Yttrium-90 (\(^90\)Y) radioembolization is a highly targeted, minimally invasive treatment for liver tumors. This procedure, formally known as selective internal radiation therapy (SIRT) or transarterial radioembolization (TARE), combines internal radiation therapy with embolization. It delivers a high dose of radiation directly to the tumor site by capitalizing on the unique blood supply of liver tumors to spare surrounding healthy tissue. This method provides an effective way to manage cancer, often for patients whose tumors cannot be removed surgically. The treatment is typically performed by an interventional radiologist, usually on an outpatient basis or with a very short hospital stay.
How Y90 Microspheres Deliver Targeted Radiation
The mechanism of Yttrium-90 radioembolization relies on the physical properties of the radioactive isotope and the unique vascular structure of the liver. The treatment uses millions of microscopic spheres, made of either glass or resin, loaded with Yttrium-90 (\(^90\)Y). These spheres are extremely small, typically measuring between 20 and 35 micrometers in diameter.
Liver tumors receive most of their blood supply from the hepatic artery, while healthy liver tissue is primarily fed by the portal vein. Interventional radiologists exploit this difference by injecting the microspheres into the hepatic artery feeding the tumor. The spheres travel through the main arteries but become physically trapped within the tumor’s capillaries because they are too large to pass through.
Once lodged, the microspheres emit high-energy beta radiation directly into the tumor tissue. Yttrium-90 is a pure beta-emitter with a short half-life of approximately 64.2 hours; 94% of the radiation is delivered within the first 11 days. The radiation penetrates tissue over a very short distance, with an average range of only 2.5 millimeters. This limited penetration allows for a highly concentrated dose of radiation while minimizing exposure to adjacent healthy liver tissue.
Conditions Treated by Radioembolization
Radioembolization treats both cancers originating in the liver and those that have spread there from other parts of the body. The primary indication is hepatocellular carcinoma (HCC), the most common form of primary liver cancer. The procedure can be used to treat HCC, sometimes with curative intent, or to slow progression and relieve symptoms.
The treatment is also used for metastatic liver disease, where cancer cells from another organ form tumors in the liver. Cancers commonly treated with Y90 include:
- Colorectal cancer
- Neuroendocrine tumors
- Cholangiocarcinoma
- Melanoma
Because Y90 treatment is highly localized, it is often chosen for patients with unresectable tumors—those that cannot be safely removed by surgery due to their size, number, or location.
In some cases, radioembolization is used as a bridge to other curative treatments, such as liver transplantation or surgical resection. The radiation shrinks the tumors enough to make the patient a better candidate for these subsequent procedures. The therapy targets the tumor’s blood supply, acting as both an embolizing agent and a localized radiation source.
The Patient’s Treatment Procedure
The Y90 radioembolization process involves two distinct phases: a preparatory mapping procedure and the treatment delivery. The initial phase, the mapping angiogram, ensures the safety and targeting accuracy of the radiation delivery. An interventional radiologist inserts a catheter, usually through an artery in the groin or wrist, and guides it into the hepatic artery using image guidance.
A contrast dye is injected to visualize the blood vessels supplying the tumors. The physician may use tiny coils to temporarily block small arteries leading toward organs like the stomach or bowel. This prevents the radioactive spheres from flowing into non-target areas. A test dose of a radioactive tracer, such as Technetium-99m macroaggregated albumin (\(^{99\text{m}}\text{Tc-MAA}\)), is then injected to simulate the flow of the Y90 microspheres.
A nuclear medicine scan is performed immediately after the tracer injection to determine the percentage of spheres that might shunt from the liver into the lungs. This measurement helps calculate the precise, safe dose of Yttrium-90. The actual Y90 infusion, the second phase, usually takes place several days to two weeks after mapping.
During the treatment phase, the catheter is re-inserted and guided to the mapped position. The Y90 microspheres are slowly injected through the catheter, allowing blood flow to carry them directly to the tumor capillaries where they become lodged. The entire infusion procedure generally lasts about one hour, and patients are typically discharged home the same day or the following morning.
Recovery and Follow-Up Care
Following the Y90 procedure, patients usually spend a few hours in a recovery area for observation before being discharged. During this time, the medical team monitors the insertion site for bleeding. Patients are instructed to keep the limb still for several hours to promote clotting, and they should arrange for a ride home and limit strenuous activity for a period of time.
Many patients experience temporary symptoms known as Post-Radioembolization Syndrome in the days to weeks following treatment. These side effects may include mild abdominal discomfort or pain in the upper right side, sometimes radiating to the back or shoulder. Fatigue is a common complaint and can last for several weeks after the infusion.
Other individuals report mild nausea, a reduced appetite, or a low-grade fever that can persist for up to two weeks. These symptoms are generally manageable with prescribed medications and indicate the treatment is affecting the tumor. The radiation from the Y90 microspheres dissipates quickly; 99% of the radiation is gone within 30 days.
Follow-up care is essential to assess the treatment’s effectiveness and is typically scheduled four to eight weeks after the procedure. Monitoring involves follow-up imaging, such as a computed tomography (CT) scan or magnetic resonance imaging (MRI), to evaluate the tumor’s response. Subsequent scans are performed at regular intervals to track the long-term impact and determine any need for further treatment.