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

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Abstract
The effect of dose rate on X-ray-induced skin reactions was determined for 1, 2 and 10 fractions using the mouse foot system. Doses of 1.6, 0.15 and 0.06 Gy/min were employed and the time-course-dependent effects were analyzed using an extension of the formulation by L. G. Lajtha and R. Oliver. The time for decay of the effective dose to 1/e of its initial value, .tau., was 114 .+-. 28 min. On the basis of this analysis, predictions were made for split-dose and pulsed irradiations. These were consistent with measurements obtained using such irradiation protocols. Dose fractionation, low-dose-rate, split-dose and pulsed irradiation effects apparently can be handled conceptually as different particular examples of variable time-course irradiations. This analysis was 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.