Author: Mingli Chen, Xuejun Gu, Mahdieh Kazemimoghadam, Weiguo Lu, Qingying Wang, Zi Yang, Kangning Zhang, You Zhang 👨🔬
Affiliation: Medical Artificial Intelligence and Automation (MAIA) Lab, Department of Radiation Oncology, UT Southwestern Medical Center, Department of Radiation Oncology, Stanford University School of Medicine 🌍
Purpose: Delivery efficiency and robustness are critical in spot-scanning proton arc therapy (SPAT), yet the conventional use of redundant energy layers (ELs) prolongs switching times and reduces efficiency. We propose mid-range proton arc therapy (MRPAT), a novel planning strategy that facilitates dynamic delivery and enhances robustness by employing a single mid-range energy layer (MREL) per beam direction.
Methods: The MREL is pre-selected before spot intensity optimization, with an adjustable range scaling factor to enhance delivery safety while reducing integral dose. By placing Bragg peak centrally within the target, MREL creates a buffer zone to account for beam range uncertainties. MREL selection was demonstrated on a cylindrical phantom. The feasibility of MRPAT was further evaluated on an elliptical phantom with a C-shaped target, and extended to clinical cases involving prostate, spine, and head-and-neck treatments, with comparisons to full-range arc plans employing all possible ELs (Full-Arc), and two-beam intensity-modulated proton therapy plans (IMPT). Plan robustness was assessed under simulated range uncertainty and setup errors, while delivery efficiency was evaluated using a machine-specific delivery time model.
Results: The selected MREL positions spot slightly beyond the mid-plane of the target. Compared to the IMPT plans, the arc plans showed substantial improvements in hot-spot control and OAR sparing. Among both phantom and clinical case tests, the MRPAT plans achieved comparable target coverage, OAR sparing, and lower integral doses compared to the baseline Full-Arc plans, demonstrating the redundancy of utilizing all possible ELs. For robustness evaluation, the MRPAT plans showed superior OAR protection and target hotspot control than Full-Arc and IMPT plans. MRPAT plans have comparable delivery time and ELs to IMPT plans, requiring under 10% of ELs and 5% of delivery time compared to Full-Arc plans.
Conclusion: MRPAT demonstrates feasibility of a mono-energetic delivery pattern for generating SPAT plans with robust performance and high efficiency.