Validity of Simplified 3′-Deoxy-3′-[(18)F]Fluorothymidine Uptake Measures for Monitoring Response to Chemotherapy in Locally Advanced Breast Cancer

PURPOSE: Positron emission tomography using 3′-deoxy-3′-[(18)F]fluorothymidine ([(18)F]FLT) has been suggested as a means for monitoring response to chemotherapy. The aim of this study was to evaluate the validity of simplified uptake measures for assessing response to chemotherapy using [(18)F]FLT in locally advanced breast cancer (LABC). PROCEDURES: Fifteen LABC patients underwent dynamic [(18)F]FLT scans both prior to and after the first cycle of chemotherapy with fluorouracil, epirubicin or doxorubicin, and cyclophosphamide. The net uptake rate constant of [(18)F]FLT, K (i), determined by non-linear regression (NLR) of an irreversible two-tissue compartment model was used as the gold standard. In addition to Patlak graphical analysis, standardised uptake values (SUV) and tumour-to-whole blood ratio (TBR) were used for analysing [(18)F]FLT data. Correlations and relationships between simplified uptake measures and NLR before and after chemotherapy were assessed using regression analysis. RESULTS: No significant differences in both pre- and post-chemotherapy relationships between any of the simplified uptake measures and NLR were found. However, changes in SUV between baseline and post-therapy scans showed a significant negative bias and slope less than one, while TBR did not. CONCLUSIONS: In LABC, TBR instead of SUV may be preferred for monitoring response to chemotherapy with [(18)F]FLT.