Dose-escalated, Hypofractionated, Definitive Proton Radiotherapy for Patients With Inoperable Soft Tissue Sarcoma.

The purpose of the study is to study if dose escalated proton radiotherapy can improve local controll for patients with inoperable soft tissue sarcomas. The standard treatment is photon-based radiation. By using proton radiotherapy instead, the hypothesis is that the dose can be increased to enhance treatment effectiveness without increasing side effects. The planned radiation dose is 56 Gy in 16 fractions (treatments) over 4 weeks (4 fractions per week), with a maximum dose escalation centrally in the tumor up to 80 Gy (5 Gy per fraction). At the same time, the study will investigate biomarkers that can predict treatment response, including changes in the tumor's genetic material (DNA), measurements of various molecules in the bloodstream, and the tumor's appearance on MRI scans. The primary endpoint is local control after 2 years, meaning that the treated tumor has not grown during this period. Secondary endpoints include overall survival, progression-free survival, radiological response rates, side effects, and quality of life. The study will be conducted in Norway, with a planned inclusion of 40 patients.