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

Purpose: 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.

Methods: 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.

Results: 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.

Conclusions: 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.

Keywords: IOERT; Monte Carlo; X-ray contamination; design method; dual foil; electron beam.