18F-fluorodeoxyglucose positron emission tomography-computed tomography for suspected recurrent papillary thyroid cancer: early experience at Sunnybrook Health Sciences Centre.

Objectives: To report the initial experience with combined 18F-fluorodeoxyglucose positron emission tomography (FDG PET)/computed tomography (CT) imaging for suspected recurrent papillary differentiated thyroid cancer (DTC) at Sunnybrook Health Sciences Centre (SHSC), Toronto.

Design: Single institution retrospective study.

Methods: Consecutive patients from SHSC who underwent FDG PET/CT imaging for suspected recurrent DTC over a period of 2.5 years were identified and their charts reviewed.

Main Outcome Measure: Qualitative appraisal of FDG PET/CT imaging in suspected recurrent DTC.

Results: Sixteen patients (14F, 2M) were identified accounting for 17 FDG PET/CT scans. Three scans (18%) in 3 different patients were reported as suspicious for recurrent disease in the neck (1-3 lesions) and were considered "positive". All were subsequently confirmed pathologically (4-13 positive lymph nodes post operatively). Prior conventional imaging was abnormal in two patients. Two patients had an elevated non-stimulated thyroglobulin (TG) < 10 ng/mL (4.9 and 9.4). The remaining patient had a TG < 0.3 ng/mL but was anti-TG antibody positive (84 IUx10-3/L). With a median follow up of 15 months (range 7-36) there were no false positive or negative scans. Incidental pathology (breast cancer, large bowel polyps) was identified on a further 2/17 scans (12%).

Conclusions: FDG PET/CT imaging is able to detect recurrent DTC in patients with low TG levels. It can complement conventional imaging findings and exclude distant FDG-avid metastases prior to surgery. It may underestimate the number of positive lymph nodes in the neck. Occult pathology may be identified with whole body FDG PET/CT.