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.

• Authors: Phillip J Taddei, Dragan Mirkovic, Jonas D Fontenot, Annelise Giebeler, Yuanshui Zheng, David Kornguth, Radhe Mohan, Wayne D Newhauser
• Journal: Physics in medicine and biology (Phys Med Biol) Vol. 54 Issue 8 Pg. 2259-75 (Apr 21 2009) ISSN: 0031-9155 [Print] England
• PMID: 19305045 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Protons

Topics

• Child
• Humans
• Male
• Monte Carlo Method
• Neoplasms, Radiation-Induced (etiology, mortality)
• Neutrons (adverse effects)
• Proton Therapy
• Radiation Dosage
• Radiotherapy (adverse effects)
• Radiotherapy Dosage
• Risk
• Scattering, Radiation
• Sensitivity and Specificity
• Skull (radiation effects)
• Spine (radiation effects)
• Time Factors