Room: Exhibit Hall
Purpose: Linear energy transfer (LET) is related to the biological effect caused from the proton therapy. Recently, LET is possible to be a parameter for optimization of proton therapy treatment plan. Therefore, being able to measure LET becomes significant. This study is to develop a LET measurement system with thermoluminescent dosimeter (TLD).
Methods: TLD-100 (LiF: Mg, Ti) is LET dependent, which makes TLD-100 be considered as not only a dosimeter but also a LET detector. High temperature ratio (HTR), which is calculated from thermoluminescent glow curves at the specified temperature region, is the ratio of the integral TL intensities from a proton beam and a photon beam (ie. cobalt-60 gamma rays or 6 MV X rays). HTR values depend on the LETs of the particles. The relationship between HTR and LET was determined in this study. The TLDs were irradiated by a cobalt-60 source at the national measurement laboratory of Institute of Nuclear Energy Research, a 6-MV photon beam (Truebeam, Varian), and a 190-MeV proton beam (Sumitomo Heavy Industry, Japan) at the Chang Gung Memorial Hospital.Â TLDs were irradiated with the same dose at several depths of a HDPE phantom. The LETs which vary with depths were simulated with TOPAS (version 3.0.1).
Results: HTRs were calculated from Co-60 (HTRp,gamma) and from 6MV photon (HTRp,x), around 0.873 to 1.40 and 0.319 to 0.511, respectively. The LET for 190-MeV proton ranges from 0.5 to 7 keV/Âµm. The correlation between HTR and LET could be modeled with exponential relationship (RÂ² > 0.92).
Conclusion: The LET measurement system for proton beam could be developed using comparing TL intensities with both Co-60 or 6MV photon. It would be more convenient to build the system with 6MV photon for most medical facilities.
Funding Support, Disclosures, and Conflict of Interest: This study was supported by grants from the Institute of Nuclear Energy Research (NL1060818). The authors express their gratitude to the Dose Assessment Core Laboratory of the Institute for Radiological Research, Chang Gung University/Chang Gung Memorial Hospital at Linkou for assistance with dose assessments.