3089 - Reducing Xerostomia and Dysphagia Risk Using Proton Arc Therapy with Shoot-Through Beams in Head and Neck Cancer
Presenter(s)
C. Henson1, E. Engwall2, and M. Newpower3; 1University of Oklahoma Health Science Center, Stephenson Cancer Center, Department of Radiation Oncology, Oklahoma City, OK, 2RaySearch Laboratories AB, Stockholm, Sweden, 3University of Oklahoma Health Sciences Center, Oklahoma City, OK
Materials/Methods: Five patients with bilateral HNC were included in this treatment planning study. All patients previously had clinically approved IMPT plans. PAT+ST plans were generated in a research version of RayStation 2024B and subsequently converted to deliverable pencil beam scanning plans for treatment on a Mevion S250i HYPERSCAN compact proton therapy system. All plans were robustly optimized using institutional uncertainty parameters and evaluated under worst-case scenarios. The Adaptive Aperture (AA) was used to sharpen the penumbra of all plans. Depending on target extent and isocenter arrangement (single vs double isocenter), PAT+ST plans consisted of 20–32 beams. IMPT comparison plans used our institutional standard multi-field arrangements, which was typically four to seven fields. Dosimetric endpoints included mean dose to the parotid glands, oral cavity, and pharyngeal constrictor muscles (PCM). NTCP for xerostomia and dysphagia were calculated using the Dutch multivariable models. Plans were evaluated for clinical acceptability by a radiation oncologist.
Results: All PAT+ST plans were clinically acceptable. Compared to IMPT, PAT+ST provided improved dose sparing to the parotid glands, oral cavity, and PCM. These reductions translated into lower predicted NTCP values for each patient. The mean absolute reduction in xerostomia NTCP was 8.6% (SD ±6.6%), and the mean reduction in dysphagia NTCP was 2.0% (SD ±1.2%). PAT+ST plans demonstrated comparable or improved sparing for other organs at risk while maintaining robustness. All plans met institutional robustness criteria, with worst-case clinical target volume (CTV) D95% exceeding 95% of prescription dose. In the worst-case analysis, 10 of 11 CTVs across these five patients were more robust with PAT+ST than with IMPT. Mean body dose increased by 6.3% on average with PAT+ST; however, 3 of 5 patients had a reduction in mean body dose compared to IMPT.
Conclusion: Proton arc therapy with shoot-through beams reduced predicted risks of xerostomia and dysphagia compared to IMPT in patients with bilateral HNC, without compromising robustness or target coverage. These improvements were achieved with modest increases, and in some cases, decreases in mean body dose. These findings suggest that PAT+ST may meaningfully improve post-treatment quality of life and support further clinical implementation of proton arc techniques in head and neck cancer. ChatGPT was used solely to assist with language editing to improve clarity and readability. All study design, data analysis, results, and conclusions were developed by the authors.