The role of lung perfusion imaging in predicting the direction of radiation-induced changes in pulmonary function tests.

Background: The aim of this study was to determine whether preradiation (pre-RT) single photon emission computed tomography (SPECT) lung perfusion scans can be used to predict RT-induced changes in pulmonary function tests (PFTs).

Methods: Ninety-four patients irradiated for thoracic tumors had pre-RT SPECT lung perfusion scans. The presence of SPECT hypoperfusion distal to a central mediastinal tumor was qualitatively assessed visually without knowledge of PFT changes. Patients were grouped based on whether the diffusion capacity (DLCO) ever increased post-RT. Comparisons of patient groups were performed using 1-tailed Fisher exact tests. Patient follow-up was 6-56 months (mean, 30 months). To assess SPECT hypoperfusion objectively, the average dose to the computed tomography (CT)-defined lung was compared with the weighted-average dose (based on relative perfusion) to the SPECT-defined lung. The ratio between the CT- and SPECT-defined mean lung dose provided a quantitative assessment of hypoperfusion. The mean ratio for patients with central tumor and adjacent hypoperfusion was compared with that of the others (Wilcoxon rank-sum one-sided test).

Results: In patients with central tumors, 41% (9 of 22) with adjacent hypoperfusion had improvements in DLCO following radiation, versus 18% (3 of 17) of those without hypoperfusion (P = 0.11). In patients with lung carcinoma, the corresponding ratios were 40% (8 of 20) and 10% (1 of 10), respectively (P = 0.10). The mean ratio of CT dose to SPECT dose was 1.35 for patients with central tumors and adjacent hypoperfusion versus 1.16 for others (P = 0.017).

Conclusions: The presence of SPECT hypoperfusion adjacent to a central mediastinal mass may identify patients likely to have improved PFTs following RT. Thus, SPECT imaging may be useful in models for predicting radiation-induced changes in PFTs.