18F-FDG PET-CT in evaluation of postoperative colorectal cancer patients with rising CEA level.

INTRODUCTION: Accurate imaging of patients with possible recurrent colorectal cancer (CRC) is vital, as it is now clear that curative surgery is still possible for a proportion of patients with metastatic disease. Follow-up is usually performed with carcinoembryonic antigen (CEA) level, computerized tomography (CT) and other conventional imaging techniques, but in the last few years, functional imaging using integrated positron emission tomography and CT (PET/CT) is being used increasingly to identify recurrent disease.

AIM: To evaluate the usefulness of integrated PET/CT in the follow-up of postoperative CRC patients with rising CEA level.

MATERIALS AND METHODS: Seventy-three histopathologically proven patients with postoperative CRC having undergone CT of chest and abdomen were subjected to PET/CT imaging. Whole-body PET/CT imaging (base of skull to mid thigh region) was performed in all patients. These patients were grouped into various categories depending on CEA level.

RESULTS: Of the total 73 patients, 22 had CEA levels within normal limits (<3 ng/ml). Among the remaining 51 patients, CT showed recurrence in 23 (45%) patients, whereas PET/CT was positive in 36 (71%) patients. In group 1 (CEA 3-5 ng/ml), CT was positive in four of 13 (30%) patients and PET/CT was positive in seven of 13 (53%) patients, in group 2 (CEA 5-10 ng/ml) CT was positive in three of nine (33%) patients and PET/CT was positive in six of nine (67%) patients, in group 3 (CEA 10-20 ng/ml) CT was positive in five of 11 (45%) patients and PET/CT was positive in seven of 11(63%) patients, in group 4 (CEA 20-50 ng/ml) CT was positive in five of nine (55%) patients and PET/CT was positive in seven of nine (77%) patients and in group 5 (CEA >50 ng/ml) CT was positive in six of nine (67%) patients and PET/CT was positive in nine of nine (100%) patients. Among 23 patients in whom both CT and PET/CT were positive, PET/CT showed extra lesions in 17 (73%) patients and changed the management in 11 (47%) patients. PET was negative in four patients with positive findings on CT, thereby changing the management. Of the total of 51 patients, PET/CT changed the management in 28 (55%) patients.

CONCLUSION: This study shows an overall detection rate of 71% for PET/CT compared with 55% for CT in postoperative CRC patients with increasing CEA. PET/CT changes the management in half of the patients, highlighting the superior role of fluorodeoxyglucose PET/CT scan over CT scan.