RESUMO
BACKGROUND: Suboptimal temporal sampling of time-activity curves (TAC) from dynamic 18F-fluoromethylcholine (FCH) PET images may introduce bias in quantification of FCH uptake in prostate cancer assessment. We sought to define an optimal temporal sampling protocol for dynamic FCH PET imaging. Seven different time samplings were tested: 5 × 60â³, 10 × 30â³, 15 × 15â³-1 × 75â³, 6 × 10â³-8 × 30â³, 12 × 5â³-8 × 30â³; 10 × 5â³-4 × 10â³-3 × 20â³-5 × 30â³, and 8 × 3â³-8 × 12â³-6 × 30â³. First, the irreversible and reversible one-tissue compartment model with blood volume parameter (VB) (respectively, 1T1K+VB and 1T2k+VB, with K1 = transfer coefficient from the arterial blood to the tissue compartment and k2 = transfer coefficient from the tissue compartment to the arterial blood) were compared for 37 lesions from 32 patients who underwent FCH PET imaging for initial or recurrence assessment of prostate cancer, and the model was selected using the Akaike information criterion. To determine the optimal time sampling, K1 values extracted from 1000 noisy-simulated TAC using Monte Carlo method from the seven different time samplings were compared to a target K1 value which is the average of the K1 values extracted from the 37 lesions using an imaging-derived input function for each patient. K1 values extracted with the optimal time sampling for each tumoral lesion were compared to K1 values extracted from each of the other time samplings for the 37 lesions. RESULTS: The 1T2k + VB model was selected. The target K1 value as the objective was 0.506 mL/ccm/min (range 0.216-1.246). Results showed a significant difference between K1 values from the simulated TAC with the seven different time samplings analyzed. The closest K1 value from the simulated TAC to the target K1 value was obtained by the 12 × 5â³-8 × 30â³ time sampling. Concerning the clinical validation, K1 values extracted from the optimal time sampling (12 × 5â³-8 × 30â³) were significantly different with K1 values extracted from the other time samplings, except for the comparison with K1 values extracted from the 10 × 5â³-4 × 10â³-3 × 20â³-5 × 30â³ time sampling. CONCLUSIONS: A two-phase framing of dynamic PET reconstruction with frame durations of 5 s (blood phase) and 30 s (tissue phase) could be used to sample the TAC for uptake quantification in prostate cancer assessment.
RESUMO
AIM: The aim of the study was to compare the kinetic analysis of 18F-labeled choline (FCH) uptake with static analysis and clinicopathological parameters in patients with newly diagnosed prostate cancer (PC). MATERIALS AND METHODS: Sixty-one patients were included. PSA was performed few days before FCH PET/CT. Gleason scoring (GS) was collected from systematic sextant biopsies. FCH PET/CT consisted in a dual phase: early pelvic list-mode acquisition (from 0 to10 min post-injection) and late whole-body acquisition (60 min post-injection). PC volume of interest was drawn using an adaptative thresholding (40% of the maximal uptake) on the late acquisition and projected onto an early static frame of 10 min and each of the 20 reconstructed frames of 30 s. Kinetic analysis was performed using an imaging-derived plasma input function. Early kinetic parameter (K1 as influx) and static parameters (early SUVmean, late SUVmean, and retention index) were extracted and compared to clinicopathological parameters. RESULTS: K1 was significantly, but moderately correlated with early SUVmean (r = 0.57, p < 0.001) and late SUVmean (r = 0.43, p < 0.001). K1, early SUVmean, and late SUVmean were moderately correlated with PSA level (respectively, r = 0.36, p = 0.004; r = 0.67, p < 0.001; r = 0.51, p < 0.001). Concerning GS, K1 was higher for patients with GS ≥ 4 + 3 than for patients with GS < 4 + 3 (median value 0.409 vs 0.272 min- 1, p < 0.001). No significant difference was observed for static parameters. CONCLUSIONS: FCH influx index K1 seems to be related to GS and could be a non-invasive tool to gain further information concerning tumor aggressiveness.
