ESTRO 2020 Abstract Book

S649 ESTRO 2020

Conclusion Long survivor patients had small tumor or intensive metastases treatment. Based on this trend, we suggest an intensification of cures (both RT and surgery on the residual tumor) in patients who had a stable disease 12 months after the end of CT. PO-1233 Perioperative Radiotherapy with a Moderate Dose-Escalation for Retroperitoneal Sarcoma (RPS). M. Nuñez Baez 1 , A. Montero 1 , X. Chen-Zhao 2 , A. Acosta 1 , B. Alvarez 1 , J. Palma 1 , M. Lopez-Gonzalez 1 , E. Sanchez 1 , O. Hernando 2 , J. Valero 1 , R. Ciervide 1 , M. Garcia-Aranda 1 , R. Alonso 1 , M. De la Casa 3 , D. Zucca 3 , J. Martí 3 , I. Flores- Cacho 3 , C. Ruiz-Morales 3 , P. Fernandez-Leton 3 , M. Rubio Rodriguez 1 1 HM Sanchinarro, Radiation Oncology, Madrid, Spain ; 2 HM Puerta del Sur, Radiation Oncology, Madrid, Spain ; 3 HM Sanchinarro, Radiophysics, Madrid, Spain Purpose or Objective Although surgery represents the main primary therapeutic approach for RPS, it carries several risks related to vital structures located in a complex space. The purpose of our study is to assess the outcome and toxicities of patients with RPS. Material and Methods We included 19 patients with diagnoses of RPS treated between November/2009- November/2018. Sex: male 9p (47%); female 10p (53%). Median age: 55y (range 36-68). Presentation: primary 14p (74%); relapsed 5p (26%). Histopathology: liposarcoma 10p (53%), leiomyosarcoma 4p (21%), pleomorphic sarcoma 3p (16%); TMI 2p (10%). Staging: 5p Ib, 1p II, 4p IIIa, 7p IIIb, 2p IV. Median tumor size: 119mm (32-320). Surgical resection: R0 11p (58%), R1 6p (32%), R2 2p (10%). Radiotherapy: according to the 6 patients who received preoperative RT (32%): 5p R0 (83%), 1p R1 (17%), 2p pathological complete response (33.3%) 2p tumor necrosis >50% (33.3%), 2p tumor necrosis <50% (33.3%); postoperative RT: 11p (58%); radical RT 2p (10%). Treatment technique: IMRT 11p (58%), VMAT 7p (37%) RT3D 1p (5%). Median dose 50.4Gy (range 50-60Gy); Fractionation: conventional (≤2Gy/day) 10p (52%), moderate hypofractionation (>2-3Gy/day) 4p (21%); extreme hypofractionation (³4Gy/day) 5p (26%). Systemic Treatment: 10p (53%). Results With a median follow-up of 24 months (range 2.43-116.4): 13p (69%) alive without tumor; 4p (21%) alive with tumor; 1p (5%) death of tumor, 1p (5%) intercurrent death. Actuarial 1, 2 and 3 years rates: local relapse free- survival (LRFS) 94 %, 77% and 67% respectively (95% CI 36.74-102.62); distant relapse free-survival (DRFS) 100 %, 100 %, 80% (95% CI 38.34-115.38); disease free-survival (DFS) 94%, 77% and 67% (95% CI 29.11-101.97); overall survival (OS) 100 %, 91 % and 68% (95% CI 54.45-120.27). Toxicity grade 2 or higher wasn´t observed. The use of hypofractionated schedules allows a moderate dose escalation compare to traditional radiotherapy. Assuming that sarcoma cells have an α/β value of 4; the equivalent doses in a 2Gy fraction (EQD2) for a conventional treatment of 50 Gy in 25 fractions at 2 Gy/ day would be 50 Gy, and the corresponding biologically effective dose (BED) would be of 75 Gy. In our study, EQD2 and BED were as follows: median EQD2 4 62Gy (range 48.7-80Gy); median BED 4 92Gy (range 73.1 112.25Gy).

Conclusion Perioperative RT reaches acceptable rates of LRFS, DRFS, DFS and OS in patients with RPS. The combination of hypofractionated schemes and IMRT/VMAT with IGRT techniques leads to a moderate dose escalation with acceptable tolerance over the traditionally used. Further studies are necessary to confirm clinical benefits of increasing radiation dose in RPS. PO-1234 RT With Hyperthermia in Locally Advanced Soft Tissue Sarcomas: Interim Analysis of Phase II Trial M. Spalek 1 , A. Borkowska 1 , K. Lewcio-Szczęsna 2 , M. Telejko 2 , P. Rutkowski 1 1 Maria Skłodowska-Curie Institute – Oncology Center, Department of Soft Tissue/Bone Sarcoma and Melanoma, Warsaw, Poland ; 2 Maria Skłodowska-Curie Institute – Oncology Center, Hyperthermia Lab- Department of Radiotherapy I- Maria Skłodowska-Curie Institute – Oncology Center, Warsaw, Poland Purpose or Objective The standard neoadjuvant treatment of unresectable and marginally resectable sarcomas (STS) is radiotherapy, commonly combined with chemotherapy. However, some patients are not candidates for neoadjuvant chemotherapy due to poor performance status, comorbidities, chemoresistant pathology or disease progression on the commonly used chemotherapy regimens. The addition of deep hyperthermia to irradiation and in the prolonged gap between the end of hypofractionated 10x 3.25 Gy radiotherapy and surgery may allow obtaining the long- term local control with the maintenance of a good Single-arm clinical trial (NCT03989596) enrolls patients with locally advanced STS, with chemoresistant pathology or who are not suitable for chemotherapy, for preoperative radiotherapy 10x 3.25 Gy plus hyperthermia twice a week, followed by 6-8 weeks gap and reassessment treatment tolerance. Material and Methods