A visual patient feedback device using optical surface measurement for the cooperative management of setup and body dynamics during radiotherapy

In this technical note we describe a real-time visual feedback device for use during radiotherapy treatment. The device displays a patient's live pose and position, relative to a reference, to them, helping them to control and maintain their motion. The device uses an optical sensor system developed at The Christie NHS Foundation Trust that is capable of real-time performance of up to 24 unique wide-area body surface measurements per second. The feedback device has integrated audio and three intuitive visualisation modes designed to show different levels of detail with varying degrees of complexity: a '2D traffic-light display', '3D flexing lamina display' and '3D colour-mapped surface display'. The performance characteristics of the system were measured, with the frame rate, throughput and latency of the feedback device being 22.4 fps, 47.0 Mbps, 109.8 ms, and 13.7 fps, 86.4 Mbps, 119.1 ms for single and three-channel modes respectively. We additionally present a novel fast method for calculating the vertical displacement map of two 3D surfaces suitable for live, real time display and evaluate its precision with respect to other methodologies.