Optimization of [18F]-DOPA PET/CT Protocol in Patients with Medullary Thyroid Carcinoma: a Prospective Study

Introduction. The method of positron emission tomography combined with X-ray computed tomography (PET/CT) with [18F]-L-dihydroxyphenylalanine ([18F]-DOPA) is the most accurate technique in the detection of tumor tissue in the patients with biochemical relapse of medullary thyroid carcinoma. According to foreign recommendations, the optimal time to [18F]-DOPA PET/CT scanning begin is considered to be an interval of 30–60 minutes after injection of the radiopharmaceutical. However, there are limited publications with a small group of patients that have demonstrated increased sensitivity of [18F]-DOPA PET/CT when scanning was started 15–20 minutes after tracer administration.

The objective was to improve the [18F]-DOPA PET/CT study protocol in patients with biochemical relapse of medullary thyroid carcinoma by selecting the optimal time to the start of PET/CT scanning after injection of the radiopharmaceutical.

Methods and materials. We analyzed the data of [18F]-DOPA PET/CT studies of 102 patients with biochemical relapse of medullary thyroid carcinoma (54 women and 25 men (68 %:32 %), the median age at the time of the study was 49 years [37;63]). PET/CT acquisition was performed in 15 minutes (early scanning) and 30 minutes (scanning in the standard time point) after intravenous administration of the radiopharmaceutical. The average specific activity of [18F]-DOPA was 3.9 (±0.16) MBq/kg of the patient’s body weight. The presence of foci of pathological accumulation of radiopharmaceutical, their number and localization, and the intensity of accumulation of radiopharmaceutical were determined on PET/CT images performed at different time points.

Results. We obtained a statistically significant advantage of early PET/CT scanning in detecting the number of foci of pathological hyperaccumulation of [18F]-DOPA (228 versus 211, p<0.001). The intensity of radiopharmaceutical accumulation in the early phase of scanning was also higher than when scanning in a standard time period, by an average of 16 % (p><0.001). Conclusion. [18F]-DOPA PET/CT should be started 15 minutes after tracer administration to improve topical diagnosis of recurrent medullary thyroid carcinoma due to more intense accumulation of the radiopharmaceutical in the tissue of the recurrent tumor. In addition, early scanning ensures a reduction in radiation exposure to the patient and optimizes the workflow.> <0.001). The intensity of radiopharmaceutical accumulation in the early phase of scanning was also higher than when scanning in a standard time period, by an average of 16 % (p <0.001)

Conclusion. [18F]-DOPA PET/CT should be started 15 minutes after tracer administration to improve topical diagnosis of recurrent medullary thyroid carcinoma due to more intense accumulation of the radiopharmaceutical in the tissue of the recurrent tumor. In addition, early scanning ensures a reduction in radiation exposure to the patient and optimizes the workflow.

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