Optimasi Dosis Terapi Kanker Lambung dengan Proton Therapy menggunakan Program PHITS Versi 3.35

Abstract

Gastric cancer is one of the leading causes of cancer-related mortality and remains a major concern in both global and national oncology. Proton therapy is based on the Bragg Peak phenomenon, in which protons deposit their maximum energy at a specific depth, allowing a high radiation dose to be concentrated within the cancer while minimizing exposure to surrounding healthy tissues or organs at risk (OARs). This study aimed to investigate the characteristics of proton distribution in gastric tissue using the Passive Scattering method in PHITS version 3.35, determine the position and shape of the Bragg Peak at different proton energy ranges, and compare the absorbed doses in the Gross Tumor Volume (GTV), Clinical Target Volume (CTV), Planning Target Volume (PTV), and OARs for Anterior Posterior (AP) and Left Lateral (LLAT) irradiation directions with clinical dose tolerance limits. Simulations were performed using clinical anatomical data from a male phantom representing the stomach and surrounding organs. The simulation results showed that the absorbed doses in the GTV, CTV, and PTV for the AP direction were 30 Gy, 17.44 Gy, and 10.79 Gy, respectively, whereas those for the LLAT direction were 30 Gy, 28.17 Gy, and 13.26 Gy, with corresponding target volumes of 40 cm³, 60 cm³, and 80 cm³. The optimal proton energy ranges were 65-106 MeV for the AP direction and 90-146 MeV for the LLAT direction. Based on the evaluation of OAR doses against clinical dose tolerance limits, the AP irradiation direction provided a more optimal dose distribution than the LLAT direction because the doses received by all OARs remained below the established clinical tolerance limits.