Purpose: To define instructions for delineation of target volumes in the neoadjuvant setting in oesophageal cancer.
Materials and methods: Radiation oncologists of five European centres participated in the following consensus process:  revision of published (MEDLINE) and national/institutional delineation guidelines;  first delineation round of five cases (patient 1-5) according to national/institutional guidelines;  consensus meeting to discuss the results of step 1 and 2, followed by a target volume delineation proposal;  circulation of proposed instructions for target volume delineation and atlas for feedback;  second delineation round of five new cases (patient 6-10) to peer review and validate (two additional centres) the agreed delineation guidelines and atlas;  final consensus on the delineation guidelines depicted in an atlas. Target volumes of the delineation rounds were compared between centres by Dice similarity coefficient (DSC) and maximum/mean undirected Hausdorff distances (Hmax/Hmean).
Results: In the first delineation round, the consistency between centres was moderate (CTVtotal: DSC = 0.59-0.88; Hmean = 0.2-0.4 cm). Delineations in the second round were much more consistent. Lowest variability was obtained between centres participating in the consensus meeting (CTVtotal: DSC: p < 0.050 between rounds for patients 6/7/8/10; Hmean: p < 0.050 for patients 7/8/10), compared to validation centres (CTVtotal: DSC: p < 0.050 between validation and consensus meeting centres for patients 6/7/8; Hmean: p < 0.050 for patients 7/10). A proposal for delineation of target volumes and an atlas were generated.
Conclusion: We proposed instructions for target volume delineation and an atlas for the neoadjuvant radiation treatment in oesophageal cancer. These will enable a more uniform delineation of patients in clinical practice and clinical trials.