Document Type : Original Research
Authors
1 Department of Medical Physics, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran
2 School of Allied Medical Sciences, Shahroud University of Medical Sciences, Shahroud, Iran
Abstract
Background: Skyshine radiation refers to the scattered radiation above the ceiling of medical accelerator rooms that can return to ground level, resulting in potentially increasing the dose rate around the accelerator.
Objective: This study aimed to measure skyshine photon dose rate-based profiles from medical linear accelerator and to then compare measured dose rates with predictions based on the National Council on Radiation Protection and Measurements (NCRP)-151 formula to evaluate its accuracy and applicability.
Material and Methods: In this cross-sectional study, direct measurements were conducted using a survey meter dosimeter in both in-line and cross-line directions outside the accelerator room. An Elekta accelerator operating at energies of 6, 10, and 18 MV was utilized with the field size 40×40 cm². Skyshine radiation dose rates were directly measured under these conditions.
Results: The maximum skyshine dose rate significantly varied across different directions and distances from the accelerator room, while calculations based on the National Council on Radiation Protection & Measurements (NCRP-151) formula exhibited a continuous decrease with increasing distance. The energy range of skyshine photons observed around the treatment room was approximately 200–700 keV.
Conclusion: This study highlights that the skyshine dose rate from medical linear accelerators is highly dependent on beam energy and direction, showing notable deviations from NCRP-151 predictions. These findings underscore the importance of implementing site-specific shielding strategies.
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