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Comparison of Absorbed Dose to Water of High-Energy Photon Beams Based On the IAEA IRS-277, TRS-398 and Direct Calibration in Megavoltage Photon Beams

K Wang

K Wang*, S Jin , Y fan , X Chang , National Institute of Metrology, Beijing, Beijing


SU-I-GPD-T-447 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: to clarify the consistency of the traceability system for linear accelerators output dose between air kerma based and water absorbed dose based formalisms, and verify the discrepancy of output dose tracing to water absorbed dose of ⁶⁰Co and photon beam of research linear accelerator.

Methods: The ionization chambers (PTW-30013, NE-2571, IBA-FC65G) were calibrated at air kerma and water absorbed dose of ⁶⁰Co, respectively, and the accelerator photon water absorbed dose was measured by the ionization chambers according to the IAEA TRS-277 and TRS-398 formalisms. The ionization chambers were calibrated at 6, 10, and 25 MV photons and the water absorbed dose of clinical accelerator photon was measured directly by ionization chambers with the radiation qualities modified.

Results: The maximum chamber-to-chamber variations of the dose obtained with the IAEA TRS-277 and TRS-398 were between 0.2% and 0.6% for the different beams. The variations of the dose obtained with IAEA TRS-398 and chambers calibrated directly by megavoltage photons were between 0.1% and 0.5%.

Conclusion: The absorbed dose of clinical accelerator is consistent after changed from old to new formalisms with the traceability of calibration factors obtained at the primary absorbed dose and air kerma standards in the ⁶⁰Co beams in China. It is technically feasible to direct calibrate the chamber in megavoltage photon beams and use for the clinical accelerator, which will reduce the uncertainty compared to the ⁶⁰Co calibration combined with the TRS-398 energy correction factor.

Funding Support, Disclosures, and Conflict of Interest: Special Fund for Quality Scientific Research in the Public Welfare (201510001)

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