Purpose: To develop a novel controller for the precise positioning of multiple trimmer blades in a Dynamic Collimation System (DCS) apparatus for Pencil Beam Scanning (PBS) Proton Therapy (PT). The controller is designed to position the trimmers within a required tolerance of Â±0.5 mm before each spot delivery to maximize the improvement in lateral dose falloff.
Methods: The DCS is proposed to be integrated into an existing proton therapy delivery system from Ion Beam Applications. The DCS controller consists of a master control module, input/output (I/O) modules, and a multi-axis motor driver module. The driver is connected to four linear motors that move the trimmers to their desired positions. The clinical proton therapy system has a real-time scanning controller that controls the scanning magnets, the beam delivery parameters and the DCS controller. The DCS controller receives set-points from the scanning controller in the form of trimmer positions for each spot delivery and provides real-time feedback about the actual trimmer positions. To test the controller, a single-spot delivery plan is simulated where motor signals are generated based on the required motor ON/OFF time and direction of motion to get the trimmers in the desired position. The actual trimmer positions are fed back to calculate any deviations. If the feedback is not within the tolerance, the beam delivery is held off until the position is corrected. Conversely, if the feedback is within tolerance, the beam is delivered and motor signals are generated for the next set point.
Results: Uncertainties in the trimmer positions when using the controller are found to be within Â±0.01 mm of the desired positions compared to Â±4 mm without it.
Conclusion: The DCS controller can be integrated with a commercial PBS-PT system and used to accurately and automatically position the trimmers for treatment delivery, improving dose conformity.
Funding Support, Disclosures, and Conflict of Interest: Research reported in this abstract was supported by the National Cancer Institute of the National Institutes of Health under award number R37CA226518. Hyer, Flynn, and Wang are co-inventors on a patent that has been licensed to Ion Beam Applications(IBA).