Abstract Book

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ESTRO 37

measures were calculated on a per-patient basis using histological verification or clinical follow up as reference standard. Multivariable logistic regression analysis was performed to determine pre-treatment predictors of interval metastasis. A prediction score was developed to predict the probability of interval metastasis. Results Of 783 patients that underwent 18 F-FDG PET/CT restaging, 65 (8.3%) were confirmed to have interval metastasis and 44 (5.6%) were deemed to have false positive lesions (5.6%). The resulting sensitivity and specificity was 74.7% (95% CI: 64.3-83.4%) and 93.7% (95% CI: 91.6-95.4%), respectively. Multivariable analysis revealed that tumor length, cN status, squamous cell tumor histology, and baseline SUV max were associated with interval metastasis. Based on these criteria, a prediction score was developed with an optimism adjusted C-index of 0.67 that demonstrated accurate 18 F-FDG PET/CT restaging detects true distant interval metastases in 8.3% of patients after chemoradiotherapy for esophageal cancer. The provided prediction score may stratify risk of developing interval metastasis, and could be used to priorities additional restaging modalities for patients most likely to benefit. OC-0164 Nomogram validation for survival in patients with esophageal cancer receiving trimodality therapy. L. Goense 1 , K.W. Merrell 2 , A.L. Arnett 2 , C.L. Hallemeier 2 , G.J. Meijer 3 , J.P. Ruurda 4 , W.L. Hofstetter 5 , S.H. Lin 6 1 UMC Utrecht, Department of Radiation Oncology and Surgery, Utrecht, The Netherlands 2 Mayo Clinic, Department of Radiation Oncology, Rochester, USA 3 UMC Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands 4 UMC Utrecht, Department of Surgery, Utrecht, The Netherlands 5 The University of Texas MD Anderson Cancer Center, Department of Thoracic and Cardiovascular Surgery, Houston, USA 6 The University of Texas MD Anderson Cancer Center, Department of Radiation Oncology, Houston, USA Purpose or Objective Recently a nomogram was developed for the prediction of overall survival (OS) after treatment with neoadjuvant chemoradiotherapy (nCRT) combined with surgery for oesophageal or junctional cancer. The aim of this study was to externally validate the nomogram in an international multi-institutional cohort of patients, and to explore the prognostic use of the nomogram for the prediction of progression-free survival (PFS) after nCRT Patients with potentially resectable oesophageal or junctional carcinoma that underwent nCRT plus surgery between 1998 and 2015 at 3 academic centres were included. The discriminative ability of the nomogram for the prediction of OS and PFS was quantified by Harrell's C-statistic. Calibration of the nomogram was visually assessed by plotting actual OS and PFS probabilities against predicted probabilities. Results Some 975 patients were included. The discriminative ability of the nomogram for OS was moderate (C-statistic: 0.61) and comparable to that of the initial cohort (C- statistic: 0.63). The nomogram was also useful for the prediction of PFS (C-statistic of 0.64). Calibration of the nomogram was accurate for both OS and PFS, with predicted estimates corresponding closely with the actual observed estimates (Figure 1). calibration. Conclusion followed by surgery. Material and Methods

Conclusion The nomogram accurately predicted OS and PFS after nCRT followed by surgery in an independent international cohort of oesophageal cancer patients. The current validated model may enable risk-stratified adjuvant treatment allocation and identify patients in need of routine surveillance after treatment. OC-0165 Effectiveness of several external beam radiotherapy schedules for palliation of oesophageal cancer I. Lips 1 , N. Walterbos 1 , M. Fiocco 2 , K. Neelis 1 , A. Langers 3 , M. Slingerland 4 , W. De Steur 5 , F. Peters 1 , Y. Van der Linden 6 1 Leiden University Medical Center LUMC, Radiation Oncology Department, Leiden, The Netherlands 2 Leiden University Medical Center LUMC, Department of Medical Statistics and Bioinformatics, Leiden, The Netherlands 3 Leiden University Medical Center LUMC, Department of Gastroenterology and Hepatology, Leiden, The Netherlands 4 Leiden University Medical Center LUMC, Department of Medical Oncology, Leiden, The Netherlands 5 Leiden University Medical Center LUMC, Department of Surgery, Leiden, The Netherlands 6 Leiden University Medical Center LUMC, Radiation Oncology Department and Center of Expertise Palliative Care, Leiden, The Netherlands Purpose or Objective Although external beam radiotherapy (EBRT) is frequently used for palliative treatment of patients with incurable oesophageal cancer, the optimal schedule for symptom control is unknown. The aim of this retrospective study was to evaluate three EBRT schedules for symptom control and to investigate possible prognostic factors associated with second intervention and survival. Material and Methods Patients with oesophageal cancer treated with EBRT with palliative intent between Jan 2009 and Dec 2015 at the Leiden University Medical Centre were evaluated. Data were retrieved retrospectively from patient files. Dysphagia was scored as 0=no dysphagia, able to eat normal diet, 1=able to swallow some solid foods, 2=able to swallow only semi solid foods, 3=able to swallow liquids only, 4=total dysphagia. We performed univariate and multivariate analyses to investigate the effect of treatment schedule on symptom control (20 Gy in 5, 30 Gy in 10 or 39 Gy in 13 fractions) and to determine prognostic factors for second intervention (with repeat EBRT, intraluminal brachytherapy or covered stent placement) and overall survival (OS).