Boron-10 concentrations of 20 or 40 micrograms/g were attained in mouse
B16 melanomas following one or two intragastric doses of
p-boronophenylalanine (750 mg/kg
body weight per dose), respectively.
Tumor-to-normal-tissue (blood, muscle)
boron concentration ratios were 4:1-6:1. The efficacy of
boron neutron capture irradiation was monitored using the Wilcoxon two-sample test in conjunction with a system of ranking outcomes of different
therapies that compared living mice and mice sacrificed because of excessive
tumor growth concomitantly. Median survivals were extended progressively as radiation doses were increased up to 38.7 gray-equivalent (gray X relative biological effectiveness), with one of five and one of six
tumors cured in each of the two highest dose groups, respectively. When comparable
tumor inhibitory doses of 250-kVp X rays were used to treat these
tumors, instead of the transient
erythema and
edema that resulted from
boron neutron capture therapy, there resulted irreversible muscle
necrosis in the irradiated zone and
atrophy of the foot distal to the irradiated zone. The improvement in treatment outcome with
boron neutron capture therapy is attributable to unprecedented
tumor-to-normal-tissue radiation dose ratios of approximately 2.8 to 3.6.