Monte Carlo Modeling of Skyshine Dose Distribution in Vicinity of Medical Accelerator Facilities

Document Type : Original Article (s)

Authors

1 MSc Student, Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

2 Professor, Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran

3 Radiation Oncologist, Department of Oncology and Radiotherapy, Milad Hospital, Isfahan, Iran

Abstract

Background: In the vicinity of some of radiation therapy centers, measured exposure may not agree with calculated values due to the skyshine phenomenon. The aim of this study was to determine a computational model to predict the dose of radiation skyshine via Monte Carlo simulations.Methods: The simulation of linear accelerator head, skyshine geometry, and skyshine dose calculation at several heights and for different roof thicknesses was done using Monte Carlo N-Particle eXtended (MCNPX) code. The simulation results were validated via measuring and then were compared with the Council on Radiation Protection-151 (NCRP151) model results.Findings: The results of dose distribution in skyshine simulated model for all thicknesses of roof and every height from ground level showed an increase in the dose up to about 10 meters distance from the isocenter and then a decrease by distance from the isocenter; while the dose in the NCRP151 model, continuously decreases by distance. In addition, the amount of dose in each point was around 50 times larger than the simulated values. Dose reduction in both methods was proportional to the inverse-square.Conclusion: The model developed in this study can be used to predict the skyshine dose when designing a radiotherapy facility. The developed model is superior to the NCRP151 model due to its ability to calculate the dose in every point, inside and outside of treatment room, to investigate the influence parameters such as ceiling thickness and height from ground level and to determine the point with maximum dose.

Keywords

References

  1. Elder DH, Harmon JF, Borak TB. Skyshine radiation resulting from 6 MV and 10 MV photon beams from a medical accelerator. Health Phys 2010; 99(1): 17-25.
  2. Mcginley PH. Radiation skyshine produced by an 18 MeV medical accelerator. Radiat Prot Manage 1993; 10: 59-64.
  3. de Paiva E, da Rosa LA. Skyshine photon doses from 6 and 10 MV medical linear accelerators. J Appl Clin Med Phys 2012; 13(1): 3671.
  4. Morgan H. NCRP Report 151 Structural shielding design and evaluation for megavoltage x-and gamma-ray radiotherapy facilities. J Radiol Prot 2006; 26(3): 349.
  5. Wieslander E. Verification of dose calculation algorithms in treatment planning systems for external radiation therapy: A monte carlo approach [Thesis]. Lund, Sweden: Medical Radiation Physics, Lund University; 2006.
  6. Gossman MS, McGinley PH, Rising MB, Pahikkala AJ. Radiation skyshine from a 6 MeV medical accelerator. J Appl Clin Med Phys 2010; 11(3): 3032.
Journal of Isfahan Medical School
Volume 35, Issue 430 - Serial Number 430
March and April 2017
Pages 545-550

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History

  • Receive Date: 07 February 2017
  • Revise Date: 29 April 2024
  • Accept Date: 06 April 2022

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