ESTRO 2021 Abstract Book

S1168

ESTRO 2021

Results Four consecutive non-metastatic patients treated between May and September 2020 were analysed. All patients received MRgRT as salvage treatment for recurrence after surgery, after a median interval of 12 months (range: 1-29 months). The cardiac sarcomas were mostly located in the right atrium (50%), with one patient presenting 3 separate lesions. The median GTV size was 22.9 cm³ (range: 2.5-56.9 cm³) and patients were treated with a median GTV dose of 38.9 Gy (range: 30.1-41.1 Gy) in 5 fractions. The RT treatment was completed without interruptions and was overall well tolerated by all patients with only mild grade 1 or 2 symptoms such as fatigue, dyspnoea or mild chest pain. After a median follow-up of 5 months, all lesions are locally controlled. Conclusion This retrospective analysis represents the first and largest European series of patients affecte by primary cardiac sarcomas treated by online adaptive MR-guided SBRT. However, further studies are needed to evaluate the impact of this new methodology on the outcome of this very rare disease. PO-1422 Perioperative HDR brachytherapy and EBRT: a winning combo for soft tissue sarcomas X. Chen-Zhao 1 , Á. Montero 1 , J. de las Heras 2 , B. Álvarez 1 , I. Barrientos 2 , A. Prado 3 , R. Ciérvide 1 , M. López 1 , M. García-Aranda 1 , E. Ortiz 2 , M. Gutiérrez 2 , E. Sánchez 1 , O. Hernando 1 , M.Á. De la Casa 3 , J. Valero 1 , R. Alonso 1 , P. Fernández-Letón 3 , C. Rubio 1 1 HM Hospitales, Radiation Oncology, Madrid, Spain; 2 HM Hospitales, Orthopedic Surgery, Madrid, Spain; 3 HM Hospitales, Medical Physics, Madrid, Spain Purpose or Objective Conservative surgery in combination with local radiation therapy is considered a standard approach for soft tissue sarcomas (STS). A close relationship exists between total radiation dose and local control. We report our experience about feasibility of perioperative brachytherapy (PoBT) with a moderate dose-escalation in the multidisciplinary management of soft tissue sarcoma. Materials and Methods From May 2015 to December 2020, 48 patients (p), 27 men and 21 women, underwent perioperative brachytherapy (PoBT) as part of a multimodal approach (For baseline data see table 1). PoBT procedure was performed by using 6F plastic catheters placed on the surgical bed at the time of tumor excision. Forty-two p (87.5%) patients obtained R0 resection and 6 p (12.5%) R1 resection. Plastic catheters were placed either parallel or perpendicular to the surgical incision at 1.5- 2 cm intervals to ensure adequate dosimetry. CT simulation with 1.5 mm slice thickness was done in the fourth or fifth day after surgery once the sewer system was retired. A total 16.5 Gy was delivered to the PTV in 3 fractions of 550 cGy. Fractions were separated at least 6 hours. Catheters were retired after the last fraction. Results All p received external beam radiotherapy (EBRT) before or after brachytherapy. Conformal 3D radiotherapy, IMRT, or VMAT planning were used according to anatomy requiring. Seventeen p underwent neoadjuvant external beam radiotherapy (35.4%) with 2 cases of complete pathological response (4.2%). Assuming an alpha/beta ratio of sarcoma cells as 4, the median accumulated BED for tumor was 96 Gy (78.7 – 98.4Gy) and the median EQD2Gy was 77.3 Gy (75.5 – 90.5Gy) (EBRT+PoBT ) . Median follow-up was 25.3 months (9.3 – 39.8 months). Related to side effects: 1 p (2.1%) grade 3 epithelitis, 30p (62.5%) grade 1-2 epithelitis; 5p (10.4%) wound dehiscence with non-difference between pre-operative EBRT or post-operative EBRT; 17p (35.4%) had seroma within 2 cases of grade 3 seroma (4.2%). By the time of analysis, all patients are alive but 1 (2.1%). The actuarial overall survival (OS) was 97.1% at 36 months. The actuarial local progression free survival (L-PFS) was 97.2% at 12 months and 72.9% at 36 months. Median OS and L-PFS were not achieved.