Dose Distribution Analysis of Proton Therapy for Medulloblastoma Cancer with PHITS 3.24

One of the developments in particle therapy is proton radiation therapy. Research related to proton therapy is difficult due to a limited number of available proton therapy facilities. Therefore, there is a need for alternative proton therapy simulations using programs other than those in proton therapy facilities. This research was aimed to simulate medulloblastoma brain cancer which is most common in children. The program used in this research was PHITS version 3.24. The human body was modeled with the revised ORNL-MIRD phantom for a 10-year-old child. The therapy scheme was a whole posterior fossa boost of 19.8 Gy RBE. The proton passive scattering was simulated by passing a uniform proton beam through the aperture and compensator with various energy levels. The proton pencil beam scanning was simulated with small cylindrical beams with a radius of 0.5 cm, which were adjusted to the planning target volume with layers variations. The total duration of the prescription dose given was 550 seconds with passive scattering and 605 seconds with pencil beam scanning. In passive scattering, the OAR(s) with the most significant percentage of absorbed dose were the skin, cranium, and muscle, i.e., 8.22 ± 0.15%, 5.51 ± 0.05%, and 1.39 ± 0.04% respectively to their maximum tolerated dose. For the pencil beam scanning, the OAR(s) with the most significant percentage of absorbed dose were the skin, cranium, and muscle, i.e., 5.42 ± 0.08%, 4.43 ± 0.05 %, and 0.51 ± 0.05% respectively to their maximum tolerated dose. In terms of dose homogeneity, dose distribution in passive scattering was relatively better than in pencil beam scanning using dose sampling analysis at some points within the planning target volume.