Monte Carlo And Phantom Calculation Of Harmful Secondary Neutron Doses In Patient Undergoing Carbon Ion Brain Tumor Radiotherapy

Radiation therapy using heavy-ion become a research hot spot as radiation therapy technology advances.Traditional radiation therapy uses X-rays or gamma rays to target tumor cells,and the tumor control rates has significantly improved with new technology of three dimensional conformal radiation therapy(3DCRT),intensity modulated radiotherapy(IMRT)and image guided radiation therapy(IGRT),dynamic adaptive radiotherapy(DART).However,traditional radiotherapy is limited in the ability to control the damage of normal cells or tissues near the tumor target in the treatment of deeply situated tumors.In comparison,the heavy-ion therapy has better physical properties as well as biological effect for treating certain resistant,oxygenated tumors.However,secondary neutrons are produced during the interaction between primary high-energy particles and treatment equipment or human body in heavy-ion radiotherapy,causing additional radiation dose—a topic that has unfortunately not been studied according to the current literature.This project aims to use representative model of different genders,different ages and different gestation periods to calculate the radiation dose of secondary neutrons in carbon-ion brain tumor therapy.The task and methods include:First,MCNPX is used to model the beam delivery system of heavy-ion tumor treatment terminal for the radiation field conform to the tumor shape.Then different computational human phantoms,RPI-AM/RPI-AF,USTC-5M/F,USTC-10M/F,USTC-15M/F and Pregnant-3/6/9,are used to calculate secondary neutron radiation dose.Different F tally cards of MCNPX Monte Carlo code are used to calculate the energy spectrum and the energy deposition of secondary neutrons in the organs.The research results indicate:when the brain tumor is treated with carbon-ion therapy,there is a plateau peak in the secondary neutron spectrum in the organs which is at a small angle to incident direction.The results of RPI-AM/RPI-AF?USTC-5M/F?USTC-10M/F?USTC-15M/F show that the difference of equivalent dose caused by secondary neutron for gender is not obvious,for example,the equivalent dose of USTC-5M/F?USTC-10M/F?USTC-15M/F lungs are 0.83mSv/0.83mSv?0.54mSv/0.51mSv?0.34mSv/0.39mSv respectively.However,the effect of age(height)is more significant.With the decrease of age(height),the equivalent dose of secondary neutrons in the organs of the chest and abdominal is increased gradually,for example,the equivalent dose of USTC-5/10/15F thyroid are 1.24mSv?0.98mSv?0.83mSv respectively.The results of Pregnan-3/6/9 show that the equivalent dose caused by secondary neutron of the fetus at different gestation period is around 0.01mSv which requires to be considered carefully because fetus is extremely sensitive to radiation.The results in this study can be used to provide references for physicians to study long-term effects of the carbon ion therapy.