31 Lesion detection by [89Zr]Zr-DFO-girentuximab and [18F]FDG PET/CT in mccRCC patients Table 2. The number of affected organ sites per patient per imaging modality (combination). CT only (median 2) [18F]FDG-PET/CT and CT (median 3)* [89Zr]Zr-DFO-girentuximab-PET/ CT and CT (median 3)* 0 2.4% - - 1 33.3% 23.8% 23.8% 2 35.7% 21.4% 26.1% 3 21.4% 38.1% 30.9% 4 7.1% 14.2% 11.9% 5 - 2.4% 4.8% 7 - - 2.4% *Significant increase of the median number of organ sites compared to CT alone (p <0∙005). Quantitative analysis of [89Zr]Zr-DFO-girentuximab and [18F]FDG-uptake In normal tissues the highest [89Zr]Zr-DFO-girentuximab-uptake was observed in healthy liver (geometric mean SUVmean 6.7 (95%CI 6.4–7.3)), lowest in healthy lung (geometric mean SUVmean 1.1 (95%CI 0.8–1.2)) (p < 0.05). The physiological biodistribution of [89Zr]Zr-DFO-girentuximab is illustrated in the supplementary data. The overall geometric mean [89Zr]Zr-DFO-girentuximab SUV max in lesions was 15.5 (95%CI 12.5–19.2), and 4.4 (95%CI 3.8–5.1) for [18F]FDG. Tracer uptake was higher in lesions with a CT diameter > 15 mm, compared to smaller lesions (geometric mean SUVmax 23.9 (95%CI 19.0–30.0) and 5.8 (95%CI 5.0–6.8 for [89Zr]Zr-DFO-girentuximab and geometric mean 11.6 (95%CI 9.3– 14.5) and 3.5 (95%CI 3.0–4.1) for [18F]FDG). Based on expert opinion, for further analyses of tracer uptake a cut-off of ≥15 mm in diameter on CT was chosen to avoid partial volume effects thwarting proper quantification (leaving 95 lesions in 26 patients for [89Zr]Zr-DFO-girentuximab, and 93 lesions in 29 patients for [18F]FDG). The [89Zr]Zr-DFO-girentuximab SUV max varied greatly, ranging from 3.8 to 230.8, with a medianfold difference of 2.8 (range 1.2–15.3) per patient. Inter-patient heterogeneity accounted for 41% of variation in [89Zr]Zr-DFO-girentuximab SUV max, and 53% for [ 18F]FDG SUV max (i.e., ICC of 0.41 and 0.53, respectively). Highest [89Zr]Zr-DFO-girentuximab-uptake was seen in kidney and adrenal gland lesions (median SUVmax 61.1 and 69.9, respectively) and lowest in lung lesions (median SUVmax 9.4) (Figure 3). Two out of six patients without prior nephrectomy showed highest [89Zr]Zr-DFO-girentuximab-uptake at primary site (SUV max 70.52 and 40.48), compared to synchronous metastatic sites. 2
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