Lung damage after hemithoracic irradiation: dependence on mouse strain.

A comparative study was performed on CBA, C57Bl mice and their F1 hybrid cross (CBBF1) after right hemithorax irradiation using doses ranging from 15 to 35 Gy. A dose-dependent increase in breathing rate was observed, corresponding to the expression of radiation pneumonitis in the irradiated lung. The use of hemithoracic irradiation enabled this to be observed without any lethality. Results obtained from X-ray computerized tomography (CT), lung weight and histology complemented the breathing rate studies. CBA mice showed a peak response at 16 weeks followed by a decline in breathing rate coincident with a compensatory hypertrophy of the shielded left lung. The manifestation of radiation pneumonitis in C57Bl mice was considerably delayed, supporting previous findings on whole-thorax irradiated animals. The latent period in CBBF1 hybrid mice was intermediate between the parent strains.