Evaluation of a radiotherapy protocol based on INT0116 for completely resected gastric adenocarcinoma

With the results of the INT0116 study, adjuvant radiochemotherapy has become the standard treatment after complete resection of gastric adenocarcinoma. However, the implementation of radiotherapy (RT) remains a concern. In response, consensus guidelines on RT technique have been published. Our objective was to measure the inter- and intraclinician variability in RT field delineation using conventional two- (2D) and three-dimensional (3D) techniques. Between 1999 and 2003, five radiation oncologists (ROs) treated 45 patients with completely resected, gastric adenocarcinoma using postoperative radiochemotherapy (INT0116). Two cases were included in this study (Patient 1 had cardia and Patient 2 had antral disease). Standardized vignettes (with surgical and pathologic findings) and preoperative and postoperative imaging for each case were developed. Each RO designed AP–PA fields for each patient (2D planning) on two separate occasions. This was repeated using a 3D planning technique. Patient 1 had a mean field area of 250.2 cm 2 (SD 12.0) and 227.9 cm 2 (SD 26.5) using 2D and 3D planning, respectively ( p = 0.03). The mean clinical target volume (CTV) volume was 468.3 cm 3 (SD 65.9). Patient 1 had a significantly greater inter- than intra-RO variation for the field area designed with 3D planning; however, no difference occurred with 2D planning or CTV contouring. Patient 2 had a mean field area of 234.8 cm 2 (SD 33.1) and 226.8 cm 2 (SD 19.3) using 2D and 3D planning, respectively ( p = 0.5). The mean CTV was 729.4 cm 3 (SD 67.3). For Patient 2, the inter-RO variability was significantly greater than the intra-RO variability for the field area using both 2D and 3D planning, and no difference was seen for the CTV. Composite beam's-eye-view plots revealed that the superior, inferior, and right lateral borders proved to be most contentious. Despite published guidelines and a departmental protocol, significant variations in the RT field areas were seen among ROs for both 2D and 3D planning. However, in general, CTV contouring was reproducible. Because 3D-RT hinges on accurate target identification, caution should be exercised before migrating to 3D planning for postoperative gastric cancer.