Author: Alonso N. Gutierrez, Daniel E. Hyer, Blake R. Smith 👨🔬
Affiliation: Miami Cancer Institute, Baptist Health South Florida, Iowa Health Care, University of Iowa 🌍
Purpose: To perform a feasibility study of optimizing and producing a compact range compensator to deliver single-energy pencil beam scanning (PBS) proton arc therapy treatments. Omitting energy changes for PBS proton arc will improve treatment efficiency and reduce delivery limitations due to the minimum deliverable spot MU.
Methods: Monte Carlo methods were used to simulate range-compensated proton arc treatments on a reconstructed patient dataset with a brain tumor in Geant4. The compensator and the associated beam delivery across the arc were iteratively optimized using a modified simulated annealing approach combined with a least-squares weight optimization using a set of dosimetric objectives for the target and healthy tissues. The arc delivery was compared against a simulated multi-field intensity modulated proton therapy (IMPT) plan. A set of compensators were 3D printed and experimentally characterized to validate the Monte Carlo methods and investigate production accuracy. An additional set of simulations were performed to characterize the dosimetric impact of production errors on the delivered dose distribution within the patient.
Results: Range-compensated PBS proton arc achieved a comparable plan quality to IMPT while using a single PBS energy and a fraction of the total beam spots. Simulated and measured dose profiles from the 3D-printed compensators agreed within a 2%/1 mm gamma criteria for all investigations. Systematic printing errors of up to 1 mm could reduce the target coverage by 6% or increase the maximum dose by 8% for a PBS proton arc delivery. However, no significant dosimetric changes were observed for systematic printing errors simulated within the manufacturer’s reported tolerance of 0.127 mm.
Conclusion: An initial study delivering PBS proton arc treatments is demonstrated using a range compensator to improve treatment efficiency without degrading plan quality. Compensators were experimentally benchmarked and sufficient 3D printing accuracy was achieved to result in minimal dosimetric errors during delivery.