rhTSH stimulation before radioiodine therapy in thyroid cancer reduces the effective half-life of (131)I.

UNLABELLED: Recombinant human thyroid-stimulating hormone (rhTSH) is effectively used for exogenous thyroid-stimulating hormone (TSH) stimulation before diagnostic (131)I scintigraphy. It is not yet widely used for preparation of patients receiving a therapeutic amount of radioiodine. METHODS: The results of 64 consecutive therapeutic applications of rhTSH with regard to clinical tolerance and side effects were evaluated in comparison with 163 radioiodine therapies (RITs) done on patients with hypothyroidism after thyroxine withdrawal during the same period. All therapies-applying 1.1-10 GBq of (131)I-used a standardized protocol of patient preparation and activity application. RITs were followed by daily whole-body uptake measurements for 2-6 d, and a biexponential curve fit was used to obtain a short initial and afterward a long effective half-life of (131)I. Patients after rhTSH were evaluated as a whole group (group A, n = 64) and as a subset of that group with normal thyroglobulin (hTG) levels (group D, n = 18). Patients after endogenous TSH stimulation were evaluated as a whole group (group B, n = 163), as a subset of that group excluding all ablative RITs (group C, n = 113), and as a subset of that subset with normal hTG levels (group E, n = 87). RESULTS: rhTSH-stimulated patients showed significantly higher TSH values than did endogenously stimulated patients (P < 0.001). Furthermore, the effective half-life of (131)I was significantly prolonged after endogenous stimulation (e.g., 0.43 d for group A vs. 0. 54 d for group B, P < 0.001). All rhTSH applications were tolerated well and without serious side effects. The only side effects were 2 cases of nausea and headache. CONCLUSION: The use of rhTSH for stimulation of TSH before RIT is safe but also significantly reduces the effective half-life of (131)I. This is mainly due to a reduced renal iodine clearance in the hypothyroid state, but the bioavailability of radioiodine may be slightly overestimated because of larger amounts of intestinal (131)I after endogenous TSH stimulation.

F-18 FDG PET in insular thyroid cancer.

PURPOSE: Insular thyroid cancer (ITC) is known to be a rare subtype of follicular thyroid carcinoma showing poor differentiation and an unfavorable prognosis. The authors evaluated the use of F-18-fluorodeoxyglucose (FDG) positron emission tomography (PET) for restaging and follow-up in ITC. METHODS: Five patients (2 male, 3 female) with elevated thyroglobulin levels (mean, 86 ng/mL; range 1.3-180 ng/mL) during follow-up underwent FDG PET (Siemens ECAT Exact 47). PET results were correlated to histopathologic and radiologic findings as well as to the results of whole-body radioiodine scintigraphy. In 1 patient a series of 4 PET scans was done. RESULTS: FDG PET showed a total of 10 tumor sites, at least 1 in each patient. Four of those lesions were detected by computed tomography (CT) as well, which in addition revealed 3 lesions that had normal glucose consumption. Five PET lesions were missed by the CT scan because they were found outside the examined volume of CT. Only 1 PET-positive lesion was also radioiodine positive. Three radioiodine-positive lesions with normal glucose metabolism were detected. CONCLUSION: As known for well and poorly differentiated thyroid cancer of the follicular epithelium, ITC may also show discordance between radioiodine studies and FDG-positive lesions. Given their initially poor differentiation, the ITC clearly showed the expected dominance of less well-differentiated, FDG-positive lesions. Therefore, FDG PET seems to be a very useful tool for the staging and restaging of such tumors.

Enchondroma: a benign osseous lesion with high F-18 FDG uptake.

A woman was referred for fluorodeoxyglucose positron emission tomography for the staging of a malignant melanoma. Although no signs of metastatic melanoma were evident on the whole-body scan, focally increased uptake within the femoral metaphysis was noted. Radiographic and magnetic resonance examinations revealed an enchondroma as the cause of the increased uptake. Histopathologic verification was obtained. The final diagnosis was actively proliferating enchondroma. A grade I chondrosarcoma could be ruled out. Enchondromas may be responsible for focally increased FDG uptake in bone lesions and must be considered when positron emission tomographic scans obtained with FDG are evaluated in cancer staging.

Urinary fluorine-18 fluorodeoxyglucose excretion with and without intravenous application of furosemide.

METHODS: Twenty patients suffering from malignancy received furosemide, twenty patients were examined by FDG-PET without diuretics. Urine volume and radioactivity were measured before and after acquisition. Bladder activity was evaluated qualitatively and quantitatively. RESULTS: Radioactivity in the bladder was lower and the image quality higher in the furosemide group. SUV values showed a median of 3.0 in the furosemide and 6.0 in the control group. With furosemide, a larger excreted volume was seen compared to the control group. The furosemide group showed a significantly higher ratio of excreted/ injected radioactivity early after injection. However, the totally excreted radioactivity was not significantly different (p = 0.93). CONCLUSION: Diuretics cause a higher urine volume with a diluted FDG concentration leading to an improved image quality. Furosemide accelerates early renal FDG elimination, reducing radiation exposure.

Positron emission tomography for the staging of Hodgkin's lymphoma--increasing the body of evidence in favor of the method.

The staging of Hodgkin's lymphoma (HL) is crucial for an optimal therapy, and fluorine-18-deoxyglucose-positron emission tomography (FDG-PET) is increasingly used in this regard. However, there is still a scarcity of available data on the staging of HL. Twenty-eight consecutive patients with newly diagnosed HL were included in this study. PET results were compared with conventional staging, including clinical workup, computerized tomography (CT) and sonography. Evaluation was focused on the description of involved lymph node (LN) regions or organs rather than on a lesion-by-lesion analysis. In supradiaphragmal LN, the results of PET and CT scans were positive in 26% and negative in 68% of cases. Furthermore, PET was positive in 5% (CT negative), and CT showed enlarged LN in 1% of cases (PET negative). In infradiaphragmal LN, PET/CT results were positive in 10% and negative in 88% of cases. In 2% of cases, PET showed additional foci, while in 1% the CT was positive. PET changed the staging in 21% of cases (4 up-stagings, 2 down-stagings) and this was confirmed during follow-up. PET should therefore be routinely used for staging HL until larger clinical studies can demonstrate patients who may not require this additional investigation or those patients who are reliably staged on the basis of PET alone.