Radioembolization, or SIRT (Selective Intravascular Radiation Therapy), is a relatively new procedure that uses small resin or glass particles that contain radioactive yttrium. The particles are injected into the arteries supplying the liver. The particles become lodged in the small arteries near the tumor. The high radiation damages the tumor and the blood vessels that feed it.
Because the radiation could damage any nearby tissue, there are several steps that must be taken to ensure the delivery is done as safely as possible without radiation getting outside the liver.
The first step is a CT angiogram. This is a special CT scan designed to better show the arteries of the body. A CT angiogram helps plan the administration of the yttrium, and better delineates how much disease there is and where it is located.
This is followed by a catheter angiogram, which consists of placing a catheter (a long thin tube) through an artery at the groin and advancing it to the arteries that supply the liver and nearby organs. Contrast is injected to better map out exactly what these arteries supply blood to. Any vessels that connect the blood supply of the liver to other organs are blocked with material placed through the catheter to stop blood from flowing through these vessels.
Finally, a very low energy radioactive material called technetium, which will behave like the yttrium, is injected to determine where the radiation will go. At the end of the procedure, pictures are taken in the nuclear medicine department to show where the technetium went and to determine if the yttrium can be safely administered.
After two to three weeks, the therapeutic yttrium radiation is administered, which involves another catheter angiogram. This consists of placing a catheter up to the vessel into which the radiation will be injected, followed by slow injection. For safety reasons, only half of the liver is treated at a time, so disease involving both sides of the liver requires two treatments, usually two to three weeks apart.
While there tends to be rapid response of symptoms, three months may be necessary to see substantial shrinkage in size of the tumors.
What to Expect
The catheter angiograms, both the initial planning study and the yttrium administrations, are done with sedation and require arriving two to three hours before the procedure to check blood work, start an IV for the sedation and administer any necessary drugs. Each procedure takes one to two hours and typically requires three to four hours of recovery, including up to four hours of lying flat in bed. There is little discomfort involved in the planning angiogram, but it is common to have short term discomfort with the yttrium administration which usually resolves before going home.
Multiple medications are given after the administration, which will be discussed fully by the radiologist or nurse after the procedure. These include medicine for any nausea that may develop, medicine to reduce inflammation and medicine to help protect the stomach, which sits next to the liver.
Before the radiation administration, the patient will meet with a nuclear medicine doctor to discuss any precautions that need to be taken when the radiation is administered, although the radiation travels less than a quarter of an inch from where it is deposited so very little leaves the body and is only a fraction of its original strength after a few days.