University of Groningen Optimization of parathyroid C-11-choline PET protocol for localization of parathyroid adenomas in patients with primary hyperparathyroidism Noltes,

Purpose: To evaluate the optimal tracer uptake time, the minimal amount of radioactivity and the inter-observer agreement for C-choline positron emission tomography/computed tomography (PET/CT) in patients with primary hyperparathyroidism (pHPT). Methods: Twenty-one patients with biochemically proven pHPT were retrospectively studied after injection of 6.3 ± 1.2 MBq/kg C-choline. PET data of the first nine patients, scanned for up to 60 min, were reconstructed in 10-min frames from 10to 60-min postinjection (p.i.), mimicking varying C-choline uptake times. Parathyroid adenoma to background contrast ratios were calculated and compared, using standardized uptake values (SUVs). Data was reconstructed with varying scan durations (1, 2.5, 5, and 10 min) at 20–30-min p.i. (established optimal uptake time), mimicking less administered radioactivity. To establish the minimal required radioactivity, the SUVs in the shorter scan durations (1, 2.5, and 5 min) were compared to the 10-min scan duration to determine whether increased variability and/or statistical differences were observed. Four observers analyzed the C-choline PET/CT in four randomized rounds for all patients. Results: SUVpeak of the adenoma decreased from 30 to 40 p.i. onwards. All adenoma/background contrast ratios did not differ from 20to 30-min p.i. onwards. The SUVs of adenoma in the scan duration of 1, 2.5, and 5 min all differed significantly from the same SUV in the 10-min scan duration (all p = 0.012). However, the difference in absolute SUV adenoma values was well below 10% and therefore not considered clinically significant. The inter-observer analysis showed that the Fleiss’ kappa of the 1-min scan were classified as “moderate,” while these values were classified as “good” in the 2.5-, 5-, and 10-min scan duration. Observers scored lower certainty scores in the 1and 2.5-min scans compared to the 5and 10-min scan durations. (Continued on next page) © The Author(s). 2019 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. * Correspondence: a.h. brouwers@umcg.nl The data presented in this paper has been presented at the EANM’18 31st Annual Congress Meeting (Oct 13–17, 2018, Düsseldorf, Germany) as an oral presentation. University of Groningen, University Medical Center Groningen, Department of Nuclear Medicine and Molecular Imaging, P.O. Box 30 001, 9700, RB, Groningen, The Netherlands Full list of author information is available at the end of the article Noltes et al. EJNMMI Research (2019) 9:73 Page 2 of 10 (Continued from previous page) Conclusion: The optimal time to start PET/CT scanning in patients with pHPT is 20min after mean injection of 6.3 MBq/kg C-choline, with a recommended scan duration of at least 5 min. Alternatively, the radioactivity dose can be lowered by 50% while keeping a 10-min scan duration without losing the accuracy of C-choline PET/CT interpretation.