Dosimetry and optimal time frame of [¹⁸F]SiTATE PET/CT in Patients with Neuroendocrine Carcinoma

Ziel/Aim Radiolabelled somatostatin analogues are well established for imaging overexpression of somatostatin receptors (SSR) in neuroendocrine tumours (NET) with positron-emission-tomography (PET). [¹⁸F]SiTATE (formerly known as ¹⁸F-SiFAlin-TATE), a novel ¹⁸F -labelled SSR-targeting peptide, has recently been introduced for combined clinical PET/computer tomography (CT) imaging. This study presents the first dosimetry and optimal time frame analysis of [¹⁸F]SiTATE-PET/CT imaging of NET patients based on longitudinal measurements.

Methodik/Methods Nine NET patients with [¹⁸F]SiTATE-PET/CT (273 ± 44 MBq) were imaged 5, 30, 60, 120, 180 min after radiotracer injection. Blood samples were taken prior to each PET acquisition. Biodistribution in normal organs and tumour uptake of SSR-positive lesions were assessed by measuring SUV_max and SUV_mean values (threshold 50 % of max). Dosimetry estimates for risk organs were determined assuming a bi-exponential pharmacokinetic, and by using ¹⁸F S-values and reference target masses for the ICRP89 adult male or female (Olinda 2.0). Tumour-to-background ratios of the most frequent tumour lesion types were compared between acquisition starting points. Time frames with most-promising tumour-to-background ratios were rated visually by six blinded readers.

Ergebnisse/Results The normal organs showed a constant tracer uptake after one hour with only minimal changes between 1h and 3h post injection, whereas the tumour uptake further increased for almost all types of metastases (bone, liver, lymph nodes), leading to increasing tumour-to-background ratios over time (SUV_mean-ratios tumour-to-liver: 1h vs. 2h +27.9 %, 1h vs. 3h + 48.3 %; SUV_mean-ratios tumour-to-spleen: 1h vs. 2h +17.8 %, 1h vs. 3h + 27.1 %). Dosimetry resulted in an effective dose of 0.03 mSv/MBq (~8.2 mSv for 273 MBq). The visual evaluation of the different imaging studies is pending.

Schlussfolgerungen/Conclusions [¹⁸F]SiTATE-PET/CT in NET shows overall high tumour-to-background ratios from 1h to 3h after injection, further increasing for later acquisition times. For clinical use of [¹⁸F]SiTATE, visual evaluation is needed to determine the best compromise between image quality and contrast to reach the highest diagnostic accuracy.

Publication History

Article published online:
08 April 2021