Radiation Therapy for Stomach Cancers

If you have stomach (or gastric) cancer, radiation therapy may be a treatment recommended by your cancer care team. Going through this journey is challenging in itself and hearing about treatment plans may add to your distress. If radiotherapy is viable for you, understanding how this treatment works can be helpful. It will help you stay on top of medical discussions and prepare you for what to expect during your treatment journey.

Radiation therapy, also known as radiotherapy, uses high-powered energy beams to kill cancer cells and prevent them from dividing. The beams can come from X-rays or other sources of radiation, such as protons or gamma rays. In the case of gastric cancers, it is mostly used for gastric adenocarcinomas. Other types of gastric cancer, like GISTs and gastric neuroendocrine tumors, are sometimes treated with radiation therapy, especially if the tumors have metastasized to other parts of the body.

Radiation therapy works by damaging the genetic material (DNA) in cancer cells located within the area where therapy is given. Subsequently, cancer cells with DNA that is beyond repair will stop dividing and die. Cells in the treated area will start to die in the days or weeks after treatment begins and continue to die for weeks or months after treatment ends.

While cancer cells can easily be eliminated by radioactive rays, healthy cells are more resistant to radiation doses. This is because normal cells are able to repair the damage caused by radiation at a much faster rate than cancer cells. This means that radiation therapy is able to destroy tumors and stop cancer growth while leaving the surrounding healthy tissue unharmed.

Radiation therapy can be administered from outside your body or inside your body.

• External beam radiation therapy (EBRT): In this type of treatment, high doses of X-ray beams emitted from a large machine called a linear accelerator (LINAC) are precisely directed at your stomach or other body parts where the cancer cells are found. Similar to the process of undergoing an X-ray, you will lie on a treatment table under the machine. EBRT is the most common method of delivering radiation therapy for gastric cancer patients.
• Internal radiation therapy: Radioactive material that is contained within a catheter, seed implant or other type of carrier is placed directly into or close to the site of the tumor. If a liquid source of radioactivity is used, it is called systemic radiation therapy. Systemic radiation therapy involves swallowing or injecting a radioactive substance that subsequently travels through your bloodstream to target and destroy cancer cells in your body.

Radiation therapy regimens typically consist of a set number of treatment sessions given over a period of time. Your doctors will determine the number of sessions you need based on the type and stage of your cancer, as well as other health considerations.

EBRT is a common form of treatment used for gastric adenocarcinomas. However, it typically isn’t used on its own. It is often given in conjunction with chemotherapy drugs, notably 5-fluorouracil. Known as chemoradiation, this combination therapy is more effective as chemotherapy makes the cancer cells more sensitive to radiation therapy. Therefore, undergoing radiation therapy along with chemotherapy increases your chances of a successful treatment outcome compared to having either treatment on its own.

EBRT is usually administered daily over the course of several weeks. Each treatment session lasts for 10 to 30 minutes. While the treatment usually only takes a few minutes, most of the session is spent getting you into the correct position on the table. In the event you are given radiation therapy or chemoradiation, you may receive it under different circumstances. This includes:

• Neoadjuvant radiotherapy: Radiation therapy or chemoradiation given before surgery is known as neoadjuvant radiotherapy. The aim of this is to shrink the gastric tumor so that it is easier to remove during the operation.
• Adjuvant radiotherapy: Radiation therapy or chemoradiation given after surgery is called adjuvant (chemo)radiotherapy. The goal of this is to kill any remaining cancer cells that were not visible during the operation and subsequently left behind. This can happen if the cancer has grown deep into the stomach wall or spread to nearby lymph nodes. Adjuvant therapy, therefore, lowers the chances of the cancer coming back, which is known as cancer recurrence.
• Perioperative radiotherapy: Radiation therapy or chemoradiation given both before and after surgery is called perioperative (chemo)radiotherapy. The objectives of this treatment are to shrink the gastric tumor so that surgical removal is easier and to reduce the chance of cancer recurrence.
• Palliative radiotherapy: Radiation therapy or chemoradiation may be recommended for advanced gastric cancers, where the cancer has spread to distant parts of the body and surgical removal may not be possible. In this case, this type of treatment aims to control cancer growth, relieve symptoms and improve your quality of life.

There are a few types of EBRT that are more commonly used in the treatment of gastric cancer.

Three-dimensional (3D) conformal radiation therapy (3D CRT)

3D CRT uses computers and other special techniques to mold radiation beams in three dimensions so that they are tailored to the size, shape and location of the stomach cancer. The beams are broken up into small doses and aimed at the gastric tumor from different directions. This helps to focus the radiation on the cancer cells, thereby shrinking the tumor while sparing nearby healthy tissues and lowering the risk of side effects.

Intensity-modulated radiation therapy (IMRT)

IMRT is an advanced, specialized form of 3D CRT commonly used to treat many types of cancer. The radioactive rays are broken up into many small, computer-controlled beams that are sculpted to tailor the tumor's specific size, shape and location. In contrast to normal 3D CRT, IMRT allows the radiation oncologist to administer higher and varying doses of radiation. As the higher-powered beams are focused on the cancer cells, the tumor can be shrunk more effectively while limiting damage to surrounding healthy tissue. As such, the risk of certain side effects associated with 3D CRT can be lowered by using IMRT.

Volumetric modulated arc therapy (VMAT)

VMAT is a type of stereotactic body radiotherapy (SBRT). In VMAT, the LINAC moves around you in one or several 360-degree rotations during the treatment session. With this form of radiation therapy, small and focused energy beams can be directed from almost any angle, allowing doctors to target your gastric tumor closely while avoiding healthy tissues. The radiation beams can also be adjusted continuously, allowing therapy to be administered without interruption. This makes VMAT a more precise form of EBRT than 3D CRT. In addition, because very small areas of the body receive high doses of radiation, it can reduce your risk of having side effects.

Treatment sessions using VMAT may last for a shorter period of time than other types of EBRT, which require the LINAC to start and stop for adjustments. VMAT is generally used for gastric cancers that have spread to other parts of the body.

With the use of more advanced imaging and specialized techniques in radiation therapy, clinical trials are studying new combinations of chemotherapy drugs and radiation therapy that could potentially be used to treat different types and stages of gastric cancer.

While EBRT is widely used to treat gastric adenocarcinomas, it is rarely used in gastrointestinal (GI) NETs, including those arising from the stomach. This is because carcinoid tumors are generally resistant to radiation that is delivered via conventional methods such as EBRT. For this reason, the use of EBRT in the treatment of NETs is limited mainly in palliative care for unresectable tumors that have spread to the brain or bones. The aim of this is to relieve any symptoms and improve your quality of life.

One type of systemic radiation therapy that is commonly used as a second- or third-line treatment for advanced gastroenteropancreatic NETs is peptide receptor radionuclide therapy (PRRT). This treatment uses a radioactively-labeled drug called 177Lu-DOTATATE to target specific proteins that are present in excessive amounts on the surface of NET cells. When injected into your bloodstream, the drug delivers radiation to the tumor directly. This damages the cancer cells’ DNA and destroys them from within. In this way, PRRT selectively targets NETs while limiting damage to the surrounding healthy cells.

If you have any questions regarding radiation therapy and its role in your treatment, please talk to your doctors and cancer care team. They may run some imaging scans or laboratory tests to find out if radiotherapy is suitable for you.