Technical Note: A proposal of air ventilation system design criteria for a clinical room in a heavy-ion medical facility.

Abstract

An optimized air ventilation system design for a treatment room in Heavy-ion Medical Facility is an important issue in the aspects of nuclear safety because the activated air produced in a treatment room can directly affect the medical staff and the general public in the radiation-free area. Optimized design criteria of air ventilation system for a clinical room in 430MeV/u carbon ion beam medical accelerator facility was performed by using a combination of MCNPX2.7.0 and CINDER'90 codes. Effective dose rate and its accumulated effective dose by inhalation and residual gamma were calculated for a normal treatment scenario (2min irradiation for one fraction) as a function of decay time. Natural doses around the site were measured before construction and used as reference data. With no air ventilation system, the maximum effective dose rate was about 3μSv/h (total dose of 90mSv/y) and minimum 0.2μSv/h (total dose of 6mSv/y), which are over the legal limits for medical staff and for the general public. Although inhalation dose contribution was relatively small, it was considered seriously because of its long-lasting effects in the body. The integrated dose per year was 1.8mSv/y in the radiation-free area with the 20-min rate of air ventilation system. An optimal air ventilation rate of 20min is proposed for a clinical room, which also agrees with the best mechanical design value.