Quantitative ⁶⁷Ga-citrate SPECT/CT for evaluating disease activity in patients with interstitial lung disease

To determine whether results of a standardized uptake value (SUV)-based semi-quantitative analytic method for gallium-67 (⁶⁷Ga)-citrate single photon emission tomography/computed tomography (SPECT/CT) reflects disease activity in patients with interstitial lung disease.

Gallium-67-citrate SPECT/CT was used to evaluate disease activity in 24 patients with interstitial pneumoniaon clinical grounds at a single institution from June 2018 to August 2020. SUV in a given volume of interest over the bilateral pulmonary parenchyma was calculated using a dosimetry software package. Correlations of maximum SUV (SUVmax) and mean SUV (SUVmean) with clinical factors, including KL-6, lactate dehydrogenase (LDH), and C-reactive protein (CRP), were evaluated in all 24, as well as in 15 patients with spirometry results using Pearson's rank correlation test.

The mean bilateral pulmonary SUVmax value showed a moderately significant correlation with KL-6 (Pearson's correlation coefficient r=0.51, P=0.012) and LDH (r=0.51, P=0.010), a weak non-significant correlation with DLCO% (r=-0.26, P=0.34), and no correlation with CRP (r=-0.01, P=0.94), FVC% (r=0.11, P=0.71), or FEV1.0% (r=0.14, P=0.62). Eleven patients with high KL-6 (≥1000U/mL) were defined as having disease activity. Maximum SUV sensitivity, specificity, and accuracy for predicting interstitial lung disease activity were 72.7%, 76.9%, and 75.0%, respectively, with a best cut-off value of 3.78.

Semi-quantitative values obtained with ⁶⁷Ga-citrate SPECT/CT showed a moderate correlation with KL-6 and moderate diagnostic performance for predicting disease activity of interstitial lung disease. It is rather unlikely that quantitative ⁶⁷Ga-citrate SPECT/CT will have a role into the algorithm of interstitial lung disease.