PET/CT in topical diagnostics of recurrent medullary thyroid cancer: which radiopharmaceutical is preferred?

Introduction. Medullary thyroid cancer (MTC) is characterized by a high risk of recurrence in the postoperative period, for the topographic localization of which, standard imaging methods are not sufficiently effective. Determination of the level of calcitonin and CEA is key test for monitoring the appearance of recurrent tumor foci, but does not indicate their localization. Based on the accumulated global experience, it has been established that the most promising methods for determining local recurrence and localization of metastases of MTC are PET/CT with [18F]-DOPA and [68Ga]-DOTA-peptides, however, data on their comparative effectiveness remain controversial.

The objective was to perform an analytical comparison of the diagnostic capabilities of PET/CT with [18F]-DOPA and [68Ga]-DOTA-peptides for the topographic diagnosis of recurrent foci and assessment of the tumor burden in biochemical recurrence of MTC.

Methods and materials. A retrospective analysis of studies of 100 patients with biochemical recurrence of MTC (calcitonin level> 10 pg/ml) who underwent PET/CT with [68Ga]-DOTA-peptides and/or with [18F]-DOPA, including the study of 31 patients with both radiopharmaceuticals. The analysis included an assessment of the number, localization and intensity of the accumulation foci of radiopharmaceuticals, an assessment of the correlation of the basal serum calcitonin level and the results of PET/CT.

Results. In 67 out of 100 patients (67%), recurrent foci were detected using PET/CT. Direct comparison of PET/CT scans with [68Ga]-DOTA-peptides and [18F]-DOPA in 31 patients did not show any statistically significant differences in the number of lesions detected between the two radiopharmaceuticals (Wilcoxon – 1.667, p=0.096). However, in some cases, discordant results were observed: in 2 patients, [18F]-DOPA revealed more foci (in the lymph nodes, liver, and bones), and in 1 patient, [68Ga]-DOTA-peptides showed significantly higher contrast of the foci. With serum basal calcitonin values below 150 pg/ml, tumor foci were detected in almost half of PET/CT patients with both [18F]-DOPA (45 %) and [68Ga]-DOT peptides (42 %). There was only a moderate positive correlation between the level of the cancer marker and the number of detected foci (Spearman 0.47 and 0.35, for [18F]-DOPA and [68Ga]-DOT peptides, respectively, p<0.05) and the total volume of PET-positive tumor tissue (Spearman 0.39 and 0.26, for [18F]-DOPA and [68Ga]-DOT peptides, respectively, p><0.05).

Conclusion. PET/CT with [18F]-DOPA and with [68Ga]-DOTA-peptides are highly informative for the topographic diagnosis of recurrent tumor foci in MTC with comparable diagnostic efficiency. In cases of common forms of MTC, it is preferable to perform a comprehensive PET/CT scan using both radiopharmaceuticals, which will ensure maximum diagnostic accuracy and determine the future strategy of personalized treatment.

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