Early retardation of Tc-99m-DTPA radioaerosol transalveolar clearance in irradiated canine lung

The alteration of Tc-99m-labeled diethylenetriaminepentaacetic acid (DTPA) transalveolar clearance in an initial phase of radiation lung injury was ex perimentally investigated. Methods: Fourteen dogs were irradiated to the he mithorax with a single dose of 20 Gy. A DTPA radioaerosol study was perform ed before irradiation and on day 12 after irradiation. On day 14, the DTPA study was repeated again, with seven animals undergoing the study after inh alation of an aerosolized synthetic surfactant. The penetration index (P.I. ) and clearance half-time (T-1/2) of DTPA were measured in each lung. To ev aluate the changes in lung surfactant after irradiation, alveolar lipids we re stained in the resected lungs (n = 14), and the amounts of alveolar surf actant phospholipid and protein were measured by a bronchoalveolar lavage s tudy in another six irradiated dogs. Results: In all of the 14 irradiated a nimals. DTPA radioaerosol distributed uniformly throughout the lungs withou t significant changes in P.I. The T-1/2 values in irradiated lungs were sig nificantly prolonged compared with the matched baseline values and those in nonirradiated lungs (P < 0.05 and 0.001, respectively). The aerosolized sy nthetic surfactant retarded the DTPA clearance both in the irradiated and i n the nonirradiated lungs (P < 0.001) without significant changes in P.I. T he histologic and bronchoalveolar lavage studies revealed an increase of al veolar surfactant materials in the irradiated lungs without substantial his tologic changes in the alveolar structures. Conclusion: DTPA transalveolar clearance was retarded soon after irradiation. Increased alveolar surfactan t may be partly responsible for this retarded DTPA clearance because the ae rosolized synthetic surfactant also prolonged the clearance in nonirradiate d lungs. A DTPA clearance test is sensitive for the early detection of radi ation lung injury and seems helpful for clarifying the association of epith elial integrity changes and lung surfactant in radiation lung injury.