Radioembolization is a minimally invasive procedure that delivers tiny radioactive beads directly into the blood vessels feeding a liver tumor. The beads lodge in the tumor’s blood supply and emit radiation over a short range, killing cancer cells while largely sparing healthy liver tissue. It is used primarily for liver cancers and cancers that have spread to the liver from other organs, particularly colorectal cancer.
How Radioembolization Works
The procedure combines two cancer-fighting strategies: cutting off a tumor’s blood supply (embolization) and delivering radiation at close range (brachytherapy). A doctor threads a thin catheter through an artery in the wrist or groin and guides it into the hepatic artery, the main blood vessel supplying the liver. Millions of microscopic beads, each loaded with a radioactive isotope called yttrium-90, are injected through the catheter. These beads are small enough to travel deep into the tiny vessels that feed the tumor, where they become permanently trapped.
Once lodged, the beads emit beta radiation with an average tissue penetration of just 2.5 mm and a maximum reach of about 11 mm. That short range is the key advantage: the radiation is intense enough to destroy tumor cells but doesn’t travel far enough to cause significant damage to surrounding healthy tissue. The therapeutic effect comes primarily from the radiation rather than from blocking blood flow, though the embolization component contributes as well. The beads remain in place permanently but stop emitting meaningful radiation within about two weeks as the yttrium-90 decays.
Who Is a Candidate
Radioembolization is most commonly used for hepatocellular carcinoma, the most common type of primary liver cancer. It has become an increasingly popular treatment for patients with intermediate-stage disease, particularly those with preserved liver function. It is also used for cancers that have metastasized to the liver, especially colorectal cancer liver metastases, as well as neuroendocrine tumors and cholangiocarcinoma.
Not everyone qualifies. Your liver needs to be healthy enough to tolerate the treatment. Patients generally need bilirubin levels at or below 2 mg/dL, a blood marker that reflects how well the liver is processing waste. Levels above 3 mg/dL are typically a hard contraindication unless the treatment can be delivered to a very targeted segment. Advanced liver disease (classified as Child-Pugh C) is also a relative contraindication, meaning the risks usually outweigh the benefits.
The Two-Phase Procedure
Radioembolization happens in two separate visits, typically spaced about two weeks apart.
The first visit is the mapping phase. A doctor performs an angiogram to chart the blood vessel anatomy supplying your liver, identifying any branches that could accidentally carry beads to the stomach or other organs. If problematic vessels are found, they may be blocked with small coils during this same session. At the end of the mapping procedure, a harmless tracer particle is injected to simulate where the radioactive beads will eventually go. You then undergo a scan to confirm the tracer landed in the right place and, critically, to measure how much of it leaked through the liver into the lungs.
This lung shunt measurement is one of the most important safety checks. If more than 20% of the tracer reaches the lungs, radioembolization is typically ruled out because the radiation dose to lung tissue would be too dangerous. Patients with moderate shunting (10% to 20%) may still be treated with a reduced dose.
The two-week gap between visits gives the medical team time to review the imaging, calculate a personalized radiation dose, and order the yttrium-90 beads, which are manufactured internationally. It also allows any coils placed during the mapping phase to fully seal off the targeted vessels. At the second visit, the actual treatment delivery follows the same catheter approach but takes the place of the tracer with the real radioactive microspheres.
What Recovery Looks Like
Most patients go home the same day or the day after treatment. The most common aftereffect is post-embolization syndrome, a cluster of symptoms that includes fatigue, abdominal pain, nausea, loss of appetite, and occasionally fever. It occurs in roughly 20% to 55% of patients. Abdominal pain affects 13% to 39%, nausea 17% to 32%, and fever 2% to 12%. In most cases, these symptoms are mild and resolve on their own within days to a couple of weeks. Fatigue tends to linger longest and can persist for several weeks.
Because the beads are radioactive, you may need to limit close contact with children and pregnant people for up to one week after treatment. The radiation exposure risk to others is low, but these precautions reduce it further. Your treatment team will give you specific guidance based on your dose.
Follow-up imaging with CT or MRI typically begins around two months after the procedure. Tumor response to radioembolization can be slow, sometimes taking many months to fully manifest. One study of colorectal liver metastases found that complete disappearance of tumors took up to 18 months, while measurable tumor shrinkage continued for up to 21 months. The first year requires the most frequent monitoring, since recurrence is about 6.5 times more likely during that period than in the second year. A typical surveillance schedule includes scans at roughly 2, 4, 6, 8, 11, 14, 18, and 24 months.
Response Rates for Liver Metastases
The evidence for radioembolization in colorectal cancer liver metastases is particularly strong. When combined with chemotherapy delivered through the hepatic artery, response rates of approximately 90% have been reported across multiple studies, measured by a drop in CEA, a blood marker for colorectal cancer activity. In one randomized trial, patients who received radioembolization plus systemic chemotherapy had a 91% response rate compared to 0% for chemotherapy alone, and their time to disease progression more than tripled: 15.6 months versus 4.7 months.
Imaging tells a similar story. In a study of 54 patients, 9% had complete disappearance of all tumors, 76% saw all tumors shrink by more than 10%, and another 9% had stable disease. Only 6% showed tumor growth on the first scan at three months. These numbers reflect that radioembolization works gradually, and early scans may underestimate its full effect.
How It Compares to Chemoembolization
The most common alternative catheter-based liver treatment is chemoembolization (TACE), which delivers chemotherapy drugs directly to the tumor along with particles that block its blood supply. A systematic review comparing the two approaches for neuroendocrine liver metastases found similar outcomes in overall survival, progression-free survival, tumor response on imaging, and symptom relief. Severe side effects were also comparable between the two.
The practical differences matter more to patients than the survival statistics suggest. Radioembolization typically requires fewer treatment sessions and is better tolerated in patients with portal vein clots, a common complication of advanced liver disease that makes chemoembolization risky or impossible. The choice between the two often depends on tumor characteristics, liver function, and the specific expertise available at your treatment center.
Serious but Rare Complications
The most significant risk unique to radioembolization is radiation-induced liver disease, sometimes called REILD. This occurs when healthy liver tissue absorbs enough radiation to cause damage, leading to fluid buildup in the abdomen or jaundice within eight weeks of treatment. In first-time treatments, the risk is low. It becomes more concerning with repeat procedures: one large study found that patients who underwent more than two radioembolization sessions had a 21.4% rate of REILD, compared to 0% in those who received two or fewer. Repeat treatments beyond two sessions were also associated with significantly higher mortality at 6 and 12 months.
Nontarget embolization, where beads end up outside the liver, can cause ulcers in the stomach or inflammation in the gallbladder. This is precisely what the mapping phase is designed to prevent. The careful pre-treatment angiography and tracer testing have made this complication uncommon in experienced centers.
Two Types of Microspheres
Two commercial products are available: glass microspheres (TheraSphere) and resin microspheres (SIR-Spheres). Both carry yttrium-90 and are delivered the same way, but they differ in size, density, and the amount of radioactivity packed into each individual bead. Glass microspheres are smaller and carry more radiation per sphere, meaning fewer beads are needed for the same dose. Resin microspheres are slightly larger and carry less radiation per bead, so more are injected, which creates a stronger embolization effect. Systematic reviews comparing the two for hepatocellular carcinoma have found similar safety profiles, and the choice between them often comes down to institutional preference and the specific clinical scenario.