Prognostic value of metabolic metrics extracted from baseline positron emission tomography images in non-small cell lung cancer

Abstract

Background: Maximum, mean and peak SUV of primary tumor at baseline FDG-PET scans, have often been found predictive for overall survival in non-small cell lung cancer (NSCLC) patients. In this study we further investigated the prognostic power of advanced metabolic metrics derived from intensity volume histograms (IVH) extracted from PET imaging.

Methods: A cohort of 220 NSCLC patients (mean age, 66.6 years; 149 men, 71 women), stages I-IIIB, treated with radiotherapy with curative intent were included (NCT00522639). Each patient underwent standardized pre-treatment CT-PET imaging. Primary GTV was delineated by an experienced radiation oncologist on CT-PET images. Common PET descriptors such as maximum, mean and peak SUV, and metabolic tumor volume (MTV) were quantified. Advanced descriptors of metabolic activity were quantified by IVH. These comprised five groups of features: absolute and relative volume above relative intensity threshold (AVRI and RVRI), absolute and relative volume above absolute intensity threshold (AVAI and RVAI), and absolute intensity above relative volume threshold (AIRV). MTV was derived from the IVH curves for volumes with SUV above 2.5, 3 and 4, and of 40% and 50% maximum SUV. Univariable analysis using Cox Proportional Hazard Regression was performed for overall survival assessment.

Results: Relative volume above higher SUV (80%) was an independent predictor of OS (p = 0.05). None of the possible surrogates for MTV based on volumes above SUV of 3, 40% and 50% of maximum SUV showed significant associations with OS [p (AVAI3) = 0.10, p (AVAI4) = 0.22, p (AVRI40%) = 0.15, p (AVRI50%) = 0.17]. Maximum and peak SUV (r = 0.99) revealed no prognostic value for OS [p (maximum SUV) = 0.20, p (peak SUV) = 0.22].

Conclusions: New methods using more advanced imaging features extracted from PET were analyzed. Best prognostic value for OS of NSCLC patients was found for relative portions of the tumor above higher uptakes (80% SUV).

Figures

Figure 1. Transverse view of CT-PET scan of NSCLC patients

Examples of Intensity-Volume Histograms for the two patients are shown on the right. Maximum SUV for patients A and B (top and bottom left) are, respectively, 10.1 and 6.3. From the RVRI curves, it can be inferred that the minimum SUV is around 8% (0.80) and 20% (1.25) of the maximum uptake. AVAI curves confirm that all the tumor volume is above these minimum uptake values for the corresponding patient.

Figure A - 1

Results for PET analysis: log rank test based on a median split for GTV (42.27), maximum SUV (10.12), peak SUV (7.92) and RVRI80 (0.04). Results for the log-rank test (p-value) are displayed in the bottom left corner of each graph.

Figure A - 2

Feature clustering based on Spearman correlation. For this clustering, only the features presented in Table 1 were used. It is evident from this diagram that the metabolic features aggregate in different cluster. Each of these clusters thus provides dissimilar information.