ESTRO 2020 Abstract Book

S650 ESTRO 2020

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 the localized stage, the radiotherapy (adjuvant or neo- adjuvant to surgery) is effective in terms of local control. There is tendency to increase in neo-adjuvant indications. The indications of neo-adjuvant versus adjuvant is based on patient criteria or criteria related to the tumour (risk of incomplete exeresis, planned reconstruction actions...), sarcomas have reputation for being radioresistants tumors however the question of response to radiation therapy and its prognostic impact on survival is underestimated in the literature. Several factors have already been studied (necrosis, percentage of viable cells fibrosis) with discordant results. Material and Methods We have therefore retrospectively studied a series of patients who have benefitedneo-adjuvant radiotherapy at the CLB from 2010 to 2018. We evaluate different histological criteria for responding to radiation therapy (necrosis - 90%,percentage of viable tumour cells - 10%, fibrosis - 90%) to find out if they are predictors of event- free survival (SSE). We also assessed the usual prognostic factors for sarcoma: tumor size, histological grade, number of initial mitosis and tumor margins Results A total of 123 patients were included. The largest diameter was > 5cm in 76% of patients and > 10cm in 40% of patients. The most common histologic groups was UPS (37%) and 88% of66sarcoma were grade 2-3. Viable tumor cells ≤ 10% has been highlighted in 34patients (34 %) with a median at 27.5 % (range 0-100%). 13 patients had ≤ 1% viable tumorcells and 5 patients had no residual viable tumor (pathologic complete response)The T1 Gadolinium median size change before and after radiotherapy was + 3 mm (range, - 77mm,+95mm). The margins status was R0 in 76%. Thirty- four percent of patients need a flap reconstruction and 30 % patients have had post-operative complications.In univariate analysis, the number of mitosis initials, the

tumor grade and the 10 cm size appear to be predictive of the SES In multivariate analysis, only the initial tumor grade remains predictive of SSE Post-therapeutic fibrosis - 10%, percentage of perennial tumor cells10% and post- therapeutic necrosis - 90% do not appear to predict ESS Conclusion Our study did not reveal a response factor therapeutic prognosis of survival. This is probably due to a lack ofstatistical power. Interestingly, we have observed that some patients, although considered "good responders" may have relapsed metastatic and this at an early age (6 months) PO-1236 Re-irradiation for recurrent spinal chordomas with high-dose stereotactic body radiation therapy C.J. Jin 1 , A. Reiner 2 , A. Schmitt 3 , D. Higginson 3 , I. Laufer 4 , E. Lis 5 , O. Barzilai 4 , P. Boland 4 , M. Bilsky 4 , Y. Yamada 3 1 The Ottawa Hospital, Radiation Oncology, Ottawa, Canada ; 2 Memorial Sloan Kettering Cancer Center, Biostatistics, New York, USA ; 3 Memorial Sloan Kettering Cancer Center, Radiation Oncology, New York, USA ; 4 Memorial Sloan Kettering Cancer Center, Neurosurgery, New York, USA ; 5 Memorial Sloan Kettering Cancer Center, Radiology, New York, USA Purpose or Objective Chordomas are known to have high rates of local recurrence and potential for metastases, with limited options for effective salvage. Spine stereotactic body radiation therapy (SBRT) outcomes support exploration of its role in the re-irradiation (re-RT) of these conventionally radioresistant tumors. The goal of the study is to evaluate safety and efficacy outcomes of SBRT re-irradiation for Clinical records were reviewed for outcomes of patients with recurrent chordomas of the spine who underwent re- RT with SBRT in 1-5 fractions between Dec 2007 and Aug 2018 at our institution. Radiographic local recurrence-free survival (LRFS), overall survival (OS), symptom response, and toxicity were assessed. Results In total, 16 patients with recurrent chordomas of the mobile spine (n=6) and sacrum (n=5) received re-RT with a median post-SBRT follow-up of 2.3 y (range: 0.7-5.8). Three (19%) underwent definitive SBRT, 7 (44%) underwent adjuvant SBRT post-operatively, and 6 (38%) were treated with palliative SBRT in the setting of metastatic disease. The median re-RT GTV volume was 89 cm 3 (26-1330 cm 3 ). Three received 24Gy single fraction, 9 received median 27Gy (range: 24-30Gy) in 3 fractions, and 4 received median 32.5Gy (range: 30-40Gy) in 5 fractions. Re-RT was at a median time of 3.8 y (range: 0.5-8.4) from initial RT, with prior regimens including combination proton/ photon RT to 80Gy in 1.8-2.0Gy fractions, photons to 45-70Gy in 1.8-2.0 Gy fractions, and photon SBRT (28.5-36Gy/3, 18- 24Gy/1). Two had 2 prior courses of RT. The median LRFS was 2.7 y (95% CI: 0.6-5.1), and the median OS was 3.2 y (0.6-6.4) (Fig 1). Among 10 patients with localized disease, the LRFS/OS rates were 90.0% (95% CI: 71.4-100.0%) at 1 y, and 80.0% (95% CI: 55.2-100.0%) at 2 y. Among 6 with metastatic disease, the LRFS/OS rates were 50.0% (95% CI: 10.0-90.0%) at 1 y and 25.0% (95% CI: 0-65.0%) at 2 y. The cumulative incidence of local failure (LF) is shown in Figure 2. The LF rate was 40.0% in both the localized and metastatic disease subsets, but median time to local progression was 4.0 y and 0.9 y respectively. Volume of disease, time from prior RT, and number of prior RT courses were not associated with LRFS or OS on univariate analyses (p>.05). The symptom response rate to treatment was 88% for pain/ radiculopathy, with 25% complete resolution. No patients had >Grade 2 acute toxicity. The long-term ≥Grade 2 toxicity rate was 38%, including 19% Grade 3 neuropathy, fracture, and recurrent chordomas. Material and Methods