Author: Simona Cacciatore, Albert Du, Ryan T. Flynn, Alonso N. Gutierrez, Patrick M Hill, Daniel E. Hyer, Eric Jensen, Kaustubh A. Patwardhan, Julien Smeets, Blake R. Smith, Nhan Vu, Karsten K. Wake 👨🔬
Affiliation: University of Wisconsin, Miami Cancer Institute, Baptist Health South Florida, Department of Human Oncology, University of Wisconsin School of Medicine and Public Health, Ion Beam Applications (IBA), University of Iowa, Iowa Health Care 🌍
Purpose: To evaluate time reduction strategies for the Dynamic Collimation System (DCS) using an IBA (Louvain-la-Neuve, Belgium) proton therapy system. Delivery time for a multi-energy-layer patient specific plan was measured for increasing jerk values, where jerk is defined as the rate of change of acceleration. The jerk value is a critical control system parameter that must be optimized to balance fast and accurate positioning of the trimmers prior to beam delivery with minimal time penalty and oscillations.
Methods: The DCS prototype consists of two pairs of orthogonal nickel trimmers independently translated by linear motors and controlled by a standalone controller that was configured and tuned using motor specifications that minimize harmonics. The DCS controller receives trimmer position set-points from the treatment system for each spot delivery and provides real-time feedback of actual trimmer positions. A 26-energy layer collimated treatment plan was delivered using the DCS for jerk values of 5 × 104, 1 × 105, 2 × 105, 3 × 105, and 4 × 105 mm/s3 to assess the impact on delivery time and motion stability.
Results: Tuning and calibration of the controller provided stable and accurate trimmer motion. A maximum overshoot of 0.05 mm was observed at the maximum jerk value of 4 × 105 mm/s3. Treatment times for the QA plans were 208.1 s, 196.2 s, 186.3 s, 181.6 s, and 178.4 s, for jerk values of 5 × 104, 1 × 105, 2 × 105, 3 × 105, and 4 × 105 mm/s3, respectively. Positional accuracy of the DCS controller was found to be within ±0.2 mm at the maximum jerk, with minimal clinical impact.
Conclusion: The DCS was successfully characterized, and the motion parameters were optimized to accurately and automatically position the trimmers for treatment delivery with significant reduction in total treatment time.