Which Is the Optimal Scan Time of 18F-DOPA PET/CT in Patients With Recurrent Medullary Thyroid Carcinoma?: Results From a Dynamic Acquisition Study

Update on Management of Medullary Thyroid Carcinoma: Focus on Nuclear Medicine

Currently, there is a discrepancy among the available guidelines on the usefulness of nuclear medicine techniques in medullary thyroid cancer (MTC) diagnosis and treatment. Aim of this review is to provide an update on diagnostic and therapeutic nuclear medicine techniques in this setting. Evidence-based data clearly demonstrates the usefulness of PET/CT with different radiopharmaceuticals in recurrent MTC (in particular when serum calcitonin is higher than 150 pg/mL or calcitonin doubling time is shortened) and 18F-FDOPA should be the preferred PET radiopharmaceutical. If 18F-FDOPA PET/CT is negative or unavailable, 18F-FDG PET/CT or 68Ga-DOTA-peptides PET/CT could be performed for MTC restaging. There is currently insufficient evidence to recommend PET/CT with several radiopharmaceuticals for MTC staging. Clinical experience on PET/MRI with different radiopharmaceuticals in MTC is still limited. Several investigational nuclear medicine therapeutic options are currently under evaluation in metastatic MTC. More data are needed to evaluate the efficacy, toxicity, and role of these therapeutic options in the management of MTC patients.

PET/CT in nuclear endocrinology: Results of the survey diffused through different social networks of the SEMNIM in Spain

AIM

To know the current use of the PET/CT technology applied in the field of endocrinology, the Endocrinology Working Group of SEMNIM proposed conducting a survey. The objective was to obtain a snapshot of the use of PET/CT in nuclear endocrinology, to know if it is being used properly and detect possible needs.

MATERIAL AND METHODS

During the first quarter of 2022, we analyzed the data obtained from a survey that was distributed through different social networks throughout the second half of 2021. The survey asked for the use of the different PET/CT techniques available in Spain in different endocrinological pathologies like differentiated thyroid carcinoma, medullary thyroid carcinoma, neuroendocrine tumors and hyperparathyroidism.

RESULTS

A total of 15 centers responded to the survey. A percentage of 79 of hospitals used ¹⁸F-FDG PET/CT in the diagnosis and/or follow-up of differentiated thyroid carcinoma (mean annual studies: 36.9; range 10-100); 85% used ¹⁸F-DOPA PET/CT for the study of biochemical recurrence of medullary thyroid carcinoma (mean annual studies: 7.8; range 2-20); 77% used ¹⁸F-DOPA PET/CT for the study of neuroendocrine tumors: 77% used ¹⁸F-DOPA PET/CT (mean of 10 scans per year; range 2-30) and 69% used 68Ga-DOTA-SA (mean of 24.7 studies per year; range 2-127); 79% used ¹⁸F-choline PET/CT for the study of hyperparathyroidism (mean of 30.1 annual studies; range 10-120).

CONCLUSIONS

We detected that the use of the PET/CT technique in endocrinology is not yet widespread, however, we saw that the indications in which it is used are, in general, those reported in the different consensus.

Early acquisition of [18F]FDOPA PET/CT imaging in patients with recurrent or residual medullary thyroid cancer is safe—and slightly better!

Purpose

The aim of this study was to compare early (15 min) and late (60 min) [18F]FDOPA PET/CT acquisition times in the detection of recurrence/residual disease in medullary thyroid cancer (MTC) patients.

Materials and Methods

Thirty-two dual-phase [18F]FDOPA PET scans were retrospectively reviewed. Scan indications were (1) suspected recurrence of MTC, (2) treatment monitoring, or (3) restaging. In four scans, no final verification could be obtained, and one scan was excluded due to non-consistency with the acquisition protocol. Images were analyzed visually and semiquantitatively (using SUVmax). On both per-scan and per-lesion basis, early (median time 15 min) and late (median time 60 min) acquisition were compared by number and SUVmax of detected MTC lesions, and a washout rate between the two acquisitions was calculated. Sensitivity and specificity of early and late acquisition were also compared.

Results

Out of the 27 eligible PET scans, twenty were classified as PET positive and 7 as PET negative. By subsequent histology and/or combination of imaging and clinical data during follow-up, the MTC diagnosis was verified, showing a scan-based sensitivity and specificity of 100% and 87.5%, respectively, for the early acquisition, and for the late acquisition both were 100%. However, there were no statistically significant difference in detection rate between the two acquisitions. Lesions on the early acquisition were significantly more intense compared to lesions on the late acquisition (median washout rate of − 33% (− 57 to + 50%)).

Conclusion

Our study confirms that it is safe to omit the late [18F]FDOPA PET/CT acquisition in the detection of recurrent/residual MTC.

Functional imaging in thyroid cancer patients with metastases and therapeutic implications

Functional imaging plays a central role in the management of thyroid cancer patients. In patients with a differentiated thyroid cancer (DTC), radioactive iodine (RAI) is used mostly with a therapeutic intent, either post-operatively or as the first line systemic treatment in patients with known structural disease. A whole body scan is performed a few days after the RAI administration, and this procedure is very sensitive to detect all tumor foci with RAI uptake. PET/CT with ¹⁸F-FDG complements the use of RAI at the initial evaluation of patients with high-risk DTC, during follow-up in those with rising serum thyroglobulin levels over time, for the work-up of patients with documented structural disease and for assessing the efficacy of focal or systemic treatment modalities. ¹⁸F-FDG uptake is a prognostic indicator in all these clinical conditions. A dosimetric approach with ¹²⁴I PET/CT showed encouraging results. Several functional imaging modalities are currently available for medullary thyroid carcinoma (MTC) patients. ¹⁸F-FDG-PET/CT may be sensitive in MTC patients with high FDG uptake that signals aggressive disease. ¹⁸F-DOPA is the most sensitive imaging technique to visualize small tumor foci, and is also highly specific in patients with a known MTC, but should be complemented by a CT scan of the chest and by a MRI of the liver to detect small metastases.

Molecular imaging of endocrine neoplasms with emphasis on 18F-DOPA PET: a practical approach for well-tailored imaging protocols

6-[18F]-L-fluoro-L-3, 4-dihydroxyphenylalanine (¹⁸F-DOPA) PET/CT can be a useful tool for the detection of different neuroendocrine tumors (NETs). The main determinants of ¹⁸F-DOPA uptake and retention by NETs are related to expression of LAT1/LAT2 transporters, expression and activity of AADC and biochemical phenotype, all being intimately inter-connected to their embryological origin. In order to improve sensitivity of ¹⁸F-DOPA PET, it is of main importance to perform indivisualized imaging protocols across primaries. This review provides a practical approach for performing well-tailored imaging protocols and describes the clinical value of the recommended radiopharmaceuticals.

Neuroblastoma Shown on 18F-DOPA PET/CT Performed to Evaluate Congenital Hyperinsulinism

ABSTRACT

18F-DOPA PET/CT was performed to evaluate congenital hyperinsulinism in a 55-day-old boy with hypoglycemia. The images revealed not only a focal 18F-DOPA-avid lesion in the pancreas but also in a left thoracic paraspinal neuroblastoma.

Evaluation of F-18 DOPA PET/CT in the detection of recurrent or metastatic medullary thyroid carcinoma: comparison with GA-68 DOTA-TATE PET/CT

OBJECTIVE

PET imaging with F-18 DOPA (FDOPA) and Ga-68 DOTATATE (TATE) shows the most promising results to detect medullary thyroid cancer (MTC) recurrence. We performed this comparative study to detect the site of recurrent or metastatic disease in MTC patients with elevated serum calcitonin (Ctn) and/or carcinoembryonic antigen (CEA) levels.

METHODS

We studied 46 MTC patients (25 women, 21 men) with elevated Ctn and/or CEA levels during follow-up who had both FDOPA and TATE PET/CT scans for re-staging purposes.

RESULTS

FDOPA PET imaging yielded an overall sensitivity of 86.8%, specificity of 100%, PPV of 100%, NPV of 61.5%, and accuracy of 89.1%, while TATE PET scan had the same values as 84.2%, 87.5%, 96.9%, 53.8%, and 84.6%, respectively, and there was no statistically significant difference between the two modalities with the exception of the specificity value that was higher for FDOPA imaging. In a subgroup of patients with overt Ctn or CEA elevation, sensitivity of FDOPA increased significantly, whereas TATE sensitivity did not change. FDOPA PET imaging was significantly superior in detecting liver and regional lymph node (LN) metastases, while TATE PET scan was significantly better in the skeletal metastases. Early FDOPA demonstrated 11 invisible lesions on late FDOPA.

CONCLUSION

Both FDOPA and TATE PET/CT imaging are useful to localize recurrences in MTC patients. While TATE imaging is superior to reveal skeletal disease, FDOPA seems better in liver and regional LN metastases; therefore, the two modalities appear complementary in monitoring MTC patients with elevated serum Ctn and/or CEA levels.