2453 - Proton Therapy for Hemithoracic Pleural Irradiation: A Step Toward Safer Radiation Treatment
Presenter(s)
D. Panse1, C. B. Simone II2, A. F. Shepherd3, N. Ohri4, N. Shaverdian5, J. L. Fox4, H. Lin2, M. Kang2, and S. Lazarev6; 1Department of Radiation Oncology, Icahn School of Medicine at Mount Sinai, New York, NY, 2New York Proton Center, New York, NY, 3Division of Radiation Oncology, University of Washington School of Medicine, Seattle, WA, 4Montefiore Einstein Comprehensive Cancer Center, Bronx, NY, 5Department of Radiation Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, 6Icahn School of Medicine at Mount Sinai, New York, NY
Purpose/Objective(s): Multimodal treatment strategies for malignant pleural mesothelioma (MPM), thymic malignancies with pleural metastases, and soft tissue sarcomas (STS) with pleural metastases include photon-based intensity-modulated pleural radiation therapy (IMPRINT) to enhance pleural disease control. However, data on the feasibility and safety of IMPRINT using proton beam therapy remain limited. This study aims to examine outcomes after proton beam IMPRINT in pleural malignancies.
Materials/Methods: We conducted a retrospective analysis of consecutive patients with MPM, thymic malignancies, and STS with pleural metastases treated with intensity-modulated proton therapy (IMPT) IMPRINT at a single institution between 12/2019 and 01/2025, with a minimum dose of 45 Gy. Dosimetric parameters and treatment-related toxicities, including acute (=6 months) and delayed adverse effects, were assessed using the Common Terminology Criteria for Adverse Events (CTCAE) v5.0.
Results: A total of 20 patients were included, with a median age of 54 years. Among them, 70% had MPM, 20% had thymic malignancies, and 10% had STS. The majority (60%) had right-sided disease, and all patients had an ECOG performance status of 0–1. Four patients (20%) had prior thoracic radiation therapy, and 50% received neoadjuvant chemotherapy followed by extended pleurectomy/decortication before adjuvant proton beam IMPRINT. The median prescribed whole pleural dose was 50.4 Gy, with a median total dose to the gross disease of 58.3 Gy delivered with a simultaneous integrated boost (SIB) (n=7) or sequential boost (n=1). The median clinical target volume (CTV) was 2,193 cm³, with a median V95 of 95.92%. Median value of mean contralateral lung dose was 0.3 Gy, total lung was 15.5 Gy, heart was 12.4 Gy, liver was 18.5 Gy, ipsilateral kidney was 7.3 Gy, contralateral kidney was 0.01 Gy, and esophagus was 22.4 Gy. Median spinal cord Dmax was 40.5 Gy, contralateral lung V5 was 0.98%, contralateral lung V20 was 0.07%, and ipsilateral lung V40 was 64.3%. With a median follow-up of 9.4 months, six patients (30%) developed acute grade 2 pneumonitis, four of these patients recovered after steroid treatment, while the remaining two progressed to late grade 3 pneumonitis. No acute grade =3 and no late grade =4 events were documented.
Conclusion: This study represents the largest series of IMPT IMPRINT for pleural malignancies, demonstrating its feasibility with acceptable toxicity. Dosimetric analysis showed more favorable organ-at-risk sparing than historically achievable with IMRT, supporting the potential role of proton therapy in optimizing pleural radiation delivery.