Motion‑Inclusive Dose Reconstruction for Scanned Pencil Beam Scanning Proton Therapy
Abstract
Purpose
Respiratory motion and delivery dynamics can affect delivered dose in scanned proton therapy, particularly for thoracic treatments. Many existing motion-evaluation approaches rely on simplified delivery assumptions or research-only implementations, limiting their applicability to clinical plan assessment. This work describes the development of a python script for a workflow that reconstructs motion-inclusive dose distributions directly from finalized treatment plans, with explicit modeling of spot delivery timing and repainting.
Methods
A computational workflow was developed using clinically approved RayStation treatment plans and corresponding 4D-CT datasets. A beam delivery timing model, parameterized by spot delivery time, spot switching time, and energy layer switching time, was used to estimate the elapsed time at which each individual spot repainting would be delivered. Based on delivery timing, spots were assigned to respiration phase–specific subplans. Phase-specific dose distributions were calculated on the corresponding 4D-CT imagesets in RayStation. Doses were then exported to Velocity for image registration and resampling onto the treatment planning CT, summed to produce a motion-inclusive dose distribution, and imported back into RayStation for plan evaluation.
Results
The workflow successfully reconstructed delivery-consistent, motion-inclusive dose distributions for clinically realistic treatment plans incorporating multiple fields, energy layers, and repainting schemes. The algorithm robustly handled spot delivery across respiratory phases and produced summed dose distributions compatible with standard RayStation analysis tools. Total processing time was approximately 30 minutes per plan, dominated by dose calculation and resampling steps.
Conclusion
A clinically deployable algorithm for motion-inclusive dose reconstruction in proton therapy has been developed. By explicitly modeling spot-level delivery timing and repainting from finalized treatment plans, the framework enables realistic evaluation of respiratory motion effects and repainting strategies using standard clinical tools. This approach provides a foundation for future investigations of delivery techniques, repainting strategies, and plan robustness in proton therapy.