医療用6 MeVと10 MeVリニアック施設の免震層実効線量評価法

Abstract

The widespread use of medical linacs for cancer treatment and seismic isolation structures in Japan led to the construction of an increasing number of buildings in which medical linac rooms are located directly above the seismic isolation layer. Extending the control area in the seismic isolation layer is advantageous for reducing the cost of floor shielding. However, establishing a simple calculation method is necessary to evaluate the effective dose in the seismic isolation layer for shielding design. We proposed and verified a simple calculation method that can be applied to evaluate the effective dose in the seismic isolation layer of 10 MeV linac facilities. The parameters of the method were investigated when applied to 6 and 10 MeV linacs and extensively validated by comparing the results with the Monte Carlo calculation. For the seismic isolation layer in which the height of the space is ≤2 m, the results of the method and the Monte Carlo calculation agree within 28% and 21% at points of half-height and ≥3 m horizontally from the linac source, respectively. Furthermore, the measured doses were compared with the proposed method values in the seismic isolation layer of a 10 MeV linac facility.