Radiation therapy and target volume delineation
tumor, Neo-CRAG, Cancer
PRIMARY TUMOR, TUMOR, CANCER
Patients in the nCRT group were treated as follows: three-dimensional conformal radiation therapy (3D-CRT) for seven patients (one in the training cohort, six in the validation cohort) and intensity-modulated radiation therapy (IMRT) for the other patients. During the scan, the patients were immobilized in the supine position with a vacuum cushion and scanned with simulation computed tomography (CT-sim), including plain and venous-enhanced scans from T4 to L5 vertebral levels. The inter-slice thickness of the CT scan was 5 mm. About 50–100 mL of prepared iopamidol solution was orally administered as the contrast agent 20 min before and at the time of CT-sim. Patients were required to fast for at least 3 h before the CT-sim and before each radiation treatment to account for inter-fractional variability in gastric distention due to gastric filling. Before the scan, gastroscopy was performed to place titanium clips at the cephalic and caudal edges of the tumor as a fiducial marker for target volume delineation.The principle of target volume delineation was designed at beginning of the Neo-CRAG trial and was based on preoperative radiation recommendations of the European Organization for Research and Treatment of Cancer (EORTC-ROC) [To elaborate, the gross tumor volume of the primary tumor (GTVt) and involved lymph nodes (GTVnd) were delineated based on baseline CT scan, gastroscopy or EUS, and exploratory laparoscopic findings. The CTV included GTVt with a 3 cm mucosal expansion and a 1.0–1.5 cm extragastric expansion, GTVnd with a 5 mm expansion, and elective regional lymphatic drainage regions. The mucosal expansion included the distal esophagus or proximal duodenum when appropriate. The inclusion of adjacent high-risk structures, including the inner half of the left diaphragm, parts of the pancreas, and neighboring parietal peritoneum were also considered. The CTV delineation had to avoid the vertebral body and include no more than 5 mm of liver tissues. The CTV was expanded by 5 mm in three dimensions to decide the planning target volume (PTV).The location of the primary tumor determined which elective lymph node groups would be included as per the JGCA classification, considering a 5 mm margin around the corresponding vessels:
Proximal 1/3 stomach and distal EGJ primaries:
Essential: groups 1, 2, 3, 4sa, 7, 9, 10 (for neighboring greater curvature tumor), 11p, 12 (for lesser curvature tumor), 16a, 19, 20, 110, and 111.Optional: groups 4sb (for greater curvature tumor), 5, 8, 11d, and 13.Middle 1/3 stomach primaries:
Essential: groups 1, 2, 3, 4sa, 4sb, 4d, 5, 6, 7, 8, 9, 10, 11p, 11d, 12, 13, and 16a.Optional: groups 14, 17, 18, and 19.Distal 1/3 stomach primaries:
Essential: groups 1, 3, 4d, 5, 6, 7, 8, 9, 11p, 12, 13, 16a, 17, and 18.Optional: groups 4sb, 10, and 11d.For dose limitations of the OAR, the liver volume percentage that received ≥ 30 Gy (VForward or inverse treatment planning was used for 3D-CRT or IMRT, respectively, based on modern Monaco (Elekta, Crawley, UK), Eclipse (Varian Medical Systems, Palo Alto, CA, USA), or Pinnacle (Philips Medical Systems, Madison, WI, USA) treatment planning systems, using the direct machine parameter optimization algorithm.