Y90 radioembolization, also known as Selective Internal Radiation Therapy (SIRT), is a minimally invasive, image-guided treatment for liver tumors performed by interventional radiologists. The procedure combines two components: embolization (blocking blood flow) and radiation therapy using the radioactive isotope Yttrium-90 (Y90). Microscopic spheres loaded with Y90 are delivered directly into the blood vessels feeding the tumor. This approach combines localized, high-dose radiation delivery with the effect of cutting off the tumor’s blood supply.
The Mechanism of Action
Y90 radioembolization exploits the unique arterial blood supply of liver tumors compared to healthy tissue. The procedure uses tiny glass or resin microspheres (20 to 35 micrometers) loaded with Yttrium-90. These spheres are injected into the liver’s arterial blood flow, lodging physically in the smaller vessels surrounding the tumor.
This lodging action achieves embolization, partially cutting off the tumor’s blood supply and trapping the radioactive material at the cancer site. Yttrium-90 emits pure beta radiation, a high-energy, short-range particle that travels less than 11 millimeters before its energy is fully absorbed.
The short path of the beta radiation is key to the therapy’s selective nature, allowing cancer cells to be irradiated with a high dose while minimizing exposure to healthy liver cells. Yttrium-90 has a half-life of approximately 64 hours, delivering the majority of its therapeutic dose over about two weeks before decaying.
Patient Eligibility and Pre-Procedure Planning
Y90 radioembolization treats primary liver cancers (HCC) and metastatic cancers, such as colorectal cancer. It is an important option for patients whose tumors are inoperable or not candidates for other local treatments. Planning ensures the therapy’s safety and effectiveness.
The initial step involves detailed imaging, such as a contrast-enhanced CT or MRI scan, to assess the size, location, and extent of the tumors. This is followed by a crucial pre-treatment mapping procedure, typically performed one to three weeks prior. This mapping is an angiogram, where a catheter is inserted into an artery, usually in the groin, and guided into the liver’s arterial system.
During the mapping angiogram, the radiologist identifies the specific blood vessels supplying the tumor. They also identify and potentially block extrahepatic vessels that could carry microspheres to non-target organs like the stomach or bowel, preventing severe inflammation. A simulation dose using Technetium-99m labeled macroaggregated albumin (MAA) is injected to mimic the flow of the Y90 microspheres.
A subsequent SPECT/CT scan tracks the MAA distribution to calculate hepatopulmonary shunting—the fraction of blood flow diverted to the lungs. This measurement is essential for calculating the safe and personalized Y90 dose (dosimetry). Dosimetry balances the need for an optimal tumor dose against the risk of radiation damage to the lungs or healthy liver tissue, ensuring the radiation is confined to the target volume.
The Y90 Treatment Procedure
The Y90 radioembolization procedure occurs one to two weeks after mapping, allowing time for the Y90 microspheres to be prepared based on personalized dosimetry. On the day of treatment, the procedure is usually performed under conscious sedation. The radiologist accesses the arterial system, typically through the femoral artery in the groin or the radial artery in the wrist.
A thin, flexible catheter is threaded through the aorta into the hepatic artery, the main vessel supplying the liver tumors. Using real-time X-ray guidance, the catheter is precisely positioned into the smaller branch of the hepatic artery feeding the target tumor. Once secured, the suspension of Y90-loaded microspheres is slowly infused into the artery.
The infusion ensures the radioactive beads are carried by blood flow directly into the tumor capillaries, where they lodge. The infusion takes only a few minutes, and the total procedure time is typically one to two hours. Immediately afterward, imaging, such as a SPECT or PET scan, confirms the successful and localized placement of the Y90 microspheres within the tumor.
Post-Procedure Care and Expected Outcomes
After the procedure, the catheter is removed, and pressure is applied to the insertion site to prevent bleeding. Patients are monitored for several hours, often requiring bed rest to ensure the arterial puncture site is stable. Y90 radioembolization is frequently performed on an outpatient basis, with most patients returning home the same day or after an overnight stay.
Immediate side effects are often called Post-Radioembolization Syndrome, including mild fatigue, low-grade fever, and abdominal discomfort or pain. These symptoms are transient, manageable with oral medications, and typically subside within a few days to a couple of weeks. Patients receive radiation safety instructions, though the risk to others is minimal because the short-range beta radiation is contained within the liver.
The primary goal of treatment is to stop tumor growth or cause necrosis (death of the cancerous tissue). Follow-up imaging, such as CT or MRI, is scheduled starting one to three months after the procedure to assess the tumor’s response. Effectiveness is measured by observing tumor shrinkage or a change in the tissue’s appearance, indicating successful destruction of cancer cells.