This study evaluates the use of the 99mTc-DTPA aerosol lung clearance method to investigate radiation-induced lung changes in eight patients undergoing radiotherapy for lung or breast carcinoma. The sensitivity of the method was compared with chest radiography for detecting radiation-induced changes in the lung, regional alterations within (irradiated region) and outside (shielded region) the treatment ports, effect of irradiated lung volume, and dependence on time after radiotherapy.
Methods: Serial DTPA lung clearance studies were performed before the first radiation treatment (baseline), then weekly during a 5- to 7-wk course, and up to 12 times post-therapy over periods of 56-574 days. The total activity deposited in the lungs for each study was approximately 150 microCi (approximately 5.6 MBq). DTPA clearance, expressed in terms of the biological half-time, t 1/2, was computed from the slopes of the least-squares fit regression lines of the time-activity curves for the first 10 min for irradiated and shielded lung regions.
Results: Major findings include: (a) significant and early DTPA t 1/2 changes were observed in all patients during and after radiotherapy; (b) changes in DTPA t 1/2 values were observed in both irradiated and shielded lung regions in all patients suggesting a radiation-induced systemic reaction; (c) changes in DTPA t 1/2 values were correlated (p < 0.05) with the irradiated lung volumes; (d) significantly reduced DTPA t 1/2 values were observed in three patients who subsequently presented with clinical symptoms and/or radiographic changes consistent with radiation pneumonitis (t1/2 felt to 19% +/- 6% of baseline values, compared with 64% +/- 17% in the remaining patients [p < 0.01]); (e) the onset of decreased DTPA t 1/2 values in these three patients occurred 35-84 days before clinical symptoms and/or radiographic changes; and (f) DTPA t 1/2 tended to approach baseline values with time after radiotherapy, suggesting a long-term recovery in lung injury.
Conclusion: These observations show significant and early alterations in DTPA lung clearance during and after radiotherapy that may provide a sensitive assay to monitor changes in radiation-induced lung injury and may facilitate early therapeutic intervention.