Radiotherapy, an important treatment for gastric cancer, is not something that can just be done. Before having radiation therapy, patients undergo a series of tests and are prepared under the guidance of their doctors, the purpose of which is to assess whether the patient can tolerate radiation therapy and whether they can receive it safely and effectively.
Getting the relevant tests
The primary purpose of gastric cancer screening is to clarify staging, which is generally divided into local staging and systemic staging.
Local staging is to assess the extent and depth of tumor invasion and the status of regional lymph nodes, usually with abdominal enhancement CT and upper gastrointestinal imaging, and gastroscopy is also performed. Gastroscopy is the first choice for evaluating gastric lesions and obtaining biopsies of tumor tissue, not only to visualize gastric cancer lesions, but also to obtain biopsies and perform some necessary treatments (e.g., hemostasis). Upper gastrointestinal tract imaging is useful to show the general boundaries of the tumor, which are not easily revealed by gastroscopy and CT, as well as the stiffness of the stomach wall and gastric retention. Ultrasound gastroscopy can also help determine the depth of tumor invasion into the gastric wall to guide the endoscopic treatment of early gastric cancer. In addition, gastric cancer is prone to regional lymph nodes, retroperitoneal lymph nodes and left supraclavicular lymph node metastasis, and physicians will carefully perform imaging and physical examinations.
Stomach cancer is also prone to peritoneal implant metastases, ovarian metastases, and liver metastases, and physicians will determine whether distant metastases are present before treatment. The examination includes a chest radiograph or CT of the chest, pelvic ultrasound or CT of the pelvis, and possibly a bone scan for bone metastases in advanced lesions. In addition, routine blood tests, blood biochemistry, and tumor markers will be performed.
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Understanding and choosing the right radiotherapy
In addition to conventional radiotherapy, your doctor may recommend something like conformal radiotherapy or intensity-modulated conformal radiotherapy (IMRT) to reduce the dose to surrounding organs (heart, lungs, liver, kidneys, etc.). When planning IMRT, the physician will consider factors such as gastric filling, the effect of respiratory motion, etc. to delineate the target area, and may also recommend 4-D CT reconstruction or other measures (e.g., image-guided radiation therapy, adaptive radiotherapy, etc.) to avoid the influence of these factors in determining the target area. Patients should communicate fully with their physicians to determine the appropriate treatment for them.
Irradiation site localization
The irradiation site will be positioned by the physician prior to radiation therapy. After the radiotherapy positioning appointment, the physician provides dietary instructions and asks the patient to train for a 4-hour period without food and small amounts of water. On the day of positioning, the patient will be asked to fast for 4 hours. Immediately prior to positioning, 500 ml of drinking water is taken orally.
Conventional analog positioning generally requires the patient to be in the supine position and is less commonly used today. Patients usually undergo CT mock localization with intravenous or oral contrast prior to localization, also in the supine position, and receive a CT scan.
Patients require gastrointestinal preparation prior to CT mock positioning, which is performed on the basis of gastric emptying and is prepared as follows:
- Patients with partial gastrectomy and preoperative radiotherapy (tumors at the gastroesophageal junction, gastric lesser curvature, and gastric sinus) should drink 400-500 ml of water (containing the contrast agent iodinated alcohol) 30 minutes before localization on a 4-hour fast, with the aim of visualizing the small intestine. The patient also takes 300 ml of oral semifluid food (e.g., thick gruel) to fill the residual stomach before CT simulation of the localized body model is fixed.
- For preoperative radiotherapy and tumors located in the greater curvature of the stomach, the stomach is kept empty and 300 ml of semifluid food is no longer consumed in addition to the above method of visualizing the small intestine.
- Patients who have undergone total gastrectomy can drink no or only a small amount of water containing contrast because of the limited volume of the small intestine in place of the stomach.
The steps for CT simulation localization are as follows.
- The patient is positioned supine with a chest and abdominal plate underneath him or her, and the hands are held up at the elbows and placed on the forehead. The surgeon will fix his or her thorax halfway to the lower abdomen with a thermoplastic body mold.
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- After the thermoplastic body mold has cooled and taken shape, the surgeon will place lead dots under the laser light in the front center of the body and on each side to mark the dots, which will be as close to the center of the target area as possible.
- A CT-enhanced scan is performed to show the anatomic location; patients with contrast allergies, advanced age, severe complications, and other conditions that preclude enhanced CT receive a CT plain scan.
Understand the dos and don’ts
During radiotherapy, patients should be closely monitored for local reactions as well as systemic adverse reactions. Local reactions include early local edema, radioactive gastric and esophageal mucosal injury, and resulting gastrointestinal symptoms such as nausea, vomiting, and dyspepsia, while late reactions include those corresponding to liver, kidney, pancreatic, and spinal cord injury, as well as local tissue fibrosis and hemorrhage. Systemic reactions are mainly allergic reactions, hematopoietic reactions and gastrointestinal reactions, mostly due to chemotherapy. The doctor will take appropriate measures to alleviate them.
There is significant uncertainty in radiotherapy for gastric cancer compared to other tumors, mainly brought about by respiratory motion, degree of filling, and target area outlining. Therefore, during positioning and treatment, the physician will ask the patient to fast for at least 3 hours or proceed on an empty stomach.
A thorough examination and adequate preparation under the guidance of a physician is the first step to successful radiotherapy. (Contributed by Xiaowan Chen, Department of Gastrointestinal Oncology, The First Hospital of China Medical University)