Reproducibility of metabolic measurements in malignant tumors using FDG PET

PET using 18F-fluorodeoxyglucose (FDG) is increasingly applied to monitor the response of malignant tumors to radiotherapy and chemotherapy. The aim of this study was to assess the reproducibility of serial FDG PET measurements to define objective criteria for the evaluation of treatment-induced changes.

Sixteen patients participating in phase I studies of novel antineoplastic compounds were examined twice by FDG PET within 10 d while they were receiving no therapy. Standardized uptake values (SUVs), FDG net influx constants (Ki), glucose normalized SUVs (SUV(gluc)) and influx constants (K(i,gluc)) were determined for 50 separate lesions. The precision of repeated measurements was determined on a lesion-by-lesion and a patient-by-patient basis.

None of the parameters showed a significant increase or decrease at the two examinations. The differences of repeated measurements were approximately normally distributed for all parameters with an SD of the mean percentage difference of about 10%. The 95% normal ranges for spontaneous fluctuations of SUV, SUV(gluc), Ki and K(i,gluc) were determined to be +/-0.91, +/-1.14, +/-0.52 mL/100 g/min and +/-0.64 mL/100 g/min, respectively. Analysis on a lesion-by-lesion basis yielded similar results.

FDG PET provides several highly reproducible quantitative parameters of tumor glucose metabolism. Changes of a parameter that are outside the 95% normal range determined in this study may be used to define a metabolic response to therapy.