(P 286) INTERSTITIAL BRACHYTHERAPY FOR ORGAN AND FUNCTION PRESERVATION IN SOFT TISSUE SARCOMAS: LONG TERM OUTCOMES

Objective: To report the long-term outcomes with a combination of organ and function preserving surgery and perioperative interstitial brachytherapy (BT) for adults with soft tissue sarcomas treated at a tertiary cancer centre.

Methods: Between December 1986 and December 2024, 345 patients with non-metastatic soft tissue sarcomas were treated with combined modality approach at our institute. The median age of the patients was 42 years (IQR: 30.3- 57.8years) and the majority (62%) were males. Sixty-nine percent had primary lesions and lesions involving the extremities. Spindle cell sarcoma was the most common histology (22%) followed by pleomorphic sarcoma (16%) and synovial sarcoma (14%). The majority (69%) had grade III lesions. Treatment included wide local excision of the primary tumor followed by BT alone in 65% and a combination of BT with external beam radiotherapy (EBRT) in 35% of the patients. The majority (88%) underwent primary closure, while 12% required flaps. Close or positive margins were seen in 17%.

Results: After a median follow-up of 60 months (range: 2-187months), the 10-year local control (LC), disease-free survival (DFS), and overall survival (OS) for the entire cohort was 82%, 64%, and 81%, respectively. On multivariate analysis, deep tumors and a positive margin significantly predicted for a worse LC. Deep tumours, positive margin, Tumor size >5cm and high grade predicted a worse DFS. Deep tumors and tumor size >5cm predicted a worse OS. Acute wound complications were seen in 9.6% patients and were not higher in patients with flap (p=0.48) or patients receiving EBRT (p=0.32). Subcutaneous fibrosis (24%, n=84) was the most common late complication and strongly correlated with additional EBRT (p=0.001). The average Musculoskeletal Tumor Society (MSTS) function score was 28.

Conclusion: Interstitial BT with or without EBRT, as a part of function-preserving protocol results in excellent local control and functional outcomes in patients with STS. BT alone results in fewer complications compared with the combination of BT and EBRT.