BORON NEUTRON-CAPTURE THERAPY OF INTRACEREBRAL RAT GLIOSARCOMAS

The efficacy of boron neutron capture therapy (BNCT) for the treatment of intracerebrally implanted rat gliosarcomas was tested. Preferential accumulation of 10B in tumors was achieved by continuous infusion of the sulfhydryl borane dimer, Na410B24H22S2, at a rate of 45-50 μg of 10B per g of body weight per day from day 11 to day 14 after tumor initiation (day 0). This infusion schedule resulted in average blood 10B concentrations of 35 μg/ml in a group of 12 gliosarcoma-bearing rats and 45 μg/ml in a group of 10 similar gliosarcoma-bearing rats treated by BNCT. Estimated tumor 10B levels in these two groups were 26 and 34 μg/g, respectively. On day 14, boron-treated and non-boron-treated rats were exposed to 5.0 or 7.5 MW·min of radiation from the Brookhaven Medical Research Reactor that yielded thermal neutron fluences of ≃2.0 x 1012 or ≃3.0 x 1012 n/cm2, respectively, in the tumors. Untreated rats had a median postinitiation survival time of 21 days. Reactor radiation alone increased median postinitiation survival time to 26 (5.0 MW·min) or 28 (7.5 MW·min) days. The 12 rats that received 5 MW·min of BNCT had a median postinitiation survival time of 60 days. Two of these animals survived >15 months. In the 7.5 MW·min group, the median survival time is not calculable since 6 of the 10 animals remain alive >10 months after BNCT. The estimated radiation doses to tumors in the two BNCT groups were 14.2 and 25.6 Gy equivalents, respectively. Similar gliosarcoma-bearing rats treated with 15.0 or 22.5 Gy of 250-kilovolt peak x-rays had median survival times of only 26 or 31 days, respectively, after tumor initiation.