Relationship Between Tumor Growth and Radiosensitivity

Abstract

To answer certain questions concerning the relationship between tumor growth and radiosensitivity, survival curves for a strain-specific murine leukemia (P-388) were determined with cells irradiated in vivo, in vitro, and “in situ” at various times following the transplantation of 10⁶ cells per recipient. It was found that the D₀ has a value of 110 r (Co⁶⁰ γ-radiation) for the survival curve of cells of 1-day growth; this value increases to about 400 r for cells 4 and 7 days post transplantation. In addition, variation of the extrapolation number was observed, which generally was inversely related to the rise in D₀ The finding of an extrapolation number for 3-day tumor cells of in vitro or in vivo in animals killed 15 minutes before exposure (referred to as irradiated in situ) at various times post transplantation. Radiosensitivity of cells irradiated in vitro or in situ appeared to be independent of growth stage. Survival-curve parameters in vitro were: n = 4.5, D₀ = 151 r; in situ n = 7.2, D₀ = 415 r. The ratio of the reciprocal of the final slopes (2.7) agrees with the oxygen-enhancement ratios reported for other mammalian cell strains.