Wednesday, January 19, 2011

Japan's National Cancer Institute running clinical trials for a new form of radiation therapy

Particle-accelerator-based boron-neutron capture therapy (BNCT), a new form of radiation therapy that promises to be more effective at eliminating certain tumors, has begun clinical trails in Japan.

Many forms of cancer are quite difficult to treat with current modalities, the dreaded glioblastoma multiforme (a particularly deadly form of brain tumor) comes to mind. It's shown nearly complete resistence to all the conventional, and some less common, treatment methods; The 5-year survival rate for someone diagnosed with a GBM sits at less than 5%. But thanks to a new form of radiation treatment being tested in Japan by the National Cancer Institute, patients with tumors like GBMs may soon see a huge improvement in survival.  

The new form of radiation therapy is called boron-neutron capture therapy (BNCT). It has actually been around for quite some time, but it's potential for clinical use has been limited for a variety of reasons; The requirement that the treatment facility house a nuclear reactor being the limiting factor.

The principle behind the entire process is that boron-10, a non-radioactive form of the element boron, is irradiated with high-energy neutrons, producing damaging alpha particles along with recoil-Lithium nuclei. The alpha particles have high energies, but because the distance they travel is so small (a few micrometres), they generally only damage cells that contain boron-10: in this case the cancer cells.

A patient going in for treatment of a GBM, for example, would get an injection of a boron-10-containing chemical. The chemical would be selective in that it would get absorbed only by the tumor cells and not by the patient's healthy, normal cells. The patient would then have their head placed near a neutron source, where a short burst of neutrons would be directed at the patient's head. The resulting alpha particles would then destroy only the cancer cells.

The treatment is specific to cancer cells, and can also treat metastatic disease: cancer that has spread to other parts of the body. So why hasn't it been used up until now? The primary reason, as mentioned earlier, is the need to build a nuclear reactor near every treatment machine that's being used, it's simply too impractical and extremely expensive.

The most recent studies show that neutrons produced by particle accelerators instead of nuclear reactors are a feasible, and far more cost effective, method of providing the much needed neutrons. These accelerators are similar to the ones currently used for external-beam radiation therapy, but much larger, more expensive,  and operating at higher energies.

Although Japan is the first country to begin using this form of therapy in clinical trials, many other countries have jumped on board to implement BNCT in hospitals and clinics, including the United States, European countries, and Argentina.

Sufferers with cancers of the liver, brain, and extremely invasive melanomas (skin cancers) have the potential to see large improvements in their survival with this new mode of therapy. An exciting development to keep posted on in the near future, that's for sure.

References:

Barth RF, Coderre JA, Vicente MGH, Blue TE. 2005. BNCT of Cancer: Current Status and Future Prospects. Clin Cancer Res; 11: 3987.
Suzuki M, Tanaka H, Sakurai Y. 2009. Impact of accelerator-based boron neutron capture therapy (AB-BNCT) on the treatment of multiple liver tumors and malignant pleural mesothelioma. Radiother. Oncol; 92(1): 89-95.
 
Suzuki M, Sakurai Y, Hagiwara S, et al. 2006. First Attempt of Boron Neutron Capture Therapy (BNCT) for Hepatocellular Carcinoma. Japanese Journal of Clinical Oncology; 37(5): 376-381. 

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