Evaluation of dosimetric parameters after electron gun and ion pump replacement in linear accelerator device and comparison of results by gATE/Geant4 simulation

This study evaluates dosimetric data such as PDD, dose profile and tissue phantom rate (TPR20/10) after replacing the LINAC device's electron gun and ion chamber pump. These values obtained after the change were compared with the standard PDD protocol, British Journal of Radiology Supplement 25 (BJR 25) report, Beam Data (measured and recorded as reference values during the setup phase, BD) and simulation results. In additional, uncertainty results were obtained for absorbed doses to water using different calculation tools. The experimental setup was created in the GATE/Geant4 simulation program, and the experimentally obtained TPR20/10, beam profile and PDD values were compared with the simulation. The difference between TPR20/10 values for 6 and 18 MV photon energies was found to be below 1% for 6 MVs and 3% for 18 MV. When different calculation tools were used, uncertainties were found in the absorbed dose measurements ranging between 0.8% and 1.87%, which is compatible with the uncertainties (1.4-2.1%) specified in the IAEA report. Even though small uncertainties were observed in the results, the differences between the calculations in the measurements of absorbed doses were insignificant. Estimated uncertainties for GATE was a little smaller than those measured using experimental methods, BD and BJR 25. Although the values obtained are within the tolerance, after such significant materials are changed in the LINAC device, a water phantom should be set up, the measurements should be repeated, and the results should be confirmed to be within the limit values.