Combined PET/CT with Iodine-124 in Diagnosis of Mediastinal Micrometastases in Thyroid Carcinoma
L Freudenberg, G Antoch, R Görges, E Knust, T Beyer, J Debatin
Citation
L Freudenberg, G Antoch, R Görges, E Knust, T Beyer, J Debatin. Combined PET/CT with Iodine-124 in Diagnosis of Mediastinal Micrometastases in Thyroid Carcinoma. The Internet Journal of Nuclear Medicine. 2001 Volume 1 Number 1.
Abstract
Iodine-124 PET is an useful 3-dimensional imaging technique for diagnosis and management of thyroid diseases. The difficulty in interpretation of the PET scans with highly selective tracers like iodine-124, is the lack of identifiable anatomical structures, so an accurate anatomical localization of foci presenting abnormal uptake is problematic. Consequently, a combined PET/CT scanner can resolve these difficulties by co-registering PET and CT data in a single session allowing a correlation of functional and morphologic imaging.
A case is presented where iodine-124 produced by a clinical cyclotron was used with a combined PET/CT scanner for clinical staging of a patient with thyroid carcinoma.
Brief Report
A 54-year-old male with a history of an well differentiated (G1) follicular thyroid carcinoma (1cm in diameter penetration of the thyroid capsule; pT4 pN0 MX) was referred to the Department of Nuclear Medicine for radioiodine therapy. The medical history was inconspicuous. The physical examination showed a patient in good general condition. On admission time the following pathologic laboratory values were seen: Thyreoglobulin: 1.8 ng/ml, recovery test: 68%, thyroid stimulating hormone: 68 mU/l, fT3 <2.9 ng/ml and fT4 2.8 ng/ml. Cervical ultrasonography showed no pathological structures. Prior to further treatment, an accurate staging was desired.
Iodine-124 PET/CT
24 hours after the oral administration of 85 MBq of the positron-emitting radionuclide [iodine-124]-sodium-iodide [1] images on a combined PET/CT system were acquired (biograph, Siemens Medical Solutions Erlangen, Germany manufactured by CPS, Knoxville, USA). Projections from head to pelvis were obtained. The biograph consists of a single slice spiral CT (Somaton Emotion) and a dedicated full-ring PET scanner (ECAT HR+). The CT data are also used for PET attenuation correction in a 3D mode [2,3]. The PET scan alone showed pathologically increased tracer uptake in two cervically or mediastinal foci (Fig. 1, left).
Figure 1
An accurate anatomical localization of these foci was not completely possible as the tracer is highly specific. The CT scan alone showed no pathology. Image fusion of PET and the co-registrated CT enabled to attribute the pathological tracer uptake to an area close to the aorta representing mediastinal micrometastases.
Iodine-131 Scan
Iodine-131 Scan; Eight days after the oral administration of the therapeutic dose of 3,000 MBq Iodine-131 a whole body scan was acquired (Bodyscan, Siemens Erlangen, Germany) using a high energy collimator. Pathological tracer uptake was documented cervically and mediastinally
Figure 2
Discussion
Patients with well-differentiated thyroid cancer (WDTC) regularly have an excellent prognosis. However, staging is crucial for appropriate surgical treatment, radioiodine therapy, and, in advanced disease, external beam radiotherapy [4]. Besides whole-body iodine-131 scintigraphy, ultrasonography, fluorine-18 fluordeoxyglucose Positron Emission Tomography (FDG-PET) is an established diagnostic tool in the follow-up of thyreoidectomized patients with WDTC [4,5,6,7,8]. Another positron emitter suitable for PET imaging is iodine-124 with a half-life of 4.2 days. It has not been widely used because of a complex decay scheme including several high energy gamma rays [1, 9,10,11,12]. This 3-dimensional imaging technique has been shown to be an useful imaging technique for diagnosis and management of thyroid diseases [11]. However, the difficulty in interpretation of the PET scans with highly selective tracers like iodine-124, is the lack of identifiable anatomical structures [2]. The low anatomical resolution of the presented PET scan is insufficient for an accurate anatomical localization of foci with abnormal uptake (Fig. 1, right). In our case, the use of a combined PET/CT system provided accurately fused PET and CT images in a single session [2-3]. Fused images revealed mediastinal micrometastases of the thyroid carcinoma. Accurate metabolical and anatomical staging was therefore accomplished. Compared to iodine-131 whole body scan, iodine-124 PET/CT has shown to be superior in exact localisation of metastases.
Correspondence to
Dr. med. L. S. Freudenberg, M.A. Clinic and Policlinic for Nuclear Medicine University of Essen Hufelandstrasse 55 D-45122 Essen Germany Tel: +49 / 201 723-2032 Fax: +49 / 201 723-5964 Email: lutz.freudenberg@uni-essen.de