Interim and end-treatment positron emission tomography scan in aggressive B-cell lymphoma: we still lack an interpretation key

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Th e awareness of the signifi cance of the prognostic value of interim PET in DLBCL fi rst started with the French experience in a retrospective cohort of patients with DLBCL, treated with a CHOP or CHOP-like regimen, with or without rituximab [2]. In this study, after completion of induction, 83% of PET-negative patients achieved a complete remission compared with only 58% of PET-positive patients. Th e interpretation key for iPET included both the number of sites involved and the intensity of the fl uorodeoxyglucose (FDG) uptake in the residual foci. However, this was not that easily reproducible, mainly because of the arbitrary grading of the residual FDG uptake. Apart from diffi culties with the interpretation criteria, the prognostic role of interim PET in DLBCL was later confi rmed in a large meta-analysis: the sensitivity and specifi city in predicting treatment outcome were 0.78 (95% confi dence interval [CI], 0.64 – 0.87) and 0.87 (95% CI, 0.75 – 0.93), respectively [3]. In 2009 an international workshop of hemato-oncologists and nuclear medicine experts held in Deauville, France, simple and reproducible criteria for iPET interpretation by visual assessment were proposed for Hodgkin lymphoma (HL) and DLBCL [4]. Here the residual FDG uptakes assessed in the foci of persisting disease were compared to the FDG uptake in the so-called “ reference ” organs (mediastinal blood pool and liver), and scored along a fi ve-point scale. Th ereafter, validation studies were proposed, which eventually confi rmed the feasibility and reproducibility of the so-called “ Deauville fi ve-point scale ” [5,6]. In the meantime, in order to increase its specifi city and positive predictive value, semiquantitative assessment of PET scans employing the standardized uptake value (SUV) was increasingly employed [7,8]. According to experts, semiquantitative results could be expressed as Δ SUV MAX , representing the diff erence between maximum SUV (SUV MAX ) of the baseline and interim PET scans. However, the most important limitation of this method of analysis for these PET results in a multicentric study was the variability of SUV measurement in the absence of a basic and more reliable program for single scanner quality assurance and quality control, to ensure inter-scanner calibration [9,10]. Very recently the same concepts were stressed