Thyroid Cancer and (FDG)PET/CT Scan

Background and Rational (Introduction) Differentiated thyroid carcinoma (DTC) have favorable prognosis. Overall 10-year survival is 93% for papillary carcinoma, and 85% for follicular carcinoma(1). After total thyroidectomy followed by radioiodine remnant ablation, DTC patients are screened for recurrence by measuring the levels of both Tg and TgAb and I-131 whole body scan (WBS) in the follow-up (2) It is reported that elevated TgAb may indicate the recurrent and/or metastatic disease and can be used as an alternative of the tumor marker for DTC . The I-131 WBS has high specificity to detect recurrence (50 to 60% in papillary thyroid carcinoma and 64 to 67% in follicular thyroid carcinoma) (3,4). The I-131WBS showed negative finding in 10 to 15% of patients with detectable serum Tg levels(5). Two factors may account for discrepancy between serum Tg and I-131 WBS . First, the tumor size might be too small to be detected by WBS. Second, the tumor cell may lose the ability to trap radioiodine while still able to secret Tg(6,7). It becomes necessary to investigate with other modalities to identify possible residual disease to initiate the appropriate treatment. (8) Positron emission tomography with 2-deoxy-2-\[fluorine-18\]fluoro- D-glucose integrated with computed tomography (18F-FDG PET/CT) has emerged as a powerful imaging tool for the detection of various cancers. (9) The combined acquisition of PET and CT has synergistic advantages over PET or CT alone and minimizes their individual limitations. (10) It is a valuable tool for staging and re staging of some tumors and has an important role in the detection of recurrence in asymptomatic patients with rising tumor marker levels and patients with negative or equivocal findings on conventional imaging techniques.(11) Aim of the study The aim of this study was to evaluate the diagnostic accuracy of (PET/CT) in patients with suspected thyroid cancer recurrence or metastasis , with differentiated thyroid cancer (DTC) patients who show elevated serum thyroglobulin (Tg) or antithyroglobulin antibody (TgAb) level with negative radioiodine whole body scan (I-WBS).

Sex

All

Minimum age

10 Years

Maximum age

80 Years

Inclusion Criteria:

* · This study will include thyroid cancer patients of wide age ranges, who underwent total thyroidectomy with negative radioactive iodine whole body scan (I-WBS) and elevated stimulated thyroglobulin (sTg) or thyroglobulin antibody (TgAb) levels.

  * Patients able to sleep in a fixed position for 20 minutes.

Exclusion Criteria:

Patients unable to sit calm without movement during imaging.

* Severely ill patients.
* Patients' blood glucose \> 11.1 mmol/L (200 mg/dL) measured by glucometer immediately prior to scan.
* Pregnancy