18F-FDG for the staging of patients with differentiated thyroid cancer: comparison of a dual-head coincidence gamma camera with dedicated PET

Overview of the management of differentiated thyroid cancer

Thyroid cancer is an uncommon tumor accounting for roughly 1% of all new malignancies. Differentiated (ie, papillary or follicular) thyroid carcinoma is usually asymptomatic, and frequently appears as a solitary thyroid nodule but few show cervical lymphadenopathy or metastasis to lung, bone, or liver. Fine needle aspiration (FNA) is recommended in the initial diagnostic test. Depending on the size of the lesion and other associated risk factors, most patients are treated with total or near total thyroidectomy. Postoperative radioiodine ablation is performed when tumor has a potential for recurrence. Recurrence rates and cancer-specific mortality is decreased by suppressing thyroid stimulating hormone (TSH). Long-term surveillance and follow-up with physical examination every 3 to 6 months for 2 years and then annually if patient remains cancer free. Whole body iodine scans are done every 12 months for follow-up until one negative scan (either withdrawal of thyroid hormone or rhodium complex -TSH). Thyroglobulin measurements (with antithyroglobulin antibodies) and ultrasound neck are suggested at 6 and 12 months and then annually if disease free.

Investigation of thyroid, head, and neck cancers with PET

PET with [(18)F]-fluorodeoxyglucose (FDG) has been accepted as a useful imaging modality for the diagnosis of a variety of malignancies. This article discusses the use of FDG-PET in the management of patients with thyroid and head or neck cancers.

Detection of recurrent colorectal carcinoma by 18F-FDG: comparison of the clinical performances of FDG PET and FDG CDET

OBJECTIVES

To assess the clinical performance of fluorodeoxyglucose positron emission tomography (FDG PET) using either a coincidence (CDET) gamma camera or PET equipment with Nal crystals for the detection of recurrences of colorectal cancer.

METHODS

From July 1997 to December 1999, 290 examinations were performed in 244 patients using a CDET gamma camera (2-dimensional system with 19 mm thick crystals). Additionally, from January 2000 to July 2002, 354 examinations were performed in 303 patients using PET (3-dimensional system with Nal crystals).

RESULTS

Four hundred and seventy-three of the 644 examinations performed were evaluable on the basis of histological data (202 examinations) or more than 6 months of follow-up (273 examinations). The performances of the two systems were equivalent on a patient basis (sensitivity, specificity and accuracy of dedicated PET was 92%, 84% and 90%, respectively; and sensitivity, specificity and accuracy of CDET was 90%, 94% and 91%, respectively). On a site basis, a highly significant reduction in sensitivity was observed for lesions < or = 10 mm vs. > 10 mm with both PET and the CDET gamma camera, but no difference was observed between PET and CDET according to the size of the lesions.

CONCLUSION

For detection of recurrent colorectal carcinoma, a 2-D coincidence gamma camera with 19 mm thick crystals and optimized acquisition and reconstruction parameters provides similar results in terms of accuracy, both per patient and per site, to those of an Nal PET camera.

[18F]Fluorodeoxyglucose Triple-Head Coincident Imaging as an Adjunct to 131I Scanning for Follow-Up of Papillary Thyroid Carcinoma

OBJECTIVE

To evaluate the feasibility of using [(18)F]fluorodeoxyglucose ((18)FDG) triple-head coincidence imaging as a potential cost-effective alternative to positron emission tomography in the setting of suspected recurrence of papillary thyroid carcinoma.

METHODS

We retrospectively studied 10 patients with suspected recurrence of papillary carcinoma of the thyroid, who underwent (18)FDG coincidence imaging,(131)I scanning, and a reference anatomic scan (computed tomography, magnetic resonance imaging, or both) within 1 year in most cases.

RESULTS

The (131)I scan detected the recurrence in five patients (62.5%) and failed to reveal recurrent cancer in three patients (37.5%); in contrast,(18)FDG imaging detected the recurrence in eight patients (100%) and was true negative in two patients in whom the scans were performed more than 1 year after effective therapy for the recurrence. The sensitivity of detection was unrelated to lesion size. The (18)FDG imaging results led to additional radiotherapy in all (131)I-negative patients, two of whom had high thyroglobulin levels and one of whom had a low thyroglobulin concentration but the presence of antithy-roglobulin antibodies.

CONCLUSION

We conclude that (18)FDG triple-head coincidence imaging is useful for routine management of patients with thyroid cancer who have no abnormalities detected on (131)I scans but have high serum thyroglobulin levels. This technique, however, may not be as sensitive as a dedicated positron emission tomographic device, particularly for the assessment of small tumors.