The stomach begins at the gastrooesophageal junction and ends at the pylorus. The greater curvature forms the left and convex border of the stomach, and the lesser curvature forms the right and concave border of the stomach (Fig. 1a). It is divided into four parts: the cardia, fundus, body and antrum. The gastric wall is divided into five layers: mucosa, submucosa, muscularis externa, subserosa and serosa.

The stomach is covered with peritoneum and is closely related to the left lobe of the liver, spleen, left adrenal gland, superior portion of the left kidney, pancreas, transverse colon and major blood vessels including the coeliac axis and superior mesenteric artery (Fig. 1b).

Probability of gastric carcinoma varies according to the primary location: ~35 % of tumours arise from the gastroesophageal junction, cardia and fundus. ~25 % of tumours arise from the body. ~40 % of tumours arise from the antrum and distal stomach.

Local extension

Regional lymph node metastases (Fig. 2, Table 1)

Prior to radiotherapy planning, it is imperative to review surgical and pathology reports and discuss with the surgeon to identify the areas considered to be the highest risk for recurrence; the type of operation, i.e. total vs. partial gastrectomy, needs to be noted.

Preoperative CT scans should be reviewed to identify the location of primary tumour and involved regional lymphatics.

Consider preradiation quantitative renal perfusion study to evaluate relative bilateral renal function.

Postoperative diagnostic CT scan with oral and intravenous contrast is required with the identification of the following:

The type of surgery performed depends on the location of tumour, histology pattern (Fig. 3).

Patients should fast for 2–3 h before CT simulation and before treatments to ensure an empty stomach and enhance daily treatment reproducibility.

Radiotherapy planning CT scans of 3–5 mm thickness should be obtained with the patient in the supine position with arms overhead, from top of the diaphragm (for stomach) or carina (for tumour of GE junction or cardia) to the bottom of L4.

Immobilisation with a Vac-Lok is recommended for treatment with IMRT.

Intravenous contrast is preferred to demonstrate blood vessels and guide clinical target volume (CTV) delineation, particularly for lymph nodes; preoperative CT scans should be used to aid identification of preoperative tumour volume and nodal groups to be treated.

CTV for adjuvant radiation therapy for gastric cancer depends on the position of the primary disease as well as the status of lymph node metastasis. Suggested target volumes for CTV coverage depending on subsite are detailed in Tables 2, 3, 4, 5 and 6.