Radioimmunotherapy (RIT)

What is Radioimmunotherapy and how is it used?

Radioimmunotherapy (RIT) is a combination of radiation therapy and immunotherapy. In immunotherapy, a laboratory-produced molecule called a monoclonal antibody is engineered to recognize and bind to the surface of cancer cells. Monoclonal antibodies mimic the antibodies naturally produced by the body's immune system that attack invading foreign substances, such as bacteria and viruses.

In RIT, a monoclonal antibody is paired with a radioactive material, or radiotracer. When injected into your bloodstream, the radiation-linked monoclonal antibody, or agent, travels to and binds to cancer cells, allowing a high dose of radiation to be delivered directly to the tumor. The agent used today is Yttrium-90 Ibritumomab Tiuxetan (Zevalin®). Iodine-131 Tositumomab (Bexxar®) is no longer on the market.

RIT is currently used to treat non-Hodgkin B-cell lymphoma (NHL), for newly diagnosed patients and for patients who have not responded to chemotherapy or treatment with the monoclonal antibody Rituximab® and other sub-types of lymphoma.

Several new radioimmunotherapy agents are under development or in clinical trials. Potential uses for RIT include the treatment of prostate cancer, melanoma, ovarian cancer, leukemia, high-grade brain glioma and colorectal cancer.

Who will be involved in this procedure?

A radiologist, nuclear medicine physician and/or radiation oncologist and other healthcare professionals, such as a medical oncologist or medical physicist, may be involved in RIT.

What equipment is used?

In addition to equipment needed to start and maintain an intravenous catheter, images of the patient may be obtained with a gamma camera before or after the therapy. Often, single-photon emission computed tomography (SPECT) imaging will also be performed. SPECT uses a gamma camera that rotates around the body to produce more detailed, three-dimensional images.

The gamma camera is capable of detecting radiation and taking pictures from different angles. It may be suspended over or below the examination table or be dual-headed with one camera above and one camera beneath the table. The camera could also be located within a large, doughnut-shaped scanner similar in appearance to a computed tomography (CT) scanner.

Who operates the equipment?

A radiologist who has specialized training in nuclear medicine or a nuclear medicine physician will supervise the technologist, who will be directly operating the gamma camera.

Is there any special preparation needed for the procedure?

Tell your doctor about all the medications you take, including herbal supplements. List any allergies, especially to local anesthetic, general anesthesia, or contrast materials. Your doctor may tell you to stop taking aspirin, nonsteroidal anti-inflammatory drugs (NSAIDs) or blood thinners before your procedure.

Women should always inform their physician or technologist if there is any possibility that they are pregnant or if they are breastfeeding. See the Safety page for more information about pregnancy and breastfeeding related to nuclear medicine imaging.

RIT is generally not administered to pregnant women or children.

You will be pre-screened to ensure proper blood counts and lack of significant bone marrow involvement with disease. Patients who have had prior bone marrow transplantation or failed stem cell collection should not receive RIT.

You will speak to a radiation safety specialist regarding radiation safety precautions.

How is the procedure performed?

RIT is usually performed on an outpatient basis and involves several separate visits to the hospital or healthcare facility.

On the first visit, you will receive a dose of the monoclonal antibody (without radioactive material) via an intravenous (IV) injection. Once in the bloodstream, the monoclonal antibody will attach to non-malignant B cells in your body and protect them from the radiation that will be used in treatment. This IV infusion may take up to two hours. You may also receive an intravenous dose of the radiotracer.

If radiotracer was injected, you will return to the hospital or healthcare facility during the next week to have a series of images taken to determine where the radiotracer has traveled in your body and how long it remains there. The information obtained from these imaging scans will determine if you are a candidate for RIT and will help in planning the treatment.

The actual treatment is given in an IV infusion usually seven to nine days after the first scan and involves an intravenous injection of both the radioactive agent and monoclonal antibody.

What will I feel during this procedure?

Except for intravenous injections, most nuclear medicine procedures are painless. Reports of significant discomfort or side effects are rare.

You will feel a slight pin prick when the technologist inserts the needle into your vein for the intravenous line. You may feel a cold sensation moving up your arm during the radiotracer injection. Generally, there are no other side effects.

Are there side effects from the procedure?

The most serious side effect of RIT therapy is a decrease in your blood counts. This side effect may occur as late as several months after treatment. As with chemotherapy or radiation therapy, this lowering of blood counts may result in bleeding or infection. It is important to follow up with your treating physician on a regular basis. Frequent blood draws will be performed to monitor your blood count. There is a small risk of bone marrow damage.

Additional side effects of RIT, which are usually short-term, may include an allergic reaction, fever, chills, low blood pressure, diarrhea and rash.

Hypersenitivity reactions from the monoclonal antibodies are rare, with occurrences increasing with multiple therapies. Typically you will be pretreated with acetaminophen (Tylenol®) or diphenhydramine (Benadryl®).