Linear energy transfer correction using Al₂O₃:Cr thermoluminescent and radiophotoluminescence glass dosimeters for therapeutic proton dosimetry.

Abstract

Solid-state luminescence dosimeters face challenge in achieving accurate dosimetry in proton therapy owing to the linear energy transfer (LET)-dependent response. In this study, we proposed a two-dosimeter-based methodology to improve the accuracy of proton dosimetry by correcting the LET-dependent response of a radiophotoluminescence glass dosimeter (RPLD) and an Al₂O₃:Cr-based ceramic-type thermoluminescence dosimeter (TLD) for postal dosimetry. The LET dependent response for the RPLD and Al₂O₃:Cr TLD was investigated using an unmodulated 235 MeV proton beam delivered by a passive scattering system. Both dosimeters were individually calibrated in terms of the absorbed dose to water using a 6 MV X-ray beam. The luminescence efficiency ratio between the RPLD and Al₂O₃:Cr TLD ( ${\eta }_{{\text{RPLD},\text{Al}}_2{\text{O}}_3:\text{Cr}}$ ) was used as an index to determine the LET dependence correction factor for the RPLD and Al₂O₃:Cr TLD ( $k_{\text{LET}}^{\text{RPLD}}$ and $k_{\text{LET}}^{{\text{Al}}_2{\text{O}}_3:\text{Cr}}$ ). Modulated proton beams with different spread-out Bragg peak (SOBP) widths were used to evaluate the feasibility of the proposed two-dosimeter methodology. ${\eta }_{{\text{RPLD},\text{Al}}_2{\text{O}}_3:\text{Cr}}$ decreased with increasing LET. $k_{\text{LET}}^{\text{RPLD}}$ and $k_{\text{LET}}^{{\text{Al}}_2{\text{O}}_3:\text{Cr}}$ were fitted using exponential curves. Proton dosimetry based on the proposed methodology underestimated the absorbed dose to water by an averages of 1.88% and 3.21% for RPLD and Al₂O₃:Cr TLD, respectively. This demonstrated the feasibility of the proposed methodology. Although the method shows promise for LET correction, the uncertainties in the LET-dependent correction factors, namely 2.39% for the RPLD and 5.84% for the Al₂O₃:Cr TLD, indicate the need for further refinement.