The therapeutic effect of interstitial brachytherapy on locally inoperable giant osteosarcoma masses.

e23501 Background: Osteosarcoma is insensitive to conventional radiotherapy, and conventional external radiation therapy for large tumors cannot meet the radiation dose limitations of organ at risk (OAR). One of the advantages of high dose rate (HDR) brachytherapy is that it allows for the specific localization of higher radiation doses onto the tumor without affecting OAR. Methods: A total of 15 masses from 13 patients between May 2023 and July 2024 were included. The inclusion criteria for HDR are as follows: (1) Pathological diagnosis of osteosarcoma; (2) Surgery cannot remove; (3) Mass ≥ 5cm; (4) Failure of multi-line chemotherapy; (5) The external irradiation plan cannot meet the OAR dose limit. The patients received HDR (7-10Gy/fraction x 1-4). The follow-up period is 5 to 19 months (median of 7 months). Results: There were no complete response (CR) and stable disease (SD) patients, 2 cases of partial response (PR), and 11 cases of stable disease (SD). Among all patients, one patient died 7 months after treatment, while the remaining patients are currently alive, with an overall survival rate of 92.3% at 6 months. No patients developed radiation dermatitis, radiation pneumonia, or radiation enteritis. During long-term follow-up, 11 masses showed calcification of the tumor after treatment. No patients showed neurological disorders or significant fibrosis. The central dose of the tumor can reach up to 200 Gy, while OAR is within the normal range. Conclusions: Our research results indicate that HDR has good local control and OS for osteosarcoma, especially for large tumors, and has no effect on surrounding OAR.