Leyli Mogheiseh - Physics Department, Hakim Sabzevari University, Sabzevar, Iran
Ali Asghar Mowlavi - Physics Department, Ferdowsi University, Mashhad, Iran
Sayyed Bijan Jia - Physics Department, University of Bojnord, Bojnord, Iran
Reza Shamsabadi - Physics Department, Hakim Sabzevari University, Sabzevar, Iran

Proton therapy of liver tumors can be challenging due to the absorbed dose of produced secondary particles in non-target organs. This study aims to evaluate the absorbed dose of secondary particles during the proton therapy of liver cancer through the MCNPX Monte Carlo (MC) code by a simplified MIRD-UF standard phantom. At first, a simplified MC model of MIRD-UF standard phantom was simulated using MCNPX. After the proper proton energies calculation ranging from ۹۰ to ۱۲۰ MeV for ۴×۴×۴ cm۳ tumor irradiation, mesh tally type ۳ and F۶ tally were used to calculate the depth dose profiles as well as the absorbed dose of protons and secondary particles in non-involved organs. The obtained results illustrated that the fluence of internal secondary particles doses was considerably small in comparison with primary protons. Furthermore, most of neutrons and photons doses were absorbed around the liver tissue for all performed proton energies (i.e., ۹۰ and ۱۲۰ MeV) which non-target organs did not receive a significant high dose. Furthermore, the absorbed dose of secondary photons and neutrons had slight variations in considered normal tissues near the liver. The calculated results in this study indicated that during the proton therapy of liver cancer, the most contribution of the secondary particle doses was absorbed inside the liver tissue. Hence, it can be expected the probable side effects (secondary cancers) associated with the liver cancer proton therapy may be decreased however, the presence of secondary particles should not be ignored.

Liver cancer, proton therapy, secondary particles, Monte Carlo simulation, non-involved organs