Boron Neutron Capture Therapy (BNCT) is treatment for cancerous tumours which lie deep within the body. It has shown great promise for glioblastoma multiforme, a very malignant type of brain tumour which is extremely difficult to treat successfully using traditional methods. It is still a relatively new treatment and there are few places in the world that offer this course of therapy.
The BNCT method exploits the fact that a naturally occurring isotope of boron, 10B, has an unusually high probability of capturing low energy neutrons. This capture can release energetic, heavy particles, which interact readily with cell tissues.
The therapy involves intravenously injecting a boronated chemical, which is known to be more readily absorbed by malignant cells than healthy cells, into the patient some time before treatment begins. This chemical, with its attached boron, then accumulates almost exclusively in the malignant cells. The patient is then exposed to a beam of neutrons in the general area that is affected.
The useful reaction path is
10B + n -> 7Li + 4He
and the energy of the particles is 2.8 MeV. These particles deposit their energy into the cell as they crash through its internal structure, killing it. They stop within a radius similar to intracellular distances, so the damage is localised to the tumour cells only.
The above only illustrates one reaction path, the most common reaction releases only gamma radiation (with energy of 478 keV), which escapes harmlessly from the patient's body. Although this does not damage the tumour in any way, it is still useful. It can be used to monitor the number of successful boron-neutron interactions. Experiments are also being carried out where this radiation is used to form a hologram of the tumour, using incoherent holography techniques. If used over successive treatments this can be used to monitor how the tumour size and shape is changing without the need for any additional observations to be carried out.
A problem with this method is that neutrons are difficult to produce, most sources are presently from a nuclear reactor, but work is being carried out on using particle accelerators as a source. This has possibility of allowing the treatment to take place in a hospital. Accelerators also produce neutrons with more desirable energies.
http://www.bnct.net/
http://www.bham.ac.uk/physics/ap/bnct/