Biodistribution of boron in dogs with spontaneous intracranial tumors following borocaptate sodium administration

Borocaptate sodium (Na2B12H11SH) is a potentially useful compound for boron neutron capture therapy of intracranial tumors. Tumor and normal tissue boron concentrations were evaluated in 30 dogs with naturally occurring intracranial tumors after i.v. borocaptate sodium infusion (55 mg boron/kg). Postmortem tissue boron concentrations were measured for three postinfusion time periods (2, 6, and 12 h) by inductively coupled plasma atomic emission spectroscopy. Mean boron concentrations for extracerebral tumors were 40.6 +/- 16.9 (2 h; n = 8), 25.9 +/- 11.7 (6 h; n = 5), and 8.6 +/- 4.5 micrograms boron/g (12 h; n = 6). Mean boron concentrations for intracerebral tumors were 30.6 +/- 17.5 (2 h; n = 7) and 2.9 +/- 1.8 micrograms boron/g (6 h; n = 4). Mean tumor boron concentrations were lower at longer postinfusion times. The tumor:normal brain boron concentration ranged from 0.8 to 19.8. Tumor:blood boron concentrations were less than one for all but three dogs and ranged from 0.04 to 1.4. Mean peritumor boron concentrations were highly variable but exceeded that of normal brain in 10 of 20 dogs. In some dogs, the mean peritumor boron concentration was similar to or exceeded the tumor boron concentration. Distant or contralateral normal brain had consistently low boron concentrations. Some cranial and systemic tissues had high boron concentrations, indicating substantial extravascular boron. The spontaneous animal tumors provided a realistic spectrum of data and enabled extensive sampling of diseased and normal tissues. The biodistribution of boron from borocaptate sodium administration was partially favorable because of high tumor boron concentrations. Empirical radiation dose tolerance studies should be used to determine the impact of the unfavorably high boron concentration of blood and some cranial tissues.