Mid-Range Arc Therapy for Efficient and Relative Biological Effectiveness Robust Proton Treatment
Abstract
Purpose
Proton arc therapy (PAT) holds promise for enhancing plan conformity while minimizing dose sparing. However, PAT faces practical barriers related to delivery inefficiency, and its effectiveness can be compromised by beam range and radiobiological uncertainties. This study introduces a novel planning approach, Mid-Range Proton Arc Therapy (MRPAT), designed to enhance delivery efficiency and mitigate range-related uncertainties in PAT.
Methods
MRPAT employs a single mid-range energy layer (MREL) per beam direction, positioning the Bragg peak near the target center to confine range uncertainty within the target while minimizing dose-averaged linear energy transfer (LETd) and relative biological effectiveness (RBE) hotspots in adjacent organs at risk (OARs). The feasibility of MRPAT was investigated on an ellipse phantom and three clinical cases (prostate, spine, and head and neck). Physical dose distributions, LETd distributions, RBE-weighted dose distributions, and delivery efficiency were compared with full-range arc employing all possible energy layers (Full-Arc) and intensity-modulated proton therapy (IMPT) plans with two beams.
Results
Across both phantom and clinical cases, the most notable advantage of MRPAT is its ability to localize elevated LETd within the central region of the target, whereas Full-Arc plans produced high-LETd near the target edge and IMPT showed LETd spillover into adjacent OARs, posing a greater risk of biological toxicity. The RBE-weighted dose exhibited a similar pattern to the LETd distribution, with MRPAT generating a distinct RBE-weighted dose boost concentrated in the central portion of the target. Moreover, MRPAT achieved comparable physical dose quality to the Full-Arc, demonstrating the redundancy of utilizing all possible energy layers. Additionally, by eliminating intra-beam energy-layer switching, MRPAT reduced delivery time to levels comparable to two-beam IMPT, substantially improving efficiency.
Conclusion
MRPAT demonstrates a simple, efficient, and high‑LETd/RBE hotspot‑containment planning concept that is practical for clinical use and adaptable to future adaptive PAT workflows.