Geant4 코드를 이용한 선형가속기 6 MV 광자선의 선량분포에 관한 연구

Geant4 Code Based Simulation of 6 MV Photon Beam for Analysis of Dose Distribution

This study is to present a Geant4 code for the simulation of the absorbed dose distribution given by a medical linac for 6 MV photon beam. The dose distribution was verified by comparison with calculated beam data and beam data measured in water phantom. They were performed for percentage depth dose(PDD) and beam profile of cross-plane for two field sizes of 10 × 10 and 15 × 15 cm² Deviations of a percentage and distance were obtained. In energy spectrum, the mean energy was 1.69 MeV. Results were in agreement with PDD and beam profile of the phantom with a tolerance limit. The differences in the central beam axis data δ1 for PDD had been less than 2% and in the build up region, these differences increased up to 4.40% for 10 cm square field. The maximum differences of δ₂ for beam profile were calculated with a result of 4.35% and 5.32% for 10 cm, 15 cm square fields, respectively. It can be observed that the difference was below 4% in δ₃ and δ₄. For two field sizes of δ50-90 and RW50, the results agreed to within 2 mm. The results of the t-test showed that no statistically significant differences were found between the data for PDD of δ1, p>0.05. A significant difference on PDD was observed for field sizes of 10 × 10 cm², p=0.041. No significant differences were found in the beam profile of δ₃, δ₄, RW50, and δ50-90. Significant differences on beam profile of δ₂ were observed for field sizes of 10 × 10 cm², p=0.025 and for 15 × 15 cm², p=0.037. This work described the development and reproducibility of Geant4 code for verification of dose distribution.