Page 38 - Wondergem

Chapter 2
apart from measuring the SUVmax of the most avid lymph node (highest SUVmax) we calculated the SUVrange, defined as the difference between maximum and minimum uptake within an individual patient.
Statistics
Correlations were calculated using the Pearson r method. To compare follow-up times and SUVs between FL and TF groups we used the non-parametric Mann Whitney U test. Discriminative ability of highest SUVmax and SUVrange to distinguish absence and presence of transformation were quantified by means of the area under the receiver operating characteristic (ROC) curve, using our definition of transformation (see before) as the reference test. From this ROC curve analysis we also determined a cut-off value for detection of transformation. The cut-off value chosen was the smallest cut-off value for which sensitivity in the sample was 100% (i.e. maximizing specificity under the restriction of no false negatives).
Sample size was based on the comparison of mean SUVmax between the FL and TF groups. The planned number of 17 per group would provide 80% power to detect a difference of one standard deviation (approximately 5 units) in mean SUVmax assuming two-sided testing at a significance level of 5%. In order to protect patients from both the physical and radiation burden of two consecutive PET scans the institutional review board requested an analysis after inclusion of half of the transformed lymphoma patients. The paper presents the results of the study after inclusion of 9 (of a planned number of 17) TF patients. By that time the planned inclusion of 17 FL patients had already been completed. Statistical analyses were performed using the IBM SPSS statistical package 20.0, except for comparison of AUCs between FDG and FLT which was performed in SAS version 9.2.
Results
From November 2008 until June 2011, we included 17 patients with FL and 9 with histologically proven transformation of FL (TF). Median clinical follow-up of all patients was 31.5 months (range:14-43). Follow-up time was similar for FL and TF patients (p=0.79, table 1). All patients with FL histology at time of PET-CT satisfied our definition of FL during their subsequent disease course : 6 did not need immediate treatment, two of them eventually required treatment during follow-up (after 17 and 21 months, respectively), and one of them was diagnosed with TF after 21 months (sudden increase
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