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An Investigation of the Energy Dependence of LiF:Mg,Ti Thermoluminescent Dosimeters in Photon Beams


G Massillon-JL

G Massillon-JL1*, R Minniti2, M O'Brien2, C Soares2, (1)Instituto de Fisica, Universidad Nacional Autonoma de Mexico, A.P. 20-364, 01000 Distrito Federal, Mexico ,,,(2) National Institute of Standards and Technology, Gaithersburg, MD

SU-E-T-86 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

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 energies

Methods:
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.

Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by DGAPA-UNAM grants IN102610 and IN105813 and Conacyt Mexico grant 127409

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