Quantification of Morphologic, Cytologic, and Kinetic Parameters of Unirradiated Swine Skin: A Histologic Model

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Abstract
The gross changes of erythema and desquamation produced by irradiation indicate population and functional variations occurring in the epidermis, microvasculature and dermis. However, the parameters do not distinguish the individual populations kinetics. A study was therefore done to determine multiple histologic and cell kinetic parameters of unirradiated swine skin. The prickle cell layer exists as a shell 3-6 cells thick. The proliferative basal layer exists as a confluent monolayer with 2031 .+-. 48 cells/cm; it has a growth fraction of 1, an average cell generation time of 12.3 .+-. 2.4 days, a TS of 9.4 .+-. 2.9 h and a TS + TG2 + T1/2M of 17-19 h. The labeling index is 3.9 .+-. 0.1% with a diurnal variation having a 5% peak at 1800 h and a 2.5% nadir at 0900-1100 h. The mitotic index varies from 1.7 to 3.2% and has no clear-cut diurnal variation. These values are similar to those available for man. These data and those published previously are utilized to define a histologic model of the irradiated epidermal cell renewal system. These measured values are compared with those derived from analysis of available time-dose isoeffect data using a single-hit multitarget and a linear-quadratic model. The derived dose-survival curve is steeper with a D0 between 97 and 255 rad compared to the measured value of 337 rad.