Page 15 - Wondergem

numerous variables can influence SUV. To minimize variability, regular calibration 1 of scanners, the use of standardised reconstruction and data analysis methods and
measuring patient parameters like body weight and glucose are necessary (21,23).
The most commonly used tracer is 18-fluorodeoxyglucose (18F-FDG), which accumulates
in cells with increased cellular uptake of glucose. After uptake in the cell, 18F-FDG is phosphorylated by hexokinase but cannot be glycolised. As a consequence 18F-FDG is essentially trapped in the cell (figure 2). Currently, 18F-FDG PET is used for staging and response evaluation both in aggressive and in more indolent types of lymphoma (24). Proliferative activity as measured by Ki67 has been shown to correlate with 18F-FDG uptake (25). Accordingly, there is a clear trend towards higher 18F-FDG uptake in more aggressive histological subtypes (26-28). Therefore, a high uptake in an indolent lymphoma supports the suspicion of transformation. However, there is a considerable overlap in SUV of 18F-FDG between aggressive and indolent lymphomas potentially impairing its use in detecting transformation. Taking into consideration that values were obtained in multiple centers, consequently on different PET scanners and in patients with different indolent lymphoma histologies, proposed SUVs predicting for aggressive histology vary from 10-14 (26-29). In spite of the high sensitivities and specificities that were reported in these series, pronounced variability was found when uptake was compared between studies: in one report up to 37% of transformed patients had
Figure 2: mechanism of tracer uptake: Tracer-P = phosphorylated tracer
Introduction and scope of this thesis
-for 18F-FDG = tracer -for 18F-FLT = tracer:
A: glucose transporter protein
B: hexokinase
C: glycolysis
A: facilitated diffusion via carrier proteins correlating with activity of B B: thymidine kinase-1
C: DNA synthesis
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