Will Supply Problems Limit Radioimmunotherapy Advances?

In the Feb. 4 issue of this magazine, William Hubble, MA, CNMT, RT(R)(N)(CT), our "View From the Hot Room" columnist talked about the problems caused by the shortage of imaging isotopes (in particular Tc-99m) because of the shutdown of the Chalk River accelerator. While that shortage had an immediate effect, the problems with isotope supply go further than just the technetium supply.

For instance, in the JNM recently reported great promise for treating brain tumors with the isotope astatine-211.

According to a press release about the article, surgeons can remove the tumor bulk from the brain but  they are unable to see any residual cancerous cells that have escaped to areas of apparently healthy tissue surrounding the tumor site. Scientists are interested in using radioimmunotherapy with alpha emitting isotopes, such as astatine-211 to seek out and destroy these cells, which can otherwise grow into new tumors.

Michael R. Zalutsky, professor of radiology and biomedical engineering at Duke University Medical Center in Durham, N.C. is quoted as saying, "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."  He noted that the ability to deliver such a potent cancer killer without causing neurotoxicity (damage to the delicate neurological system that controls brain function) would be a tremendous step forward in combating this lethal disease.

In this first study 18 patients with recurrent malignant brain tumors were injected with astatine-211 linked to an antibody known to seek out and bind specifically to brain tumor cells. The injection was made into the surgical cavity from with the tumor was removed.  Although the study was being performed only to evaluate the dose-limiting toxicity of the agent, they found that many patients experienced an extended survival rate, ranging from an average of 52 weeks to 3 years (compared to 26 weeks for most recurrent brain tumor patients), according to the SNM press release.

Although this seems to give promise to the use of radioimmunotherapy, study of this and other radiotherapy agents may be delayed because there are only three places in the U.S. where this isotope is produced.

The article quotes Dr. Zalutsky, who contributed to the 2007 National Academy of Sciences report that encouraged Congress to increase funding for nuclear medicine research and treatment as saying, "Patients eligible for such studies will be put on hold until our nation invests significantly in the research needed to eradicate these killer diseases."

It is disheartening to think that potential radiotherapies might be lost because of the lack of radioisotopes for research into new treatments. I remember talking to one researcher a few years ago who noted that she had get her supply of a particular therapy isotope from Russia.

As Hubble notes we need to make sure we have an adequate and reliable supply of radioisotopes if we are going to evolve as a modality promoting molecular imaging and therapy. The SNM is working hard at this task, but it needs the help of each of us to respond to calls to contact our legislators when SNM representatives go to congress to ask for funding. It only takes a minute to send a personal message to your congressman supporting CARE or opposing budget cuts. And though the reply you get may come from their assistant, the voice of a constituent does matter to them and to the continuing success of the nuclear medicine field.