
Tiny beads of glass or resin, called microspheres, can be impregnated with Yttrium-90, a radioisotope.  These beads can be injected into the hepatic artery, the main artery feeding the liver cells, and liver tumor cells. Tumor intake of the microspheres is much higher than that of normal liver tissue.  The microspheres serve not only to embolize [block or clot off supplying blood vessels to the tumor] but also to irradiate the tumor locally.   This would spare normal tissue from having as great an exposure to the radiation as the tumor would get.

This has been used for liver tumors which no longer respond to chemoembolization.  

Yttrium-90 impregnated GLASS microspheres are called TheraSpheres.  There is some concern that the glass is heavier than the resin, and tends to settle out downward during administration.

Yttrium-90 impregnated RESINS microspheres are called SirSpheres.  The resin, being lighter, is hoped to distribute more evenly in the blood supply.  I believe that SirSpheres are in clinical trial for liver tumors only, at this time.

This is a news release of May 2001, from the University of Maryland Medical Center:

"Cancer specialists from the University of Maryland Greenebaum Cancer Center report that early results of a new treatment for inoperable liver cancer, known as TheraSphere, are promising. They will report their findings at the 37th annual meeting of the American Society of Clinical Oncologists on May 15." 

"Forty-five patients have undergone the procedure there since its introduction last fall, ...Most patients have shown a positive response, as marked by a reduction in tumor size or number of lesions, with minimal side effects,..."

"Millions of microscopic glass beads containing the radioactive element, yttrium 90, are delivered via catheter into the femoral and hepatic arteries and transported directly to the liver. This mechanism allows a more concentrated dose precisely where it is needed most."

"... TheraSphere was approved by the U.S. Food and Drug Administration (FDA) last March for the treatment of liver cancer that cannot be treated surgically. The FDA granted MDS Nordion, which makes TheraSphere, a Humanitarian Device Exemption. This exemption, which permits the FDA to approve devices based on proof of patient safety alone, encourages further research and development for diseases that affect few patients."
 
"... Those less responsive to TheraSphere as a treatment option are patients who have larger liver tumors, for example. TheraSphere is a non-surgical outpatient procedure. Patients can return home the same day and treatment poses no safety threat to caregivers or family members."

" Side effects can include vomiting, mild fever, abdominal pain and gastric ulcers. Toxicities are evident in about 20 percent of patients treated. And though patients initially were treated with a single dose, the procedure is being evaluated as a two-part process in which the right lobe of the liver is treated and the left lobe is treated two to four weeks later. ... by splitting the dose, we are exposing the surrounding tissue to less radiation and decreasing the chance of the patient developing gastrointestinal toxicities. ... "


Int J Radiat Oncol Biol Phys 1990 Mar;18(3):619-23 
<b>Tolerance of the liver to the effects of Yttrium-90 radiation. </b>
Gray BN, Burton MA, Kelleher D, Klemp P, Matz L. 
University Department of Surgery, Royal Perth Hospital, Western Australia. 

There are no reliable data documenting the tolerance of the human liver to ionizing radiation from a continuous Yttrium-90 source. As Yttrium-90 incorporated into microspheres is being used to treat patients with liver cancer, it is imperative that the tolerance of the human liver to this form of radiation damage be determined. Four patients with metastatic liver cancer were treated with Yttrium-90 to deliver radiation doses above that considered tolerable when given by conventional external sources. Patients were monitored with serial estimations of liver function tests and between 7 and 9 months after treatment liver biopsies were performed. Histological examination of the liver biopsies confirmed only minimal changes in the normal liver parenchyma. <b>These data indicate that the human liver may tolerate relatively large radiation doses when delivered by Yttrium-90 microspheres embedded in the liver parenchyma as a number of discrete point sources.</b> PMID: 2318695 


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