title: Repair in the mouse lung during low dose-rate irradiation.
abstract: The thorax of CBA mice was exposed to 60Co gamma-rays at dose rates ranging from 100 to 2 cGy/min. Iso-effect doses (ED50) were calculated for early and late lung damage from dose-response curves for breathing rate and lethality. A continuous increase in tolerance for early radiation pneumonitis was seen as the dose rate was reduced, reaching a dose recovery factor (DRF) of 2.6 at 2 cGy/min. There was significantly less dose sparing with 2 cGy/min for the rise in breathing rate during expression of late damage (DRF = 2.1). The lower DRF compared well with that obtained from late measurements of pleural fluid levels. Comparison with fractionation experiments indicated incomplete repair at 2 cGy/min with further dose recovery expected at even lower dose rates or at doses per fraction below 200 cGy. Since the dose-rate dependence of damage to haemopoietic tissue is less marked, this study predicts an advantage of employing low dose-rate total-body irradiation (TBI) in the treatment of bone-marrow transplant patients. A further gain in the therapeutic index may be expected using a hyperfractionated regime with small doses per fraction.
mesh_terms: D000818:Animals; D003037:Cobalt Radioisotopes / Q000009:adverse effects*; D004307:Dose-Response Relationship, Radiation; D008168:Lung / Q000473:pathology; D008297:Male; D051379:Mice; D008808:Mice, Inbred CBA; D009929:Organ Size / Q000528:radiation effects; D010101:Oxygen Consumption / Q000528:radiation effects; D010996:Pleural Effusion / Q000209:etiology; D011014:Pneumonia / Q000209:etiology*; D011833:Radiation Injuries, Experimental / Q000209:etiology*; D011867:Radioisotope Teletherapy / Q000009:adverse effects*; D011879:Radiotherapy Dosage; D014916:Whole-Body Irradiation / Q000009:adverse effects*
chemical_list: D003037:Cobalt Radioisotopes