Quantification of uptake in 68Ga-DOTATATE PET: Correlation between standardized uptake values and patient factors

435 Objectives: Quantitative analysis of physiological DOTATATE uptake in various tissues and pathological uptake in neuroendocrine malignancies and other lesions that overexpress somatostatin receptors requires an understanding of how patient factors such as weight and body composition and scan parameters such as uptake time affect measured activities. We aim to investigate the correlation between these factors and uptake values using various normalization methods originally used for other PET radiotracers such as FDG. Methods: Physiological activity in 37 structures and uptake in up to 5 dominant lesions per organ were measured in 104 consecutively scanned patients undergoing 68Ga-DOTATATE PET/CT for evaluation of known or suspected neuroendocrine malignancies at our institution. We calculated the Pearson correlation between standardized uptake values (SUV) and body mass index (BMI), age, and uptake time and applied various SUV correction methods by normalizing measured activity based on body weight (SUVbw), body surface area (SUVbsa), lean body mass (SUVlbm), and ratio of uptake to a reference normal liver region of interest (SUVr). Additionally, we used Receiver Operating Characteristic analysis to examine how different measures of SUV can distinguish benign and malignant lesions. Results: A significant positive correlation (p 45) including organs with high uptake such as spleen (p<.0001, r=.5), renal parenchyma (r=.4), pancreas (r=.54), stomach (r=.43), small bowel (r=.49), pituitary (r=.38), liver (p<.001, r=.35), and adrenals (p=.01, r=.24). A similar correlation was found between BMI and uptake in 127 benign lesions (p=.002, r=.28). Uptake in 497 malignant lesions was high but quite variable (mean=23.7 g/ml, sd=19.4) and a significant correlation with BMI was not established. The correlation between BMI and SUVbsa, SUVlbm, or SUVr was significant in only 6, 1, or 1 normal structures, respectively. A weak correlation was present between age and physiological pituitary (p=0.02, r=-0.22) or salivary SUVbw (p=.02, r=.21). A weak negative correlation was present between uptake time (mean=56.6, range=45-80 min) and liver SUVbw and SUVbsa (p=.046, r=-0.2). In comparison, a statistically significant negative correlation was found between uptake time and SUVlbm in liver (p<.01, r=-0.26) as well as spleen, renal parenchyma, jejunum, pancreas, and left atrial blood pool. SUVbw of benign or malignant lesions did not significantly vary with uptake times. Different SUV measures had similar accuracy (90%) and performance for classifying benign versus malignant lesions (AUC=.942-.945 for SUVbw, SUVlbm, SUVr, and SUVbsa in increasing order, with no statistically significant difference between AUCs). Conclusions: Our results validate the use SUV and normalization based on body surface area, lean body mass, or uptake ratio to liver in 68Ga-DOTATATE PET. Measurements of physiological uptake are affected by body composition. However, the accuracy of 68Ga-DOTATATE PET and discriminability of benign and malignant lesions based on uptake remain robust with respect to variability in patient factors and uptake time regardless of normalization method.