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Direct megavoltage photon calibration service in Australia
D J Butler1, G Ramanathan, C Oliver
1Australian Radiation Protection and Nuclear Safety Agency, 619 Lower Plenty Road, Yallambie, VIC, 3085, Australia, Duncan.Butler@arpansa.gov.au.
Australasian Physical & Engineering Sciences in Medicine
|August 23, 2014
Summary
Australian primary standards for absorbed dose now include megavoltage linac beams, improving radiotherapy accuracy. Direct calibration in linac beams reduces absorbed dose measurements compared to cobalt-60, aligning with international standards.
Area of Science:
- Medical Physics
- Radiation Dosimetry
- Radiotherapy
Background:
- ARPANSA holds Australia's primary standard for absorbed dose, historically calibrated using (60)Co gamma rays.
- Radiotherapy clinics use (60)Co calibrations with correction factors (k Q) for linac photon beams due to spectral differences.
- Adapting primary standards to megavoltage linac beams is crucial for accurate clinical dosimetry.
Purpose of the Study:
- To detail ARPANSA's new calibration service for megavoltage linac beams (6, 10, 18 MV).
- To validate the new calibration method and its application with IAEA's TRS-398 Code of Practice.
- To quantify expected changes in absorbed dose measurements in clinical settings.
Main Methods:
- Adaptation of the Australian primary standard for absorbed dose to operate in megavoltage linac beams.
- Development and validation of a new calibration service using an Elekta Synergy linac.
- Application of new calibration factors according to the IAEA TRS-398 dosimetry Code of Practice.
Main Results:
- A new calibration service is established for 6, 10, and 18 MV photon beams.
- For a Farmer chamber (model 2571), calibration coefficients are expected to decrease by 0.4%, 1.0%, and 1.1% respectively, compared to (60)Co derived factors.
- Results align with international absorbed dose standards and Monte Carlo calculations.
Conclusions:
- ARPANSA's new service enables direct calibration in linac beams, enhancing radiotherapy dosimetry.
- The shift from (60)Co to direct linac beam calibration is expected to reduce absorbed dose measurements.
- The findings support the adoption of the new service for improved clinical dosimetry accuracy.
