Energy response of CaSO4:Dy thermoluminescence detector to medical linear accelerator photon beams

The study aims to evaluate the energy response of the thermoluminescent dosemeter (TLD) CaSO4:Dy from high energy photon beams produced from medical linear accelerator. The test was performed on the polymethyl methacrylate phantom surface and at the depth of dose maximum with a source-to-surface distance of 100 cm and the radiation field size of 12 x 12 cm. The results were compared with the TLD response exposed to Co-60 standard source. The results show that the TLD response to the linac's photon differs >30% compared to the TLD response to Co-60 exposure when measured at the phantom surface, while at the depth of maximum dose the response is similar (< +/- 10%), indicating that the TLD response is no longer dependent on the energy. This implies that the current dose reading evaluation based on Co-60 calibration curve should be corrected to obtain more accurate dose report of the radiation workers.