Radioembolization

Radioembolization or SIRT (Selective Intravascular Radiation Therapy) is a relatively new procedure that injects small resin or glass particles that are complexed with radioactive Yttrium into the arteries supplying the liver to treat tumors in the liver.   The particles become lodged in the small arteries and release very high energy radiation with poor penetrance (travels a very short distance) exposing the tumor to high radiation that damages the tumor and the blood vessels that feed it.

The liver is unusual in that it has two sources of blood supply- the hepatic artery and the portal vein, with the portal vein typically supplying about 75% of the blood to the liver.  When tumor develops in the liver, either arising as a new cancer or arising from the spread of tumor from other places in the body, its blood supply generally comes from the hepatic artery, so injecting radiation into that artery will affect tumor more than healthy liver.   Because carcinoid tumors tend to have a particularly rich blood supply provided by well developed arterial vessels, that makes them a particularly good candidate for treatment by this method.  Chemoembolization takes advantage of the same principle.

Because the radiation which is administered can damage any nearby tissue, there are several steps which must be taken to insure the delivery is done as safely as possible without radiation getting outside the liver.

The first step is a CT angiogram, which is a special CT scan designed to better show the arteries of the body to help plan the administration and better delineate how much disease there is and where it is located.

A catheter angiogram is then done which consists of placing a catheter (a long thin tube) through the artery at the groin to the arteries that supply the liver and nearby organs. Contrast is injected to better map out exactly what these arteries supply blood to, and 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 behaves like the yttrium will is injected to determine where the radiation will go to.  At the end of the procedure pictures are taken in the nuclear medicine department to show where the technetium went and determine if the yttrium can be safely administered.

After 2 to 3 weeks, the therapeutic yttrium radiation is administered.  This involves another catheter angiogram and merely involves placing a catheter up to the vessel the radiation is to be injected into and then very slowly injecting it.  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 2 to 3 weeks apart.

While the tends to be rapid response of symptoms, 3 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 2 to 3 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 and 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.  Some time 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.  

Further general information on radioembolization will be posted at www.radiologyinfo.org/en/info.cfm?pg=radioembol