Page 92 - Quantitative Imaging of Small Tumours with Positron Emission Tomography

Bland-Altman plots with 95% limits of agreement, R2 and intraclass correlation coefficients (ICC) were calculated were calculated to assess inter- and intrascan variability (24). ICCs represent the fraction of the total variability attributable to between lesion variability, and were calculated using a two-way mixed model with absolute agreement definition (25). To test for differences in repeatability between 100% and 50% count scans we used a Wilcoxon signed-rank test designed to compare variances of dependent data (p<0.05) (26). Results 4 Fourteen patients with a median age of 65 (IQR 47-75) years were included. Median Gleason score was 8 (IQR 5-10) and median PSA at imaging was 103 (IQR 11-1602) ng/ml. Median injected dosages of [18F]FDHT on day 1 and day 2 were 194 MBq (range 152-216) and 193 MBq (range 186-215) with residual activity in syringes/tubes of 37 MBq (range 26-63) and 36 MBq (18-54), respectively (12). In two patients, no FDHT-avid lesions were detected. In the remaining 12 patients, 336 FDHT-avid lesions were visually detectable on both test and retest PET-CT scans. [18F]FDHT PET repeatability 25 20 15 10 5 0 Figure 4.3: Liver COV% for 100% count and 50% count EARL1 and EARL2 images. 91 liver COV% EARL1: 100% counts EARL2: 100% counts EARL1: 50% counts EARL2: 50% counts