Paola Sbragia MD, Presenter: Nothing to Disclose

Lorenzo Faggioni MD, Abstract Co-Author: Nothing to Disclose

Francesca Cerri, Abstract Co-Author: Nothing to Disclose

Assuero Giorgetti, Abstract Co-Author: Nothing to Disclose

Valeria Bottici MD, Abstract Co-Author: Nothing to Disclose

Francesca Bianchi, Abstract Co-Author: Nothing to Disclose

Aldo Pinchera MD, Abstract Co-Author: Nothing to Disclose

Carlo Bartolozzi MD, Abstract Co-Author: Nothing to Disclose

00030490-DMT et al, Abstract Co-Author: Nothing to Disclose

To investigate the diagnostic efficacy of CT and total body FDG-PET in patients affected by differentiated thyroid carcinoma (DTC) negative post-131I (RAI) therapy whole body scan (WBS) and detectable serum thyroglobulin (Tg) level following total or near-total thyroidectomy and RAI treatment.

We studied 49 pts (mean age 36±12.2 yrs, 32 females, 17 males) with DTC (45 papillary e 4 follicular) with post-therapy 131I WBS negative and detectable Tg (mean 56±290 ng/ml, range 0.58-1725). In all pts Tg stimulation test with recombinant human TSH (rhTSH) at the start of the study was performed. The second day after the second vial of rhTSH, total body FDG-PET was performed and images were compared with those obtained with CT scan performed at the first day.

The mean value of serum Tg level after rhTSH stimulation was 74.4±314.4 ng/ml. CT was negative in 53% of pts (26/49) and positive in 47% (23/49), and revealed local disease in 12 pts, lymph node mets in 3, and lung mets in 8. FDG-PET was negative in 75% (37/49) pts and showed local disease in 6 pts, lymph node mets in 2, and lung mets in 4. In patients with negative post-RAI WBS and detectable serum Tg levels, CT demonstrated a higher number of lesions than FDG-PET (p=0.02). CT and FDG-PET findings were concordant in 36/49 (74%) pts, being both positive in 11 pts and both negative in 25 pts. CT and FDG-PET were discordant in 13/49 (26%), 12 being CT+/FDG-PET- and 1 CT-/FDG-PET+ (aspecific lung uptake). Mean Tg serum levels after rhTSH were significantly higher in FDG-PET+ pts than in FDG-PET- ones (221.45±594.26 vs 19.7±25.15 ng/ml, p<0.05), with no significant difference between CT+ and CT- pts. Moreover, a difference of serum Tg levels after rhTSH, although not statistically significant, was found in CT+/FDG-PET+ pts (285.6 ±671.6 ng/ml) compared with CT-/FDG-PET- (17.2±23.8ng/ml) and CT+/FDG-PET- pts (26.7±27.9 ng/ml) (p=0.059).

In conclusion our study evidence that in the pts with negative post RAI whole body scan and detectable serum Tg levels, the CT scan was more able to demonstrate a great number of lesions with respect to the FDG-PET. The serum Tg levels was more increased in patient PET+, moreover the pts with more increase of the Tg levels were positive with both methods.

CT  imaging has the potential to improve detectability and characterization of pts with persistence of disease.

Sbragia, P, Faggioni, L, Cerri, F, Giorgetti, A, Bottici, V, Bianchi, F, Pinchera, A, Bartolozzi, C, et al, 0, Comparative Benefit of CT Scan and Total Body FDG-PET in the Follow-up of Patients with Differentiated Thyroid Cancer with Negative Post-therapy 131I-WBS and Serum Tg Levels Detectable (Persistence of Disease).  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8011691.html