A Novel Uniform Beam Delivery Time Optimization Framework for Spot-Scanning Proton Arc Therapy
Abstract
Purpose
This study aimed to develop a novel optimization framework for spot-scanning proton arc therapy (SPArc) to simultaneously achieve highly uniform beam delivery time (BDT) across control points, improved delivery efficiency, and optimal dose distribution.
Methods
We proposed a Uniform Time Optimization (UTO) model formulated as a constrained inverse planning problem. It combines a dose fidelity term with structured L1 regularization (for inter-spot time consistency) and global L1 regularization (for spot sparsity). This large-scale, non-smooth problem is efficiently solved using the Alternating Direction Method of Multipliers (ADMM). UTO was compared against a particle swarm optimization (PSO) method and a spot-sparsity-only (SSO) method in ten clinical cases. All plans adhered to identical beam geometry, clinical constraints , and robustness settings. Quantitative evaluation included BDT uniformity (CVBDT, MaxBDT), spot sparsity, dosimetric indices, and plan robustness.
Results
The newly proposed Ultra Time-Optimized(UTO) method demonstrated superior performance over conventional methods. UTO significantly enhanced plan sparsity to 48.76 ± 12.01,representing a 2.06-fold improvement over PSO(23.66 ± 10.66).This increased sparsity directly improved temporal delivery consistency. Most notably, the coefficient of variation for spot spill time(CVSSPT) was dramatically reduced by 20-fold, from 0.80 ± 0.51(PSO) to 0.04 ± 0.02(UTO),while CVBDT decreased from 0.66 ± 0.40(PSO) to 0.23 ± 0.06(UTO).Exceptional stability was also observed in the maximum segment delivery time(MaxBDT). UTO achieved the lowest value(1.66 ± 0.65), outperforming SSO(3.14 ± 1.91) and PSO(3.01 ± 1.88), indicating consistent delivery per segment.Importantly, these improvements in sparsity and uniform beam delivery timewere achieved while maintaining clinically acceptable plan quality throughout optimization.
Conclusion
The ADMM-based UTO framework successfully balances temporal uniformity with dosimetric fidelity in SPArc planning. By delivering more stable beam-on times, it promises to enhance gantry motion control and delivery reproducibility while preserving high plan quality, representing a significant step toward reliable and efficient clinical implementation of proton arc therapy.