An experimental study on the determination of gantry angle and SSD dependencies of TLD and MOSFET dosimeter systems

Background: The purpose of this study was to investigate the various gantry angle and SSD dependencies of TLD and MOSFET dosimeters. Materials and Methods: LiF (Mg) TLD and MOSFET were used in this study. Dosimeter systems were calibrated and then irradiated at various gantry angle and SSD by applying 6 MV photon energy. Results: Based on the results, MOSFET changes were found to be in 2% range between ±50º gantry angles and the rate of dose change was found to be increasing as gantry angle was at the extremes of graph. This increase was especially obvious in tail end of the asymmetric axes. Change in the gantry angle dependency of TLD was -2% till ± 60º gantry angle and -5% between 60º to 90º. Dependency of SSD was ±1% for TLD and MOSFET. Conclusion: Results indicate that properties of dosimeters must be well known by users for accurate determination of the entire doses on the patient. These observations may lead to better treatment quality and prevention of probable dose errors.