Feasibility and limitations of a postal dosimetry audit system using RPLGD for high-dose-rate brachytherapy

Abstract

International recommendations and South Korean regulations emphasize the need for dosimetry audit systems to ensure treatment accuracy in high-dose-rate brachytherapy. In this study, we designed and tested a prototype polycarbonate postal audit phantom to assess its feasibility. Using six GD-302M radiophotoluminescent glass dosimeters. Dose measurements were performed at points A and B based on the treatment planning system (TPS) and PHITS. These were validated in the Korea laboratory accreditation scheme and secondary standard dosimetry laboratory using Co-60 beam. Reproducibility and linearity tests showed stable responses; however, a maximum deviation of 13.5 % was observed between the measured and TPS doses at point A. The PHITS simulations revealed that the TPS overestimated the dose by approximately 10 %, whereas glass dosimeters showed up to 20 % overestimation because of low-energy gamma rays from the Ir-192 source. Additional water phantom measurements demonstrated that the RPLGD can provide reasonably consistent dose readings under water-equivalent conditions. The discrepancies observed in the audit phantom were found to follow a consistent trend and could be assessed using normalization. The combined expanded uncertainties were calculated as 3.1 % and 3.2 % (k = 2) for the source holder models 70010 and 72280, respectively. The audit phantom showed potential for application in nationwide postal audits, pending further validation. To ensure clinical applicability, future work should focus on addressing the energy dependence of the RPLGD and conducting a multi-institutional pilot study.