Dosimetric characteristics of radiophotoluminescent glass dosimeters for proton beams

Abstract

Background: The study of radiophotoluminescent glass dosimeters (RGDs) in the clinical usage of proton beams is limited. The aim of this study was to investigate the dosimetric characteristics of RGDs for pencil beam scanning proton therapy. The feasibility of using an RGD in end-to-end testing of intensity-modulated proton therapy (IMPT) plans at various treatment sites was also evaluated. Materials and methods: The dosimetric characteristics of the GD-302M type glass dosimeter were studied in terms of uniformity, short-term and long-term reproducibility, stability of the magazine position readout, dose linearity in the range from 0.2-20 Gy, energy response in 70-220 MeV, MU/spot, dose rate response, and fading effect. The reference conditions of the spot scanning beam from the Varian ProBeam Compact system were operation at 160 MeV, a 2 cm water equivalent depth in a solid water phantom, a 10×10 cm field size at the isocenter, and 2 Gy dose delivery. End-to-end testing of IMPT plans for the head, abdomen, and pelvis was verified by using the Alderson Rando phantom. The overall uncertainty analysis was confirmed in this study. Results: The relative response of RGDs for the uniformity test was within 0.95-1.05. The %CVs of the short-term and long-term reproducibility were 1.16% and 1.50%, respectively. The FGD-1000 automatic reader showed stable magazine position readout. The dose linearity was found to have an obviously good linear relationship, with R2 = 0.9988. The energy response relative to 160 MeV was approximately within 4.0%. The MU/spot and dose rate had less effect on the RGD readout. The fading effect was relatively stable for 10 weeks of storage, within 2.4%. For the end-to-end test, the maximum difference between the treatment plan and RGD measurement showed a very good result that was within 1.0%. The overall uncertainty of the RGD measurement for the proton beam was 4.6%. Conclusion: RGDs have confirmed the potential for proton dosimetry, including in end-to-end testing. The appropriate correction factor for the energy response can be applied for dose verification of scanning proton beams.