Correction of stopping power and LET quenching for radiophotoluminescent glass dosimetry in a therapeutic proton beam

• Published in: Physics in medicine & biology Vol. 62; no. 23; pp. 8869 - 8881
• Main Authors: Chang, Weishan, Koba, Yusuke, Katayose, Tetsurou, Yasui, Keisuke, Omachi, Chihiro, Hariu, Masatsugu, Saitoh, Hidetoshi
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 09.11.2017
• Subjects: Calibration; dosimetry; Glass; Humans; LET dependence; Linear Energy Transfer; Luminescence; Monte Carlo Method; Proton Therapy; Radiometry - methods; radiophotoluminescent glass dosimeter
• ISSN: 0031-9155; 1361-6560; 1361-6560
• DOI: 10.1088/1361-6560/aa9155

To measure the absorbed dose to water Dw in proton beams using a radiophotoluminescent glass dosimeter (RGD), a method with the correction for the change of the mass stopping power ratio (SPR) and the linear energy transfer (LET) dependence of radiophotoluminescent efficiency εLETRGD is proposed. The calibration coefficient in terms of Dw for RGDs (GD-302M, Asahi Techno Glass) was obtained using a 60Co γ-ray. The SPR of water to the RGD was calculated by Monte Carlo simulation, and εLETRGD was investigated experimentally using a 70 MeV proton beam. For clinical usage, the residual range Rres was used as a quality index to determine the correction factor for the beam quality kQ,Q0RGD and the LET quenching effect of the RGD kLETRGD. The proposed method was evaluated by measuring Dw at different depths in a 200 MeV proton beam. For both non-modulated and modulated proton beams, kQ,Q0RGD decreases rapidly where Rres is less than 4 cm. The difference in kQ,Q0RGD between a non-modulated and a modulated proton beam is less than 0.5% for the Rres range from 0 cm to 22 cm. εLETRGD decreases rapidly at a LET range from 1 to 2 keV µm−1. In the evaluation experiments, Dw using RGDs, Dw,QRGD showed good agreement with that obtained using an ionization chamber and the relative difference was within 3% where Rres was larger than 1 cm. The uncertainty budget for Dw,QRGD in a proton beam was estimated to investigate the potential of RGD postal dosimetry in proton therapy. These results demonstrate the feasibility of RGD dosimetry in a therapeutic proton beam and the general versatility of the proposed method. In conclusion, the proposed methodology for RGDs in proton dosimetry is applicable where Rres  >  1 cm and the RGD is feasible as a postal audit dosimeter for proton therapy.