A Patient-Specific Winston-Lutz System for Multi-Target Single Isocentre Radiotherapy

Abstract

This work introduces a novel quality assurance (QA) system for verifying patient-specific radiation targeting accuracy in multi-target, single-isocentre, stereotactic radiosurgery (SRS). A phantom with a 3D array of possible target positions and associated software were developed. Target positions and gantry/couch/collimator angles for the QA test are chosen to correspond to the patient’s SRS treatment plan. Target positions relative to the field centroid are detected using the Hough circle detection algorithm, and the radiation field is detected using image thresholding. Validation against independent software showed agreement within 0.19 mm. Validation using synthetic data yielded targeting errors of at most 0.53 mm, which is within image resolution limits. Field area discrepancies were 2.60% (mean) and 3.33% (maximum) of the expected field size. Multi-target test cases including intentional misalignments were carried out to demonstrate the accuracy and sensitivity of the QA system. This system defines patient-specific machine isocentricity according to a chosen tolerance.