comparison of the light charged particles on scatter radiation dose in thyroid hadron therapy

bachground: hadron therapy is a novel technique of cancer radiation therapy which employs charged particles beams, 1 h and light ions in particular. due to their physical and radiobiological properties, they allow one to obtain a more conformal treatment, sparing better the healthy tissues located in proximity of the tumor and allowing a higher control of the disease.   objective: as it is well known, these light particles can interact with nuclei in the tissue, and produce the different secondary particles such as neutron and photon. these particles can damage specially the critical organs behind of thyroid gland. methods: in this research, we simulated neck geometry by mcnpx code and calculated the light particles dose at distance of 2.14 cm in thyroid gland, for different particles beam: 1 h, 2 h, 3 he, and 4 he. thyroid treatment is important because the spine and vertebrae is situated right behind to the thyroid gland on the posterior side. results: the results show that 2 h has the most total flux for photon and neutron, 1.944e-3 and 1.7666e-2, respectively. whereas 1 h and 3 he have best conditions, 8.88609e-4 and 1.35431e-3 for photon, 4.90506e-4 and 4.34057e-3 for neutron, respectively. the same calculation has obtained for energy depositions for these particles. conclusion: in this research, we investigated that which of these light particles can deliver the maximum dose to the normal tissues and the minimum dose to the tumor. by comparing these results for the mentioned light particles, we find out 1 h and 3 he is the best therapy choices for thyroid glands whereas 2 h is the worst.