title: Multifraction radiation response of mouse lung.
abstract: The response of mouse lung to repeated doses of 60Co gamma-rays of as low as 115 cGy per fraction was measured using death from pneumonitis between 80 and 120 days after irradiation as the endpoint. A fractionation interval of 3 h was maintained for most regimens but in the longer experiments some 12 h intervals were introduced for logistic reasons. The longest overall duration (for a 43 fraction regimen) was 8 days. The total doses required to produce 50 per cent mortality increased continuously as dose/fraction was decreased, even from 160 to 115 cGy per fraction. Of clinical relevance, the steepness of the isoeffect curve over the dose range 115-500 cGy indicates that the lung shows greater sparing from dose fractionation than is characteristic of more rapidly-responding normal tissues, resembling, in this respect, other more slowly-responding tissues such as spinal cord. The plot of the reciprocal of the LD50 values as a function of dose per fraction was non-linear, suggesting that a linear quadratic dose response model may not be appropriate or that repair of cellular injury in lung is not complete in 3 h, or both.
mesh_terms: D000818:Animals; D003037:Cobalt Radioisotopes; D005260:Female; D005720:Gamma Rays; D007928:Lethal Dose 50; D008168:Lung / Q000528:radiation effects*; D008297:Male; D051379:Mice; D011829:Radiation Dosage; D011833:Radiation Injuries, Experimental / Q000401:mortality
chemical_list: D003037:Cobalt Radioisotopes