Stray radiation dose and second cancer risk for a pediatric patient receiving craniospinal irradiation with proton beams

Abstract

Proton beam radiotherapy unavoidably exposes healthy tissue to stray radiation emanating from the treatment unit and secondary radiation produced within the patient. These exposures provide no known benefit and may increase a patient's risk of developing a radiogenic cancer. The aims of this study were to calculate doses to major organs and tissues and to estimate second cancer risk from stray radiation following craniospinal irradiation (CSI) with proton therapy. This was accomplished using detailed Monte Carlo simulations of a passive-scattering proton treatment unit and a voxelized phantom to represent the patient. Equivalent doses, effective dose and corresponding risk for developing a fatal second cancer were calculated for a 10-year-old boy who received proton therapy. The proton treatment comprised CSI at 30.6 Gy plus a boost of 23.4 Gy to the clinical target volume. The predicted effective dose from stray radiation was 418 mSv, of which 344 mSv was from neutrons originating outside the patient; the remaining 74 mSv was caused by neutrons originating within the patient. This effective dose corresponds to an attributable lifetime risk of a fatal second cancer of 3.4%. The equivalent doses that predominated the effective dose from stray radiation were in the lungs, stomach and colon. These results establish a baseline estimate of the stray radiation dose and corresponding risk for a pediatric patient undergoing proton CSI and support the suitability of passively-scattered proton beams for the treatment of central nervous system tumors in pediatric patients.

Measurement of Neutron Dose Equivalent and its Dependence on Beam Configuration for a Passive Scattering Proton Delivery System

“…However, this estimate is hard to prove without an accurate measurement of the neutron spectrum. Monte Carlo simulations for a 10-year-old boy receiving craniospinal treatment of 30.6 Gy plus a boost of 23.4 Gy to the clinical target showed the maximum equivalent dose to the head region is 1429 mSv (16). If we use the simulation's beam configuration, then the dose equivalent to the head is estimated to be 1016 mSv, which is within 30% of the simulation.…”

The evolution of proton beam therapy: Current and future status (Review)

“…Although there has been significant progress in RT technology (61), there remain concerns on treatment-related acute and long-term side effects. This problem is more pronounced in pediatric populations due to the development of organs and tissues and the longer life expectancy, which include the effect of radiation on growth, intellectual development, endocrine organ function and secondary cancer development; thus, the pediatric radiation dose to normal tissues should be reduced as much as possible (62)(63)(64)(65)(66). PBT has the advantage of reducing the dose exposure of normal tissue, which may lead to fewer adverse effects.…”

Proton beam therapy in Japan: current and future status

“…Furthermore, the relationship between RT and secondary cancer has been clarified. For example, the risk of breast cancer after chest irradiation is reportedly 16-fold higher than normal (4), and glioma and meningioma develop in 3-20% of patients after intracranial irradiation (5). PBT reduces the incidence of secondary cancer, because a smaller amount of normal tissue is irradiated.…”