A Hybrid Transmission–IMPT Planning Approach for Efficient Proton Treatment of Extremity and Metastatic Bone Targets
Abstract
Purpose
Proton transmission fields, treating through the target rather than stopping spots in the target, have a substantial but largely unrealized clinical potential, offering inherently robust delivery with minimal range uncertainty and faster treatment times. To improve delivery efficiency and reduce patient on‑table time for palliative and metastatic bony targets, we evaluated a hybrid proton therapy planning strategy integrating transmission fields with intensity modulated proton therapy (IMPT) fields. The goal was to reduce the total number of energy layers relative to each patient’s reference IMPT plan while maintaining target coverage and robustness. This study aimed to determine if leveraging this approach could maintain high‑quality dose distributions while enabling more rapid treatments.
Methods
Ten IMPT patients, primarily extremity targets, were retrospectively planned in RayStation v23b using a hybrid planning approach. For each case, a proton transmission field was forward planned to deliver 30–35% of the prescription dose. The remaining dose was planned with a single IMPT field inversely optimized to meet coverage goals and complement the transmission component. Hybrid plans were compared with IMPT‑only plans based on target coverage, robustness to setup and range uncertainties, and total delivery time obtained from machine‑recorded data.
Results
Hybrid plans achieved target coverage and robustness comparable to IMPT‑only plans. Dosimetric quality was preserved across all cases, with no clinically meaningful differences in target coverage. As expected, integral dose increases in the hybrid plans, but the treatment sites were sufficiently far from critical OARs. Delivery time was reduced by an average of 39.3%, driven by a substantial decrease in energy layers.
Conclusion
These findings highlight the practicality of integrating proton transmission fields and IMPT fields in clinically appropriate scenarios. By preserving high‑quality dose distributions and enabling significantly faster treatments, this underutilized treatment planning approach demonstrated potential clinical value that may improve workflow efficiency.