Abstract
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Objectives Measure the variance under clinical conditions of standardized uptake values (SUV) for 18F-FDG PET in metastatic colorectal cancer for potential use as a surrogate biomarker for therapy response.
Methods With institutional review board approval, all patients gave informed consent to participation in this research. Twenty-one patients with metastatic colorectal cancer were studied on two occasions about 110 min after the intravenous injection of 370 MBq of 18F-FDG. At each examination, mean and maximum SUVs (SUVmean, and SUVmax) were measured for volumes of interest, for a total of 62 tumors. A Discovery VCT PET/CT (TM) system (GE Medical Systems) was used for each examination.
Results Inter-tumor SUVmax and SUVmean ranged from 1.07-21.47 and 0.91-14.69, respectively. The Pearson correlation coefficients between non-normalized SUV measures at baseline and follow-up were 0.83 and 0.86 for the SUVmax and SUVmean, respectively. The scalar differences between the two measurements were -0.21 ± 1.93 (95% CIs -3.99 and +3.56) for SUVmax and -0.06 ± 1.10 (95% CI -2.21 and +2.09) for SUVmean.
Conclusions Under clinical conditions, SUVmean was a more reproducible measure compared to SUVmax. Decreases in SUVmean or SUVmax greater than 12% or 27%, respectively, would be significant. The value of these parameters as biomarkers in a clinical setting will depend on these numbers relative to the magnitude of therapy induced changes, and ultimately upon clinical outcomes.
Research Support This work was supported and part by Merck & Co., Inc