Electron-equivalent dose for the effect of gadolinium neutron capture therapy on the growth of subcutaneously-inoculated Ehrlich tumor cells in mice.

The present in vivo study estimates the dose resulting from the gadolinium neutron capture reaction and the gadolinium enhancement extent of the thermal neutron effect. The assay is based on the time required from cell inoculation to the formation of tumors with an arbitrary size of 200 mm2. Mice were inoculated subcutaneously with Ehrlich tumor cells with or without meglumine gadopentetate (1.2 mg 157Gd/0.2 ml), and were exposed to 1.1 x 10(12) thermal neutrons cm-2(n 8), or 3 MeV electrons at three dose levels (each n 10). To reach 200 mm2 in size, it took 18.8 days for tumors treated with neutrons only and 34.7 days for those treated with gadolinium and neutrons. From the time-dose relation obtained with 3 MeV electrons, the equivalent doses corresponding to delays of 34.7 and 18.8 days were 15.0 and 7.4 Gy, respectively. Thus, gadolinium enhanced the thermal neutron effect two-fold (15.0/7.4) in the present study.