Implementation of geant4 application for tomography emission Monte Carlo Code in the calculation of dose distribution in external radiation therapy

Background: The "Geant4 Application for Tomography Emission" (GATE) toolkit comprises advanced open-source Monte Carlo (MC) code for use in medical imaging and radiotherapy simulations. This study aimed to verify the GATE toolkit results against a water phantom and then to show the dose calculation capabilities of the GATE for radiotherapy. The results were compared with three dose calculation algorithms using patients' Computerized Tomography (CT) data. Materials and Methods: A Linac with a 6 MV photon beam was simulated in the GATE code. The code was verified, head CT images of three patients were inserted into the GATE as realistic phantoms , and simulations were performed for different field sizes and angles. The Percent Depth Doses (PDDs) and transverse profiles were extracted from the GATE simulation and calculation algorithms. Their results were compared regarding the Dose Difference (DD) and gamma index for the PDDs and the Full Width at Half Maximum (FWHM) for the profiles. Results: Using the patient CT data for the PDDs, the gamma pass rate with 3%/3 mm criteria in the comparison between the GATE simulation and algorithms for all fields ranged from 89.4% to 98.8%, with an average of 92.8%. The extracted FWHMs from the GATE and algorithms were in good agreement, and their differences ranged from 0.1 to 1.2 mm. Conclusions: The GATE MC toolkit has good potential for implementation in radiotherapy Treatment Planning Systems (TPS) for dose calculations.