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

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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