Safe bunker designing for the 18آ MV Varian 2100 Clinac: a comparison between Monte Carlo simulation based upon data and new protocol recommendations.

Abstract

The aim of this study was to compare two bunkers designed by only protocols recommendations and Monte Carlo (MC) based upon data derived for an 18آ MV Varian 2100Clinac accelerator.High energy radiation therapy is associated with fast and thermal photoneutrons. Adequate shielding against the contaminant neutron has been recommended by IAEA and NCRP new protocols.The latest protocols released by the IAEA (safety report No. 47) and NCRP report No. 151 were used for the bunker designing calculations. MC method based upon data was also derived. Two bunkers using protocols and MC upon data were designed and discussed.From designed door's thickness, the door designed by the MC simulation and Wu-McGinley analytical method was closer in both BPE and lead thickness. In the case of the primary and secondary barriers, MC simulation resulted in 440.11آ mm for the ordinary concrete, total concrete thickness of 1709آ mm was required. Calculating the same parameters value with the recommended analytical methods resulted in 1762آ mm for the required thickness using 445آ mm as recommended by TVL for the concrete. Additionally, for the secondary barrier the thickness of 752.05آ mm was obtained.Our results showed MC simulation and the followed protocols recommendations in dose calculation are in good agreement in the radiation contamination dose calculation. Difference between the two analytical and MC simulation methods revealed that the application of only one method for the bunker design may lead to underestimation or overestimation in dose and shielding calculations.