2366 - Updated Outcomes of Moderately Hypofractionated Definitive Radiotherapy (MHDT) Using a Simultaneous Integrated Boost (SIB) for Inoperable Non-Extremity Sarcomas

Purpose/Objective(s):

Patients with inoperable non-extremity sarcoma have limited treatment options with poorer outcomes due to proximity to organs at risk, presence of metastatic disease, significant comorbidities or patient preference. Evidence for definitive radiotherapy in this setting is restricted to small retrospective series. Preclinical radiosensitive studies support a role for hypofractionated radiotherapy, particularly in extremity sarcomas, but data for non-extremity sites remain sparse because of adjacent critical radiosensitive structures. We present updated outcomes from one of the largest single-institution experiences, focusing on local control (LC), progression-free survival (PFS), overall survival (OS), early and late toxicity, and exploratory dose-volume correlates.

Materials/Methods:

Between July 2021 and December 2025, 100 patients (102 courses) with =6-month follow-up and post-treatment imaging were included. Diagnoses included STS (n=61), high-grade bone tumours (HGBT; n=24) and chordomas (n=17). Radiotherapy doses were predominantly 63Gy in 28 fractions (STS), and 70Gy in 28 fractions (HGBT and chordomas), delivered in two dose volumes using MHDT with SIB. Survival outcomes were assessed using Kaplan–Meier analysis. Predictors of local recurrence were evaluated using multivariable Cox proportional hazards regression.

Results:

Median follow-up was 14.1 months. The 12- and 24-month outcomes were as follows: STS - LC was 87% and 82.4%, PFS 55.9% and 37.8%, OS 86.5% and 63.3%. In HGBT - LC was 61.5% and 41%, PFS 35.3% and 11.8%, OS 64.2% and 31.2%. In chordomas - LC 84.6% and 84.6%, PFS 72% and 60%, OS 93% and 93%. Among 66 patients without metastatic disease, 24-month metastatic-free survival was 70% (STS), 51% (HGBT) and 63.3% (chordomas). Acute grade =3 toxicity occurred in 8 patients (7.8%), and late grade =3 toxicity in 13 patients (12.8%). On multivariable Cox regression, neither GTV (median 416cm³; IQR 791cm³) nor PTV coverage (D95%, D90%, D80%) were independently associated with local recurrence (all p > 0.05).

Conclusion:

MHDRT provides a new treatment option for inoperable non-extremity sarcomas. Our data demonstrates encouraging LC and survival outcomes with acceptable toxicity. This data will form the backbone for funding a prospective national clinical trial.