Evaluation of neutron dose equivalent levels at the maze entrance of medical accelerator treatment rooms.

This paper evaluates the accuracy of Kersey's method of calculation of the dose level due to photoneutrons at the maze entrance of medical accelerators. In this study measurements and calculations of the neutron dose equivalent were made for 13 medical accelerator facilities. The group of accelerators was composed of four different models from two manufacturers. The maze length for the treatment rooms varied from 3.0 to 8.54 m and 10 of the mazes had a single 90-deg turn with the remaining having two 90-deg turns. Moderated activation detectors and a portable neutron remmeter were used for measurements in the treatment room and maze, respectively. It was found that the maximum disagreement between the measured and calculated values was a factor of 2.3 with the calculated value exceeding the measured value. The majority of the measured values were within 25% of the calculated levels. It was concluded that Kersey's method is suitable for use in designing medical accelerator mazes.