Abstract
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Aim: To determine the most suitable compartment model for tumour uptake of the amino acid tracer [18F]-fluciclovine in patients with invasive breast cancer (IBC), through the use of dynamic PET imaging, and study differences in tracer kinetics between the main tumour receptor subtypes.
Methods: Forty patients with biopsy proven IBC underwent dynamic 18F-fluciclovine PET/CT imaging of the breasts for 20 minutes post injection (370 ± 20% MBq). Reversible and irreversible one- and two-tissue compartment (1TC and 2TC) models were fitted to the 40 time-activity-curves (TACS). The most suitable compartmental model to describe the uptake was evaluated using Akaike and Bayesian information criteria (AIC and BIC) and the precision of the kinetic parameters from these fits were determined using Monte Carlo simulation techniques. Differences in kinetics between tumour receptor subtypes [ER+HER2-, HER2+ (including HER2+ER and HER2+ER+) and triple-receptor negative (TN)] were then evaluated, and correlations between the kinetic parameters and SUV were assessed.
Results: A reversible 2TC model provided the best description of fluciclovine uptake in breast tumours according to AIC and BIC evaluations. However, the Monte Carlo simulation study indicated that a reversible 1TC model provided more accurate estimates of the individual kinetic parameters. 1TC K1 values (mL/cm3/min) ranged from 0.09 to 0.38 with a mean of 0.20, 1TC k2 values (min-1) ranged from 0.04 to 0.29 with a mean of 0.13. There was no significant difference (p>0.05) between kinetic parameters, described by the one-tissue compartment model, for the three tumour sub-types. There were also no significant differences (p>0.05) in SUV for the three tumour-subtypes. Good correlations between SUV and K1 (R = 0.804), and SUV and VT (R = 0.756) were observed.
Conclusions: A reversible 1TC model provides the most precise estimates of the kinetic parameters of 18F-fluciclovine in IBC. The kinetic parameters obtained from the TAC fits that describe the uptake of fluciclovine are independent of tumour sub-type. Future work will compare the SUVs and kinetic rate constants for the optimal compartment model, with a range of biological parameters.
