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The beam quality correction factor for the proton beam provided by TRS-398 is calculated regardless of the initial energy of the radiation particle and the energy spectrum at the measurement position, and the same value is applied to all depths to calculate the absorbed dose. In this study, the proton beam nozzle of the National Cancer Center was modeled using the Monte Carlo simulation code TOPAS to im- plement proton beams under various conditions, and the beam quality correction factor for the PTW-30013 farmer type ionization chamber was calculated. First, in a proton beam with a range distance of 15 g/cm2 and the SOBP width of 15 g/cm2, the beam quality correction factor was calculated at depths of 1.5 g/cm2, 4.5 g/cm2, 7.5 g/cm2, 10.5 g/cm2, and 13.5 g/cm2 and compared with the beam quality cor- rection factor of Rres 7.5 g/cm2 provided by TRS-398, all It was confirmed that the depth was consistent within the error range. Second, the beam quality correction factor was calculated at the reference depth of three proton beams with the range of 10 g/cm2, 15 g/cm2, and 20 g/cm2 and the SOBP width of 5 g/cm2, and compared with the beam quality correction factor of Rres 2.5 g/cm2 provided by TRS-398, all it was confirmed was consistent within the error range. Finally, in a single energy proton beam with a range of 28 g/cm2, the beam quality correction factor was cal- culated at 5 g/cm2 intervals from a depth of 3 g/cm2 to 28 g/cm2. As a result, the beam quality correction factor gradually increased with depth, and the correction factor calculated at depth 28 g/cm2 increased by about 7% compared to the correc- tion factor calculated at 3 g/cm2. Through this study, it was confirmed that in the case of a single energy proton, it was not suitable to measure the absorbed dose using a farmer type ionization chamber, and the beam quality correction factor of the proton beam forming SOBP was consistent within the error range provided in TRS-398.
Supervisor: Prof. Hyun Suk Jo