Technical Note: Monte Carlo study on the reduction in x-ray contamination of therapeutic electron beams for Intraoperative Radiation Therapy by means of improvements in the design of scattering foils.

Abstract

This work is aimed at studying the feasibility of reducing stray x-ray contamination of therapeutic electron beams used in Intraoperative Radiation Therapy (IOERT) through improvements in the design of the dual foil beam forming system. We assess the validity of a known method for designing the primary scattering foil. To this end, we perform, for the first time, a systematic computational study of the performance of beam forming systems equipped with primary scattering foils of different thicknesses, including a foil designed according to the currently used method. In this study, we further develop and apply a recently proposed method for optimization of dual foil systems. For each of the considered primary foils, a secondary foil that minimizes the stray x-ray contamination was designed under additional conditions on the clinically acceptable therapeutic range and flatness of off-axis dose profile. For comparison, we also designed secondary foils that enable the production of the best flattened beams irrespective of x-ray contamination and therapeutic range. By means of a comparative analysis, we demonstrated that currently employed design methods do not lead to an optimal solution in terms of stray x-ray contamination and therapeutic range. It is further demonstrated that, in comparison to older designs, reduction in x-ray contamination exceeding 30% may be expected in a system designed using the novel method developed here. Such a reduction is beneficial for IOERT delivered in a regular, unshielded operating room.