Benchmarking the AlignRT surface deformation module for the early detection and quantification of oedema in breast cancer radiotherapy

To determine the accuracy of AlignRT surface deformation module in detecting and quantifying oedema in breast cancer radiotherapy. A female torso phantom and water-equivalent boluses of different thicknesses (0.5–1.5 cm) were used. The variation of surface displacement and the percentage of surface within tolerance, as a function of bolus thickness and Region of Interest (ROI) size, were investigated. Additionally, a dynamic phantom was used to study the impact of patient breathing on the swelling estimation. Lastly, a flowchart was derived to alert physicians in the case of breast swelling. Average displacement value proved to be inversely correlated with ROI size (R2 > 0.9). As such, for a ROI smaller than the bolus size (2.5x2.5 cm2), the average displacement (1.05 cm) provides an accurate estimate of the oedema thickness (within 5%). In opposition, with a clinical ROI, the 1 cm-thick bolus was largely underestimated with an average displacement value of 0.28 cm only. To limit the impact of patient breathing on surface deformation, dynamic surface captures and the use of the corrected patient position should be privileged. Using AlignRT, a clinical workflow for breast swelling follow-up was developed to help in the decision for repeat simulation and dosimetry. The surface deformation module provides an accurate, simple, and radiation-free approach to detect and quantify breast oedema during the course of radiotherapy.