ratio
0
1
2
3
4
5
6
7
8
9
10
1 2 3 4 5 6 7 8 9
Patient Number
Max/Min Volume Ratio
CT Fusion
Compare Max/Min Contoured Volume for each patient between observers
o More Interobserver Variation with CT
o Volumes contoured with Fusion more consistent between observers
CT Fusion
Interobserver VariationMaximum Variation Ratio
Intraobserver VariationMaximum Variation Ratio
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
1 2 3 4 5 6 7 8 9
Patient number
max/min ratio
ct fuse
Compare Max/Min Contoured Volume for each patient within observers
oMore Intraobserver Variation with CT
o Contoured Tumour Volumes (GTV) o Mean CT volumes by pt were larger then Fusion volumes o Mean CT gross tumour volumes for each patient were 1.2 times
larger (range 0.90-1.56) then CT/MRI fusion images o p=0.04
o Interobserver Variation (Maximum Variation Ratio) o CT 3.72 (range 1.19- 9.0)o Fusion 1.72 (range 1.16-3.07)o Less interobserver variation with fusion p=0.001
o Intraobserver Variation (Maximum Variation Ratio) o CT 1.41 (range 1.03-1.72)o Fusion 1.10 (range 1.01-1.27)o Less intraobserver variation with fusion p=0.02
ResultsContoured Tumour Volumes
ResultsSurvey
o 10 question survey completed by Radiation Oncologists and Radiation Therapists involved in sarcoma planning after completing planning
o Radiation Oncologists unanimously felt better able to delineate tumour from normal tissue with fusion
o Radiation therapists felt fusion aided in their ability to prepare images (contour critical structures) in preparation for planning by Radiation Oncologists
Conclusions A Role for Fusion in Sarcoma Planning?
o One of first studies to formally evaluate use fusion for planning sarcomas
o Results justify use of fusion o Fusion allows Radiation Oncologists to define smaller more
accurate volumes which may:o decrease dose to normal tissueso Improve tumour coverage
o Fusion increases consistency and reproducibility of treatment planning
Results show the optimal modality for planningsarcoma is CT-MRI Fusion to ensure gross diseaseappropriately represented
Thank you
o CTOS Abstract Review Committee
o BCCA Musculoskeletal Tumour Group
o Dr. C. Candisho Dr. K. Goddardo Dr. C. Grafton o Dr. L. Weir
o Dr. C. Keogh (Radiology)o C. Marlowe, K. Dahle, C. Mengerink
(Radiation Therapy)o V. Morovan (Statistics)
“Imaging Matters”
Questions?
Supplementary Slides
ResultsCT with Bowel Contrast
CT with Contrast MRI
ResultsCT with IV Contrast
CT with Contrast MRI
ResultsImaging and Registration
Registration Error
Patient # MRI Type avg error (cm) max error (cm)
1 T2FS 0.15 0.33
2 STIR 0.34 0.41
3 T1FS 0.28 0.61
4 T2FS 0.26 0.38
5 T2FS 0.31 0.63
6 T2FS 0.4 0.77
7 T2FS 0.57 0.79
8 T2FS 0.16 0.23
9 T2FS 0.28 0.45
0.305556 0.511111
MRI slices 5mm
ResultsContoured Tumour Volumes
CT Fuse
ResultsContoured Tumour Volumes PTV’s
CT Fuse
Results Underestimate Tumour Extent
ResultsContoured Tumour Volumes
ResultsGross Tumour Volumes by Observer
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 200 400 600 800 1000 1200 1400 1600 1800 2000
MRI Volume (cc)
CT Volume (cc)
ResultsGross Tumour Volume By Patient
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1 2 3 4 5 6 7 8 9
Patient Number
Volume cc
doc1 ct doc2 ct doc3 ct
doc1 fuse doc2 fuse doc3 fuse
ResultsMean Gross Tumour Volume By Patient
o CT volumes 1.2 times larger then fusion, p=0.04
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1 2 3 4 5 6 7 8 9
Patient Number
Volume cc
CT Fusion
ResultsMean PTV By Patient
0
1000
2000
3000
4000
5000
6000
1 2 3 4 5 6 7 8 9
Patient Number
Volume cc
CT Fuse
ResultsMeasuring Variation
ResultsMEAN X,Y,Z Variation
CT Fusion
avg SD avg SD
med 3.74 1.12 3.63 0.4
lat -4.44 1.63 -4.28 0.4
ant 4.93 0.7 4.3 0.4
post -3.91 1.4 -3.78 0.6
sup 7.43 1.8 6.57 0.8
inf -7 2.36 -6.28 0.8
Standard Deviation smaller for fusion all directions
All dimensions smaller for Fusion
(sup/inf most significant)
ResultsVariation Superior to Inferior
-15
-10
-5
0
5
10
15
20
0 5 10 15 20 25
Series2
Series3
Series4
Series5
Series6
Series7
Series8
Series9
Series10
Series11
Series12
Series13
Series14
Series15
Series16
Series17
Series18
Series19
Series20
Series21
Series22
ResultsMedial and Lateral Variation
ct ct fuse fuse
med lat med lat
6 -5.5 5 -4
1 -1.5 1 -2
3 -2.67 3 -2
3.333 -6.33 5.2 -5
2 -2.67 0 -3.167
1.333 -1.83 1.3 -3
6 -6 5.5 -7.333
5 -5.5 4.7 -5
6 -8 7 -7
3.741 -4.44 3.6 -4.278
ResultsCompletion Survey
Survey completed for each image set at completion of contouring (N=88)Linear Analog Rating Scale
Rate the general quality of this CT (fusion) image set? (1 – poor, 5-meets expectations, 10 – exceeds expectations)
o CT score 4.9, Fusion 6.7o Both image sets were “acceptable” for contouring
Rate the quality of this CT (fusion) image set for delineating: (1- can not delineate to 10 –exceeds expectations)
a. Tumor volumeo CT 4.0, Fusion 7.8
b. Critical Structures o CT 4.2, Fusion 7.4
Indicates Subjectively “Better" Delineation of
Tumour and Critical Structures with Fusion
ResultsRadiation Oncologists Completion Survey
Using a linear analog scale (poor to exceeds expectations)
rate the quality of this CT (fusion) image set for delineating:
Tumour Volumes
o CT 4.0, Fusion 7.8
1 2 3 4 5 6 7 8 9 10
1
Fuse
CT
1 2 3 4 5 6 7 8 9 10
1
Fuse
CT
Normal Tissues CT 4.2, Fusion 7.4
Improved Delineation of Tumour and Normal Structures with Fusion
poor meets expectations exceeds poor meets expectations exceeds
ResultsRadiation Therapists Opinions
8 question survey for Radiation therapists (n=4) involved in sarcoma fusions
1. Average time for fusiono 35.5 minutes
2. Usefulness of Fusion for delineating normal structureso Extremely useful
3. Difficulty of Performing Fusions compared to other siteso Slightly more difficult, (extremities the most difficult)
4. Important factors in image fusiono Tumour location, MRI quality, time availableo IMMOBILIZATION and Position
ConclusionsA Role for Fusion in Sarcoma Planning?
o CT/MRI fusion is valuable to the planning process for sarcoma
o Contoured Tumour Volumeso More normal tissue included in the target volumes with CTo Disease excluded on CT
o Volume Variation o More consistency in contours with Fusion
o Completion Survey o Radiation Oncologists and Therapists felt fusion was
valuable