Bone growth retardation induced by single and multifractionated irradiation

The right hind legs of 12- to 14-week-old mice were exposed to single and multifractionated courses of gamma-ray irradiation. The recovery curves, time-dose relationships, and fraction number-dose relationships were analyzed using femoral growth retardation as an endpoint. The bones grew 2 mm, about a 10% increase over their original lengths, in 12 months; and 63% and 85% in volume in 6 and 12 months, respectively. The ratio of the volume increase of the irradiated right leg per unit time, the actual growth, to the volume increase of the non-irradiated left leg, the potential growth, was calculated for each mouse. The doses necessary to produce a given degree of bone growth retardation in 50% of the tested animals were calculated for each treatment schedule. The isoeffect doses for a given degree of bone growth retardation after 2 and 4 equal fractionation exposure increased (peak at one day-interval) and decreased (trough at 2-day interval), and later increased additionally with increasing time intervals between doses.