One major challenge in treating gastric cancer either pre- or postoperatively is that the abdominal contents move with respiration, with excursions of greater than 2 cm in the cranio-caudal direction. In the past, this has necessitated large margins around the tumor or postoperative bed to account for motion. More recently, there are novel motion-management techniques to account for respiratory motion, such as respiratory gating. Respiratory gating allows for reduction in the treatment margin and the consequent radiation exposure to normal tissues, thereby limiting treatment-related toxicities [26] by just turning the radiation beam on at a certain time during the breathing cycle when the tumor or postoperative bed is in a certain position. To facilitate confirmation that the radiation beam is turning on at the appropriate time during the respiratory cycle, radio-opaque markers or operative clips can be visualized on daily pretreatment x-rays to confirm that the position of the tumor or postoperative bed is in the treatment field.

The clinical target volume for adjuvant radiation treatment for gastric cancer depends on the location of the primary disease as well as the status of the lymph nodes involved by disease. Diverse and widespread patterns of direct extension and lymphatic drainage oblige the radiation oncologist to treat very large fields to cover areas of potential relapse and high rates of acute and late toxicity. In addition, older studies such as the INT 0116 were conducted in the era of 2D planning, commonly involving anterior–posterior opposed fields, leading to unnecessary irradiation of large volumes of highly sensitive abdominal organs. Consequently, studies have explored the feasibility and safety of 3D conformal radiation treatment and IMRT [27–30]. The type of operation depends on the location and extent of the primary tumor. For proximal cancers involving the cardia or the proximal third of the stomach, a total gastrectomy with Roux-en-Y esophagogastrectomy is indicated. During this type of procedure, the right and left gastric arteries are dissected at their respective bases, and the entire stomach is removed from the GEJ to the duodenum just below the pylorus. For distal cancers involving the antrum, pylorus, or distal third of the stomach, a subtotal gastrectomy is adequate. During this type of surgery, the left gastric artery is often dissected at its base. However, in contrast to a total gastrectomy, because the proximal stomach is left intact in this case, the right paracardial and left paracardial nodes and portions of the lesser curvature and greater curvature lymph nodes are not surgically dissected [31].

The nodal sites to include in the target volume depend on the T- and N-stage and on the location of the primary tumor. In case the lymph nodes are pathologically negative for disease (pN0), covering the perigastric lymph nodes is recommended. For pT4b disease, nodes related to the sites of adherence should also be included. In the case that the lymph nodes are pathologically involved with disease (pN+), then the nodal coverage will depend on the site of the primary tumor in the stomach. For proximal tumors, including the perigastric, celiac, and splenic lymph nodes is recommended. The pancreaticoduodenal, porta hepatic, periesophageal, and mediastinal nodes could also be included at the discretion of the physician. For distal tumors, including the perigastric, celiac, pancreaticoduodenal, porta hepatic, and splenic nodes is recommended. The splenic hilum could also be included. The planning target volume is delineated by adding margins to the clinical target volume to account for organ motion and setup uncertainties. The target is usually large and results in the inclusion of significant portion of the kidney, bowel, and liver.

The prescription dose is 45 Gy given in 180 cGy per daily fraction, with a cone down to 50.4–54 Gy in 180 cGy per fraction to any residual disease. Radiotherapy is given concurrently with capecitabine or infusional 5-fluorouracil.