Effective Dose from Stray Radiation for a Patient Receiving Proton Therapy for Liver Cancer

摘要

Because of its advantageous depth-dose relationship, proton radiotherapy is an emerging treatment modalityfor patients with liver cancer. Although the proton dose distribution conforms to the target, healthy tissues throughoutthe body receive low doses of stray radiation, particularly neutrons that originate in the treatment unit or in the patient.The aim of this study was to calculate the effective dose from stray radiation and estimate the corresponding risk ofsecond cancer fatality for a patient receiving proton beam therapy for liver cancer. Effective dose from stray radiationwas calculated using detailed Monte Carlo simulations of a double-scattering proton therapy treatment unit and avoxelized human phantom. The treatment plan and phantom were based on CT images of an actual adult patientdiagnosed with primary hepatocellular carcinoma. For a prescribed dose of 60 Gy to the clinical target volume, theeffective dose from stray radiation was 370 mSv; 61% of this dose was from neutrons originating outside of the patientwhile the remaining 39% was from neutrons originating within the patient. The excess lifetime risk of fatal secondcancer corresponding to the total effective dose from stray radiation was 1.2%. The results of this study establish abaseline estimate of the stray radiation dose and corresponding risk for an adult patient undergoing proton radiotherapyfor liver cancer and provide new evidence to corroborate the suitability of proton beam therapy for the treatment of livertumors.