The kinetics of cellular recovery in exponential and plateau growth phase human glioma cells following gamma-irradiation.

PURPOSE

In this study the kinetics of recovery following irradiation was examined in a human glioma cell line. Specific objectives were: to determine whether recovery is mono- or biexponential in nature; to determine if recovery half-times are different in exponential and plateau growth phase cells; to compare recovery half-times as a function of dose or recovery levels; and finally, to compare the kinetics of sublethal damage recovery and potentially lethal damage recovery in plateau growth phase cells.

METHODS AND MATERIALS

U-87MG cells were irradiated in exponential and plateau growth phases and then subjected to incubation at 37 degrees C for various periods of time following or between doses prior to assaying for survival. Survival recovery curves were fit to a sum of exponential terms.

RESULTS

Potentially lethal damage recovery was monoexponential in both exponential and plateau growth phase cells and occurred at the same rate when isorecovery values were compared. Recovery half-times increased in an exponential manner within the observed dose range. Recovery between doses of radiation (sublethal damage recovery) proceeded at a slower rate than recovery following a single dose of radiation (potentially lethal damage recovery).

CONCLUSIONS

This study suggests that potentially lethal damage recovery is a saturated process and that the recovery half-time may increase in a linear-quadratic exponential function of dose similar to the absolute recovery level. In addition, if iso-recovery levels are compared, the recovery half-time is similar in rapidly and slowly proliferating cell populations.