The Effect of Neutron Contamination on Probability of Secondary Cancer in Radiotherapy of Pelvic Region with 18-MV Photons

Document Type : Original Article (s)

Authors

1 MSc Student, Department of Medical Physics, Student Research Committee, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran

2 Assistant Professor, Department of Medical Physics, School of Medicine, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran

3 Assistant Professor, Department of Nuclear Engineering, School of Advanced Sciences and Technologies, University of Isfahan, Isfahan, Iran

4 Assistant Professor, Department of Physics, Isfahan University of Technology, Isfahan, Iran

Abstract

Background: Todays, radiotherapy with high-energy photons is used as a common modality for cancer treatment. Unfortunately, high-energy photons can produce unwanted neutrons, and subsequently lead to increase the risk of secondary cancer in unshielded healthy organs.Methods: Using Monte Carlo (MC) code (MCNPX®), the main parts of a typical Medical Linear Accelerator (LINAC) was modeled in 18 MV. Then, neutron source strength (Q) of the LINAC and neutron mean energy were evaluated for different treatment fields, and also different points at the treatment table. Additionally, to estimate the probability of secondary cancer risk, the neutron equivalent dose was calculated at some of the human’s critical organs. For this purpose, the female medical internal radiation dosimetry (MIRD) phantom was included in the MC simulations.Findings: The Q was found as 1.25-1.38 (all in 1012 n/Gy) for different treatment fields meaning significant portion of neutrons with a mean energy of 0.59-0.90 MeV around the LINAC. Additionally, the total secondary cancer risk in unshielded healthy organs was calculated as 0.0924% which maximum and minimum were related to stomach (0.0216%) and thyroid (0.0005%), respectively.Conclusion: Regarding the estimated values for the probability of secondary cancer risk, it is suggested that in conventional radiotherapy of deeply seated tumors, the 15-MV photons are preferred instead of using 18-MV photons due to their less biological side effects.

Keywords

References

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Journal of Isfahan Medical School
Volume 37, Issue 519 - Serial Number 519
January and February 2019
Pages 222-227

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History

  • Receive Date: 16 March 2019
  • Revise Date: 02 June 2024
  • Accept Date: 06 April 2022

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