Radiation therapy may be an integral part of the treatment of gastric cancer. However, since gastric cancer is not exclusively treated with radiation therapy, it is important for patients to be treated at a medical center that can offer multi-modality treatment involving medical oncologists, radiation oncologists, surgeons, medical gastroenterologists, and nutritionists.
The objective of radiation therapy to the stomach is to kill cancer cells that could otherwise persist and cause the cancer to relapse. Radiation therapy uses high energy x-rays to kill cancer cells that remain in or near the stomach and surrounding lymph nodes. Radiation therapy is usually delivered to the stomach and surrounding lymph nodes from a machine outside the body, called a linear accelerator.
Radiation therapy alone is not usually recommended for primary treatment of gastric cancer because radiation administered in combination with chemotherapy appears superior when compared to treatment with radiation alone. Radiation therapy, however, is utilized as palliative therapy for patients who have inoperable gastric cancer or for patients who cannot undergo surgery or chemotherapy. Radiation therapy can also be utilized to treat patients who have a recurrence after surgery. However, in this situation patients typically also receive simultaneous chemotherapy and radiation therapy.
ADJUVANT THERAPY (TREATMENT AFTER SURGERY)
It is important to understand that some patients with gastric cancer already have small amounts of cancer that have spread beyond the stomach and cannot be detected with any of the currently available tests. Undetectable areas of cancer are referred to as micrometastases. It is the presence of micrometastases that causes cancer recurrence following treatment with surgery alone. For some patients, additional treatment aimed at these micrometastases can improve duration of survival and potential for a cure. The delivery of cancer treatment following local treatment with surgery is referred to as adjuvant therapy. Adjuvant therapy for gastric cancer may involve chemotherapy alone or in combination with radiation therapy.
NEOADJUVANT THERAPY (TREATMENT BEFORE SURGERY)
Some patients may receive treatment with chemotherapy or chemotherapy plus radiation therapy prior to surgery. This treatment can help to reduce the extent of cancer, making it easier to remove the cancer during surgery.
METASTATIC OR RECURRENT CANCER
The role of radiation therapy is limited in patients with unresectable or stage IV metastatic cancer. The primary treatment remains combination chemotherapy. Radiation therapy alone, however, can be used to decrease the symptoms from gastric cancer in patients with more advanced disease who are medically unable to receive surgery or chemotherapy or for patients who have a recurrence after surgery. However, patients with recurrent cancer usually receive combination chemotherapy.
DELIVERY OF RADIATION THERAPY FOR GASTRIC CANCER
Modern radiation therapy for gastric cancer is delivered via machines called linear accelerators that produce high energy external radiation beams that penetrate the tissues and deliver the radiation dose deep into the areas where the cancer resides. These modern machines and other state-of-the-art techniques have enabled radiation oncologists to significantly reduce side effects, while improving the ability to deliver a curative radiation dose to cancer-containing areas and minimizing the radiation dose to normal tissue. For example, with modern radiation therapy, skin burns almost never occur, unless the skin is being deliberately targeted or because of unusual patient anatomy.
After an initial consultation with a radiation oncologist, the next session is usually a planning session, which is called a simulation. The simulation session is used to determine radiation treatment fields and most of the treatment planning. Of all the visits to the radiation oncology facility, the simulation session may actually take the most time. During simulation, detailed pictures are taken of the cancer and the areas surrounding the cancer, often using computed tomography (CT) scans. Temporary marks may be made on the patient’s skin with magic markers. Body molds or other devices may be constructed to help the patient stay in one position. The radiation oncologist is aided by one or more radiation technologists and often a dosimetrist, who performs calculations necessary in the treatment planning. The simulation may last anywhere from fifteen minutes to an hour or more, depending on the complexity of what is being planned.
Once the aspects of the treatment fields are satisfactorily set, the patient may be given multiple “tattoos” which mark the treatment fields and replace the marks previously made with magic markers. These tattoos are not elaborate and consist of no more than pinpricks followed by ink, appearing like a small freckle. Tattoos enable the radiation technologists to set up the treatment fields each day with precision, while allowing the patient to wash and bathe without worrying about obscuring the treatment fields. Radiation treatment is usually given in another room separate from the simulation room. The treatment plans and treatment fields resulting from the simulation session are transferred over to the treatment room, which contains a linear accelerator focused on a patient table. The treatment plan is verified and treatment started only after the radiation oncologist and technologists have rechecked the treatment field and calculations, and are thoroughly satisfied with the “setup”.
SIDE EFFECTS OF RADIATION THERAPY
The majority of patients are able to complete radiation therapy without significant difficulty. Side effects and potential complications of radiation therapy are limited to the areas that are receiving treatment with radiation. The chance of a patient experiencing side effects, however, is highly variable. A dose that causes some discomfort in one patient may cause no side effects in other patients. If side effects occur, the patient should inform the technologists and radiation oncologist because treatment is almost always available and effective.
Radiation therapy to the abdominal/pelvic area may cause diarrhea, abdominal cramping or increased frequency of bowel movements or urination. These symptoms are usually temporary and resolve once the radiation is complete. Occasionally, abdominal cramping may be accompanied by nausea.
Blood counts can be affected by radiation therapy. In particular, the white blood cell and platelet counts may be decreased. This is dependent on how much bone marrow is in the treatment field and whether the patient has previously received or is receiving chemotherapy. These changes in cell counts are usually insignificant and resolve once the radiation is completed. However, many radiation therapy institutions make it a policy to check the blood counts at least once during the radiation treatments. It is not unusual for some patients to note changes in sleep or rest patterns during the time they are receiving radiation therapy and some patients will describe a sense of tiredness and fatigue.
Late complications following radiation treatment of gastric cancer are infrequent. Potential complications do include bowel obstruction, ulcers or second cancers caused by the radiation. The probabilities of these late complications are also affected by previous extensive abdominal or pelvic surgery, radiation therapy and/or concurrent chemotherapy.
STRATEGIES TO IMPROVE TREATMENT
The progress that has been made in the treatment of gastric cancer has resulted from improvements in multi-modality treatment and doctor and patient participation in clinical studies. Future progress in the treatment of gastric cancer will result from continued participation in appropriate studies. Currently, there are several areas of active exploration aimed at improving the treatment of gastric cancer.
Supportive Care: Supportive care refers to treatments designed to prevent and control the side effects of cancer and its treatment. Side effects not only cause patients discomfort, but also may prevent the optimal delivery of therapy at its planned dose and schedule. In order to achieve optimal outcomes from treatment and improve quality of life, it is imperative that side effects resulting from cancer and its treatment are appropriately managed. For more information, go to Managing Side Effects.
Newer Approaches to Delivering Radiation Therapy: As the technology for radiation therapy evolves, physicians become better able to precisely target the cancer while sparing nearby normal tissues. A newer approach that may prove beneficial for gastric cancer is intensity-modulated radiation therapy (IMRT). IMRT starts with a three-dimensional image of the cancer and allows physicians to deliver different doses of radiation to different areas. Other technology may be combined with IMRT to further improve patient outcomes. Image-guided radiation therapy (IGRT), for example, assesses the exact location of the cancer each day that a patient comes in for treatment.
New Approaches to Neoadjuvant or Adjuvant Therapy: Researchers continue to explore how best to use chemotherapy, radiation therapy, and targeted therapies in combination with surgery to improve gastric cancer outcomes. New approaches may involve new drugs, new combinations of drugs, new ways of combining radiation therapy with other treatments, or new doses or schedules of radiation therapy.
Ethyol®: Over the past 50 years, many drugs, called radiation protectors, have been tested in the laboratory for prevention of radiation damage to normal cells and tissues. For such drugs to work effectively, they have to protect normal cells, but not cancer cells, from radiation damage. Ethyol® is the only drug in this category that has been approved for use in patients receiving radiation for cancers of the head and neck. Ethyol® may be effective in preventing the side effects of radiation induced by treatment of gastric cancer.