Carbon Radiotheraphy For Head and Neck Cancer: Dosimetric Comparison with Photon Plans

Radiation therapy is one of the most widely used treatment methods for tumors. The therapeutic use of carbon ions is more advantageous than other radiotherapy techniquies especially photon-based irradiation due to its physical properties and radiobiological effects, and therefore it has received more attention. One of the most important reasons for that carbon ion beams are more effective than photon beams while minimizing the dose in the normal tissues around the target, it offers an improved dose distribution that leads to sufficient dose concentration in tumors. In addition, the carbon beam reaches its maximum at the end of its range, which increases with depth, and due to this feature, it provides a higher biological efficiency. In radiotherapy studies, Monte Carlo simulation is widely used to determine the dose distributions and to obtain the correct properties of the beams. With MC simulation, it helps to understand the relative biological efficiency as well as the spatial model of energy storages. In this study, a geometry with critical organs (skull, brain, nasopharynx and thyroid) based on a MIRD phantom was modeled with the Monte Carlo simulation tool GATE (vGATE 9.0). In this experiment, the tumor was irradiated with different carbon beam energies and photon beams. The aim is to calculate the energy accumulations in the region and surrounding organs with the MC method, and as a result, to show the dosimetric advantages of carbon radiotherapy over photon radiotherapy.