ESTRO 2025 - Abstract Book

S1599

Clinical – Mixed sites & palliation

ESTRO 2025

was to report feasibility and early toxicity profile of patients treated with hypofractionated (Hypo) PT at the Proton Center of the European Institute of Oncology, Milan, Italy.

Material/Methods: All consecutive patients (pts) treated with Hypo PT between November 2023 and October 2024 were retrieved. Toxicity has been defined at the end of the treatment using Common Terminology Criteria Adverse Event (CTCAE V4.0) scale. Data have been prospectively collected in a proton registry (“Power Registry” NCT0586036). Results: Among 129 pts treated with PT in the considered period, 76 (59 %) pts (mean age 66 yrs, 28 female) have been treated with Hypo PT. Distribution of tumor site were reported in Fig.1. The majority (44 pts, 58%) of pts were treated in the curative setting, while 16 (21%) pts and 7 (9%) pts were treated in the postoperative and palliative setting, respectively. Nine patients had benign disease, mainly intracranial meningioma. Dose/fraction according tumor site were reported in Fig.2. Re-irradiation was performed in 52 pts. At the end of treatment, toxicity data were available for 55 (72%) pts. Grade 2 toxicity were recorded 4 (5%) pts (2 breast, 1 prostate and 1 central nervous system cancer). Two pts (breast and central nervous system cancer pts) experienced a G3 toxicity. None of the patients experienced a G4 toxicity. Clinical follow up (mean 4 months, range 1-9 months) was available for 30 (39%) pts. Among curative treatments with available follow up (17 pts) those treated with curative intent, 14 (82%), 2 (12%) and 2 (12%) achieved a complete response, partial response and stable disease, respectively. In the post-operative setting (9 pts), when follow-up available, all pts were free from disease. Three patients had a systemic progressed and died before the first follow up.