ESTRO 2023 - Abstract Book

S1266

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ESTRO 2023

Results The medial follow-up was 34 months, and the two-year overall survival rate was 78.9%. Acute toxicities of radiotherapy included gastrointestinal toxicities (grade 1-2: 8 patients), nausea (grade 1-2: 4 patients, grade 3-4: 3 patients), vomiting (grade 1-2: 3 patients, grade 3-4: 2 patients), neutropenia (grade 1-2: 2 patients, grade 3-4: 1 patients), and fatigue (grade 1-2: 5 patients). In patients without metastatic disease at diagnosis, two-year overall survival rate was 83.3%, and two year disease-free survival rate was 64.6%. There were 8 recurrences (2 local alone, 2 distant metastasis alone, 1 local plus regional, 2 local plus distant metastasis, and 1 local plus regional plus distant metastasis), and 5 deaths. Recurrent metastatic locations included lung (n=1), liver (n=1), bone (n=2), peritoneum (n=1), distant lymph nodes (n=1), and soft tissue of thigh (n=1). One patient with metastatic disease at diagnosis expired due to disease progression with 8 months survival. Conclusion Radiotherapy in retroperitoneal sarcoma provided an acceptable two-year survival rate with tolerable toxicities, but recurrence rate was still high. About 62.5% of recurrent events consisted of local recurrence, so close follow up of primary tumor area is necessary. 1 Institut Jules Bordet, Radiation Oncology Department, Brussels, Belgium; 2 Institut Jules Bordet, Medical Physics Department, Brussels, Belgium; 3 Institut Jules Bordet, Orthopaedic Oncology Surgery Department, Brussels, Belgium Purpose or Objective To evaluate the local control (LC), distant metastasis free survival (DMFS) and overall survival (OS) of extremity soft tissue sarcomas (ESTS) treated with adjuvant radiotherapy (RT) at our institution. Furthermore we will evaluate factors influencing outcome and report on toxicity, especially regarding the use of a bolus. Materials and Methods Patients with ESTS treated with adjuvant radiotherapy between 01/2005 and 08/2022 were included in this retrospective study. Histology, tumor, localization, grade, surgical margin, start of RT, RT technique (VMAT or 3DCRT), dosimetry information and the use of bolus were collected. Aalen-Johansen competing risk analysis was performed for LC, DMFS and OS comparing groups using log-rank test analysis with p<0.05 considered as statistically significant. Dermatitis was evaluated after 3 months, fibrosis and lymphedema at 3, 6, 12 and 24 months. Results We identified 54 patients treated with adjuvant RT, with a median follow up 37 months (range 4-140). Additional patient characteristics are presented in the Table 1. All patients received at least 60 Gy. Four patients had a local recurrence and distant metastasis discovered simultaneously, while respectively one and fifteen had an isolated local and distant failure diagnosed. All five local failures (9.3%) were located in depth, four of them being irradiated with a bolus. Distant metastasis (35.2%) occurred in lung (n=16), liver (n=1) and bone (n=2). In total, there were 16 disease-related deaths (29.6%). For LC and OS worst outcome was observed in patients with a positive surgical margin (p=0.017 and p =0.048, respectively). The absence of a bolus did not worsen the LC (Figure 1B). No other characteristic (gender, tumor , RT technique, histology, tumor grade) showed a significant impact on the outcome. Grade ≥ 2 toxicities (with/without bolus) at 3 months were 19 (10/9) and 17 (11/6) for dermatitis, similar to fibrosis with 20 (11/9) and 1 (1/0) respectively. While for lymphedema no relevant differences were observed with 15 (8/7) and 4 (2/2) grade 2 and 3 toxicity respectively. We did not observe any grade 3 toxicity after 6 months. PO-1560 Outcome and toxicity after adjuvant radiotherapy +/- bolus for extremity soft tissue sarcomas M. Delavigne 1 , A. Gulyban 2 , F. Shumelinsky 3 , S. Beauvois 1 , C. Al Wardi 1 , D. Van Gestel 1