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Use of PET for Monitoring Cancer Therapy and for Predicting Outcome^*

¹ Department of Molecular and Medical Pharmacology, Ahmanson Biological Imaging Center, UCLA David Geffen School of Medicine, Los Angeles, California

View larger version (66K): [in a new window]   FIGURE 1. Examples of errors in calculation of SUVs. This patient with distal esophageal cancer was imaged before preoperative chemotherapy and after 2 wk of therapy. According to mean tumor SUVs in baseline and follow-up scans, tumor metabolic activity seems to have decreased significantly from 7.5 to 4.8. However, follow-up scan also demonstrates marked decrease in 18F-FDG uptake by all normal organs, for example, liver and brain. This finding indicates error in calculation of SUVs. In this case, injected dose had not been properly decay corrected for follow-up PET study. Thus, for calculation of SUVs, tissue activity concentration was divided by incorrectly high injected dose; accordingly, all SUVs in follow-up study were too low. Correct SUV in follow-up study was 7.0, indicating that there was no significant change in tumor metabolic activity.

View larger version (36K): [in a new window]   FIGURE 2. Marked changes in tumor 18F-FDG uptake may be missed by visual interpretation of 18F-FDG PET studies if images are not correctly scaled for display. In this example, patient with non–small cell lung cancer was studied before chemotherapy and after first cycle of chemotherapy. Images in top row are scaled to SUV of 5. Visually there seems to be no change in intensity of 18F-FDG uptake in tumor tissue from baseline scan to follow-up scan. However, maximum SUV of tumor in baseline scan was 11.5. In follow-up scan, SUV had decreased by more than 50% to 5.4; this value is still higher than maximum SUV used for scaling of display in top row. Accordingly, intensity of tumor 18F-FDG uptake appears to be unchanged. When baseline and follow-up images are scaled to maximum SUV of 12 (bottom row), marked decrease in tumor 18F-FDG uptake becomes obvious.

View larger version (65K): [in a new window]   FIGURE 3. By comparing baseline and follow-up scans, radiation-induced inflammation frequently can be differentiated from viable tumor tissue. This patient with esophageal cancer was studied by 18F-FDG PET before and 3 wk after completion of chemoradiotherapy. In scan obtained after chemoradiotherapy, there is linear uptake along esophagus. Comparison with baseline scan demonstrates that intensity of tumor 18F-FDG uptake has decreased markedly. Esophageal tracer uptake in area of tumor is not higher than in other parts of esophagus, indicating that findings in follow-up scan are related to esophagitis and not to residual tumor tissue.