Baseline Total Metabolic Tumor Volume measured with fixed or different adaptive thresholding methods equally predicts outcome in Peripheral T cell lymphoma.

Abstract

To compare in a large series of Peripheral T cell lymphoma (PTCL), as a model of diffuse disease, the prognostic value of baseline Total Metabolic Tumor Volume (TMTV) measured on FDG-PET/CT with adaptive thresholding methods to TMTV measured with a fixed 41% SUV_max threshold method. Methods: 106 patients with PTCL, staged with a PET/CT were enrolled from 5 LYSA centers. In this series TMTV computed with the 41% SUV_max threshold is a strong predictor of outcome (Ann Oncol, 2016). On a dedicated workstation, we measured the TMTV with four adaptive thresholding methods based on characteristic image parameters: Daisne (Da) modified based on signal/background ratio, Nestle (Ns) on tumor and background intensities, Fit including a 3D geometric model based on spatial resolution (Fit) and Black (Bl) based on mean SUV_max. The TMTV values obtained with each adaptive method were compared to those obtained with 41% SUV_max method. Their respective prognostic impacts on outcome prediction were compared using ROC analysis and Kaplan Meier survival curves. Results: The median value of TMTV41%, TMTVDa, TMTVNs, TMTVFit, TMTVBl were respectively 231 cm³ (range 5-3824), 175 cm³ (8-3510), 198 cm³ (3-3934), 175 cm³ (8-3512), and 333 cm³ (3-5113). The intra-class correlation coefficients were excellent from 0.972 to 0.988 for TMTVDa, TMTVFit, TMTVNs, less good for TMTVBl (0.856). The mean differences obtained from the Bland Altman plots were 48.5, 47.2, 19.5 and -253.3 cm³ respectively. Except for Black there was no significant difference within the methods between the ROC curves (p>0.4) for Progression Free Survival (PFS) and for Overall Survival (OS). Survival curves with the ROC optimal cutoff for each method separated the same groups of low risk (volume≤cutoff) from high risk patients (volume>cutoff) with similar 2y-PFS (range 66-72% vs 26-29%; HR 3.7-4.1) and 2y-OS (79-83% vs 50-53%, HR 3.0-3.5). Conclusion: The prognostic value of TMTV remained quite similar whatever the methods, adaptive or 41% SUV_max. This supports its use as a strong prognosticator in lymphoma. However for implementation of TMTV in clinical trials one single method easily applicable in a multicentric PET review must be selected and kept all along the trial.