SAN FRANCISCOGlass microspheres embedded with yttrium-90 (TheraSphere)
infused into the liver appears to be a promising treatment strategy for mixed
hepatic cancers, with possible application in other cancers, according to a
poster presented at the 37th Annual Meeting of the American Society of Clinical
Oncology (ASCO abstract 1038).
The insoluble glass microspheres are delivered through a catheter to the
hepatic artery (via the femoral artery), and are trapped in the hepatic
capillaries. The mean sphere diameter ranges from 20 to 30 µm, and each
milligram contains between 22,000 and 73,000 microspheres.
The half-life of the beta radiation is 64.2 hours, said David A. Van Echo,
MD, professor of medicine, University of Maryland School of Medicine, and
director, New Drug Development Program, Greenebaum Cancer Center, Baltimore.
"The problem with radiation traditionally," Dr. Van Echo said,
"has been damage to normal tissues. This may be a way to overcome that and
deliver doses that sterilize tumors."
The extreme vascularity of tumors, along with the tortuosity and smaller
size of their vessels, allows preferential delivery of the microspheres to the
tumors rather than to normal tissues. "It is real simpleit is not
high-tech," he said.
Two to 5 weeks prior to TheraSphere treatment, patients underwent a hepatic
artery angiogram (HAA) to determine vascular anatomy and a technetium 99 MAA (macroaggregated
albumin) scan via HAA to determine regional perfusion and to detect
extrahepatic shunting. Six of 51 patients treated to date have been excluded
due to shunting to the lungs or GI tract of greater than 5% to 10%.
Dr. Van Echo said that the MAA scan predicts the microsphere capture rate
for the tumor and for normal tissue, because the albumin particles are the same
size as the microspheres.