The Non-Lethal Effects of - and High-Let Radiation on Cultured Mammalian Cells.

In analyzing post-irradiation growth kinetics of cultured mammalian cells, specifically T1-E human cells, this investigation shows that the shift in post-irradiation clone-size distributions toward small colonies is due to both radiation-induced division delay and increased generation times of the irradiated population. Evidence also indicates that the final shape of the final clone-size distribution is influenced by the age density distribution of the parent cells at the time of plating. From computer-generated delay time distributions it was determined that a large percentage of the parent population was found to be in the plateau phase at early growth times and evidence indicates that these cells may contribute heavily to the total population response to radiation. Clone-size distributions of cells exposed to various LETs were obtained by an image analysis technique, and it was found that the loss of large colonies was dose and LET dependent in what appeared to be a systematic way. Dose response data suggest two predominant subpopulations, resistant and sensitive cells, as evidenced by their biphasic behavior. It appears that the sensitive population responds via "single hit" kinetics and the resistant population via "dose squared" kinetics. The (alpha)-component for the sensitive population varied as a function of LET in a similar way to that for survival. The (beta)-component for the resistant population increased with LET in the range between. (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI). and decreased for higher LET values. The action cross section for this form of heritable damage appears to equal that of the geometric nuclear cross section of the cell, but was found to be different for resistant and sensitive cells. This difference may be due to the distribution of nuclear cross section which depends on the age distribution of the cell population at the time of radiation exposure. The RBE for the induction of small colonies, and the reduction of mean colony area resembles that for cell killing.