Audiovisual guidance for beam stopper positioning in intraoperative electron radiotherapy

PURPOSE: Mobile linear accelerators used for intraoperative electron radiotherapy (IOERT) require precise alignment between the radiation beam and the beam stopper to ensure adequate shielding in operating room environments. In clinical practice, beam stopper positioning is usually performed manually based on visual estimation, making alignment operator-dependent and difficult under operating-room constraints. This study presents and evaluates a laboratory-scale feasibility demonstration of a human-guided positioning system designed to assist beam stopper alignment during IOERT treatments. METHODS: The proposed system combines geometric modelling of the radiation beam with robotic localization techniques to estimate the beam-floor intersection point and guide beam stopper placement. Real-time audiovisual feedback provides intuitive cues to the operator during alignment. The system was evaluated in a laboratory environment reproducing the spatial configuration of an IOERT treatment. Twenty participants performed positioning tasks both with and without audiovisual assistance. Positioning accuracy, task duration and operator workload (NASA-TLX) were analysed. RESULTS: Audiovisual guidance significantly improved positioning accuracy, reducing the mean error from 0.311 ± 0.118 m to 0.056 ± 0.022 m (p < 0.001). Task completion time showed no significant difference between assisted and non-assisted conditions. Significant reductions were observed in mental demand, temporal demand, effort and frustration. CONCLUSION: The proposed system improves the accuracy and usability of beam stopper positioning in a laboratory environment and demonstrates the feasibility of combining geometric beam modelling, robotic localization and audiovisual guidance to support beam stopper alignment during IOERT procedures. Further clinical validation is required.