Tissue Distribution of Boron Compounds in Relation to Neutron-Capture Therapy of Cancer. ∗

Summary and Conclusions

1) Recent application of the atomic pile to the neutron-capture therapy of human brain tumors has focussed attention on the biological behavior of boron compounds. 2) Studies reported in mice and man indicate that borax and boric acid are rapidly absorbed and distributed throughout the body. Uptake by the various organs and tumor describes a family of similar curves such that the faster the rise in concentration, the higher and earlier is the peak. All tissues studied, except brain, reach a peak by 30 minutes. Borate is rapidly excreted by the kidneys as a “low-threshold substance” in a class with urea and sulphate, and clearance from the blood in mice proceeds with an exponential half-time of approximately 65 minutes. 3) Concentrations of borate in the tissues of normal mice are directly proportional to dosage for at least 2 hours after injection over a range of 18 to 700 μg/g body weight. 4) At equilibrium distribution, studied in nephrectomized mice, borate is uniformly distributed throughout the body water, with a 10 to 20% excess bound in the intracellular compartment. This excess is bound more tenaciously in brain than in other tissues and appears to be responsible for the toxicity of these compounds. 5) Study of the factors determining the concentration ratio between neoplasm and surrounding normal tissues indicates that boron-neutron treatment offers little promise for malignant tumors other than those of the brain.