Abstract
Purpose: To investigate the energy dependence of thermoluminescent dosimeters (TLDs) and the effect of irradiating them on different phantom materials for a broad range of photon energiesMethods: Thermoluminescent dosimeters (TLDs), are widely used to estimate the absorbed dose received by patients during diagnostic and/or medical treatment. For this purpose, TLDs are typically mounted in phantoms to simulate human tissue. To analyse the effect of the phantom material on the TLD response, TLD‐100 dosimeters were irradiated in x‐ray and gamma‐ray beams mounted against phantoms made of three different materials (polymethyl methacrylate (PMMA), solid water (wt1) and polystyrene) and free in air. The study was conducted over a broad range of photon energies generated by 20 kV‐300 kV x‐ray narrow spectra and 137Cs and 60Co gamma‐ray beams provided by the National Institute of Standards and Technology. Air kerma values delivered to the dosimeters at each photon energy were between 50 mGy and 150 mGy for x‐rays and 50 mGy for 137Cs and 60Co beams. Results: The TL response was evaluated using two dimensionless quantities: the TL response per unit of air kerma, R, and the relative efficiency, RE, which corresponds to the TL energy response per unit dose delivered by the primary beam. Both R and RE are normalized to the responses in a 60Co beam. The results show that for a given photon energy, the values of both quantities R and RE depend on the phantom material. However the energy dependence of R and RE are significantly different. Conclusion: The observed energy dependence of TLDs expressed in terms of R and RE, suggest that R does not reflect the physical interaction process when used to measure absorbed dose in a medium. Instead, RE is found to be a more adequate parameter for describing the TL dose response to photon energies. This work was partially supported by DGAPA‐UNAM grants IN102610 and IN105813 and Conacyt Mexico grant 127409
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