These images were taken in a 73-year-old man who underwent radioembolotherapy for an unresectable hepatocellular carcinoma. An intravenous contrast-enhanced computed tomography scan (left) shows the hypervascular tumor mass (designated with arrows). In an outpatient procedure, resin microspheres carrying a therapeutic dose of yttrium 90 were delivered via the hepatic artery under angiographic guidance. A post-implantation non–contrast-enhanced single photon emission computed tomography scan (right) demonstrates radioactivity (soft glow) confined to the tumor.

Radioembolotherapy Using Yttrium 90

By Sunni Hosemann

One of the newer applications of interventional radiology is a form of brachytherapy for unresectable liver neoplasms that uses glass or resin microspheres to carry yttrium 90 (90Y), a high-energy, beta particle–emitting isotope. The microspheres, about the diameter of a human hair, are administered via a catheter by intra-arterial hepatic injection guided by fluoroscopy.

Once injected, the particles embed in the capillary network of the tumor. “The fact that this is not gamma radiation but short-penetrating beta radiation is of critical importance,” said Ravi Murthy, M.D., an associate professor in the Section of Interventional Radiology at M. D. Anderson. “Because the radiation is effective on adjacent tissue but does not ‘travel’ beyond the tumor, there are minimal effects outside the tumor itself.” Once placed, 90Y emits therapeutic doses of radiation for the next few days.

This procedure takes advantage of the fact that liver neoplasms are highly vascular and receive their blood supply via the hepatic artery, whereas the liver parenchyma receives its blood supply primarily through the portal vein. Since the blood supplies are independent, the injection can target tumor tissue and spare normal tissue.

A detailed arteriogram of the vessels leading to the tumor is done prior to the procedure to detect anatomic variations and aberrant vessels. An important part of this interrogation is to identify potential ways for the radioactive microspheres to disperse to locations other than the intended target, such as the gastrointestinal tract. Variations in anatomy are not unusual. For example, the gastric arteries may branch from the left hepatic artery in some patients and from the common, proper, or right hepatic arteries in other patients. A detailed study of vessels branching from the hepatic artery to supply various other organs is therefore essential before delivering radioactive microspheres into the hepatic vasculature. When potential outflow vessels are found, they are occluded by small coils.

Liver tumors also have a tendency to cause arteriovenous shunting. In such cases, there is a danger that the 90Ymicrospheres could pass through the tumor to the lung, causing radiation pneumonitis. To avoid this complication, a diagnostic dose of like-sized but harmless “surrogate” particles, technetium-99m–labeled macroaggregated albumin, is injected prior to radioembolotherapy. The distribution of the technetium-99m–labeled macroaggregated albumin will predict the distribution of the 90Y microspheres, allowing the radiologist to detect any risks from arteriovenous shunting.

At M. D. Anderson, 90Y radioembolotherapy of the liver is done with the patient under sedation, on an outpatient basis. Most patients experience mild side effects (fatigue and mild abdominal pain) for about 2 weeks following the procedure. Initially, treatments were given to half of the liver at a time, separated by a period of about 4 weeks, but with improvements in technique and supportive care, patients now generally receive only one treatment.

Currently, this procedure is offered only when other treatments have failed or are not feasible, but Dr. Murthy believes it has greater potential. “This treatment has a theoretical advantage in that it may significantly augment the benefits seen with systemic treatments when administered early in the disease process in select patients. Furthermore, the mild toxicities associated with radioembolotherapy may offer an effective alternative to diseases that are traditionally combated with other more toxic embolotherapies,” he said. And for that reason, he is eager to see it integrated into mainstream therapy.

For more information, call M. D. Anderson’s Division of Diagnostic Imaging at 713-745-4794.

Other articles in OncoLog, July/August 2008 issue:

• Multiple Myeloma: Increasing Response, Remission, and Survival Rates in a Complex Disease
• Beyond Images: Advances in Interventional Radiology
• House Call: A Guide to Radiation Therapy
• In Brief

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