Y-90 Radioembolization

Yttrium-90 is a pure beta-emitting isotope. Its radiation travels only a few millimetres in tissue, which is what makes it suitable for treatment delivered inside the body: the dose is deposited where the spheres lodge and falls away sharply beyond them. The spheres themselves are about a third of the width of a human hair, made of glass or of resin, and are not designed to block the artery in the way that particles used for chemoembolisation do. They are carried by the blood into the dense network of tumour vessels, where they become trapped and irradiate the tumour continuously as the isotope decays, with almost all the dose delivered within about two weeks. The spheres remain permanently in the liver but are no longer radioactive after that period. The treatment is also referred to as selective internal radiation therapy.

Radioembolization is recommended for hepatocellular carcinoma that cannot be removed or ablated, including tumours that involve a branch of the portal vein, and it is used to control a tumour while a patient waits for transplantation or to shrink it to within transplant criteria. It is widely used for liver metastases from colorectal cancer that persist after chemotherapy, and for neuroendocrine tumour metastases where it also helps hormonal symptoms. Cholangiocarcinoma within the liver is another indication. A further use is radiation lobectomy, in which one side of the liver is treated so that the untreated side enlarges over the following months, making major liver surgery possible. It is not suitable where liver function is poor, where bilirubin is significantly raised, where disease outside the liver dominates the outlook, or where the mapping study shows that too much of the dose would reach the lungs or the stomach and bowel.

The first stage is a mapping angiogram. Through a puncture in the radial artery at the wrist or the femoral artery in the groin, a catheter is guided into the hepatic arteries and the vascular anatomy of the liver is charted in detail. Vessels that run from the liver arteries to the stomach or duodenum are blocked with tiny coils so that no spheres can reach them. A test dose of technetium-labelled particles is then injected and a nuclear medicine scan measures how much would pass through the liver into the lungs, and whether any would reach the gut. The physics team uses this study, together with the volume of the tumour and the liver, to calculate the exact activity to be administered. One to two weeks later the delivery is performed by the same route: the catheter is placed in the same position, and the yttrium-90 spheres are infused slowly under fluoroscopic control. A scan afterwards, either single photon emission or positron emission tomography, confirms where the spheres have gone. Treatment may be given to one lobe, to a segment or to the whole liver in stages.

Candidacy is decided by a multidisciplinary team of interventional radiologists, oncologists, hepatologists and nuclear medicine physicians. Assessment includes cross-sectional imaging of the liver with contrast, tumour markers, blood tests of liver and kidney function and clotting, an assessment of performance status, and often positron emission tomography to check for disease elsewhere. Adequate liver reserve and a bilirubin within acceptable limits are essential. Certain chemotherapy drugs are paused around the treatment. Patients are advised on the short radiation precautions that apply for a few days after delivery, which are limited but specific for close contact and for young children. For international patients, imaging and blood results can be reviewed remotely to give a preliminary opinion, but the mapping angiogram must be performed at the treating centre, so the visit is planned around two procedures.

Both stages are usually day cases or a single overnight stay, with a few hours of bed rest to protect the arterial puncture. After the delivery, a post-embolisation reaction is common: tiredness, a mild fever, loss of appetite, nausea and a dull ache in the right upper abdomen, generally lasting a few days to two weeks and managed with simple medicine. Most people resume ordinary activity within a few days, though fatigue can persist for several weeks. Blood tests check liver function in the weeks that follow. The first assessment of response is made with imaging at around 3 months, because the tumour often changes in appearance and blood supply before it changes in size. Treatment abroad is best planned as a stay of about 2 to 3 weeks so that mapping, delivery and the post-treatment scan are all completed, with the 3-month imaging arranged near home and shared with the treating team.

The most important risks come from spheres reaching tissue outside the liver, which is why the mapping stage exists. If they reach the stomach or duodenum they can cause an ulcer that is difficult to heal; if too many reach the lungs they can cause radiation pneumonitis. Both are uncommon when mapping and dosimetry are done properly. Radiation-induced liver disease can occur if too much normal liver is irradiated, particularly in a liver already damaged by cirrhosis. Other risks include the post-embolisation syndrome described above, damage or bleeding at the arterial puncture, infection, inflammation of the gallbladder, and a temporary rise in liver blood tests. Compared with chemoembolisation, radioembolization tends to cause less immediate discomfort and is generally given as an outpatient treatment. Reported outcomes include tumour control and prolonged time to progression in selected liver-dominant disease, successful downstaging of some tumours to surgery or transplantation, and useful symptom control, with the benefit depending on tumour type, liver function and the dose delivered.