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Annals of Nuclear Medicine
Published in: Annals of Nuclear Medicine 4/2022

01-04-2022 | Computed Tomography | Original Article

Conversion from dose length product to effective dose for the CT component of whole-body PET/CT

Authors: Yusuke Inoue, Yu Ohkubo, Kazunori Nagahara, Ayuka Uehara, Makoto Takano

Published in: Annals of Nuclear Medicine | Issue 4/2022

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Abstract

Objective

For dose management of CT, the ratio of effective dose (ED) to dose length product (DLP) is often used to convert DLP to ED. We evaluated this ratio in the CT component of whole-body PET/CT performed under various imaging conditions to determine a practical method for ED estimation applicable to PET/CT.

Methods

In total, 400 patients who underwent whole-body PET/CT were enrolled. The imaging conditions were variable in terms of the scanner model, setting of automatic exposure control (AEC) setting and arm positioning. The scan range was divided into six anatomical regions. DLP was calculated for each region, and multiplied by the conversion factor for the respective region to determine regional ED. The six regional EDs were summed together to determine ED by the regional DLP method (EDrDLP). Additionally, regional ED was assessed using CT-Expo, software dedicated to CT dose estimation, and the total of six regional EDs were defined as ED by the CT-Expo method (EDCT-Expo). EDrDLP/DLP and EDCT-Expo/DLP were calculated using DLP automatically provided by the scanner.

Results

EDrDLP/DLP ranged from 0.0121 to 0.0128 mSv/mGy/cm with the arms up and from 0.0127 to 0.0134 mSv/mGy/cm with the arms down. Putting the arms down slightly increased EDrDLP/DLP, presumably due to an increased contribution of the chest and abdomen to total radiation exposure. The AEC setting and scanner model also influenced EDrDLP/DLP significantly but slightly. EDCT-Expo/DLP showed apparent scanner dependence, which appeared mainly attributable to differences in the constants used for DLP calculation between the scanner and CT-Expo.

Conclusion

Multiplication of scanner-derived DLP by a conversion factor of 0.013 mSv/mGy/cm provides acceptable ED estimates.
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Metadata
Title
Conversion from dose length product to effective dose for the CT component of whole-body PET/CT
Authors
Yusuke Inoue
Yu Ohkubo
Kazunori Nagahara
Ayuka Uehara
Makoto Takano
Publication date
01-04-2022
Publisher
Springer Singapore
Published in
Annals of Nuclear Medicine / Issue 4/2022
Print ISSN: 0914-7187
Electronic ISSN: 1864-6433
DOI
https://doi.org/10.1007/s12149-022-01720-0

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