Response of cells to fast neutrons, stopped pions, and heavy ion beams

Abstract

The delta-ray theory of the inactivation of cells by energetic heavy ions, shown earlier to represent experimental survival curves for bacterial spores, haploid yeast, HeLa, Chinese hamster, and T-1 human kidney cells, in the cellular grain-count regime (where inactivated cells are strung on the path of a heavy ion) is here extended to bacteria, diploid yeast, leukemia cells, and the cellular track-width regime (where even cells which are not intersected by the ion's path are activated, by energetic delta-rays). When the four cellular radiosensitivity parameters of the model are known for a cellular variety in a specific set of ambient conditions, the model may be applied to the evaluation of cellular survival in an arbitrary radiation environment, for which the secondary particle spectrum is known or negligible. For such a mixed environment, the solution to the problem of cellular survival is formulated in general terms, and is then made specific to 14 MeV neutrons, stopped pions (as in the Bragg peak of a pion beam), and heavy ion beams. Calculated survival data for 14 MeV neutrons and energetic nitrogen beams are compared to existing data. Difficulties arising from the use of incomplete parameterizations of experimental data (based on the assumption that response is a single valued function of LET, and so on) are discussed.