Gross Tumor Delineation in Esophageal Cancer on MRI Compared With F-FDG-PET/CT

Purpose: Current delineation of the gross tumor volume (GTV) in esophageal cancer relies on computed tomography (CT) and combination with F-fluorodeoxyglucose (FDG) positron emission tomography (PET). There is increasing interest in integrating magnetic resonance imaging (MRI) in radiation treatment, which can potentially obviate CTor FDG-PET/CTebased delineation. The aim of this study is to evaluate the feasibility of target delineation on T2-weighted (T2W) MRI and T2W including diffusion-weighted MRI (T2W þ DW-MRI) compared with current-practice FDG-PET/CT. Methods: Ten observers delineated primary esophageal tumor GTVs of 6 patients on FDG-PET/ CT, T2W-MRI, and T2W þ DW-MRI. GTVs, generalized conformity indices, in-slice delineation variation (root mean square), and standard deviations in the position of the most cranial and caudal delineated slice were calculated. Results: Delineations on MRI showed smaller GTVs compared with FDG-PET/CTebased delineations. The main variation was seen at the cranial and caudal border. No differences were Disclosures: The authors have no conflicts of interest to disclose. * Corresponding author. Departments of Surgery and Radiation Oncology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands. E-mail address: j.nijkamp@nki.nl (J. Nijkamp). 1 Co-first authors. https://doi.org/10.1016/j.adro.2019.04.004 2452-1094/ 2019 The Authors. Published by Elsevier Inc. on behalf of American Society for Radiation Oncology. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Advances in Radiation Oncology (2019) 4, 596-604 www.advancesradonc.org observed in conformity indices (FDG-PET/CT, 0.68; T2W-MRI, 0.66; T2W þ DW-MRI, 0.68) and in-slice variation (root mean square, 0.13 cm on FDG-PET/CT; 0.10 cm on T2W-MRI; 0.14 cm on T2W þ DW-MRI). In the 2 tumors involving the gastroesophageal junction, addition of DW-MRI to T2W-MRI significantly decreased caudal border variation. Conclusions: MRI-based target delineation of the esophageal tumor is feasible with interobserver variability comparable to that with FDG-PET/CT, despite limited experience with delineation on MRI. Most variation was seen at cranial-caudal borders, and addition of DW-MRI to T2W-MRI may reduce caudal delineation variation of gastroesophageal junction tumors. 2019 The Authors. Published by Elsevier Inc. on behalf of American Society for Radiation Oncology. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).