The application of a low-background neutron autoradiographic technique for determining10 B concentration and intracellular distribution in mammalian tissue is described. Knowledge of10 B concentration and distribution on a cellular level is necessary to evaluate the effects of irradiation when using the <tex-math>${}^{10}{\rm B}({\rm n},\alpha)^{7}{\rm Li}$</tex-math> reaction in experimental therapeutic procedures. Conventional boron analysis is not capable of extracting this information. The use of freeze-dried tissues, dry-mounted on nuclear emulsion, makes the technique applicable to water-soluble compounds used in previous clinical trials, as well as to water-insoluble proteins. Absolute concentrations of10 B in the form of sodium pentaborate were measured in mouse spleen, liver, kidney, muscle, tumor, and brain, 30 minutes after intraperitoneal injection, and compared to results from three other laboratories using conventional analysis. Boron concentrations similar to those used in previous clinical trials were evaluated to demonstrate the feasibility of the method. No intranuclear or extracellular concentration was observed; evidence is given to demonstrate the absence of leaching of the water-soluble compound. The method described will be useful in evaluating the newer boron compounds attached to proteins. The intracellular distribution of these compounds is of particular interest, since it is not clear that all proteins are capable of penetrating cell walls.

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