Estimation of Secondary Skin Cancer Risk Due To Electron Contamination in 18-MV LINAC-Based Prostate Radiotherapy

Document Type: Original Paper

Authors

1 Department of Radiology, Paramedical School, Tabriz University of Medical Sciences, Tabriz, Iran

2 Medical Radiation Sciences Research Team, Tabriz University of Medical Sciences Tabriz, Iran

Abstract

Introduction
Accurate estimation of the skin-absorbed dose in external radiation therapy is essential to estimating the probability of secondary carcinogenesis induction
Materials and Methods
Electron contamination in prostate radiotherapy was investigated using the Monte Carlo (MC) code calculation. In addition, field size dependence of the skin dose was assessed. Excess cancer risk induced by electron contamination was determined for the skin, surface dose, and prostate dose-volume histogram (DVH) using MC calculation and analytical methods.
Results
MC calculations indicated that up to 80% of total electron contamination fluence was produced in the linear accelerator. At 5 mm below the skin surface, surface dose was estimated at 6%, 13%, 27%, and 38% for 5×5 cm2, 10×10 cm2, 20×20 cm2, and 40×40 cm2 field sizes, respectively. Relative dose at Dmax was calculated at 0.92% and 5.42% of the maximum dose for 5×5 cm2 and 40×40 cm2 field sizes, respectively. Excess absolute skin cancer risk was obtained at 2.96×10-4 (PY) -1 for total 72 Gy. Differences in prostate and skin DVHs were 1.01% and 1.38%, respectively.
Conclusion
According to the results of this study, non-negligible doses are absorbed from contaminant electrons by the skin, which is associated with an excess risk of cancer induction.

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Volume 13, Issue 4
November and December 2016
Pages 236-249
  • Receive Date: 30 July 2016
  • Revise Date: 15 August 2016
  • Accept Date: 24 September 2016