Dose Deposition and Secondary Particle Production of Carbon-12 Ion Beams in Lung, Brain, and Water Phantoms: A PHITS Monte Carlo Study

Carbon ion radiation therapy (CIRT) provides a highly localized dose with improved biological effectiveness. Precise prediction of dose distribution in diverse tissues is essential, as nuclear interactions generate secondary particles that affect the total dose. This study investigates dose deposition and secondary particle production from Carbon-12 ion beam in lung, brain, and water phantoms. Monte Carlo (MC) simulations were conducted using the Particle and Heavy Ion Transport code System (PHITS) version 3.30. Lung, brain, and water phantoms with 30 × 30 × 30 cm³ dimensions were irradiated by Carbon-12 ion beams with varying energies of 100.07 MeV/u, 145.47 MeV/u, and 190.75 MeV/u. Simulations were conducted with monoenergetic carbon ion beams with a 1-cm radius at a source-to-source distance (SSD) of 100 cm. Dose deposition and secondary particle production were investigated and compared. The simulated PDD curves exhibited the characteristics of Bragg peak behavior of Carbon-12, with peak positions shifting to greater depths as beam energy increased. The lung phantom exhibited the greatest penetration depth, while the brain and water showed similar dose deposition characteristics. Comparison with the experimental data showed good agreement, with a percentage difference of 3.8%, 5.8%, and 0.25% for 100.07 MeV/u, 145.47 MeV/u, and 190.75 MeV/u, respectively. Secondary particle analysis revealed the production of alpha, protons, deuterons, and Carbon-11 fragments, with particle yields increasing with beam energy. Alpha and proton particles were identified as the dominant secondary fragments. Neutron dose contributions remained small, ranging from 5.07×10¯³ to 1.47×10¯² of the total absorbed dose. The results demonstrate the reliability of PHITS for modeling Carbon-12 ion transport and provide insights into the influence of the beam energy and tissue composition on dose deposition and secondary particle production in carbon-ion radiotherapy.