Radioisotope may extend brain cancer survival rate

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Researchers at Duke University have discovered that the isotope astatine-211 has enough potency to kill residual cancer cells without damaging sensitive healthy brain cells, as well as extend survival rates among patients, according to a study published in the January issue of the Journal of Nuclear Medicine.

“Astatine-211 has as much as five times or more cell-killing efficiency than the standard treatments of external beam radiation or beta-particle injection,” said Michael R. Zalutsky, professor of radiology and biomedical engineering at Duke University Medical Center in Durham, N.C., and co-author of the study.

The purpose of the study was to determine safe dosages of the isotope astatine-211 for treating patients with recurring brain tumors. The radioisotope was chemically linked to the antibody 81C6, and was then administered to 18 patients with recurrent malignant brain tumors by injection into a surgically created cavity from which the visible tumor had been removed.

According to researchers, because alpha particles, such as those emitted by astatine-211, are large and more highly charged, compared to the much smaller and faster beta particles, they are able to travel to a depth of only two to three cells into the affected area, which is enough to deliver the fatal payload.

Compared to other alpha emitters, astatine-211 has a relatively short lifespan (approximately seven hours), which means that the radioactivity falls off rapidly and patients experience few if any side effects.

In this first study evaluating astatine-211 as a targeted radiotherapeutic agent in cancer patients, researchers expected to determine only dose-limiting toxicity (the amount of isotope necessary to destroy the cancer without killing healthy tissue). However, they also discovered that many patients experienced an extended survival rate, ranging from an average of 52 weeks to three years (compared to 26 weeks for most recurrent brain tumor patients).

“There is an incredible need for brain cancer treatments, and this finding gives us a potentially valuable weapon in this fight,” said Zalutsky, who noted that brain tumors recur with an extremely poor prognosis.

The researchers said that future studies may use a “radiotherapeutic cocktail” of both alpha and beta particles attached to the same monoclonal antibody to deliver a treatment with a wider range for larger tumors along with a more focused radiation for smaller tumors or residual cancer cells.

Additional studies propose using astatine-211 on other “compartmentalized” cancers, such as ovarian and breast cancers that have spread to the central nervous system. All of these studies, however, will be delayed unless adequate quantities of astatine-211 can be produced, according to Zalutsky and colleagues.