Dynamic and static approaches to quantifying 18F-FDG uptake for measuring cancer response to therapy, including the effect of granulocyte CSF.

UNLABELLED

The response of cancer to chemotherapy can be quantified using (18)F-FDG to indicate changes in tumor metabolism. Quantification using the standardized uptake value (SUV) is more feasible for clinical practice than is the metabolic rate of (18)F-FDG (MRFDG), which requires longer, dynamic scanning. The relationship between MRFDG and SUV depends in part on how each accounts for blood clearance of tracer. We tested whether chemotherapy and treatment with granulocyte colony-stimulating factor (CSF) changed the blood clearance curves and therefore affected the relationship between MRFDG and SUV.

METHODS

Thirty-nine patients with locally advanced breast cancer underwent (18)F-FDG PET before and after chemotherapy, including granulocyte CSF. The area under the curve (AUC) for blood clearance was determined before and after therapy. MRFDGs were determined by graphical analyses, whereas SUVs were calculated using the standard formula normalized by body weight. MRFDG and SUVs were compared with each other and with tumor response. Paired percentage changes in MRFDG and SUV were also divided into tertiles based on pretherapy SUV to investigate differences in the relative sensitivity of SUV changes to MRFDG changes due to baseline tumor uptake.

RESULTS

Despite a small but statistically significant 6% decrease in blood AUCs after therapy (P = 0.02), SUV and MRFDG did not differ significantly in slope (P = 0.53) or in correlation before and after therapy (r = 0.95 for both). Percentage changes in MRFDG and SUV between serial scans correlated with each other (r = 0.84) and with patient response (P <or= 0.06). The maximum detectable percentage change in SUV and the slope of percentage changes in MRFDG versus SUV for the patient tertile with the lowest baseline SUVs (65% +/- 5% [+/-SE], slope (m) = 0.40 +/- 0.12, n = 13) were significantly lower than for the other patients (86% +/- 3%, m = 0.85 +/- 0.10, n = 26, P = 0.01 for both).

CONCLUSION

Chemotherapy and granulocyte CSF treatment resulted in a lower (18)F-FDG blood AUC. The maximum detectable percentage change in (18)F-FDG uptake is less when quantifying via static SUV than via dynamic MRFDG. This effect is small in most patients but may have clinical significance for measuring the response of patients with a low pretherapy (18)F-FDG uptake.