Quantitative SPECT/CT Imaging in Pre Op Evaluation of Patients for Bronchoscopic Lung Volume Reduction (BLVR)

Introduction: Bronchoscopic lung volume reduction (BLVR) is a minimally invasive procedure for the treatment of hyperinflated COPD. The importance of targeting areas of low perfusion has been previously shown using nuclear scintigraphy and more recently using quantitative SPECT. In this prospective study we used the ratio of perfusion count to lobar volume to help identify the ideal target for BLVR. We sought to determine how deviations from this target affect clinical outcomes.

Methods: Patients with severe emphysema (RV >150%, TLC >100%) on maximal therapy were consecutively assessed for BLVR. Target lobes were chosen by assessing lobar volume, fissure integrity (a marker of collateral ventilation (CV)), and % emphysema destruction (using -950 Hounsfield Unit cutoff) as assessed by commercially available quantitative CT analysis programs. Then, all patients underwent perfusion lung scan using 5.0 mCi of Tc99m MAA intravenously. Both major fissures and right minor fissure were identified. The ratio of perfusion to volume was measured. BLVR was performed by one-way bronchoscopically-placed valves implanted in the target lobe bronchus to achieve complete lobar occlusion and volume reduction. Chartis® flow measurements are performed to ensure the absence of CV between the target and ipsilateral nontreated lobes. Clinical endpoints included improvement in FEV1 by spirometry and target lobe volume reduction as determined by quantitative CT at 45-days post BLVR. Patients were divided into two groups based on whether the lobe with the lowest perfusion/volume ratio by SPECT was selected for valve insertion (concordant group) or not (discordant group). Statistical analysis was performed with Student’s t test or Chi Square analysis.

Results: 55 patients were consecutively evaluated for BLVR, 22 were excluded (11 had incomplete follow up data, 7 were CV+ by Chartis®, 2 died soon after implantation, 1 had valves removed for persistent pneumothorax, and 1 was transplanted). 33 patients were therefore included for analysis, 24 in the concordant group and 9 in the discordant group. Of the 9 patients in the discordant group, 3 were due to CV+, 2 for low fissure integrity on baseline CT (a surrogate for CV+), 3 for more favorable emphysema pattern, and 1 due to pleural adhesions (increased procedural risk). Overall, the group had a 0.54+0.21 perfusion/volume ratio, with a baseline FEV1 0.85+0.23L, baseline target lobe volume of 1.83+0.39L, emphysema destruction of 43.7+14.2%, and fissure integrity of 90.7+14.1%. The concordant group were more likely to have a lower perfusion/volume ratio (0.49 vs. 0.69, p=0.01) and more emphysema destruction (46.8% versus 35.3%, p=0.04). Between the concordant and discordant groups, we did not find any statistically significant differences in FEV1 improvement (1.03+0.3% vs. 15.5+20.2%, p=0.8) or target lobe volume reduction (51.4+39.2% versus 69.1+24.6%, p=0.28).

Conclusions: Quantitative SPECT/CT can help in BLVR pre-procedure planning to target areas of low perfusion. However, other procedural considerations may prohibit use of lowest perfusion areas. SPECT/CT can still identify alternative targets that can provide clinically meaningful benefits of BLVR and should be used in conjunction with traditional quantitative CT analysis. Furthermore, SPECT/CT offers the advantage over nuclear scintigraphy of providing precise lobar information as regional hyperinflation can affect predictions made by scintigraphic zonal approximations.