ESTRO 38 Abstract book

S331 ESTRO 38

M. Thomas 1,2 , G. Defraene 1,2 , M. Lambrecht 1,2 , W. Deng 3 , J. Moons 4 , P. Nafteux 4 , S.H. Lin 3 , K. Haustermans 1,2 1 KU Leuven – University of Leuven, Department of Oncology – Laboratory Experimental Radiotherapy, B- 3000 Leuven, Belgium ; 2 UZ Leuven – University Hospitals Leuven, Department of Radiation Oncology, B-3000 Leuven, Belgium ; 3 The University of Texas MD Anderson Cancer Center, Department of Radiation Oncology, Houston – Texas, USA ; 4 UZ Leuven – University Hospitals Leuven, Department of Thoracic Surgery, B-3000 Leuven, Belgium Purpose or Objective To develop a normal tissue complication probability (NTCP) model for postoperative pulmonary complications after neoadjuvant chemoradiotherapy (nCRT) followed by surgery in esophageal cancer (EC) patients. The added value of dosimetry to clinical information was verified. Material and Methods We analyzed data from 697 patients with EC treated with nCRT followed by surgery at two major institutions between 2002-2017 (287 patients) and 2007-2017 (410 patients, including 134 patients treated with proton beam therapy (PBT)). A multivariable (forward stepwise built) logistic regression analysis studied the predictive value of clinical and treatment-related variables (gender, age, body mass index, smoking behavior, chronic obstructive pulmonary disease, histology and tumor and nodal stage) and additionally dosimetric variables (absolute and relative lung and heart volumes receiving 5Gy (V5) to 55Gy (V55), mean dose and radiation technique: 3D-CRT (reference category), IMRT, VMAT and PBT) for the presence of a postoperative pulmonary complication, which were extracted from prospectively obtained databases. Model performance was assessed by the Area Under the Curve (AUC) of the receiver operating characteristic curve. Model validation was performed using a nonrandom split-sample (TRIPOD type 2B study) of 90 patients selected based on treatment date (last 30 patients of each institution treated with photons and last 30 patients treated with PBT). Results In total, 221 of 607 patients (36.4%) developed a pulmonary complication. Dosimetric information significantly improved the apparent AUC from 0.67 (95%CI 0.63-0.71) to 0.77 (95%CI 0.73-0.81) (likelihood ratio test p<0.001). In the optimal multivariable logistic regression model (Table 1 and Figure 1), the mean lung dose (OR 1.066), increasing age (OR 1.022), squamous cell carcinoma (OR 2.072) and radiotherapy technique (IMRT: OR 0.326; VMAT: OR 2.372; PBT: OR 0.276) were selected as predictors associated with the development of a pulmonary complication. In the validation set, the NTCP model had an AUC of 0.64, which increased to 0.71 after a refit of the model coefficients.

Conclusion Based on 697 patients with EC treated with nCRT followed by surgery at two major institutions, a useful NTCP model for the development of a postoperative pulmonary complication was obtained. Model validation suggests that updating the model is necessary when applied in a different patient cohort. The radiation technique variable was selected as a predictor independently from the mean lung dose, indicating the need to continuously update and adapt dose-volume models to new treatment conditions. By applying this NTCP model, we can select EC patients at high risk of treatment-induced complications in which we can further investigate the benefit of PBT. PV-0623 Tumor-stroma ratio for predicting pathologic response after chemoradiotherapy in esophageal cancer I. Lips 1 , G.W. Van Pelt 2 , F.P. Peters 1 , J.A. Krol 1 , D. Van Klaveren 3 , J.J. Boonstra 4 , W.O. De Steur 2 , A. Farina Sarasqueta 5 , W.E. Mesker 2 , M. Slingerland 6 1 Leiden University Medical Center LUMC, Radiation Oncology Department, Leiden, The Netherlands ; 2 Leiden University Medical Center LUMC, Department of Surgery, Leiden, The Netherlands ; 3 Leiden University Medical Center LUMC, Medical Statistics, Leiden, The Netherlands ; 4 Leiden University Medical Center LUMC, Gastroenterology and Hepatology, Leiden, The Netherlands ; 5 Leiden University Medical Center LUMC, Pathology, Leiden, The Netherlands ; 6 Leiden University Medical Center LUMC, Medical Oncology, Leiden, The Netherlands Purpose or Objective Standard treatment for patients with resectable esophageal cancer (EC) is neoadjuvant chemoradiotherapy (nCRT) followed by surgery. Treatment with nCRT leads to a pathologic complete response (pCR) in approximately 30% of patients. Surgery might be safely omitted in this selected group of patients, however with the current available options, predicting pCR after nCRT is insufficient. The tumor micro-environment, including the supportive stromal component, plays a crucial role in the progression and spread of cancers. The amount of stroma in direct relation to the tumor has been was proven to be a prognostic factor for survival in breast cancer, colon cancer and EC. For esophageal adenocarcinoma (EAC) scoring tumor-stroma ratio (TSR) in biopsy specimens was proven to be representative, reproducible and easy. In addition, in patients with EAC TSR was proven to correlate with response to neoadjuvant chemotherapy. The main focus of this study was to investigate the value of TSR in the prediction of pathologic response (PR) after nCRT in EC. Material and Methods