Abstract
The International Atomic Energy Agency (IAEA), jointly with the World Health Organization (WHO), has operated a postal dosimetry audit program for radiotherapy centers worldwide since 1969. In 2017 the IAEA introduced a new methodology based on radiophotoluminescent dosimetry (RPLD) for these audits. The detection system consists of a phosphate glass dosimeter inserted in a plastic capsule that is kept in measuring position with a PMMA holder during irradiation. Correction factors for this holder were obtained using experimental methods. In this work these methods are described and the resulting factors are verified by means of Monte Carlo simulation with the general-purpose code PENELOPE for a range of photon beam qualities relevant in radiotherapy. The study relies on a detailed geometrical representation of the experimental setup. Various photon beams were obtained from faithful modeling of the corresponding linacs. Monte Carlo simulation transport parameters are selected to ensure subpercent accuracy. The simulated correction factors fall in the interval 1.005-1.008 (±0.2%), with deviations with respect to experimental values not larger than 0.2(2)%. This study corroborates the validity of the holder correction factors currently used for the IAEA audits.
Highlights
The International Atomic Energy Agency (IAEA), jointly with the World Health Organization (WHO), operates a worldwide postal dosimetry audit program for radiotherapy centers since 1969 [1]
Small dosimeters are sent by the IAEA to participating centers for irradiation with clinical high energy photon beams used for cancer treatment
The influence of the IAEA holder on the thermoluminescent dosimeters (TLDs) readings was investigated, both experimentally and analytically, by Izewska and coworkers [5,6] who derived holder correction factors for the determi nation of absorbed dose to water. These results were compared with those obtained from Monte Carlo simulations performed by Hultqvist and co-workers [7] and good agreement was found within the associated uncertainties
Summary
The International Atomic Energy Agency (IAEA), jointly with the World Health Organization (WHO), operates a worldwide postal dosimetry audit program for radiotherapy centers since 1969 [1]. Small dosimeters are sent by the IAEA to participating centers for irradiation with clinical high energy photon beams used for cancer treatment Upon their return to the IAEA Dosimetry Laboratory, dosimeters are processed to obtain the absorbed dose to be compared with that stated by the participant. The influence of the IAEA holder on the TLD readings was investigated, both experimentally and analytically, by Izewska and coworkers [5,6] who derived holder correction factors for the determi nation of absorbed dose to water These results were compared with those obtained from Monte Carlo simulations performed by Hultqvist and co-workers [7] and good agreement was found within the associated uncertainties. Results are presented and conclusions drawn in the last part of the paper
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