Secondary radiation doses of intensity-modulated radiotherapy and proton beam therapy in patients with lung and liver cancer

Abstract

PurposeTo compare the secondary radiation doses following intensity-modulated radiotherapy (IMRT) and proton beam therapy (PBT) in patients with lung and liver cancer. Methods and materialsIMRT and PBT were planned for three lung cancer and three liver cancer patients. The treatment beams were delivered to phantoms and the corresponding secondary doses during irradiation were measured at various points 20–50cm from the beam isocenter using ion chamber and CR-39 detectors for IMRT and PBT, respectively. ResultsThe secondary dose per Gy (i.e., a treatment dose of 1Gy) from PBT for lung and liver cancer, measured 20–50cm from the isocenter, ranged from 0.17 to 0.086mGy. The secondary dose per Gy from IMRT, however, ranged between 5.8 and 1.0mGy, indicating that PBT is associated with a smaller dose of secondary radiation than IMRT. The internal neutron dose per Gy from PBT for lung and liver cancer, 20–50cm from the isocenter, ranged from 0.03 to 0.008mGy. ConclusionsThe secondary dose from PBT is less than or compatible to the secondary dose from conventional IMRT. The internal neutron dose generated by the interaction between protons and body material is generally much less than the external neutron dose from the treatment head.