Standardized uptake value of normal organs on routine clinical [18F]FDG PET/CT: impact of tumor metabolism and patient-related factors.

BACKGROUND: To evaluate the effect of patient-related factors such as age, gender, body mass index (BMI), blood glucose (BG), diabetes, serum creatinine and injected dose on 18F-Fluorodeoxyglucose ([18F]FDG) uptake of tumor and normal organs, as well impact of [18F]FDG uptake of tumor on normal organs, in clinical positron emission tomography-computed tomography (PET/CT). MATERIAL AND METHODS: In this retrospective study, data of 200 patients who underwent clinical [18F]FDG PET/CT with (n = 192) and without (n = 8) intravenous contrast was evaluated. Ten target organs and tumor [18F]FDG uptake were measured with a standardized uptake value maximum (SUVmax). Pearson correlation coefficient was calculated for continuous variables while t-test/Wilcoxon rank sum tests were used to compare continuous outcomes. Multivariate linear regression analysis was done to exclude covariates, followed by posthoc multiple linear regression analysis after adjusting the levels of significance. RESULTS: Significant but weak positive correlation was seen between tumor [18F]FDG uptake with uptake in the pancreas (r = 0.43, p < 0.001) and heart (r = 0.19, p = 0.049), but not other organs. With age, a significant negative correlation was seen with the brain (r = -0.183, p = 0.009) and a positive correlation was seen with the blood pool (r = 0.205, p = 0.003). With BG, significant negative correlation was seen with the brain (r = -0.449, p < 0.0001) and heart (r = -0.15, p = 0.033), while a positive correlation was seen with fat (r = 0.143, p = 0.043). BMI showed a significant positive correlation with [18F]FDG uptake of all organs except the pancreas and heart, as well as tumor. No significant correlation was seen with serum creatinine and injected [18F]FDG dose. Significantly higher uptake was seen in the brain, spleen, and muscles of females. Between obese and non-obese, a significant difference was seen for all organs except for the pancreas and heart, and tumor. Comparison between non-diabetic and diabetic patients showed significant differences only for bone. Multivariate linear analysis adjusting for cofactors showed only BMI (p = 0.0009) and BG (p = 0.0002) to be independently correlated with [18F]FDG uptake. Post-hoc multiple regression analysis showed a significant positive correlation between [18F]FDG uptake of the brain (ß = 0.118, p < 0.001), liver (ß = 0.02, p = 0.002), and fat (ß = 0.01, p < 0.0006) with BMI, and significant negative correlation of brain uptake with BG (ß = 0.03, p < 0.0001). CONCLUSIONS: Tumor [18F]FDG uptake has no significant effect on the uptake in organs, except for the pancreas and heart. Age, gender, BMI, and BG, but not creatinine and injected [18F]FDG dose show correlation with uptake in tumor and organs. BG and BMI are independent significant factors, with a positive correlation of BMI with the brain, hepatic and fat uptake, and a negative correlation of BG with brain uptake.

Comparison of the prognostic values of 68Ga-DOTANOC PET/CT and 18F-FDG PET/CT in patients with well-differentiated neuroendocrine tumor.

PURPOSE: To determine the prognostic value of (68)Ga-DOTANOC PET/CT in patients with well-differentiated neuroendocrine tumor (NET), and to compare the prognostic value with that of (18)F-FDG PET/CT and other conventional clinicopathological prognostic factors. METHODS: Data from 37 consecutive patients (age 46.6 ± 13.5 years, 51% men) with well-differentiated NET who underwent (68)Ga-DOTANOC PET/CT and (18)F-FDG PET/CT were analyzed. All patients underwent a baseline visit with laboratory and radiological examinations. Clinical and imaging follow-up was performed in all patients. Progression-free survival (PFS) was measured from the date of the first PET/CT scan to the first documentation of progression of disease. RESULTS: (68)Ga-DOTANOC PET/CT was positive in 37 of the 37 patients and (18)F-FDG PET/CT was positive in 21. During follow-up 10 patients (27%) showed progression of disease and 27 (73%) showed no progression (24 stable disease, 3 partial response). The median follow-up was 25 months (range 2 - 52 months). Among the variables evaluated none was significantly different between the progressive disease and nonprogressive disease groups, with only SUVmax on (68)Ga-DOTANOC PET/CT being borderline significant (P = 0.073). In the univariate analysis for PFS outcome, SUVmax on (68)Ga-DOTANOC PET/CT (HR 0.122, 95% CI 0.019 - 0.779; P = 0.026) and histopathological tumor grade (HR 4.238, 95% CI 1.058 - 16.976; P = 0.041) were found to be associated with PFS. Other factors including age, sex, primary site, Ki-67 index, TNM stage, (18)F-FDG PET/CT status (positive/negative), SUVmax on (18)F-FDG PET/CT and type of treatment were not significant. In multivariable analysis, only SUVmax on (68)Ga-DOTANOC PET/CT was found to be an independent positive predictor of PFS (HR 0.122, 95% CI 0.019 - 0.779; P = 0.026). CONCLUSION: SUVmax measured on (68)Ga-DOTANOC PET/CT is an independent, positive prognostic factor in patients with well-differentiated NET and is superior to SUVmax on (18)F-FDG PET/CT and conventional clinicopathological factors for predicting PFS.