A self‐checking treatment couch coordinate calculation system in radiotherapy

PURPOSE: Traditionally, the treatment couch coordinates (TCCs) for patients undergoing radiotherapy can only be determined at the time of treatment, placing pressure on the treating therapists and leaving several pathways for errors such as wrong‐site treatment or wrong treatment table shift from a reference point. The purpose of this work is to propose an accurate, robust, and streamlined system that calculates TCC in advance. METHODS: The proposed system combines the advantages of two different calculation methods that use an indexed immobilization device. The first method uses an array of reference ball bearings (BBs) embedded in the CT scanner’s couch‐top. To obtain the patient‐specific TCC, the spatial offset of the treatment planning isocenter from the reference BB is used. The second method performs a calculation using the one‐to‐one mapping relationship between the CT scanner’s DICOM (Digital Imaging and Communications in Medicine) coordinate system and the TCC system. Both methods use a reference point in the CT coordinate system to correlate a point in the TCC system to perform the coordinate transfer between the two systems. Both methods were used to calculate the TCC and the results were checked against each other, creating an integrated workflow via automated self‐checking. The accuracy of the calculation system was retrospectively evaluated with 275 patients, where the actual treatment position determined with cone‐beam CT was used as a reference. RESULTS: An efficient workflow transparent to the therapists at both CT simulation and treatment was created. It works with any indexed immobilization device and can be universally applied to all treatment sites. The two methods had comparable accuracy, with 95% of the calculations within 3 mm. The inter‐fraction variation was within ± 1.0 cm for 95% of the coordinates across all the treatment sites. CONCLUSIONS: A robust, accurate, and streamlined system was implemented to calculate TCCs in advance. It eases the pressure on the treating therapists, reduces patient setup time, and enhances the patient safety by preventing setup errors.