A self‐checking treatment couch coordinate calculation system in radiotherapy

Abstract

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. K E Y W O R D S patient setup, couch coordinate, workflow automation, error prevention ---

Automatic couch position calculation using eclipse scripting for external beam radiotherapy

“…The feasibility and accuracy of estimating treatment couch position based on the CT couch‐top has been demonstrated in previous studies 5,6 as well as this study. Positioning the treatment couch‐top at the calculated coordinates has been used on EBRT of approximate 300 patients without wrong‐site treatment errors 6 .…”

“…The dependence on immobilization devices with radiographic landmarks limited the clinical use of the method. The recent method manually selected a couch‐top BB on the CT images and referred it to another BB with known couch coordinate for couch position calculation 5 . Sueyoshi et al 6 manually chose a couch indexing notch for longitudinal reference and placed the user origin at the midline of the CT couch surface during treatment planning.…”

“…In these cases, or as an independent second check, a user can manually select a BB line on CT images, determine the index level, and manually calculate the couch position in the way the script does. An in‐house software could implement the computation logic based on the inputs of a central BB coordinate, corresponding index level, and treatment isocenter position 5 …”

“…Similar to previously reported CT‐based approaches, 4–6 our method relies on that the patient is set up on a treatment couch with exactly identical indexing of the same immobilization device as in the simulation. Incorrect immobilization or indexing lead to deviation of the actual treatment table position from the calculated values, which could alert therapists for correction.…”

“…Using this correspondence, Saenz et al 4 predicted the couch position based on the radio‐opaque landmark on immobilization devices. Instead, treatment couch coordinates were estimated from the couch either based on its embedded ball bearings (BBs) by Tsai et al 5 or indexing notches by Sueyoshi et al 6 Both methods involved manual selection of a point (a reference BB 5 or the user origin 6 ) on CT images during treatment planning, which is potentially subjected to user error and alters the planning workflow. In light of this, we developed an automated solution to determine the treatment couch position by computerized detection of the embedded BBs and index levels on the couch from simulation CT images.…”