Regeneration of bone marrow in rabbits following local, fractionated irradiation

Serial studies have been designed to examine the in-field regeneration of bone marrow in rabbit limbs treated with various fractionated dose schedules of irradiation. The total dose levels ranged from 2,000-5,000 rads with doses of 200 rads/day to 1000 rads/week. This schedule was followed to simulate the clinical setting. A double marker of 99mTc-S colloid and 59Fe was employed to measure the activity in the reticuloendothelium (RE) and erythron compartments. The results of these studies are at variance with the published animal data which utilized single exposures and indicated that suppression of bone marrow is permanant at doses exceeding 2,000 rads. The presented evidence indicates that bone marrow tolerance is greater for fractionated dose irradiation than for single exposures to the same levels.