Patient's weight: a neglected cause of variability in SUV measurements? A survey from an EARL accredited PET centre in 513 patients

Dear Sir, F-Fluorodeoxyglucose (FDG) positron emission tomography (PET) is being increasingly used for assessment of early effects of conventional chemotherapy and/or tyrosine kinase inhibitors (TKI). In these settings, when using standardized uptake values (SUVs) as non-invasive quantitative imaging biomarkers in multicentre trials or in sites equipped with multiple PET scanners, adequate reproducibility is mandatory so that SUVs are comparable, regardless of the PET system used. Adequate reproducibility of SUVs can be achieved by harmonizing patient preparation as well as acquisition and reconstruction parameters [1–4], as recommended by the European Association of Nuclear Medicine Research Ltd (EARL) accreditation programme [5] and other groups [6]. Harmonization programs such as EARL are meant to reduce sources of SUV variability [7], which can be classified into technical, biological and physical factors [8–10]. The purpose of this survey was to shed light on an unreported technical cause of variability in SUVmeasurement that may hamper efforts to meet quantitative harmonizing standards. Indeed, variability in local standards of care in the use of PETacross centres has been well documented [11, 12], and compliance with PET imaging guidelines in clinical trials has been studied [13, 14]. However, although the SUV formula displayed below obviously shows that an overestimation of patient’s weight can lead to an overestimation of SUV metrics and vice versa, there is, to the best of our knowledge, no large survey about this potential confounding factor in SUV measurement.