Room: AAPM ePoster Library
Purpose: evaluate the dose response characteristics of the radiophotoluminescent glass dosimeters (RGD) in the output measurements and the impact of the dose averaged linear energy transfer (LETd) in the plateau region for a spot scanning proton beam.
Methods: We compared the doses measured by the ionization chamber (TM31016: PTW; D(IC)) and the RGD (GD-302M: Asahi Techno Glass Inc; D(RGD)) using a spot scanning proton beam system (PROBEAT-III: Hitachi,Ltd). This study evaluated the dose response characteristics of the RGD in 9 energies and 6 field sizes. The dose was measured on the plateau region: the depth at 2 cm and 4 cm depth were used. Additionally, the LETd in the measurement depth of each energy was calculated by the Monte Carlo simulation (PHITS ver.3.13). The relationship between the calculated LETd and the dose difference between the D(IC) and the D(RGD) was evaluated.
Results: dose differences for the energy and the field size changes between the D(IC) and the D(RGD) showed good agreement within 2% and 2.5%, respectively. Then, the dose differences between the D(IC) and the D(RGD) showed no correlation with the energy or the field size changes. Because the change in the LETd was small from 3.6 to 5.4 keV/µm, the dose difference between the D(IC) and the D(RGD) was not significant in this study.
Conclusion: dose response characteristics of the RGD were confirmed for a spot scanning proton beam. The dose differences agreed within 2.5% between the D(IC) and the D(RGD). The dose response of the RGD was not affected because the change of LETd was small in the plateau region. We will investigate the dose response characteristics of the RGD in clinical conditions in a future study.