Radioembolization (TARE, Y90)
Radiotherapy is one of the most important treatment modalities in oncology, but its use is limited in some areas as radiation also damages normal tissue around the tumor. In the liver for example, it is often difficult to reach the high doses required for tumors using classical radiotherapy because the normal liver tissue is also sensitive to radiation and the risk of damage to adjacent organs such as the heart and the spinal cord is always possible. Because of these limitations of external radiotherapy, the idea of giving high doses of radiation directly into the tumor through the feeding vessels has been developed. In radioembolization, the radioactive material in the desired dose is pre-loaded into very small particles and these particles are injected directly into the tumors via the liver artery with angiography. In this way, the tumor is given very high doses of radiation while the normal liver tissue and surrounding organs are preserved.
Radioembolization is an intraarterial high-dose brachytherapy, that is why it is also called "selective internal radiation therapy" or SIRT. This treatment was originally developed in the 1960s, tested in liver tumors in the 1980s and only after long clinical trials, it has become one of the standard treatment methods for liver tumors in the 2000s. The radioactive substance used in radioembolization is an isotope called Yttrium-90 (Y-90) which is loaded into special particles made of resin or glass at an individual dose for each patient. The radiation range of the Y-90 is about 2.5mm, meaning it only damages the area a few millimeters around it, not the surrounding liver tissue and other healthy tissues.
How is it done?
In contrast to chemoembolization, radioembolization is a two-stage angio procedure. In the first stage, a "test" angiography is performed. For this purpose, liver artery is accessed from the groin and angiography + cone beam tomography is performed to determine the number and location of tumors as well as their feeding arteries. In addition, it is checked whether there is any connection between liver arteries and gastrointestinal arteries. A test drug is then given to the liver artery and the angio procedure is terminated. After angiography, the patient is sent to the nuclear medicine department to check if the test drug has reached the target tumors in the liver. In addition, the rate at which the drug passes to the lung (rate of shunt) and whether it passes into the vessels of nontarget organs such as the stomach and bowel are examined. If the drug has gone to the desired sites, there is no passage to the nontarget organs and the shunt rate to the lung is below 20%, the patient is considered suitable for radioembolization. In this case, the volume of the liver lobe to which the drug will be administered is calculated and the appropriate dose is ordered from the manufacturer.
The second stage of radioembolization is the treatment itself and is usually performed 7-10 days after the test angiography. The ordered Y-90 is delivered in special glass containers after being loaded into very small particles (microsphere) made of either resin or glass. The radiation emitted by the loaded Y-90 decreases (half life is about 2.5 days) by time. The radioembolization must be performed exactly when the radiation has dropped down to the calculated dose for the patient. Otherwise, the patient would receive an either insufficient or excessive radiation dose. For this reason, the close cooperation of the interventional radiologist and nuclear medicine physician is extremely important to achieve the best possible result in radioembolization.
After radioembolization, the patient is usually kept in the hospital for 1 day. Since the radiation range of the Y-90 is only a few millimeters, no special isolation is required for patients. However, it is recommended that pregnant women and children do not have very close contact. If the radioembolization is performed for a single lobe of the liver and proves successful, it can be applied to the other lobe of the liver in due time. In some cases, TARE can be performed in the same lobe. In many patients, radioembolization and chemoembolization can be performed in a specific order and may have a complementary effect.
Which cancers are suitable for TARE?
Like chemoembolization (TACE), radioembolization is also performed only for liver tumors. Although both chemoembolization and radioembolization have been rarely used and proved successful in other organs, there is not enough scientific evidence to support such a use. Radioembolization has been applied mostly in primary tumors of the liver (HCC, cholangiocarcinoma) and some metastases (colorectal cancers, NET, breast, lung, etc.), like chemoembolization. Although radioembolization is widely used in HCC, it is not yet mentioned in its classical treatment guidelines, unlike TACE. However, the most important advantage of TARE is that, unlike TACE, it can be safely used in HCC patients with main portal vein occlusion. TARE was also used in some moderate and advanced stage HCC patients with chemotherapy and successful results were obtained.
Cholangiocarcinoma, such as HCC, is another primary liver tumor in which TARE is highly beneficial. These tumors are generally not suitable for surgical treatment or percutaneous ablation when diagnosed, so treatments such as radioembolization and chemoembolization are of great value.
Radioembolization has been also used successfully in many types of metastases, particularly in colorectal cancer metastases. In colorectal metastases, its efficacy can be increased by using chemotherapy drugs that increase sensitivity to radiotherapy. Similarly, radioembolization may increase the sensitivity to chemotherapy and can make tumors suitable to chemotherapy, which were previously chemotherapy-resistant.
Side effects (complications):
Radioembolization is a well-tolerated treatment modality in general. However, abdominal pain, nausea and fatigue may occur after the procedure. The most important complication of radioembolization is the passage of radioactive particles into the gastrointestinal arteries and causing ulcers. This event occurs in less than 5% of radioembolization procedures.
Chemoembolization or radioembolization?
Both treatments have superiority and weaknesses against each other. A few days after chemoembolization, pain, nausea, fever (postembolization syndrome) are seen, but this process is much lighter in radioembolization. Chemoembolization cannot be performed in portal vein occlusions but radioembolization may also be performed in these patients. However, radioembolization is usually a one-time treatment, whereas chemoembolization can be performed repeatedly. In addition, chemoembolization is more cost-effective and can be combined with many chemotherapy drugs.
Some patients may be more suitable for chemoembolization and others for radioembolization. However, it should be kept in mind that both treatments act in different mechanisms, so it may be more appropriate to use them together in some patients at different times
Interventional oncology in cancer management
Prof Saim Yilmaz, MD