Author: Uriel Aura, Qing Chen, Arpit M. Chhabra, J Isabelle Choi, Chanda Guha, Meng Wei Ho, Sheng Huang, Minglei Kang, Stanislav Lazarev, Nancy Y Lee, Yang Lei, Haibo Lin, Hang Qi, Mahbubur Rahman, Charles B. Simone, Shouyi Wei, Irini Yacoub, Francis Yu, Anna Zhai, Ajay Zheng 👨🔬
Affiliation: DYN'R Medical System, New York Proton Center, Montefiore Medical Center and Albert Einstein College of Medicine, Icahn School of Medicine at Mount Sinai, Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, Tianjin Medical University Cancer Institute&Hospital, Department of Human Oncology, University of Wisconsin-Madison 🌍
Purpose: Managing tumor motion during pencil beam scanning proton therapy remains challenging. This study investigated the feasibility and dosimetric benefits of Free-Breathing Respiratory-Gated Delivery (FBRGT) with a DYN’R SDX spirometer on Varian ProBeam systems.
Methods: The interplay effect was assessed for FBRGT versus repainting approach to address large-motion uncertainties. The SDX syringe was attached to a dynamic lung phantom to generate airflow. 4DCTs of the moving phantom were acquired with motion of 12mm (A12) and 20mm (A20) peak-to-peak amplitudes at 12 breaths/min. Gating windows (GW) were selected at the end of exhalation. Three-field proton plans (30Gy/5fx) were robustly optimized using the clinical protocol on average 4DCT with 3 (A12) or 4 (A20) repaintings, or on averaged CT within different amplitude GW. Interplay effects were assessed via film measurements and compared to Monte Carlo (MC) simulations, considering spot-phase delivery time sequences. Gating latencies were evaluated by repeating measurements by restricting phantom motion within GW. Delivery times were extracted from machine logs.
Results: The comparison of DVHs from interplay simulations shows that all plans achieved comparable target coverage, GTV D95% and V95%/GTV+5mm vary between 99.9%-101.3% and 1.2-1.4. The lung dose was high for repainting plans due to larger iGTV (DmeanLung-GTV: 20.0%-22.2%, V50%lung: 14.7%-16.1%) and increased with larger GW (DmeanLung-GTV: 14.8%-18.8%, V50%lung: 10.7%-13.5%) and breathing amplitude. MC simulation and film measurements showed high agreement with the planned dose, with gamma passing rates (GPR; 3%/2mm, 10% threshold) of 92.0%-98.2%, indicating the effectiveness of gated delivery. No significant latency effect was observed (GPR: 93.9%-94.6%). Treatment times increased with narrow GW (126-165s) and more repaintings (214-264s).
Conclusion: FBRGT was successfully demonstrated through a motion-phantom study. Dosimetric consistency and target coverage were maintained with improved OAR-sparing, and shorter treatment times were achieved with gated delivery compared to repainting strategy. More validation is warranted for future clinical implementation.