ESTRO 2021 Abstract Book

S1163

ESTRO 2021

Fig

2:PCA clustering using T 1

-features and box plots of groups.

Conclusion Shape-related T 1

- and T 2 - MRI derived radiomics features of STS correlated with Sarculator but less well with radiomic values differentiated patient groups with different Sarculator scores, suggesting potential to non-invasively identify aggressive STS phenotypes. Radiomic profiling of STS is feasible and further study is worthwhile. HS. The T 1 PO-1416 Definitive photon radiation therapy for adult unresectable soft tissue sarcoma. B. Allignet 1 , W. Waissi 1 , A. Meurgey 2 , A. Bouhamama 3 , M. Karanian 2 , P. Meeus 4 , G. Vaz 4 , F. Gouin 4 , M. Brahmi 5 , A. Dufresne 5 , I. Ray-Coquard 5 , J. Blay 5 , C. Moncharmont 6 , M. Sunyach 1 1 Centre Léon Bérard, Radiation Oncology, Lyon, France; 2 Centre Léon Bérard, Pathology, Lyon, France; 3 Centre Léon Bérard, Radiology, Lyon, France; 4 Centre Léon Bérard, Surgery, Lyon, France; 5 Centre Léon Bérard, Medical Oncology, Lyon, France; 6 Centre Léon Bérard, Radiation oncology, Lyon, France Purpose or Objective Definitive radiotherapy (RT) in unresectable soft-tissue sarcomas (STS) is still controversial. The aim of this study was to evaluate clinical outcomes after definitive irradiation in a subset of patients with unresectable STS or gross residual disease after surgery. Materials and Methods Between 2009 and 2019, 108 STS patients were treated with RT for unresectable or gross residual disease after R2 surgery. Local progression free survival (LPFS), progression-free survival (PFS), overall survival (OS), and systemic treatment-free survival (STFS) rates were evaluated using Kaplan-Meier method. Prognostic factors were determined by log-rank test for univariate analyses and Cox model for multivariate analyses. Results The median follow-up was 49 months (range 5–120 months) and the patients’ median age was 72 (range 18– 92). Thirty-one patients (29%) had recurrent disease. The majority of tumors were deep-seated (n=104, 96%) and presented with high FNCLCC grade (43% and 43% of grade 2 and grade 3, respectively). Sarcoma was located in the trunk for 38%, in the extremities for 36%, retroperitoneal for 19%, and in the head and neck for 6% of patients. The most common histology was liposarcoma (n=41, 38%) followed by undifferentiated pleomorphic sarcoma (n=17, 16%) and leiomyosarcoma (n=10, 9%). Fifty-nine patients (54%) received systemic treatment before RT. Median size in the largest axis was 7 cm (range 1–38), and median clinical target volume (CTV) was 731.6 cm3 (range 38–5722 cm3). Treatment was delivered by Tomotherapy®, VMAT, or stereotactic RT in 41%, 16% and 8%, respectively. Median dose was 59.4 Gy (range 5.4–71.4), and median equivalent dose in 2 Gy fractions (EQD2; considering alpha beta ratio 4 Gy) was 60Gy (range 5.2–80). The 2-year LPFS, PFS and OS rates were 29.0%, 23.3% and 42.8%, respectively. The median and 5-year OS were 21.3 months and 17.3%, respectively. The majority of local failures (98%) occurred within 3 years. The median