Tuning, Calibration and Testing of a Dynamic Collimation System Controller for Pencil Beam Scanning Proton Therapy
K Patwardhan*, T Geoghegan, B Smith, R Flynn, D Hyer, University of Iowa Hospitals and Clinics, Iowa City, IA
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PO-GePV-T-121 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: The purpose of this work was to tune and calibrate the Dynamic Collimation System (DCS) controller and measure the delivery time of an example treatment plan for a number of different jerk values where jerk is defined as the rate of change of acceleration. The control system needs to be tuned for the given electro-mechanical setup and the desired motion parameters in order to reduce oscillations in the motion.
Methods: A DCS prototype was built consisting of two pairs of orthogonal nickel trimmers independently translated by Parker T1S linear motors. Test motions were used to identify the motor response and tune the control system. Trimmer motion was observed for different jerk values before and after tuning the controller. The trimmer sequence from a sample test plan consisting of 244 trimmer positions and 3 ms dwell times was simulated with variable jerk values to determine the impact of this parameter on treatment time. Trimmer position accuracy was also tested for different DCS orientations of 90 and 180 degrees.
Results: Controller tuning and calibration provided stable and accurate trimmer motion. A maximum overshoot of 0.7 mm was observed prior to tuning as compared to 0.04 mm after tuning. Treatment time for the sample test plan with a jerk of 4x10⁵ mm/s³ was 21.6% (98 s) faster than with a jerk of 5x10⁴ mm/s³ (125 s). Trimmer position profiles were nearly identical for different orientations of the DCS with the positional accuracy found to be within ±0.1 mm.
Conclusion: The DCS controller can be integrated within a commercial Ion Beam Applications (IBA) Pencil Beam Scanning (PBS) system and used to accurately and automatically position the trimmers for treatment delivery, improving dose conformity with minimal impact to treatment time.
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 and Flynn are co-inventors on a patent that has been licensed to IBA.
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Keywords
Beam Shaping, Collimation, Penumbra
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