Reducing stray radiation dose to patients receiving passively scattered proton radiotherapy for prostate cancer

Abstract

Proton beam radiotherapy 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 second cancer. The aim of this study was to explore strategies to reduce stray radiation dose to a patient receiving a 76 Gy proton beam treatment for cancer of the prostate. The whole-body effective dose from stray radiation, E, was estimated using detailed Monte Carlo simulations of a passively scattered proton treatment unit and an anthropomorphic phantom. The predicted value of E was 567 mSv, of which 320 mSv was attributed to leakage from the treatment unit; the remainder arose from scattered radiation that originated within the patient. Modest modifications of the treatment unit reduced E by 212 mSv. Surprisingly, E from a modified passive-scattering device was only slightly higher (109 mSv) than from a nozzle with no leakage, e.g., that which may be approached with a spot-scanning technique. These results add to the body of evidence supporting the suitability of passively scattered proton beams for the treatment of prostate cancer, confirm that the effective dose from stray radiation was not excessive, and, importantly, show that it can be substantially reduced by modest enhancements to the treatment unit.

Assessing the risk of second malignancies after modern radiotherapy

“…The models found a negligible difference between lifetime risk of SMN incidence from passive versus scanned proton craniospinal irradiation: the risk was mostly attributable to therapeutic radiation, not leakage neutrons 93–95 . Similar findings were obtained for several patients treated for prostate cancer 91,96 . Perhaps the most important findings, however, are from comparative studies of passively scattered proton therapy and photon IMRT.…”

Risk of Secondary Malignant Neoplasms From Proton Therapy and Intensity-Modulated X-Ray Therapy for Early-Stage Prostate Cancer

“…Because the primary beam predominated the second cancer risk for both modalities, the impact of stray neutrons from proton therapy appears to be of secondary importance. However, these results also suggest that reducing stray radiation exposures—either through the use of beam scanning or with local shielding techniques (24)—can lower the risk of SMNs.…”

Estimate of the uncertainties in the relative risk of secondary malignant neoplasms following proton therapy and intensity-modulated photon therapy

“…However, the inherent length of such studies limits their feasibility as well as their relevance to the latest treatment technologies. To overcome this problem, several investigations have instead focused on predicting the risk of SMN (Fontenot et al 2009b, Newhauser et al 2009c, Taddei et al 2008, 2009, Schneider et al 2006, 2007, 2008, Zacharatou Jarlskog et al 2008). In this approach, dose-response models from the literature have been combined with new dosimetric data to predict the risk of SMN incidence and mortality.…”