RESUMO
PURPOSE: To identify the main difficulties in postoperative clinical target volume (CTV) delineation in gastric cancer (GC). METHODS: Before and after a training course, 20 radiation oncology residents were asked to delineate the CTV for the postoperative GC case on four computed tomography scans: dome of the diaphragm, anterior abdominal wall, duodenal stump and porta hepatis level, and to determine the lower CTV border. CTV volume was reconstructed from requested planar contours. Area of intersection (AI) for each requested scan and volume of intersection (VI), defined as the overlap of delineated area/volume with respective reference area (RA)/reference volume (RV) proposed by the senior radiation oncologist, were computed. The degree of agreement between the reference and participants' contours was quantified using the Concordance Index (CI): AI/RA × 100% or VI/RV × 100%. The lower CTV border was analyzed separately. Pre- and post-training CIs were compared. A questionnaire investigated the difficulties with contouring. RESULTS: Mean CI value was the lowest for the dome of the diaphragm (24% pre-training, 35 % post-training) and for the duodenal stump (49% pre-training, 61% post-training). Mean CI for the CTV volume was 49% pre-training and 59% post-training, p = 0.39. Mean distance from the reference to the participants' lower CTV borders was 2.73 cm pre-training and 2.0 cm post-training, p = 0.71. In a questionnaire, 75% of respondents indicated the elective nodal area as the main difficulty. CONCLUSIONS: Delineation of the dome of the diaphragm and the duodenal stump, as yet not recognized as the source of variation, should be addressed in the international consensus guidelines and clarified.