Selective Internal Radiation Therapy (SIRT) is a treatment for liver tumors that cannot be removed with surgery. This form of internal radiation therapy uses a radioactive element, Yttrium-90 (Y90), attached to millions of microscopic beads. An interventional radiologist performs this minimally invasive procedure, delivering targeted radiation through the bloodstream directly to tumors while sparing healthy liver tissue.
How SIRT Y90 Targets Liver Tumors
SIRT Y90 leverages the liver’s unique blood supply. Healthy liver tissue receives most of its blood from the portal vein, while liver tumors get their blood almost exclusively from the hepatic artery. This difference allows for the targeted delivery of treatment directly to cancer cells.
During the treatment, millions of tiny beads called microspheres, each coated with Y90, are released into the hepatic artery. These microspheres are small enough to travel deep into the liver but become lodged in the small blood vessels surrounding the tumor. This effectively traps the radiation source directly at the site of the cancer.
The trapped microspheres emit beta radiation, a type of energy that travels only a few millimeters. This delivers a high dose of energy to the tumor cells, damaging their DNA and causing them to die. Because the radiation’s reach is limited, it minimizes damage to the surrounding healthy liver tissue, which is nourished by the portal vein.
Conditions Treated and Patient Eligibility
SIRT Y90 treats cancers within the liver, including primary liver cancer like hepatocellular carcinoma (HCC) and metastatic tumors that have spread from other parts of the body, such as colorectal cancer. The treatment is for patients whose tumors cannot be surgically removed.
A multidisciplinary team of specialists determines if a patient is a suitable candidate. They assess several factors to ensure the treatment is safe and likely to be effective. A primary consideration is that the cancer is confined to the liver, as SIRT does not treat disease outside this organ.
A patient’s overall liver function is a key factor. To qualify for the procedure, a patient must have adequate liver function, assessed through blood tests. These tests measure liver enzymes and proteins to ensure the liver can withstand the treatment, and also check blood cell counts and clotting ability.
The medical team reviews imaging scans like CT or MRI to map the tumors’ size, number, and location. This confirms the tumors have the necessary arterial blood supply. Patients with abnormal blood flow that could divert the microspheres to other organs, such as the stomach or pancreas, may not be eligible.
The SIRT Y90 Treatment Procedure
The treatment process occurs in two phases, starting with a planning session one to two weeks before the procedure. This mapping phase involves a hepatic angiogram, where a catheter is guided into the hepatic artery. A contrast dye is injected to create a detailed map of the liver’s blood vessels, allowing the interventional radiologist to identify the arteries feeding the tumor.
During this mapping, the doctor performs a simulation using a non-therapeutic radioactive agent, Technetium-99m macroaggregated albumin (MAA). MAA particles are similar in size to the Y90 microspheres and are injected into the arteries supplying the tumor. A scan then shows where these particles travel, confirming blood flow will carry the treatment to the tumor and not other organs, which also helps calculate the radiation dose.
The second phase is the treatment day. The procedure is similar to the mapping angiogram and is performed in an angiography suite with the patient under sedation. Using live X-ray imaging for guidance, the interventional radiologist navigates a catheter from an artery in the groin or wrist to the mapped blood vessels feeding the tumor.
The prescribed dose of Y90 microspheres is then slowly infused through the catheter over 60 to 90 minutes. After the infusion is complete, the catheter is removed, and pressure is applied to the entry site to prevent bleeding. Patients are monitored for a few hours before being discharged the same day.
Recovery and Potential Side Effects
For the first few days after the procedure, patients follow specific radiation safety precautions. Because Y90 emits beta radiation with a very short range, these precautions are minimal and may include avoiding prolonged close contact with others. The radioactivity from the microspheres diminishes over approximately two weeks.
The most common side effects are known as post-embolization syndrome, which can include fatigue, low-grade fever, nausea, and abdominal pain. These symptoms are generally mild to moderate and resolve within about a week. Fatigue may last longer, sometimes for two to four weeks, as the body recovers.
While most side effects are manageable, there are less common but more serious complications that can occur. These can include unintended radiation damage to other organs if some microspheres travel outside the liver. The medical team discusses these risks with the patient beforehand.
Patients have follow-up appointments with their oncology team to monitor recovery. Several weeks to months after the procedure, imaging scans like a CT or MRI are performed. These scans help doctors assess the tumors’ response to the treatment and determine the next steps in the patient’s care plan.