Monte Carlo verification of the holder correction factors for the radiophotoluminescent glass dosimeter used by the IAEA in international dosimetry audits

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.

IAEA/WHO postal dosimetry audit methodology for electron beams using radio photoluminescent dosimeters

“…For the electron beam energies used in this study (6–22 MeV), the product of the holder and energy correction factors ranged between 1.04 and 1.05, compared to photons where it ranges from 1.01 to 1.04 for energies between 6 and 18 MV 23,30 . Whilst a different RPLD holder design was used in photon beams, holder corrections are of comparable magnitude for both modalities.…”

“…For the electron beam energies used in this study (6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22), the product of the holder and energy correction factors ranged between 1.04 and 1.05, compared to photons where it ranges from 1.01 to 1.04 for energies between 6 and 18 MV. 23,30 Whilst a differ-ent RPLD holder design was used in photon beams, holder corrections are of comparable magnitude for both modalities. The observed holder correction behavior in electron beams that gradually decreases at high energies is most likely related to the higher irradiation depth (z ref ) that as a result, has proportionally less PMMA to water (Figure 2).…”