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

Abstract

Aim

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 18[[ce:hsp sp="0.25"/]]MV Varian 2100Clinac accelerator.

Background

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.

Materials and methods

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.

Results

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 440.11[[ce:hsp sp="0.25"/]]mm for the ordinary concrete, total concrete thickness of 1709[[ce:hsp sp="0.25"/]]mm was required. Calculating the same parameters value with the recommended analytical methods resulted in 1762[[ce:hsp sp="0.25"/]]mm for the required thickness using 445[[ce:hsp sp="0.25"/]]mm as recommended by TVL for the concrete. Additionally, for the secondary barrier the thickness of 752.05[[ce:hsp sp="0.25"/]]mm was obtained.

Conclusion

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.