Imaging with (124)I in differentiated thyroid carcinoma: is PET/MRI superior to PET/CT?

PURPOSE: The aim of this study was to compare integrated PET/CT and PET/MRI for their usefulness in detecting and categorizing cervical iodine-positive lesions in patients with differentiated thyroid cancer using (124)I as tracer. METHODS: The study group comprised 65 patients at high risk of iodine-positive metastasis who underwent PET/CT (low-dose CT scan, PET acquisition time 2 min; PET/CT2) followed by PET/MRI of the neck 24 h after (124)I administration. PET images from both modalities were analysed for the numbers of tracer-positive lesions. Two different acquisition times were used for the comparisons, one matching the PET/CT2 acquisition time (2 min, PET/MRI2) and the other covering the whole MRI scan time (30 min, PET/MRI30). Iodine-positive lesions were categorized as metastasis, thyroid remnant or inconclusive according to their location on the PET/CT images. Morphological information provided by MRI was considered for evaluation of lesions on PET/MRI and for volume information. RESULTS: PET/MRI2 detected significantly more iodine-positive metastases and thyroid remnants than PET/CT2 (72 vs. 60, p = 0.002, and 100 vs. 80, p = 0.001, respectively), but the numbers of patients with at least one tumour lesion identified were not significantly different (21/65 vs. 17/65 patients). PET/MRI30 tended to detect more PET-positive metastases than PET/MRI2 (88 vs. 72), but the difference was not significant (p = 0.07). Of 21 lesions classified as inconclusive on PET/CT, 5 were assigned to metastasis or thyroid remnant when evaluated by PET/MRI. Volume information was available in 34 % of iodine-positive metastases and 2 % of thyroid remnants on PET/MRI. CONCLUSIONS: PET/MRI of the neck was found to be superior to PET/CT in detecting iodine-positive lesions. This was attributed to the higher sensitivity of the PET component, Although helpful in some cases, we found no substantial advantage of PET/MRI over PET/CT in categorizing iodine-positive lesions as either metastasis or thyroid remnant. Volume information provided by MRI for some iodine-positive lesions might be useful in dosimetry.

Cancer of unknown primary.

FDG-PET has been proven to be very sensitive in detecting a large variety of carcinomas. The FDG accumulation in malignant tumors is quite stereotyped and often reflects the aggressiveness of the tumor. Therefore, FDG appears to be suitable to detect unknown primaries independent of the type of disease. Being unaware of the site of the primary and also being unaware of the intensity of glucose metabolism, the interpretation of FDG-PET images needs rules accepting a reduced specificity for the definition of malignancy. However, due to physiological FDG-uptake in the head and neck area, especially in lymphatic tissue and vocal cords, one has to accept a high rate of equivocal findings interpreting FDG-PET alone. In this situation, the use of dual-modality PET/CT is of particular value. It allows for correlating the suspicious or unclear PET finding directly with morphology and by that the rate of false-equivocal or false-positive findings is reduced. In addition, PET/CT can precisely define the site of the PET finding in terms of anatomy, helping to direct the surgeon. This characteristic is of different value depending on the location of the primary and tends to be of utmost importance in the head and neck area. Finally, CT by itself may contribute with the detection of PET-negative findings. Thus in conclusion, PET and PET/CT can help localize the primary in CUP in approximately 40% of all cases, even after a thorough work-up with a variety of other investigations.

Pioglitazone therapy in progressive differentiated thyroid carcinoma.

AIM: Rosiglitazone achieved promising results in progressive differentiated thyroid carcinoma (DTC) with redifferentiative and antiproliferative effects, but has been taken off the market. Thus we evaluated another glitazone, pioglitazone, expecting similar positive results. PATIENT, MATERIALS, METHODS: Five patients with progressive DTC and no or only negligible iodine uptake were enrolled. Oral pioglitazone treatment was applied for 6 months. The re-differentiative effect was assessed by 124I-NaI PET/CT dosimetry and the anti-proliferative effect by 18F-FDG PET/CT imaging. RESULTS: A redifferentiative effect of pioglitazone could not be shown. Lesion dosimetry indicated that 3/5 patients had unchanged no lesion absorbed dose per administered activity (LDpA) in any tumour lesion, 2/5 patients had a deterioration of LDpA within some lesions, thus radioiodine therapy was not performed in any patient. Volumetric analysis, using RECIST criteria, revealed progressive disease in 3/5 patients and stable disease in 2/5 patients. Metabolic changes, using EORTC criteria, revealed 3/5 patients with progressive metabolic disease, 1/5 patient with stable metabolic disease and 1/5 patients with partial metabolic response. The medication was well-tolerated, and no patient developed clinically important toxicity associated with the treatment. CONCLUSION: Pioglitazone revealed some positive effects in radioiodine negative and progressive DTC patients but it did not fulfill the expectations given by the results of rosiglitazone therapy.

Estimation of tumour mass in patients with differentiated thyroid carcinoma using serum thyroglobulin.

UNLABELLED: Serum thyroglobulin (Tg) is a reliable tumour marker in follow-up of patients with differentiated thyroid carcinoma (DTC). A positive correlation between Tg level and tumour mass was recently observed, but no attempts were made to derive a numerical relation. The aim of this study was to derive a numerical relationship between serum Tg level and tumour mass that allows optimizing the diagnostic procedures. PATIENTS, METHOD: 78 DTC patients with tumour lesions in either 124I-NaI or 18F-FDG PET/CT were included. For each patient, the total tumour mass was determined functionally in iodine- and FDG-positive lesions as well as morphologically in only CT-positive lesions. The serum Tg level was measured under TSH stimulation prior to imaging. Regression analyses were performed to derive an approach for estimation of the total tumour mass based on Tg levels. RESULTS: A positive correlation of serum Tg and tumour mass was confirmed and a mathematical expression was given to estimate the tumour mass along with its 95% confidence interval using only the serum Tg level. The results demonstrated that the range of predicted tumour mass was higher per serum Tg unit for iodine-positive lesions than for FDG-positive tumour lesions and was higher for follicular than for papillary thyroid carcinoma. CONCLUSION: This study provides an approach to estimate the tumour mass and its 95% confidence intervals in DTC patients using the serum Tg level. The range of the estimated tumour mass for a given Tg level is rather large, and therefore, the approach is of limited value in clinical application.

[Impact of nuclear medicine imaging techniques for lymph node surgery]. / Bedeutung der nuklearmedizinischen Bildgebung für die Lymphknotenchirurgie.

Nuclear medicine imaging techniques allow the noninvasive in vivo visualization of cellular and subcellular molecular processes. In the context of lymph node surgery and patient management in uro-oncology, two molecular nuclear imaging techniques deserve special interest: positron emission tomography (PET) for staging, restaging, and follow-up, and preoperative identification and subsequent biopsy of the sentinel lymph node (the first lymph node in the lymphatic drainage system of the tumor). Both methods and their clinical potential are described in this review. Future trends in molecular imaging in uro-oncology are also discussed.