Dynamic and Static Approaches to Quantifying ¹⁸F-FDG Uptake for Measuring Cancer Response to Therapy, Including the Effect of Granulocyte CSF

¹ Department of Bioengineering, University of Washington, Seattle, Washington; Division of Nuclear Medicine, University of Washington, Seattle, Washington
² Division of Nuclear Medicine, University of Washington, Seattle, Washington
³ Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, Washington
⁴ Department of Bioengineering, University of Washington, Seattle, Washington; Division of Nuclear Medicine, University of Washington, Seattle, Washington; and

^* To whom correspondence should be addressed. E-mail: dam{at}u.washington.edu.

	Abstract

The response of cancer to chemotherapy can be quantified using ¹⁸F-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 ¹⁸F-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 ¹⁸F-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 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 ¹⁸F-FDG blood AUC. The maximum detectable percentage change in ¹⁸F-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 ¹⁸F-FDG uptake.

Key Words: SUV, MRFDG, ¹⁸F-FDG, granulocyte CSF, response to therapy

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