Review of the dose-to-water energy dependence of alanine and lithium formate EPR dosimeters and LiF TL-dosimeters – Comparison with Monte Carlo simulations

Abstract

The dose-to-water energy dependence may be defined as the dosimeter reading per absorbed dose to water for a given radiation beam relative to that for 60 Co γ rays. The purpose of this work was to review the literature on the dose-to-water energy dependence of lithium formate and alanine EPR dosimeters and LiF:Mg,Ti TL-dosimeters for clinical beam qualities and to compare the findings with Monte Carlo simulations. Monte Carlo simulations of the energy dependence of lithium formate and alanine EPR dosimeters and LiF:Mg,Ti TL-dosimeters were performed using the EGSnrc code. The following common clinical radiation qualities were applied: 4–24 MV photons, 4–20 MeV electrons, 50–200 kV p X-rays, 192 Ir γ rays, and 60 Co γ rays as the reference. All dosimeter materials showed measured and Monte Carlo simulated energy responses around unity for MV photons, electrons and 192 Ir γ rays, except LiF TL-dosimeters which showed an average underresponse of approximately 3% for electrons. For medium energy X-rays (50–200 kV p ), LiF displayed an increasing overresponse with decreasing energy to a maximum of about 40% for 50 kV p X-rays. The two EPR dosimeter materials showed decreasing energy response with decreasing X-ray energy, but lithium formate was less dependent on energy than alanine. Comparisons between Monte Carlo simulations and measurements revealed some deviations for medium energy X-rays, which may be due to LET-effects caused by low energy electrons. In conclusion, lithium formate is the dosimeter material with the lowest energy dependence over a wide range of clinically relevant radiation qualities, which clearly is advantageous for accurate dosimetry.