Radiation Pneumonitis and Fibrosis in Mouse Lung Assayed by Respiratory Frequency and Histology

Abstract

The response of mouse lung to radiation was assessed by measuring breathing frequency up to 52 wk after graded single doses of X-rays to both lungs. Breathing frequency was increased after lethal and sublethal doses, with damage appearing sooner after higher doses. Dose-response curves were obtained after 14 wk with a threshold of 12 Gy [gray]. All mice given doses greater than 15 Gy died by 22 wk. Some return of function was observed in the lower dose groups by 36 wk, but breathing frequency remained elevated for 52 wk after a nonlethal dose. The changes in breathing frequency were compared with histological changes in the same mice at sacrifice. The increased breathing frequency between 14 and 24 wk was associated with radiation pneumonitis seen histologically. After 36 wk, the elevation in breathing frequency above the control value was associated with fibrosis. Comparison of dose-response curves for the pathological changes and for breathing frequency 16, 36 and 52 wk after irradiation indicated that increases in breathing frequency were associated with increases in the severity of the histological changes scored. [The lung is often included in the radiation field in the treatment of malignant tumors of the thoracic region and is often the dose-limiting tissue.].