How Long of a Dynamic 3′-Deoxy-3′-[¹⁸F]fluorothymidine ([¹⁸F]FLT) PET Acquisition Is Needed for Robust Kinetic Analysis in Breast Cancer?

Purpose: To quantitatively evaluate the minimally required scanning time of 3′-deoxy-3′-[¹⁸F]fluorothymidine ([¹⁸F]FLT) positron emission tomography (PET) dynamic acquisition for accurate kinetic assessment of the proliferation in breast cancer tumors. Procedures: Within a therapeutic intervention trial, 26 breast tumors of 8 breast cancer patients were analyzed from 30-min dynamic [¹⁸F]FLT-PET acquisitions. PET/CT was acquired on a Gemini TF 64 system (Philips Healthcare) and reconstructed into 26 frames (8 × 15 s, 6 × 30 s, 5 × 1 min, 5 × 2 min, and 2 × 5 min). Maximum activity concentrations (Bq/ml) of volume of interests over tumors and plasma in descending aorta were obtained over time frames. Kinetic parameters were estimated using in-house developed software with the two-tissue three-compartment irreversible model (2TCM) (K₁, k₂, k₃, and K_i; k₄ = 0) and Patlak model (K_i) based on different acquisition durations (T_d) (10, 12, 14, 16, 20, 25, and 30 min, separately). Different linear regression onset time (T₀) points (1, 2, 3, 4, and 5 min) were applied in Patlak analysis. K_i of the 30-min data set was taken as the gold standard for comparison. Pearson product-moment correlation coefficient (R) of 0.9 was chosen as a limit for the correlation. Results: The correlation of kinetic parameters between the gold standard and the abbreviated dynamic data series increased with longer T_d from 10 to 30 min. k₂ and k₃ using 2TCM and K_i using Patlak model revealed poor correlations for dynamic PET with T_d ≤ 14 min (k₂: R = 0.84, 0.85, 0.86; k₃: R = 0.67, 0.67, 0.67; K_i: R = 0.72, 0.78, 0.87 at T_d = 10, 12, and 14 min, respectively). Excellent correlations were shown for all kinetic parameters when T_d ≥ 16 min regardless of the kinetic model and T₀ value (R > 0.9). Conclusions: This study indicates that a 16-min dynamic PET acquisition appears to be sufficient to provide accurate [¹⁸F]FLT kinetics to quantitatively assess the proliferation in breast cancer lesions.