(P 281) LOCAL CONTROL WITH MODERATELY HYPOFRACTIONATED DEFINITIVE RADIOTHERAPY DELIVERED WITH A SIMULTANEOUS INTEGRATED BOOST TECHNIQUE TO NON-EXTREMITY SOFT TISSUE AND BONE SARCOMAS

Objective: While surgery is the primary treatment for soft tissue sarcomas (STS) and primary bone sarcomas, a notable proportion of patients with non-extremity tumours do not undergo resection. Outcome data for definitive radiotherapy in this context are limited, as is evidence on the use of hypofractionation at non-extremity sites near sensitive organs at risk. We report our institutional experience delivering moderately hypofractionated definitive radiotherapy (MHDRT, 2.2-2.5 Gy per fraction) to patients with inoperable non-extremity STS and primary bone sarcomas including those who were unfit for, or declined, surgery.

Methods: 59 adult sarcoma patients received MHDRT to non-extremity disease between July 2021 and September 2024 in 60 treatment courses (Table 1). Radiotherapy was delivered over 28 fractions in 95% of patients, with a dose of 50.4 Gy to the low dose target volume and a simultaneous integrated boost (SIB) to the high dose target volume of 63 Gy for STS (equivalent dose in 2 Gy fractions, EQD2 65.3 Gy, α/β = 5) and 70 Gy for bone sarcomas (EQD2 77.0 Gy, α/β = 3).

Results: With a median follow-up of 17.7 months, local control at 1 year was 90.8% for STS (n=37), 100% for chordoma (n=14) and 55.6% for high-grade bone sarcomas (n=9). Progression-free survival and overall survival at 1 year were 59.9% and 94.4% for STS, 85.7% and 92.3% for chordoma, and 27.8 and 47.4% for high-grade bone sarcomas. Acute and late grade 3 toxicities were observed in 5 (8.3%) and 6 (10%) patients respectively.

Conclusion: These data indicate that MHDRT can be delivered to inoperable non-extremity sarcomas with acceptable toxicity and promising early local control rates, representing an important radical treatment option in this patient group.

Table 1. Baseline and treatment characteristics.