ALTERED REGIONAL CLEARANCE OF TC-99M-DTPA IN RADIATION PNEUMONITIS

Tc-99(m)-diethylene triaminepenta-acetic acid (Tc-99(m)-DTPA) lung scintigrams were investigated in 11 patients with radiation pneumonitis to assess the alteration of clearance of this small solute. Thirty minutes after the injection of Tc-99(m)-DTPA, all 11 patients showed abnormal accumulation. This uptake was seen in the areas with reduced Tc-99(m)-macroaggregated albumin activity. The curves of the lung/heart ratios obtained after 1 min after injection of Tc-99(m)-DTPA in areas showing abnormal accumulation were of three types. Comparison of the slope for the initial 5 min of the lung/heart curves between the abnormal accumulation sites and the contralateral non-irradiated lung revealed a significant difference. The uptake ratio (the mein counts of the last frame divided by initial peak count) was related to the degree of abnormal accumulation in the radiation pneumonitis. Moreover, study of rabbits with radiation pneumonitis revealed similar behaviour by Tc-99(m)-DTPA as observed clinically. This simple and rapid method may be useful in detecting and monitoring the altered regional kinetics of Tc-99(m)-DTPA in radiation pneumonitis.