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49% of the time, a 478 keV photon is emitted in the nuclear decay of 7Li.
The range in tissue of 7Li and 4He (alpha particle) is approximately 5 m m and 8 m m respectively, i.e. about the diameter of a tumor cell (~ 10 m m).
A few alpha particles suffice to destroy a tumor cell. The killing
effect of the capture reaction would occur mainly in those cancer cells
that have selectively accumulated boron. The normal cells that have not
incorporated important amounts of boron will not suffer significant
damage.
The total dose deposited by BNCT results from the 10B capture reaction
(large capture cross section), capture reactions with tissue hydrogen
and nitrogen which produce gamma-rays and protons respectively, the
gamma component of the beam, epithermal and fast neutrons. The nature
and distribution of these dose components depend on the source of
neutrons, the filters employed, the concentration and distribution of
the boron compounds and the tissue composition.
Clinical Applications BNCT is mainly being used in Japan, Europe and the United States
for malignant brain tumors such as glioblastoma multiforme
(GBM). Although the statistics is no better than those with the
standard methods, new strategies are under development to
improve the results. Melanoma in different locations is also an encouraging BNCT
application, with good results in Japan, United States and
Argentina. BNCT applied to head and neck tumors is also giving
interesting results in Finland and Japan, It is worth mentioning
the Italian innovative contribution for treatment of hepatic
colorectal metasatases. |
