Selective Internal Radiation Therapy (SIRT)
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Patients with liver cancer may be eligible for SIRT, or selective internal radiation therapy, a type of brachytherapy.
Also called radioembolization, SIRT sends radiation through the liver’s blood vessels feeding the tumor. This blocks blood flow to the tumor and delivers up to 40 times more radiation than conventional chemotherapy while avoiding healthy tissue.
This non-surgical, outpatient targeted therapy uses Y-90, a radioactive form of rare-earth metal yttrium, in microscopic beads made of glass or biocompatible resin.
Tiny catheters, called microcatheters, are used to inject radioactive microscopic glass or biocompatible resin beads directly in the liver thru the bloodstream. These beads are selectively absorbed by the liver tumors are get trapped in their blood vessels.
How SIRT Works
SIRT takes advantage of the fact that the liver is unique in having two blood supplies – the hepatic artery and the portal vein. A normal liver gets most of its blood supply from the portal vein, which drains blood to the liver from the gastrointestinal tract, spleen and pancreas. Liver tumors get most of their blood supply from the hepatic artery, which drains blood to the liver from the gastrointestinal tract, spleen and pancreas. Liver tumors get most of their blood supply from the hepatic artery.
This allows the radioactive beads to embolize, or block, blood flow in the hepatic artery while the portal vein remains open to maintain blood supply to normal liver tissue. The radioactive beads not only stop blood flow to the tumor but also flood it with radiation that will shrink and kill it
Types of SIRT
Although the SIRT procedure is the same, there are two types of microscopic beads: SIR-Spheres and TheraSphere. They each use Y-90 to treat liver cancer. The main difference is the material they are made from.
These are microscopic polymer resin beads coated with radioactive Y-90. An interventional radiologist inserts a catheter, a hollow flexible tube, into an artery in your upper thigh, guides it to the liver artery and infuses the SIR-Spheres. Millions of microscopic beads are delivered to the tumor without affecting the surrounding tissue.
The procedure takes about an hour. Before you go home after your procedure you may have a gamma camera scan. A gamma camera can detect radiation and make sure the microbeads are in place.
SIR-Spheres blanket the tumor in radiation for about two weeks. After two weeks they lose most of their radiation, which disappears after about 30 days. The harmless microspheres remain in your liver.
TheraSphere uses microscopic glass matrix beads that incorporate Y-90. It is best for patients with only liver cancer or whose cancer first developed in the liver.
We usually treat one side of the liver at a time with TheraSpere. If there are tumors on both sides of your liver, you will have a second procedure.
As with SIR-Spheres, an interventional radiologist infuses TheraSphere using a catheter inserted in an artery in your thigh and guided to the liver.
During the infusion, blood flow carries TheraSphere to the targeted tumor, and radiation is emitted from the glass beads. The procedure takes about an hour. The glass beads deliver most of their radiation in about two weeks and it disappears after 30 days. TheraSphere beads will remain in your liver.
What to Expect During SIRT
SIRT is an outpatient procedure that usually takes less than an hour. You may have two procedures about four weeks apart, one for each lobe of your liver. Due to sedation, recovery can take up to six hours and you will need someone to take you home after each treatment. We will monitor your progress with periodic blood tests and scans.
SIRT can treat multiple liver tumors of different sizes at the same time.