(P 346) BRACHYTHERAPY FOR SOFT TISSUE SARCOMA: MAINTAINING LOCAL CONTROL WHILE MINIMIZING COMPLICATIONS

Objective: The purpose of this study is to assess the clinical and oncologic outcomes of high-dose brachytherapy (BRT) versus both preoperative and postoperative external beam radiation therapy (EBRT) in the setting of high-grade soft tissue sarcoma.

Methods: This is a retrospective cohort study of 144 patients treated surgically for soft tissue sarcoma at the same institution from 2010 to 2021. Patients treated for a soft tissue sarcoma with surgery and radiation therapy in the form of BRT, Neoadjuvant EBRT (Neo-EBRT) or adjuvant EBRT (AD-EBRT) were included.

Results: 56 patients were treated with BRT, 42 treated with Neo-EBRT, and 46 treated with AD-EBRT. There was a greater incidence of grouped wound complications in Neo-EBRT with 50% compared to both BRT with 25% and AD-EBRT with 28.3% (p = 0.02). Specific incidences of surgical site infection (SSI) were 29%, 11% and 11% respectively (p = 0.04). Local recurrence rates were similar between all treatment groups (p = 0.66). Univariate analysis showed that there was an increased risk of wound complications with Neo-EBRT (HR= 2.999, 95% CI [1.289, 7.195]) when compared to brachytherapy (p = 0.03), specifically, surgical site infections (p = 0.04). Univariate analysis showed that there was no difference in risk of LR for Neo-EBRT and AD-EBRT when compared to brachytherapy (p = 0.28). On multivariate analysis, Neo-EBRT (HR= 4.028 95% CI [1.483, 11.590]) was predictive of wound complications when compared to brachytherapy, (p = 0.007). BMI >40 was predictive of wound complications (p = 0.006).

Conclusion: Brachytherapy is a valuable treatment modality that offers clinical and logistical advantages when compared to the conventional Neo-EBRT in soft tissue sarcomas. Brachytherapy offers a lower risk of wound complications and a comparable local control. This study proposes that brachytherapy should be used in tumors that are less than 15cm in greatest diameter where neoadjuvant tumor size reduction will not change surgical resection. Brachytherapy can be even more beneficial in areas like the pelvic girdle, and proximal thigh that are at risk for wound complications, particularly in obese patients. In contrast, Neo-EBRT should be used when expecting very close margins to vital structures, where there is a need for additional tumor size reduction in conjunction with chemotherapy, if there is a need for unplanned excision tumor bed sterilization, or when there is no available brachytherapy at an institution. AD-EBRT may be used when the tumor is fungating or there is a medical indication for immediate tumor resection.