With its beryllium and graphite-reflected core
and flux of 6 x 1014 n/(cm2 sec),
MURR can produce the needed flow of neutrons to make even minute
amounts of "target" material highly radioactive in
a precisely controlled manner. This pure, highly concentrated
sample of radionuclide can be attached to the guiding biomolecule,
often using another molecule as a go-between—a kind of "super
glue." Upon injection into the patient, the biomolecule
seeks out the tumors, bringing along with it the radionuclide
to destroy the "bad" cells with its radiations. An
advantage of using a nuclear reactor to produce these radionuclides
is that the radiation they emit—beta radiation—cannot travel
more than 1/4 inch in the body, limiting its damage to the cancerous
tissue and avoiding neighboring healthy cells.
In recent years researchers at MU and MURR have focussed on
a class of radioactive atoms called the radiolanthanides. These
radionuclides all have very similar chemical behavior, but they
have different beta radiation energies and emit their radiation
at different rates. These rates are called "half lives."
Because of chemical similarity, the radiolanthanides can all
use the same super glue to attach to guiding biomolecules. However,
some guiding biomolecules take longer than others to reach their
targeted tumor sites in the body; radiolanthanides with longer
half lives are best with these. On the other hand, a shorter
half-life is better for guiding molecules that attach to sites
of cancer quickly. The range of energy and half-life choices
of the radiolanthanides, when coupled with the precise targeting
ability of the biomolecule, gives great versatility for treating
tumors of different types and sizes.
Often, the guiding molecules can be used in the body in only
very small amounts, and each molecule can have only one radioactive
atom attached to it. Thus, it is important that as high a fraction
of the sample as possible be radioactive. This is called achieving
a "high specific activity." MURR is one of the few
reactors in the world that can supply very high specific activity
radiolanthanides such as Lutetium-177, Samarium-153, and Holmium-166.
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University of Missouri-Columbia
