Radiation effect of gadolinium-neutron capture reactions on the survival of Chinese hamster cells.

In gadolinium-neutron capture reactions, prompt gamma rays with an energy spectrum of up to 7 MeV, X-rays and electrons are released. We measured the effect of radiation as a result of capture reactions on cultured Chinese hamster cells. Cells in the medium containing 5000 ppm gadolinium were exposed to thermal neutrons from a nuclear reactor. The survival curve for those cells exhibited a shoulder in the low neutron fluence region. The survival curve for cells exposed to thermal neutrons in the absence of gadolinium was a simple exponential function. To obtain 10% survival levels, 5.4 x 10(12) neutrons/cm2 were required for cells irradiated in the absence of gadolinium, and 1.55 x 10(12) neutrons/cm2 for those irradiated in the presence of gadolinium. The therapeutic ratio in gadolinium-neutron capture therapy depends on the difference in 157Gd concentrations between the tumor and normal tissues. Thus, our current effort has been to develop a method of selectively delivering 157Gd to tumors.