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. 2021 Oct;48(11):3571-3581.
doi: 10.1007/s00259-021-05351-x. Epub 2021 Apr 29.

Dosimetry and optimal scan time of [18F]SiTATE-PET/CT in patients with neuroendocrine tumours

Leonie Beyer  1 , Astrid Gosewisch  1 , Simon Lindner  1 , Friederike Völter  1 , Lena M Mittlmeier  1 , Reinhold Tiling  1 , Matthias Brendel  1 , Clemens C Cyran  2 , Marcus Unterrainer  2 , Johannes Rübenthaler  2 , Christoph J Auernhammer  3   4 , Christine Spitzweg  3   4 , Guido Böning  1 , F J Gildehaus  1 , Klaus Jurkschat  5 , Carmen Wängler  6 , Björn Wängler  7 , Ralf Schirrmacher  8 , Vera Wenter  1 , Andrei Todica  1   3 , Peter Bartenstein  1   3 , Harun Ilhan  9   10
Affiliations

Dosimetry and optimal scan time of [18F]SiTATE-PET/CT in patients with neuroendocrine tumours

Leonie Beyer et al. Eur J Nucl Med Mol Imaging. 2021 Oct.

Abstract

Purpose: Radiolabelled somatostatin analogues targeting somatostatin receptors (SSR) are well established for combined positron emission tomography/computer tomography (PET/CT) imaging of neuroendocrine tumours (NET). [18F]SiTATE has recently been introduced showing high image quality, promising clinical performance and improved logistics compared to the clinical reference standard 68Ga-DOTA-TOC. Here we present the first dosimetry and optimal scan time analysis.

Methods: Eight NET patients received a [18F]SiTATE-PET/CT (250 ± 66 MBq) with repeated emission scans (10, 30, 60, 120, 180 min after injection). Biodistribution in normal organs and SSR-positive tumour uptake were assessed. Dosimetry estimates for risk organs were determined using a combined linear-monoexponential model, and by applying 18F S-values and reference target masses for the ICRP89 adult male or female (OLINDA 2.0). Tumour-to-background ratios were compared quantitatively and visually between different scan times.

Results: After 1 h, normal organs showed similar tracer uptake with only negligible changes until 3 h post-injection. In contrast, tracer uptake by tumours increased progressively for almost all types of metastases, thus increasing tumour-to-background ratios over time. Dosimetry resulted in a total effective dose of 0.015 ± 0.004 mSv/MBq. Visual evaluation revealed no clinically relevant discrepancies between later scan times, but image quality was rated highest in 60 and 120 min images.

Conclusion: [18F]SiTATE-PET/CT in NET shows overall high tumour-to-background ratios from 60 to 180 min after injection and an effective dose comparable to 68Ga-labelled alternatives. For clinical use of [18F]SiTATE, the best compromise between image quality and tumour-to-background contrast is reached at 120 min, followed by 60 min after injection.

Keywords: Dosimetry; NET; PET/CT; [18F]SiTATE.

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Conflict of interest statement

C.J.A. has received research contracts (Novartis) and lecture honorarium (Ipsen, Novartis, Advanced Accelerator Applications). H.I. has received research contracts (Novartis).

Figures

Fig. 1
Fig. 1
Blood activity curves from time of injection to 3 h after injection. Different colours represent different patients
Fig. 2
Fig. 2
Biodistribution of [18F]SiTATE over time for acquisition starting points 10, 30, 60, 120 and 180 min after injection for a SUVmax and b SUVmean values of normal organs with highest radiotracer accumulation. SUV, standard uptake value; p.i., post-injection. Error bars represent standard deviations
Fig. 3
Fig. 3
a, d Exemplary maximum intensity projection images from all scan times (10, 30, 60, 120, 180 min p.i.) in two exemplary patient cases (upper image: patient 3, female, 114 MBq [18F]SiTATE, no SSA medication, creatinine 0.9 mg/dl, GFR 66 ml/min; bottom image: patient 6, male, 316 MBq [18F]SiTATE, SSA medication, creatinine 1.3 mg/dl, GFR 56 ml/min) with corresponding time activity curves of three exemplary metastatic lesions (vertebra, lymph node, liver) from b, e SUVmax and c, f SUVmean values. p.i., post-injection; SUV, standardised uptake value; SSA, somatostatin analogues; GFR, glomerular filtration rate
Fig. 4
Fig. 4
Tumour uptake values (a SUVmax and b SUVmean) and tumour-to-background ratios (c TLR SUVmax, d TLR SUVmean, e TSR SUVmax, f TSR SUVmean) for all types of metastatic lesions (bone, liver, lymph nodes, peritoneal) and different scan times. SUV, standardised uptake value; TLR, tumour-to-liver; TSR, tumour-to-spleen
Fig. 5
Fig. 5
Image quality ratings of acquisition starting points 60, 120 and 180 min after injection. The lines with dots display average ratings separately for LER (grey line) and MER (black line). LER, less experienced readers; MER, more experienced readers; p.i., post-injection
Fig. 6
Fig. 6
Visual rating of all metastatic tumour lesions. Each row displays the rating in one patient with the deviation between different scan times in the bottom row. Different columns represent ratings (majority read) for less experienced (LER) and more experienced (MER) readers with the deviation between both in the rightmost column. OSS, bone metastases; HEP, liver metastases; LYM, lymph node metastases; PER, peritoneal metastases; p.i., post-injection
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