Kunihiro Nakada, Presenter: Nothing to Disclose

Masayuki Sakurai MD, PhD, Abstract Co-Author: Nothing to Disclose

Yuko Kawai MD, PhD, Abstract Co-Author: Nothing to Disclose

Hiroki Sugie MD, Abstract Co-Author: Nothing to Disclose

Ysushi Furuta Furuta MD, PhD, Abstract Co-Author: Nothing to Disclose

Hiromasa Takahashi, Abstract Co-Author: Nothing to Disclose

Mutsuo Beniko MD, PhD, Abstract Co-Author: Nothing to Disclose

The purpose of the study was to determine diagnostic value of PET/CT with F-18 FDG in detection of residual or metastatic tumor in post-surgical differentiated cancer under thyrotropin (TSH) stimulation.

45 patients with differentiated thyroid cancer who had previously undergone total thyroidectomy were included. Patients underwent PET/CT with FDG and SPECT/CT with I-131 on the same day under TSH stimulation. TSH stimulation was achieved either by 2 consecutive days injection of rhTSH or by 14 days withdrawal of T3. Low iodine diet was applied from 7 days before to the next day of I-131 ingestion. 48-I-131 SPECT/CT and FDG PET/CT were acquired 48-73hrs after I-131 ingestion..Also, blood tests of TSH, Tg and TgAb were done. Serum TSH (μU/ml) levels at I-131 administration in patients with rhTSH stimulation and those with hypothyroidism were 185±34 and 53±15, respectively. SPECT/CT and PET CT findings were interpreted by 2 independent nuclear medicine physicians. Final confirmation was made by pathologic correlation in 36 and by comparison with other imaging modalities and clinical course in 9.

In 12 patients with positive TgAb, stimulated Tg remained undetectable in 11. PET/CT was positive in 9 while SPECT/CT was positive in 3. PET/CT detected I-131 negative lesions in 4 out of 12 patients (33%). In 33 patients with negative TgAb, stimulated Tg was >10 (ng/ml)) in 28. PT/CT was positive in 22 while SPECT/CT was positive in 13. PET/CT detected I-131 negative lesions in 7 of 33 patients (24%) . However, pathologic correlation confirmed that false positive FDG uptake was seen in 9 (18%) of 45 patients. The cause of false positive uptake was reactive lymph node in 3, lung cancer in 2, colon cancer in 2, and granuloma in 2, respectively. In 3 patients, co-exitence of true positive and false positive FDG uptake was observed. False negative PET/CT results were seen in 5 out of 45 patients(11%). .,

FDG PET/CT under TSH stimulation detectedI-131 negative tumors in 22% of the patients. However, false positive results were also found in 18% of the patients. Thus, pathologic correlation and comparison with other modalities should be essential before considering aggressive therapies on basis of FDG PET/CT findings.

False positive rate of FDG PET/CT with TSH stimulation could be higher than expected.

Nakada, K, Sakurai, M, Kawai, Y, Sugie, H, Furuta, Y, Takahashi, H, Beniko, M, Clinical Value of TSH-stimulated FDG PET/CT in Detection of Residual or Metastatic Tumor in Differentiated Thyroid Cancer.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12020345.html