18F-5-fluorouracil dynamic positron emission tomography/computed tomography shows decreased tracer activity after bevacizumab in colorectal metastases

Objective The aim of this study was to evaluate the potential of fluorine-18 (F-18)-5-fluorouracil (F-18-5-FU) positron emission tomography/computed tomography (PET/CT) to show differences in 5-FU activity in metastatic colorectal cancer before and after treatment with bevacizumab. Methods This was a pilot study of five patients with newly diagnosed and untreated metastatic colorectal adenocarcinoma. The presence of cancer was confirmed by histopathological analysis before enrollment. Patients underwent F-18-5-FU PET/CT scanning before treatment and at approximately 24 h postbevacizumab. PET/CT scanning consisted of a dynamic acquisition of images taken 0-20 min after injection of radiotracer. The degree of F-18-5-FU activity at the metastatic sites was assessed using visual interpretation and semiquantitative standardized uptake value analyses. Results The sizes of the metastatic lesions ranged from the smallest lesion measuring 3.04 x 1.50 cm to the largest measuring 4.19 x 2.76 cm. By drawing regions of interest, time-activity curves were generated at each tumor site and area under the curve (AUC) analyses were carried out. At baseline, during the first 5 min after F-18-5-FU injection the mean AUC(tumor)/AUC(aorta) ratio was 1.24 +/- 0.30 (range, 0.424-2.14). Less than 24 h after the administration of bevacizumab, the AUC(tumor)/AUC(aorta) ratio decreased to 1.06 +/- 0.32 (range, 0.23-2.13, P=0.04), which represented an average decline of 20.2% (range, 0.4-45%). Radiotracer uptake on the 5, 10, 15, and 20-min images did not show any significant change between baseline and posttreatment. Follow-up CT imaging showed stable tumor size in one patient and a decrease in metastasis size in the remaining four patients. Conclusion In this pilot study of five patients with metastatic colorectal carcinoma, F-18-5-FU PET/CT scanning showed a significant perfusion-related decrease in tracer activity 24 h postbevacizumab. Nucl Med Commun 32:343-347 (C) 2011 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.