ESTRO 2020 Abstract book

S697 ESTRO 2020

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 in DWI-MR or CT. Then surgery or second part of radiotherapy (4x 4 Gy plus hyperthermia) is applied. The primary endpoint is rate of grade 3 or higher early treatment toxicity, according to EORTC/RTOG scale. Results Fifteen patients met eligibility criteria: eleven of them due to predicted chemoresistance, two due to progression after neoadjuvant chemotherapy, and two who were not fit for chemotherapy. Seven patients finished the whole planned protocol treatment, six are currently undergoing treatment, one patient developed metastatic disease after the first part of treatment, one patient refused surgery due to the poor performance status. Among patients who completed the protocol, four underwent surgery, and three underwent the second part of radiotherapy with hyperthermia. Early tolerance of the treatment was good, none of patients developed grade 3 or higher toxicity. In two patients who underwent surgery, complete pathological responses (EORTC STSBG grade A) were observed. In patients after surgery no local recurrences were observed, in patients treated with radiotherapy only no disease progression were noted. Conclusion Preliminary results of the trial suggests that preoperative radiotherapy with hyperthermia is a feasible method of the management of patients with locally advanced STS who are chemoresistant or not fit for chemotherapy, providing good pathological responses and very good treatment tolerance. PO-1235 Histologic response following pre operative radiotherapy for soft tissue sarcoma S. Prapant 1 , M.P. Sunyach 1 1 Centre Leon Berard, Radiotherapy, Lyon, France Purpose or Objective Soft tissue sarcomas are rare tumours that includes more than 50 histological subtypes that do not all have the sensitivity to treatment or the same risk of recurrence. At treatment tolerance. Material and Methods

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