2217 - Advancing Proton Therapy: Dosimetric Superiority of Proton Arc Therapy over IMPT in Esophageal Cancer Treatment

Purpose/Objective(s): Esophageal cancer presents significant treatment challenges due to its proximity to critical structures such as the heart, lungs, and spinal cord. While Intensity-Modulated Proton Therapy (IMPT) improves dose conformity, it is limited by factors such as the number of beam angles and lateral penumbra. Proton Arc Therapy (PAT) may overcome these issues by utilizing continuous gantry rotation to enhance conformity and spare organs at risk (OARs). This study compares PAT and IMPT in esophageal cancer, focusing on dosimetric outcomes, and dose-averaged Linear Energy Transfer (LETd) distributions.

Materials/Methods: A retrospective analysis was conducted on ten esophageal cancer patients with variable tumor characteristics. Treatment plans were created using Monaco v6.1 treatment planning system for both PAT and IMPT, maintaining identical robustness parameters (±5 mm setup and ±3.5% range uncertainties). Both modalities were prescribed a total dose of 50.4 Gy (RBE) in 28 fractions, ensuring =95% Clinical Target Volume (CTV) coverage in the worst-case scenarios. Key metrics, including conformity index (CI), heterogeneity index (HI), and LETd, were compared. Robustness evaluations were performed across 21 worst-case scenarios to assess plan quality and OAR sparing.

Results: PAT demonstrated superior dose conformity (CI: 0.67 ± 0.17 vs. 0.54 ± 0.13; p < 0.01) and reduced lung V20 (6.88% vs. 13.44%; p < 0.01) compared to IMPT. Critical structure sparing, including reduced spinal cord doses (23.22±9.55Gy vs 30.93±10.85Gy, P=0.02), was achieved without compromising CTV coverage. PAT exhibited a trend towards increased LETd within the CTV, suggesting enhanced tumor control potential, and reduced LETd in adjacent OARs, potentially minimizing late toxicities.

Conclusion: PAT emerges as a promising modality for esophageal cancer treatment, delivering improved dose conformity, and reduced OAR exposure. These advantages suggest PAT's potential to decrease radiation-associated complications and improve therapeutic outcomes, warranting further clinical validation.