Purpose: An important aspect of any add-on accessory in radiation therapy is understanding the associated quality assurance that must be performed prior to use. Since the Dynamic Collimation System (DCS) has been designed to be used as an aftermarket add-on collimator that mounts via the accessory tray, an investigation of the mounting accuracy and reproducibility must be conducted prior to clinical use. The purpose of this work was to characterize the reproducibility of the mounting mechanism used to attach the DCS to the IBA Proteus Plus nozzle.
Methods: The DCS mounts to the beamline via a tray that accepts a locking pin from the gantry. A small clearance between the DCS tray and the locking pin exists to allow the locking pin to engage freely. To characterize the variation in the mounting alignment, we rigidly affixed a crosshair to the base of the DCS that could be used as a spatial registration point. We then mounted and unmounted the DCS 10 times, acquiring an x-ray using the nozzle mounted imaging system each time the system was mounted. The change in position of the rigidly affixed crosshair, in both x and y-directions, was then evaluated using the x-ray images acquired.
Results: Results indicate that the tray’s locking mechanism is very repeatable. The largest variation occurred on the y-axis with a 300 µm range and a standard deviation of 116 µm. The x-axis variation was only 100 µm with a standard deviation of 48 µm. This level of deviation has been previously studied to not have a substantial impact on the dose distribution on a per beamlet basis.
Conclusion: Because of the repeatable nature of the docking mechanism, end user may not need to perform alignment of the DCS to the radiation beam every time the DCS is mounted to the nozzle.
Funding Support, Disclosures, and Conflict of Interest: Research reported in this publication was supported by the National Cancer Institute of the National Institutes of Health under Award Number R37CA226518. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.