Impact of apertures on the out-of-field secondary neutron dose in collimated proton pencil-beam scanning

The measurement results were compared to the respective calculations with the TOPAS MC simulation framework. Main results: Collimating the edges of 10 × 10 cm2 fields with apertures increased the H∗n(10) on average by 23%. This increase was up to 74% in lateral direction to the initial beam and up to 6% in forward direction.

With a reduction of H∗n(10) down to 50% and 33% on average, nickel proved to be more favorable than brass. Placing a range-shifter upstream of the aperture is more favorable compared to the downstream placement since the H∗n(10) was on average 20% lower. Considering the associated uncertainties, the simulations and the experiments agreed well with an average deviation of 11.7% (1% to 34%).

Significance: Concluding, the increase of H∗n(10) caused by apertures for shaping scanned proton fields is small to moderate with 23% on average. The out-of-field neutron dose can be optimized by material selection and the arrangement of beam-shaping devices. TOPAS is suited for the application under consideration.

This repository refers to the corresponding publication in a scientific journal.