The effect of age on the long-term response of bone marrow to local fractionated irradiation

The in-field long-term progressive response of bone marrow to localized fractionatedradiation to the thoracic spine was observed in weanling and adult rats. Total dose levels were 1800,3600 and 5400 rads given in daily fractions of 180 rads for 900 rads perweek, to simulate the clinical setting. Animals were sacrificed at 4 1/2, 6, 8, and 10months after irradiation, and bone marrow from within the treated area was ezamined. The juvenile marrow repopulated to higher levels of cellularity and after higher doses of radiation than the adult. The degree of marrow depletion, time of repopulation, and ultimate level of repopulation after cessation of irradiation were all dependent on the total dose. Some of the suggested clinical implications include re-evaluation of the lower doses given to children.