The energy dependence of lithium formate and alanine EPR dosimeters for medium energy x rays

Purpose To perform a systematic investigation of the energy dependence of alanine and lilthium formate EPR dosimeters for medium energy x rays. Methods Lithium formate and alanine EPR dosimeters were exposed to eight different x‐ray beam qualities, with nominal potentials ranging from 50 to 200 kV. Following ionometry based on standards of absorbed dose to water, the dosimeters were given two different doses of approximately 3 and 6 Gy for each radiation quality, with three dosimeters for each dose. A reference series was also irradiated to three different dose levels at aC60 o unit. The dose to water energy response, that is, the dosimeter reading per absorbed dose to water relative to that forC60 oγ ‐rays, was estimated for each beam quality. In addition, the energy response was calculated by Monte Carlo simulations and compared to the experimental energy response. Results The experimental energy response estimates ranged from 0.89 to 0.94 and from 0.68 to 0.90 for lithium formate and alanine, respectively. The uncertainties in the experimental energy response estimates were typically 3%. The relative effectiveness, that is, the ratio of the experimental energy response to that following Monte Carlo simulations was, on average, 0.96 and 0.94 for lithium formate and alanine, respectively. Conclusions This work shows that lithium formate dosimeters are less dependent on x‐ray energy than alanine. Furthermore, as the relative effectiveness for both lithium formate and alanine were systematically less than unity, the yield of radiation‐induced radicals is decreased following x‐irradiation compared to irradiation withC60 oγ ‐rays.