Dosimetry audits in radiotherapy using a radiophotoluminescent
glass dosimeter in Japan
H. Mizuno a, A. Fukumura a, Y. Kusano b, S. Sakata ca National Institute of Radiological Sciences (NIRS), Chiba, Japanb Kanagawa Cancer Center, Yokohama, Japanc Association for Nuclear Technology in Medicine (ANTM), Chiba, Japan
Status of Radiotherapy (RT) in Japan
RT InfrastructureFacilities: 765LINACs: 807
RT Human ResourcesRadiation Oncologists: 645Medical Physicists: 488 RT Quality Managers: 7080
1 x 105
2 x 105
0
50
100
150
200
250
300
1990 1995 2000 2005
new
pat
ient
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diot
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new patients / institute
year
236.1
1.81×105
Number of RT Patients in Japan(JASTRO 2007)
(The majority of physicists and RT QM are employed as RT technologists.)
Pilot study• From 2001, pilot study has been initiated
based on a national research group funded by Ministry of Health, Labour and Welfare.
• Dosimeter– Radiophotoluminescent Glass Dosimeter (RGD)
(Dose Ace; ASAHI GLASS CO.)• Phantom
– Tough Water Phantom (KYOTO KAGAKU CO.)
Radiophotoluminescent Glass Dosimeter (RGD)
• Silver activated phosphate glass• Density 2.61 g/cm3
• 1.3mmΦ×12mm length
12mm
The advantages of Glass dosimeter compared with TLD
• Repeatable readout• Little Fading• Easy handling (Numbering)
*Disadvantage- TLD is more tissue-equivalent.
(However, we confirmed the energy dependence can be corrected like TLD.)
Tough water phantom• A water equivalent solid phantom
Material Density Mean atomic number
Electron density
Tough Water Phantom
1.01 g/cm3 7.42 3.25×1023 /cm3
Water 1.00 g/cm3 7.42 3.34×1023 /cm3
Irradiation under standard condition
Any solid phantom(size ≧
30x30 cm)
Glass dosimeter containedTough water phantom
Aligned to isocenter bycross wire and laser
Pile up tough water phantom to 10cm depth
Irradiate 1Gy to RGD.30~60 min./1 linac (2 beams)
Audit development done by NIRS
From 2005, pilot study took over by National Institute of Radiological Sciences (NIRS) and system improvement and evaluation was performed for
• RGD Calibration using SSDL 60Co-γ ray.• Systematic correction for beam energy by
experiment and MC simulation.• Comparison with TLD system.• Uncertainty estimation.
Feasibility study for RGD system
106 facilities (192
beams)
Center= 0.3%σ=1.3%
Within ±3%- 182 beams(95%)
Test audit for final check (2006-2007)
External audit has been initiated
Since Nov. 2007, external audit using RGD was initiated.• Actual audit operation is performed by Association for Nuclear Technology in Medicine.• Not mandatory (Recommendation is in every 3 years.)• Cost ~ $ 1,100 (790 €) for 2 X-ray beams• NIRS system (RGD system and 60Co unit) is used.• NIRS physicists are supervising the audit.
Distribution of the results of the audits of radiotherapy hospitals for the delivery of absorbed dose to water under reference condition during 2007-2009.
We got excellent results, in that the mean ratio was 1.005, its standard deviation was 0.9%.
Inter-comparison with IAEA/WHO TLD audit system
IAEA (TLD) NIRS (RGD)
Annually
TLD(IAEA→NIRS)
RGD(NIRS→IAEA)
Almost all elementswere agreed within 2%.(Mean=0.995, SD=0.9%)
Application to the non-reference condition
From Apr. 2010, we applied followingnon-reference conditions to the audit.- Field size variation
(Correction factor is applied due to energy spectrum change with field size.)
- Wedged beam(No systematic dependence on wedge angle
could be detected.)
Future plan
• Electron beam• IMRT beam• SRT beam (Cyberknife)
Thank you