Repeatability of Quantitative 18F-Fluoromethylcholine PET/CT Studies in Prostate Cancer

Repeatable quantification is essential when using (18)F-fluoromethylcholine PET/CT to monitor treatment response in prostate cancer. It has been shown that SUV normalized to the area under the blood activity concentration curve (SUVAUC) provides a better correlation with full kinetic analysis than does standard SUV. However, the precision of SUVAUC is not known yet. The purpose of this study was to assess the repeatability of various semiquantitative (18)F-fluoromethylcholine parameters in prostate cancer.

Methods: Twelve patients (mean age ± SD, 64 ± 8 y) with metastasized prostate cancer underwent two sets of (18)F-fluoromethylcholine PET/CT scans, on consecutive days. Each set consisted of a 30-min dynamic PET/CT scan of the chest after intravenous administration of 200 MBq of (18)F-fluoromethylcholine, followed by a whole-body PET/CT scan at 40 min. The dynamic scan was used to derive the area under the blood activity concentration curve. Lesion uptake was derived from the whole-body scan using various types of volumes of interest: maximum, peak, and mean. Each of these parameters was normalized to injected activity per body weight, area under the blood activity concentration curve, and blood concentration itself at 40 min, resulting in several types of SUVs: SUV, SUVAUC, and SUVTBR The test-retest repeatability of these metrics, as well as metabolic tumor volume (MTV) and total uptake of choline in the lesion, were studied. The level of agreement between test-retest data and reliability was assessed using Bland-Altman plots, repeatability coefficients, and intraclass correlation coefficients (ICCs).

Results: A total of 67 choline-avid metastases were identified: 44 bone lesions and 23 lymph node lesions. In the case of SUVmax, the repeatability coefficients for SUV, SUVAUC, and SUVTBR were 26% (ICC, 0.95), 31% (ICC, 0.95), and 46% (ICC, 0.89), respectively. Similar values were obtained for SUVpeak and SUVmean The repeatability of SUVAUC was comparable to that of SUVmax, SUVpeak, and SUVmean. Tissue type and tumor localization did not affect repeatability. An MTV of less than 4.2 cm(3) had larger variability than larger volumes (repeatability coefficient, 45% vs. 29%; P = 0.048). The repeatability coefficient did not significantly differ between lesions with SUVpeak above or below the median value of 8.3 (19% vs. 28%; P = 0.264).

Conclusion: The repeatability of SUVAUC was comparable to that of standard SUV. The repeatability coefficients of various semiquantitative (18)F-fluoromethylcholine parameters (SUV, MTV, and total uptake in the lesion) were approximately 35%. Larger differences are likely to represent treatment effects.