The relationship and optimal cutoff value between dual-phase corrected whole-body uptake ratio (CUR) and serum CEA level in recurrent/metastatic colorectal carcinoma: Dual-phase whole body protocol using time-of-flight (TOF) imaging

Objectives: We evaluate whether the corrected SUR has a lineal relationship with a serum CEA level, and to determine the cutoff level of SUV and CEA level in metastatic focus of recurrent colorectal carcinoma. Tumor to background contrast in whole-body PET/CT at 1 hour and 2 hour The relationship and optimal cutoff value between % change max SUV and serum CEA level in metastatic colorectal carcinoma: ROC analysis.

Methods: 48 patients (M: F=32:16, mean age 56.1+/-11) who were previously operated for primary colorectal carcinoma enrolled for evaluating metastasis from April 2007 to Feb 2008. An one hour and two hour whole body PET/CT (brain to foot) (Gemini TF PET/CT, Philips Medical Systems) was performed after injection of 370-555 MBq of F-18 FDG. The serum CEA level (CEA) measured. The time interval between the PET/CT and the CEA 6.8 +/- 3.1 days. Background (BG) correct uptake ratio (CUR)[CUR/BG]= maximum SUV of the ROI/ background value (mean SUV of the liver) calculated and then % change of the CUR at 1 hour and CUR at 2 hour were calculated. Results: Among the 48 patients, recurrence was confirmed in 41patients, and the remaining 9 patients were disease-free. A significant lineal correlation between % change of the CUR at 1 hour and CUR at 2 hour and CEA was founded using ROC analysis (P<0.05). The optimal cutoff value of the % change of the CUR at 1 hour and CUR at 2 hour and CEA were 71 % (sensitivity86.7, specificity 83.3, AUC 0.8780.047) and 9.44ng/ml (sensitivity 73.3, specificity 87.5, AUC 0.857+/-0.051) respectively. The difference of AUC between max SUV and CEA was not significantly different (0.0220.065 , P = 0.739). Conclusions: The SUV of metastatic focus was shown a lineal correlation with serum CEA level in patients with recurrent colorectal carcinoma. The max SUV of 5.37 and the CEA level of 11.44 ng/ml was best cutoff value in detecting the metastatic focus.