Room: AAPM ePoster Library
Purpose: The dynamic collimation system (DCS) has been shown to provide improved healthy tissue sparing during pencil beam scanning (PBS) proton therapy. While interest in this technology has grown, recent works have remained theoretical as a clinical device is still in development. Therefore, it was the purpose of this work to develop an experimental DCS and integrate it within a commercial beamline to benchmark source and collimation models between two modern Monte Carlo codes.
Methods: The experimental DCS was designed and constructed in-house consisting of two moving collimators and a removable external range shifter. A model of the experimental collimator was developed using both MCNP6 and the Geant4 user toolkit. Simulations were performed using each Monte Carlo code to evaluate differences in integral depth dose (IDD) and lateral profiles resulting from collimation along and off the central axis. Differences were quantified with respect to the measured IDDs and lateral using the PBS proton beam at the Northwestern Proton Center.
Results: Overall, excellent agreement was observed from all lateral and depth dose profiles collimated on- and off-axis. All simulated lateral profiles had at least a 95% gamma pass rate with a 1mm/1% gamma criteria to measurement. The simulated output and centroid positional shifts due to collimation matched within 3% and 0.2 mm, respectively. MCNP6 more closely matched the measured IDD resulting from scatter off the collimators than Geant4 by 2%, and the simulations differed by 1.7% when estimating the water equivalent thickness of the range shifter.
Conclusion: This work provides some of the first experimental dosimetry of beamlets collimated by a DCS. In addition to providing proof-of-concept integration of a DCS within a commercial PBS system, these measurements also serve as a benchmark against the Monte Carlo models that have been used previously to study the DCS.
Funding Support, Disclosures, and Conflict of Interest: Dr. Daniel Hyer is an inventor on a patent that has been licensed to IBA.