ESTRO 2020 Abstract book

S698 ESTRO 2020

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 rectosigmoid ulceration. No patients had >Grade 3 toxicity.

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

Fig 1: Kaplan-Meier estimates of LRFS and OS.

recurrent chordomas. Material and Methods

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