Metabolic Tumor Volume: We Still Need a Platinum-Standard Metric

Abstract

In this issue of The Journal of Nuclear Medicine, Cottereau et al.(1) retrospectively evaluate data compiled from a cohort of 106 peripheral T cell lymphoma patients, 50% of whom were previously enrolled in Lymphoma Study Association (LYSA) studies coordinated by 5 French and Belgian centers between 2006 and 2014. The objective was to determine the prognostic value of baseline total metabolic tumor volume (TMTV) calculated with adaptive thresholding methods as compared with TMTV measured with a fixed threshold. The methods used to calculate TMTV included the Daisne method, based on the tumorto-background ratios to segment tumor volumes, and the Nestle method, which compares the intensity of the tumor to that of the background. Despite substantial differences in cutoff values across different TMTV computing methods (631%), the authors reported excellent intraclass correlation coefficients (from 0.97 to 0.98) for discriminating low versus high TMTV.Tumor burden has long been considered an important prognostic marker in several lymphoma subtypes, hence its surrogates See page 276 such as bulky lesions, stage III-IV, or extranodal disease have been incorporated in several prognostic models including the IPI (international prognostic index), IPS (international prognostic score for Hodgkin lymphoma [HL]), FLIPI 1 and 2 (prognostic score for follicular lymphoma), MIPI (prognostic score for mantle cell lymphoma), PIT (prognostic index for peripheral T cell lymphoma), and AIP (prognostic model for angioimmunoblastic lymphoma). These prognostic models, however, are not considered sufficient to accurately stratify disease risk categories across patient populations. With the advent of advanced imaging techniques such as 18 F-FDG PET/CT and the availability of software offering sophisticated computer algorithms necessary for accurate tumor segmentation to calculate the sum of voxels of the tumor bulk, it became possible to quantify the functional activity and the total tumor burden.Earlier 18 F-FDG PET/CT studies found that a high metabolic tumor volume (MTV) was independently associated with progressionfree survival (PFS) and overall survival (OS) in HL patients treated with standard ABVD (doxorubicine, bleomycine, vinblastine, and dacarbazine), with or without involved-field radiotherappy (2,3), suggesting that pretherapy MTV as a measure of metabolically active whole-body tumor bulk was a predictor of outcome when the conventionally described tumor burden did not reach a significance. However, there is also evidence for contrasting results, showing that baseline MTV could not predict survival when IPS did, whereas percentage change (D) in both MTVand SUV max at interim PET was associated with PFS and OS (4). It is difficult to generalize these divergent results on the basis of retrospective analyses associated with no statistical design to determine a sufficiently high number of patient cohorts, inherent risk of bias for population selection, treatment protocols, and segmentation methodologies resulting in various MTV cut...

[18F]FDG-PET/CT in Hodgkin Lymphoma: Current Usefulness and Perspectives

“…As availability and easiness of calculation appears crucial to implement this technique, free and open source software for PET/CT image processing with semi-automatic TMTV calculation are being proposed to develop the standardized software package and increase TMTV availability for researchers ( ). However, this approach still needs better standardization, especially regarding the methodological segmentation rule and the TMTV cut-off definition [ 43 ].…”

Reply to the letter

“…Nonetheless measurement of disease burden remains an important parameter for study [8] and will no doubt become integrated into preclinical risk assessment of patients in the not too distant future.…”