Effect of Beam Angle and Energy on the Dose Distribution of Carbon-12 Ion Beams in a Water Phantom Using PHITS

Purpose Carbon ion radiation therapy (CIRT) is a highly effective form of radiation therapy due to its distinct physical and biological advantages, enabling more precise and efficient destruction of tumor cells. This study investigates the effect of beam angle and energy on the dose distribution of carbon-12 ion beams in a homogeneous water phantom using PHITS Monte Carlo (MC) code. Methods: This study utilizes PHITS version 3.30 to simulate Carbon-12 (12C) ion irradiating water phantom. A 30 × 30 × 30 cm3 phantom at a Source-to-Surface Distance (SSD) of 100 cm is irradiated with 2 × 10^8 primary particles at initial energies of 135 MeV/u, 195 MeV/u, 200 MeV/u, 270 MeV/u, 300 MeV/u, 330 MeV/u and 400 MeV/u using a mono-energetic axial source with a 0.10 cm radial size. The beam angle is varied at 0°, 0.1°, 0.2°, 0.3°, 0.4°, 0.6°, 0.8°, 1°, 2°, and 3°. Results: The result shows that varying the source angle alters the location and form of the Bragg peak. The Bragg peak location shifts from 4.26 cm (135 MeV/u) to 29.79 cm (400 MeV/u). Small angles (0°, 0.1°, 0.2°, 0.3° and 0.4°) showed nearly constant peak positions, while larger angles (0.6°, 0.8°, 1°, 2° and 3°) produced noticeable variations in the penetrationrange. The calculated deviations were less than 1%, demonstrating good accuracy of the simulation results. Conclusion: The study shows that the dose distribution of 12C ion beams has a significant impact by changes in beam angle and energy. Higher beam energies cause the Bragg peak in the Water Phantom shift to deeper depths, while increasing the beam angle changes the Bragg peak's location and shape. These results offer valuable information for carbon ion radiation therapy beam parameter optimization.