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the first follow up and 1 was followed in another hospital). In 5 pts asymptomatic radionecrosis was found in subsequent MRI: 3 received BRAF inhibitor ± MEK inhibitor and 2 anti-PD1. At the time of analysis 20 pts were dead of disease and 6 were alive with disease. Conclusion The association of SRS with modern systemic target therapies resulted to be safe and no severe toxicities were reported in our cohort of pts. Outcome results of the present serie are in line with literature confirming the poor prognosis of pts with MBM. Further studies are needed to determine the optimal timing of SRS in combination with systemic therapies. EP-1626 Tumour volume influences outcome after surgery and photon RT for chordoma and chondrosarcoma E.R. Gatfield 1 , D.J. Noble 2 , G.C. Barnett 1 , N.Y. Early 3 , A.C.F. Hoole 3 , N.F. Kirkby 4 , S.J. Jefferies 1 , N.G. Burnet 2 1 Addenbrooke's Hospital, Neuro-oncology Unit, Cambridge, United Kingdom 2 University of Cambridge, Department of Oncology, Cambridge, United Kingdom 3 Addenbrooke's Hospital, Department of Medical Physics and Clinical Engineering, Cambridge, United Kingdom 4 University of Manchester, Division of Molecular and Clinical Cancer Sciences, Manchester, United Kingdom Purpose or Objective To evaluate the long term outcomes of patients with chordoma and low-grade chondrosarcoma, of the skull base and spine, following surgery and high-dose X-ray radiotherapy. Material and Methods High-dose photon radiotherapy was delivered to 28 patients at the Neuro-oncology Unit at Addenbrooke’s Hospital (Cambridge, UK) between 1996 and 2016. Twenty-four patients were treated with curative intent, 17 with chordoma, 7 with low-grade chondrosarcoma, with a median dose of 65 Gy (range 65-70 Gy). Eight required metal reconstruction. Local control and survival rates were calculated using the Kaplan-Meier method. Results The median follow up was 83 months (range 7-205 months). The five year disease-specific survival for chordoma patients treated with radical intent was 85%, and the local control rate was 74%. The five year disease- specific survival for chondrosarcoma patients treated with radical intent was 100%, and the local control rate was 83%. The mean planning target volume (PTV) was 274.6 ml (median 124.7 ml). A PTV of 110 ml or less was a good predictor of local control, with 100% sensitivity and 63% specificity. For patients treated with radical intent, this threshold of 110 ml or less for the PTV revealed a statistically significant difference when comparing local control with disease recurrence (P=0.019, Fisher’s exact test). Electronic Poster: Clinical track: Sarcoma

Conclusion Our results show that refined high-dose photon radiotherapy, following tumour resection by a specialist surgical team, is effective in the long-term control of chordoma and low-grade chondrosarcoma, even in the presence of metal reconstruction. Results presented here will provide a useful source for comparison between high- dose photon therapy and proton beam therapy in a UK setting, in order to establish best practice for the management of chordoma and low-grade chondro- sarcoma. N.R. Khanna 1 , A. Sasidharan 1 , G. Chinnaswamy 2 , T. Vora 2 , J. Bajpai 2 , M. Ramadwar 3 , B. Rekhi 3 , A. Janu 4 , S. Desai 4 , N. Purandare 5 , P. Nayak 6 , A. Gulia 6 , A. Puri 1 , S. Laskar 1 1 Tata Memorial Hospital, Radiation Oncology, Mumbai, India 2 Tata Memorial Hospital, Medical Oncology, Mumbai, India 3 Tata Memorial Hospital, Pathology, Mumbai, India 4 Tata Memorial Hospital, Radiology, Mumbai, India 5 Tata Memorial Hospital, Nuclear Medicine, Mumbai, India 6 Tata Memorial Hospital, Surgical Oncology, Mumbai, India Purpose or Objective Upfront metastatic Ewing Sarcoma (except isolated lung metastasis) has dismal outcome despite aggressive chemotherapy and local treatment. In low resource settings, these patients are offered upfront palliation. Some patients with less extensive disease are challenged with aggressive protocol. There is a lack of guidelines which can help in selecting patients who may benefit with curative intent treatment. Material and Methods After evaluation in a multidisciplinary tumor board, patients were treated with curative intent multimodality treatment comprising of EFT-2001 multi-agent chemotherapy protocol (induction, concurrent and maintenance phase) and definitive radiotherapy to the primary as well as sites of metastasis. Metastasis within primary tumor portals were treated to a dose of 55.8 Gy in 31 fractions, while the distant metastatic sites were treated with hypofractionated regimen (20 – 33 Gy in 5 to 11 fractions). Results Seventeen patients diagnosed Ewing sarcoma with limited metastatic disease (excluding isolated lung metastases) treated with curative intent between 2010 and 2015 were retrospectively analysed. Median age was 22 years (range: 10 - 43 years) with majority being extrapelvic EP-1627 Outcomes of Ewing Sarcoma with limited metastatic disease treated with curative intent