TheraSphere
Encyclopedia
TheraSphere is a hepatocellular carcinoma
(HCC) treatment therapy
that consists of millions of microscopic, radioactive glass microspheres (20–30 micrometre
s in diameter) being infused into the arteries that feed liver tumors. These microspheres then embolize, lodging themselves in the liver's capillaries and bathing the malignancy in high levels of yttrium
-90
radiation. It is currently approved for patients as a neoadjuvant to surgery or transplantation by the U.S. Food and Drug Administration and is being used at a number of clinical centers in the United States.
(physical half-life of 64.2 hours or 2.67 days) and decays to stable zirconium-90. The average energy of the beta emissions
from yttrium-90 is 0.9367 MeV.
Following embolization
of the yttrium-90 glass microspheres in tumorous liver tissue, the beta radiation emitted provides a therapeutic effect. The microspheres are delivered into the liver tumor through a catheter
placed into the hepatic artery that supplies blood to the tumor (This is usually performed in a hospital's radiology suite and patients remain conscious throughout the procedure). The microspheres are unable to pass through the vasculature of the liver due to arteriolar capillary blockade and are trapped in the tumor. There they exert a local radiotherapeutic effect with some damage to surrounding normal liver tissue.
(RECIST), meaning their overall tumor burden decreased by 50% or more.
In a separate study based on follow-up data from 43 treated patients, 20 patients (47%) had an objective tumor response based on percent reduction in tumor size and 34 patients (79%) had a tumor response when percent reduction and/or tumor necrosis were used as a composite measure of tumor response.
Hepatocellular carcinoma
Hepatocellular carcinoma is the most common type of liver cancer. Most cases of HCC are secondary to either a viral hepatitide infection or cirrhosis .Compared to other cancers, HCC is quite a rare tumor in the United States...
(HCC) treatment therapy
Radiation therapy
Radiation therapy , radiation oncology, or radiotherapy , sometimes abbreviated to XRT or DXT, is the medical use of ionizing radiation, generally as part of cancer treatment to control malignant cells.Radiation therapy is commonly applied to the cancerous tumor because of its ability to control...
that consists of millions of microscopic, radioactive glass microspheres (20–30 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
s in diameter) being infused into the arteries that feed liver tumors. These microspheres then embolize, lodging themselves in the liver's capillaries and bathing the malignancy in high levels of yttrium
Yttrium
Yttrium is a chemical element with symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and it has often been classified as a "rare earth element". Yttrium is almost always found combined with the lanthanides in rare earth minerals and is...
-90
Isotopes of yttrium
Natural yttrium is composed of only one isotope 89Y. The most stable radioisotopes are 88Y which has a half-life of 106.65 days and 91Y with a half-life of 58.51 days. All the other isotopes have half-lives of less than a day, except 87Y, which has a half-life of 79.8 hours, and 90Y, with 64 hours...
radiation. It is currently approved for patients as a neoadjuvant to surgery or transplantation by the U.S. Food and Drug Administration and is being used at a number of clinical centers in the United States.
Description
TheraSphere consists of insoluble glass microspheres where yttrium-90 is an integral constituent of the glass. Each milligram contains between 22,000 and 73,000 microspheres. Yttrium-90 is a pure beta emitterBeta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
(physical half-life of 64.2 hours or 2.67 days) and decays to stable zirconium-90. The average energy of the beta emissions
Beta particle
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay...
from yttrium-90 is 0.9367 MeV.
Following embolization
Embolization
Embolization is a non-surgical, minimally-invasive procedure performed by an interventional radiologist and interventional neuroradiologists. It involves the selective occlusion of blood vessels by purposely introducing emboli.-Therapeutic applications:...
of the yttrium-90 glass microspheres in tumorous liver tissue, the beta radiation emitted provides a therapeutic effect. The microspheres are delivered into the liver tumor through a catheter
Catheter
In medicine, a catheter is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, or access by surgical instruments. The process of inserting a catheter is catheterization...
placed into the hepatic artery that supplies blood to the tumor (This is usually performed in a hospital's radiology suite and patients remain conscious throughout the procedure). The microspheres are unable to pass through the vasculature of the liver due to arteriolar capillary blockade and are trapped in the tumor. There they exert a local radiotherapeutic effect with some damage to surrounding normal liver tissue.
Efficacy
Low-risk patients with unresectable liver cancer appear to gain control over their malignancies for at least 2 years when treated with TheraSphere. They survived a median of 800 days compared with a median of 258 days for high risk patients (P <.0001) in a study of 140 patients (106 male). The patients underwent 238 administrations of the particles. Approximately 34% of patients responded to the treatment according to evaluation by Response Evaluation Criteria in Solid TumorsResponse Evaluation Criteria in Solid Tumors
Response Evaluation Criteria In Solid Tumors is a set of published rules that define when cancer patients improve , stay the same , or worsen during treatments...
(RECIST), meaning their overall tumor burden decreased by 50% or more.
In a separate study based on follow-up data from 43 treated patients, 20 patients (47%) had an objective tumor response based on percent reduction in tumor size and 34 patients (79%) had a tumor response when percent reduction and/or tumor necrosis were used as a composite measure of tumor response.