Optimization of injection dose in 18F-FDG PET/CT based on the 2020 national diagnostic reference levels for nuclear medicine in Japan

Hiroaki Sagara; Kazumasa Inoue; Hideki Yaku; Amon Ohsawa; Takashi Someya; Kaori Yanagisawa; Shuhei Ohashi; Rikuta Ishigaki; Masashi Wakabayashi; Yoshihisa Muramatsu; Hirofumi Fujii

doi:10.1007/s12149-021-01656-x

Optimization of injection dose in ¹⁸F-FDG PET/CT based on the 2020 national diagnostic reference levels for nuclear medicine in Japan

Ann Nucl Med. 2021 Nov;35(11):1177-1186. doi: 10.1007/s12149-021-01656-x. Epub 2021 Jul 21.

Authors

Affiliations

¹ Department of Radiologic Technology, National Cancer Center Hospital East, 6-5-1 Kashiwanoha, Kashiwa, 277-8577, Japan.
² Department of Radiological Sciences, Graduate School of Human Health Sciences, Tokyo Metropolitan University, 7-2-10 Arakawa‑ku, Tokyo, 116‑8551, Japan.
³ RYUKYU ISG Co., Ltd, 3-78-4 Nantan, Kyoto, 622-0041, Japan.
⁴ Optical Information Engineering, Systems Innovation Engineering, Graduate School of Advanced Technology and Science, Tokushima University, 2-1 Minamijyousanjima-cho, Tokushima, 770-8506, Japan.
⁵ Department of Radiation Technology, Faculty of Medical Science, Kyoto College of Medical Science, 1-2 Nantan, Kyoto, 622‑0041, Japan.
⁶ Clinical Research Support Office, National Cancer Center Hospital East, 6-5-1 Kashiwanoha, Kashiwa, 277-8577, Japan.
⁷ Division of Functional Imaging, Exploratory Oncology Research and Clinical Trial Center, National Cancer Center, 6-5-1 Kashiwanoha, Kashiwa, 277-8577, Japan. hifujii@east.ncc.go.jp.

Abstract

Objective: Recently, the national diagnostic reference levels (DRLs) in Japan were revised as the DRLs 2020, wherein the body weight-based injection dose optimization in positron emission tomography/computed tomography using ¹⁸F-fluoro-2-deoxy-D-glucose (¹⁸F-FDG PET/CT) was first proposed. We retrospectively investigated the usefulness of this optimization method in improving image quality and reducing radiation dose.

Methods: A total of 1,231 patients were enrolled in this study. A fixed injection dose of 240 MBq was administered to 624 patients, and a dose adjusted to 3.7 MBq/kg body weight was given to 607 patients. The patients with body weight-based injection doses were further divided according to body weight: group 1 (≤ 49 kg), group 2 (50-59 kg), group 3 (60-69 kg), and group 4 (≥ 70 kg). The effective radiation dose of FDG PET was calculated using the conversion factor of 0.019 mSv/MBq, per the International Commission on Radiological Protection publication 106. Image quality was assessed using noise equivalent count density (NEC_density), which was calculated by excluding the counts of the brain and bladder. The usefulness of the injection dose optimization in terms of radiation dose and image quality was analyzed.

Results: The body weight-based injection dose optimization significantly decreased the effective dose by 11%, from 4.54 ± 0.1 mSv to 4.05 ± 0.8 mSv (p < 0.001). Image quality evaluated by NEC_density was also significantly improved by 10%, from 0.39 ± 0.1 to 0.43 ± 0.2 (p < 0.001). In no case did NEC_density deteriorate when the effective dose was decreased. In group 1, the dose decreased by 32%, while there was no significant deterioration in NEC_density (p = 0.054). In group 2, the dose decreased by 17%, and the NEC_density increased significantly (p < 0.01). In group 3, the dose decreased by 3%, and the NEC_density increased significantly (p < 0.01). In group 4, the dose increased by 14%, but there was no significant change in the NEC_density (p = 0.766).

Conclusion: Body weight-based FDG injection dose optimization contributed to not only the reduction of effective dose but also the improvement of image quality in patients weighing between 50 and 69 kg.

Keywords: Diagnostic reference levels (DRLs); Image quality; Injection dose; PET/CT.

MeSH terms

Fluorodeoxyglucose F18*

Substances

Fluorodeoxyglucose F18