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This experimental study was performed to evaluate the soft tissue radiographic and HRCT findings of radiation pneumonitis and fibrosis as well as to ascertain the usefulness of HRCT in detecting the early findings of radiation pneumonitis, A total of 15 rabbits used for experiment received one-fraction dose of 2000 rads of radiation on the right lung by using 6 Mv linear accelerator, A group of 3 rabbits was sacrificed at 4, 6, 12, 20 and 24 weeks after irradiation, and then the lungs were isolated for soft-tissue radiographic and HRCT studies, On soft-tissue radiogram radiation pneumonitis as consolidation with air-bronchogram occurred in 3 cases after 6 weeks of irradiation and in 1 case after 12 weeks of irradiation, Fibrosis as collapse with bronchiectatic change appeared in 20 and 24 weeks(N=7), HRCT findings of radiation pneumonitis were homogeneous, increased attenuation in 4 weeks(N=3), 6 and 12 weeks (each N=1), patchy consolidation in 6 and 12 weeks (each N=2) and discrete consolidation, HRCT showed radiation fibrotic changes as collapse of lung with traction bronchiectasis in 20 and 24 weeks after irradiation (each N=2), Through HRCT, the author was able to detect not only the early radiation pneumonitis in 4 weeks after irradiation but also radiation fibrosis as contraction of pleural surface(N=9) and peribronchial thickening(N=11), which were not seen in soft tissue radiogram, In conclusion, HRCT is more precious in detecting early radiation pneumonitis and fibrosis as well as in analyzing those findings detailed,
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