Computed tomographic assessment of radiation induced damage in the lung of normal and WR 2721 protected LAF1 mice.

LAF1 mice were irradiated with single, graded doses of X rays to the thorax in the range of 0 to 14 Gy unprotected, or 0 to 18 Gy after injecting the radioprotective aminothiol compound, WR 2721. Computed tomographic (CT) scanning of the thorax was performed at intervals for a period of 42 weeks after irradiation. The gravimetric density was determined for both left and right lungs by averaging the CT numerical data within lung slices traced on a magnified video image of the thorax. Significant elevations in CT density occurred at post-irradiation times corresponding to pneumonitis and late phase, as evidenced by the pneumopathic decline in survival. The threshold dose yielding a significant increase in CT density in the pneumonitis phase was 11 Gy, a dose at which only 3% of the animals died. A single peak of increased CT density was observed for the pneumonitis phase for unprotected animals, whereas a transient return of CT density toward control values at 21-22 weeks produced two peaks from the WR 2721 treated group. The CT density of lung increased in a stepwise manner in the dose range of 11-14 Gy. For the isoeffect dose that produced equal animal survival (14 Gy and 18 Gy + WR 2721), the lung density increased by approximately 27% over control values for both treatments, suggesting that CT density is related to survival. Periodic computed tomographic analysis of the lungs of patients sustaining radiotherapy to large pulmonary fields may be of value in assessing the degree and progression of pulmonary complications.