The investigation of angle dependence effect on the radiation dose in computer-aided linear accelerators by two-dimension array ion chambers

This study was carried out at the Akdeniz University Faculty of Science Department of Physics, the comparison of the durability of two-dimensional ion chambers required for the measurement of radiation dose intensity, which is used for control of plan applicability techniques in Intensity Modulated Arc Therapy (IMAT). In this study, 10 YRART sample plan was made in the Treatment Planning System (TPS) using 6 MV energized X-ray beam. In TPS, 2D dose maps of the prepared plans were obtained on reference phantoms. The OmniPro-I'mRT was used with MatriXX, MULTICube Lite Phantom and an angle sensor fixed on the gantry of the linear accelerator. For the YRART plans, the measurements were taken in active and passive conditions and dose distributions were evaluated using the OmniPro-I'mRT software. The dose 2D maps obtained for both cases were compared with TPS dose maps using the gamma analysis method. Plan measurements were evaluated according to international acceptance criteria (3% dose difference and 3 mm distance). The average percentage difference of the gamma indices between the measured dose when the angle sensor was active and the dose maps calculated in the reference phantom was found to be ˗0.52%. This percentage difference was found to be ˗4.1% when the angle sensor is in the passive state. The calibration of the two-dimensional ion chambers in MatriXX is done only in the plane perpendicular to the beam. However, this difference has been reduced for YRART plan measurements as the software in the system has enabled the angle sensor factor. The result of this thesis has shown that the applicability of the YRART plans can only be checked by two-dimension array ion chambers with active angle sensor to achieve reliable limits.