A new PET/CT volumetric prognostic index for non-small cell lung cancer

Abstract

Objectives: Whole-body metabolic tumor volume (MTVWB) has been shown of prognostic value for non-small cell lung cancer (NSCLC) beyond that of TNM stage, age, gender, performance status, and treatment selection. The current TNM staging system does not incorporate tumor volumetric information. We propose a new PET/CT volumetric prognostic (PVP) index that combines the prognostic value of MTVWB and TNM stage.

Materials and methods: Based on 328 consecutive NSCLC patients with a baseline PET/CT scan before treatment, from which MTVWB was measured semi-automatically, we estimated hazard ratios (HRs) for ln(MTVWB) and TNM stage from a Cox proportional hazard regression model that consisted of only ln(MTVWB) and TNM stage as prognostic variables of overall survival. We used the regression coefficients, which gave rise to the HRs, as weights to formulate the PET/CT volumetric prognostic (PVP) index. We also compared the prognostic value of the PVP index against that of TNM stage alone and ln(MTVWB) alone with univariate and multivariate survival analyses and C-statistics.

Results: Univariate analysis C-statistic for the PVP index (C=0.71) was statistically significantly greater than those for TNM stage alone (C=0.67, p<0.01) and for ln(MTVWB) alone (C=0.69, p=0.033). Multivariate analyses showed that the PVP index yielded significantly greater discriminatory power (C=0.74) than similar models based on either TNM stage (C=0.72, p<0.01) or ln(MTVWB) (C=0.73, p<0.01). Lower values of the PVP index were associated with significantly better overall survival (adjusted HR=2.70, 95%CI [2.16, 3.37]).

Conclusion: The PVP index provides a practical means for clinicians to combine the prognostic value of MTVWB and TNM stage and offers significantly better prognostic accuracy for overall survival of NSCLC patients than the current TNM staging system or metabolic tumor burden alone.

Keywords: (18)F-FDG PET/CT; Metabolic tumor volume (MTV); Non-small cell lung cancer (NSCLC); Prognosis; TNM stage; Tumor burden.

Conflict of interest statement

CONFLICT OF INTEREST STATEMENT

The authors declare that they have no conflict of interest and have not used writing assistance.

Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Figures

Figure 1

Kaplan-Meier curves of overall survival based on 52 stage-IIIA NSCLC patients stratified by the median value of ln(MTVWB) (calculated from the entire study cohort of 328 patients), showing that MTVWB provides prognostic value in patients of the same TNM stage. This observation provides motivation for the proposed PVP index, which combines ln(MTVWB) with TNM stage to allow clinicians to take advantage of the additional prognostic value from MTVWB.

Figure 2

Graphical representation of the PET/CT volumetric prognostic (PVP) index as defined by Eq. (1). For patients within a single TNM stage, the PVP index is linearly related to ln(MTVWB), with a slope of 0.360. For a given value of ln(MTVWB), advanced stage yields greater PVP index. The values on the x-axis correspond to the 5th, 25th, 50th, 75th, and 95th percentiles of ln(MTVWB) for the entire study cohort.

Figure 3

Kaplan-Meier curves of overall survival based on 328 stage-IA to stage-IV NSCLC patients stratified by the quartiles of the values of the PVP index, showing that increasing values of the PVP index are associated with worsening overall survival.