Radiobiological considerations concerning the development of compounds for boron neutron capture therapy.

An analysis is carried out to evaluate the suitability of compounds for boron neutron capture therapy (BNCT). Suitable boron compounds are not necessarily those that show a high uptake ratio between tumor and healthy tissue. Compounds with lower uptake ratios, but higher concentrations in both healthy tissue and tumor, can be as effective in increasing the dose to the tumor over that of healthy tissue. In compound synthesis and evaluation, the parameters for optimization should therefore not be limited to the uptake ratio. A final assessment of the question whether and how well a given compound is suitable for BNCT can only be made after a study of its radiobiological effects on tissue. The analysis also illustrates the importance of beam quality in thermal and epithermal BNCT. An increase of adventitious radiation must be compensated by higher absolute tissue levels of a given boron compound and/or a higher uptake ratio, in order to arrive at the same dose differential between tumor and healthy tissue.