Shielding at the egress of a 23 mV linear accelerator.

Radiation shielding is required in radiotherapy accelerators to limit the dose equivalent rate from x-rays produced at the target in all directions except that of the useful forward directed beam. Calculations were made in terms of weekly workload of 50,000 cGy delivered to the isocenter per 5-day week, treating 25 patients per day at 400 cGy per patient. It is desirable to reduce the total exposure at the maze door below 30 Rem (0.30 Sv)/wk assuming full-time occupancy. The maze was designed to reduce the neutron dose to an acceptable level by slowing the neutrons to thermal velocities and then absorbing them in a low Z material in the egress.