782 PATTERNS OF FAILURE AND ADEQUACY OF CLINICAL TARGET VOLUME (CTV) MARGINS IN PATIENTS TREATED WITH DEFINITIVE CHEMO-RADIATION IN ESOPHAGEAL CANCER

Abstract

Abstract   Esophageal cancer is a locally aggressive malignancy with dismal overall survival (OS) rates. Approximately 50–60% of patients fail loco-regionally after definitive chemoradiation (CTRT). There is a lack of consensus regarding clinical target volume (CTV) margins. Improved diagnostic investigations and patterns of failure (POF) data, suggested scope of reduced CTV margins. In this retrospective study, we evaluated the POF (defined as first site of failure) and the adequacy of CTV margins. Methods All patients treated with CTRT between Jan 2013 to Dec 2017 were included. CTV margin was given as 3–5 cm cranio-caudal and 1–1.5 cm radial from gross tumor volume (GTV). Patients were treated either with combined technique (anterior–posterior followed by conformal) or with volumetric arc radiotherapy to a dose of 60-63Gy in 30–35 fractions. PET-CT/CT thorax and upper GI-endoscopy were performed at regular intervals. Loco-regional failure (LRF) was defined as recurrence at local site or regional nodes respectively and classified as infield, marginal and out-field. CT was co-registered with planning CT to document these failures. Results 158 patients were eligible. Twenty-one patients were excluded as they either progressed or did not attend the first follow-up. Median age was 57 years, >90% had squamous histology, and most common subsite was upper third. Median follow-up was 45.8 months, 53 patients (41.7%) had progression. Local recurrence (LR) was seen in 37 (69.8%), followed by regional in 25 (47.1%) and distant in 21 patients (39.6%). All LR were within the GTV. Of regional failures, 50% were within GTV and 50% were outside the radiotherapy portals. This suggest that 3 cm cranio-caudal CTV margin was adequate. Conclusion Our study demonstrated that loco-regional recurrence was the most common pattern of failure after definitive CTRT. As majority of loco-regional failures were within the GTV, hence, 3 cm cranio-caudal CTV margins appear to be adequate enough for control of microscopic disease. Further prospective studies are needed to validate the use of 3 cm CTV margins in definitive CTRT for esophageal cancer.