CAPACITY AND KINETICS OF SLD REPAIR IN MOUSE TONGUE EPITHELIUM

The effect of dose fractionation- on the radiation response of mouse t ongue epithelium was quantified in fractionation protocols involving 1 , 3, 4, 5 and 10 fractions, separated by at least 4 h. Fractionated ir radiation was given either to the whole snout by 300 kV X-rays or loca lly to the tongue using 25 kV X-rays. Each protocol was terminated by a final local top-up dose (25 kV X-rays) of 5 Gy. The frequency of com plete local denudation within the test area was used as the quantal en d point. The kinetics of repair of sublethal damage was studied by sno ut irradiation with four equally spaced fractions, delivered at interv als of 35, 60, 90, 480 or 540 min, again followed by a local top-up do se of 5 Gy. The linear-quadratic model gave a satisfactory fit to the data [40] with the exception of the four fraction/30-h data, suggestin g cell cycle effects in this schedule. Analysis of the results with di fferent two-step methods and with direct analysis [371 yielded similar results. The alpha/beta ratio was determined to be approximately 11 G y (direct analysis: 11.6 Gy with 95% confidence limits of 8.1 and 16.4 Gy) and T1/2 was found to be 46 min (35-69 min). Both these values ar e in the range described for other acutely responding rodent tissues.