The Minimum D₀ for Cell Killing for Alpha-Particle Emitters Uniformly Distributed in an Extended Medium

For cells irradiated by α particles in suspension, there is presently no simple test to show that the cell killing can be attributed to α-particle passages through the nuclei. In this communication, for a uniform distribution of α-particle sources and spherical nuclei, a D₀ is calculated such that at least 63% of the cell nuclei have at least one α-particle passage. For a uniform distribution of α-particle sources and spherical nuclei, it is shown that the average dose for 63% of the cell nuclei to be hit (37% not hit) is equal to the average dose per hit. For this condition an energy deposition of any size would result in cell death and the average dose is the minimum D₀ possible. Minimum D₀ values are calculated using a Monte Carlo treatment for nuclear diameters from 4 to 10 μm and initial α-particle energies between 3.18 and 8.38 MeV.