Explanation of Dose-Rate and Split-Dose Effects on Mouse Foot Reactions Using the Same Time Factor

The effect of dose rate on X-ray-induced skin reactions was determined for 1, 2, and 10 fractions using the mouse foot system. Data for 1.6, 0.15, and 0.06 Gy/min were obtained, and the time-course-dependent effects of these experiments were analyzed using an extension of the formulation by L. G. Lajtha and R. Oliver (Br. J. Radiol. 34, 252-257, 1961). r, the time for decay of the effective dose to 1/e of its initial value, was determined to be 114 + 28 min. On the basis of this analysis, predictions were made for split-dose and pulsed irradiations. These were consistent with experimentally measured results obtained using such irradiation protocols. Thus it has been shown that dose fractionation, low-dose-rate, split-dose, and pulsed irradiation effects can be handled conceptually as different particular examples of variable time-course irradiations. In addition, this analysis has been used to generate guidelines for minimum acceptable dose rates consistent with acute exposure and minimum fraction intervals consistent with complete repair, to assist in the design of future multifraction experiments using the mouse foot system.