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Determination of appropriate conversion factors for calculating size-specific dose estimates based on X-ray CT scout images after miscentering correction

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Abstract

In this study, we proposed and evaluated the validity of an optimized size-specific dose estimate, a widely used index of radiation dose in X-ray computed tomography (CT) examinations. Based on miscentering correction of scout images, we determined the appropriate conversion factors (CF) by using a phantom. Scans were conducted using a multi-detector CT system (Aquilion ONE, Canon Medical Systems). Four cylindrical phantoms were taken in the anteroposterior (AP) and axial directions to determine the relationship between pixel value and water-equivalent length (Lw). In the AP scout image, the pixel values at the selected slice positions were converted to Lw to calculate the water-equivalent diameter (Dw). The CF was derived from Dw and CF values before and after miscentering correction was calculated. Finally, the CF values were compared to those calculated from the axial image using the conventional methodology of the American Association of Physicists in Medicine. Before miscentering correction, the maximum difference between the CF values of the axial and scout images was 7.26%. However, after miscentering correction, the maximum difference was 1.34%. Validation using a whole-body phantom generally revealed low maximum differences between the CF from the axial image and the values from the miscentering-corrected scout images. These were 2.41% in the chest, 6.30% in the upper abdomen, 1.43% in the abdomen, and 2.45% in the pelvic region. Consequently, we concluded that our miscentering correction method for deriving the appropriate CF values based on scout images is advantageous.

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Acknowledgements

The authors thank Dr. Jared Boasen, Research Associate of Faculty of Health Sciences in Hokkaido University, for correcting our English expressions.

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Author notes

  1. Kazufusa Mizonobe

    Present address: Department of Radiation Oncology, Kobe Minimally Invasive Cancer Center, Kobe, Japan

Authors and Affiliations

  1. Graduate School of Health Sciences, Hokkaido University, Sapporo, Japan

    Marin Terashima

  2. Division of Radiology and Nuclear Medicine, Sapporo Medical University Hospital, Sapporo, Japan

    Kazufusa Mizonobe

  3. Faculty of Health Sciences, Hokkaido University, Sapporo, Japan

    Hiroyuki Date

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  1. Marin Terashima
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  2. Kazufusa Mizonobe
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  3. Hiroyuki Date
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Correspondence to Hiroyuki Date.

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Terashima, M., Mizonobe, K. & Date, H. Determination of appropriate conversion factors for calculating size-specific dose estimates based on X-ray CT scout images after miscentering correction. Radiol Phys Technol 12, 283–289 (2019). https://doi.org/10.1007/s12194-019-00519-5

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  • DOI: https://doi.org/10.1007/s12194-019-00519-5

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