Using the liver's unique vascular supply, millions of tiny microspheres charged with Y-90 are released into the hepatic artery in a carefully chosen location unique to that patient. The radioactive microspheres become implanted in the microvascular supply of the tumor where they become permanently trapped. The microspheres emit beta radiation over a period of two weeks.

Two forms of microsphere therapy are in use today: SIR-Sphere microspheres are made of resin, and TheraSphere's of glass. SIR-Sphere, manufactured by Sirtex, was approved by the FDA in 2003 and marked the first entry in the U.S. market of this form of targeted therapy for advanced liver tumors.

It is currently the only microsphere therapy approved by the FDA for use in treating colorectal liver metastases.

TheraSphere is manufactured by MDS Nordion and is available in the U.S. for treatment of hepatocellular carcinoma under a humanitarian device exemption from the FDA. Over time, our research regarding the role of microspheres has expanded to treating primary liver tumors, carcinoid tumors, and other forms of liver metastases originating in the breast and lung as well as ocular melanoma.

CLINICAL PRACTICE

The targeted nature of SIRT allows us to deliver 40 times more radiation directly to tumors than is possible with conventional radiation, resulting in extremely high response rates with very few serious adverse events.

This finding is particularly surprising given that the liver is one of the most radiation-sensitive organs in the body.

But chemotherapyinsensitive, unresectable tumors are being completely destroyed with a single treatment.

Microsphere therapy is succeeding where everything else has failed, especially when used early in the disease course. Microspheres have also been found to be more effective when given concurrently with state-of-the-art chemotherapy.

In our practice, we mostly use microspheres without concurrent chemotherapy, as a majority of patients are on a chemotherapy "break" to recover from some side effects, or their cancer is not responding to the current "best" chemotherapy.

Many less common tumors that do spread to the liver are also being eradicated. This is rewarding, since we are able to provide patients with a better quality of life with fewer side effects while in treatment and extend their life expectancy despite a disease state for which no treatment was previously available.

Due to significant advances in technology, the use of radiation therapy for liver tumors has increased greatly and is offered at hundreds of medical centers across the country. A recent report by the Millennium Research Group stated that embolization particle therapies such as radioembolization spheres are increasingly being used to treat liver cancer.

MRG anticipates that radioembolization procedures will increase at a compound annual growth rate of almost 20%, thanks to a growing number of institutions adopting radioembolization techniques and increased reimbursement coverage.

GROWING BODY OF RESEARCH

At the 2008 American Society of Clinical Oncology annual meeting, researchers from the Italian Society of Locoregional Therapies in Oncology reported data from a phase II study evaluating the use of microspheres in patients with advanced colorectal liver metastases refractory to standard chemotherapy. According to the prospective trial, the use of Y-90 microspheres resulted in a median survival of 13 months.¹