Definitive proton therapy for unresectable trunk soft tissue sarcoma: a single-institution prospective registry-based...

Optimal management for locally confined unresectable trunk soft tissue sarcomas (STS) has not been established, and the role of radiotherapy remains unclear. We evaluated clinical outcomes and quality of life (QOL) after definitive proton therapy (PT).

We conducted a retrospective and single-institution review of patients with unresectable trunk STS treated with definitive PT, drawn from a prospective registry. Endpoints included overall survival (OS), local control (LC), progression-free survival (PFS), toxicity, and QOL.

Thirty-three patients were included. Median age was 61 years (range, 19-85). PT was most commonly delivered as 70.2 Gy (RBE) in 26 fractions (58%) or 60.8 Gy (RBE) in 16 fractions (30%). Spot scanning technique was used in 26 patients (79%). The most common histological subtype was dedifferentiated liposarcoma (42%). Median follow-up was 27 months (41.5 months for survivors). Three-year OS, LC, and PFS rates were 51% (95% CI: 31-68%), 81% (60-92%), and 39% (23-55%), respectively; median OS was 39 months. Gross tumor volume ≥300 cm³ was associated with worse OS (p = 0.03). No grade ≥3 toxicities were observed. QOL was generally maintained, and the global health status showed no clinically significant deterioration.

Reports on PT for this disease are scarce. Our findings suggest that PT is a safe and effective treatment option for unresectable trunk STS. Given its favorable safety profile and dosimetric advantages, PT is well suited for multidisciplinary treatment strategies and should be actively considered for these patients.