Abstract
Treatment of thoracic malignancies by radiotherapy is often limited by normal lung tissue's tolerance of the radiation. Nuclear magnetic resonance imaging (MRI) can be used to follow changes in lung tissue and can be repeated serially without adverse effects to the patient. We assessed the usefulness of this technique in 41 male Wister rats, producing pneumonitis in the right lung of each animal by administering 14-Gy irradiation, and using the left lung of each animal as control. Longitudinal and transverse nuclear magnetic resonance (NMR) relaxation times and pulmonary blood flow were measured during the development of pneumonitis. Lungs of representative animals were examined microscopically for lymphocytic foci. Spin-lattice relaxation time (T1) of the irradiated lung increased significantly (P < 0.05) between 60 and 80 days; otherwise it was not different from that of the control (left) lung. For 80 days after treatment spin-spin relaxation time (T2) initially increased compared to that of the control lung, and then it returned to normal values. Pulmonary blood flow had decreased significantly by 60 days (P < 0.05) and remained significantly below control values. Lymphocytic foci had increased to 350% of initial values by Day 80 (P < 0.05) and then quickly decreased to pre-radiation values by Day 100. These results suggest that there is a significant change in the T1 of lung tissue during the development of pneumonitis, which begins at the onset of radiation fibrosis.
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