Akademik Veri Yönetim Sistemi
International Conference on Radiation and Applications in Various Fields of Research (RAD 2024), Herceg Novi, Karadağ, 17 - 21 Haziran 2024, cilt.1, ss.102, (Özet Bildiri)
In order to calculate the radiation risk of patients in diagnostic and therapeutic imaging, it is very important to measure the absorbed dose at the exposed region. For this purpose, ion chambers, solid state detectors, luminescence dosimeters, etc. are used to measure the radiation dose. Thermoluminescence (TL) dosimeters are usually preferred because they are small and can be placed in the exposed regions without causing shadow effects or artifacts on the radiographic image. Today, the most preferred TL dosimeter for this purpose is the commercial TLD-100 (LiF:Mg,Ti). The effective atomic number of TLD-100 dosimeter (Zeff = 8.2) is very close to soft tissue, its energy dependence is low (at the energies above 100 keV), it can be produced in millimetric geometries, and its linear dose-response range is wide (from μGy to Gy orders). In diagnostic and interventional radiology, where low-energy X-rays (<100 keV) are used, the dosimeter used to determine the absorbed dose with the TL method should be calibrated with a known radiation dose. This requires consideration of the energy dependence of the dosimeter irradiated at low energies. In this study, TL intensity obtained as a result of irradiation of TLD-100 dosimeters (Thermo Scientific Co., USA) to be calibrated with 5 mGy radiation dose at different energies in the diagnostic energy range (40-120 kVp) was investigated. The same dosimeters were irradiated with a high-energy Cs137 photon source (Eγ = 661.7 keV) to compare the TL intensities obtained as a result of low and high energy irradiation and also to obtain whether the change in sensitivity depending on the energy. Irradiations were performed in a conventional X-ray system (General Electric Silhouette VR) and the radiation dose was measured with a 6 cc ion chamber (Radcal Corporation, calibrated at SSDL). The energy spectra of irradiations at different tube voltages were simulated using XCOM5R software (Nowotny and Höfer 1985) their average energies were calculated. Accordingly, it has been observed that TLD-100 dosimeters irradiated with a high energy photon source have an increase of approximately 25-35% in TL sensitivity when irradiated with the same dose with low-energy X-rays at 40-120 kVp. This result shows that if TLD-100 dosimeters are used for radiation dose measurement in radiological studies performed with low-energy X-rays, dose-response calibration should be performed with the same tube voltage/energy spectrum planned in the study. Only then the absorption of radiation in the relevant tissue can be measured or compared with the TLD-100 dosimeter. Once the energy dependence is known, TL dosimeters can be used to measure the absorbed dose after calibration performed at the same energy as the energy used during therapy.