Korean J Radiol.  2018 Dec;19(6):1179-1186. 10.3348/kjr.2018.19.6.1179.

Size-Specific Dose Estimation In the Korean Lung Cancer Screening Project: Does a 32-cm Diameter Phantom Represent a Standard-Sized Patient in Korean Population?

• Kim EY
• Kim TJ
• Goo JM
• Kim HY
• Lee JW
• Lee S
• Lim JT
• Kim Y

• KMID: 2424857
• DOI: http://doi.org/10.3348/kjr.2018.19.6.1179

Abstract

OBJECTIVE
The purposes of this study were to evaluate size-specific dose estimate (SSDE) of low-dose CT (LDCT) in the Korean Lung Cancer Screening (K-LUCAS) project and to determine whether CT protocols from Western countries are appropriate for lung cancer screening in Korea.
MATERIALS AND METHODS
For participants (n = 256, four institutions) of K-LUCAS pilot study, volume CT dose index (CTDI(vol)) using a 32-cm diameter reference phantom was compared with SSDE, which was recalculated from CTDI(vol) using size-dependent conversion factor (f-size) based on the body size, as described in the American Association of Physicists in Medicine Report 204. This comparison was subsequently assessed by body mass index (BMI) levels (underweight/normal vs. overweight/obese), and automatic exposure control (AEC) adaptation (yes/no).
RESULTS
Size-specific dose estimate was higher than CTDI(vol) (2.22 ± 0.75 mGy vs. 1.67 ± 0.60 mGy, p < 0.001), since the f-size was larger than 1.0 for all participants. The ratio of SSDE to CTDI(vol) was higher in lower BMI groups; 1.26, 1.37, 1.43, and 1.53 in the obese (n = 103), overweight (n = 70), normal (n = 75), and underweight (n = 4), respectively. The ratio of SSDE to CTDI(vol) was greater in standard-sized participants than in large-sized participants independent of AEC adaptation; with AEC, SSDE/CTDI(vol) in large- vs. standard-sized participants: 1.30 ± 0.08 vs. 1.44 ± 0.08 (p < 0.001) and without AEC, 1.32 ± 0.08 vs. 1.42 ± 0.06 (p < 0.001).
CONCLUSION
Volume CT dose index based on a reference phantom underestimates radiation exposure of LDCT in standard-sized Korean participants. The optimal radiation dose limit needs to be verified for standard-sized Korean participants.

Keyword

Low-dose CT; Radiation dose; Radiation dosage; Early detection

MeSH Terms

Body Mass Index
Body Size
Cone-Beam Computed Tomography
Humans
Korea
Lung Neoplasms*
Lung*
Mass Screening*
Overweight
Pilot Projects
Radiation Dosage
Radiation Exposure
Thinness
Tomography, X-Ray Computed

Figure

• 

  Fig. 1 Body size measurement using low-dose screening chest CT. AP diameter and lateral diameter are measured at mid-liver level.AP = antero-posterior

• 

  Fig. 2 Distribution of radiation dose estimates based on 32-cm diameter reference phantom (CTDIvol), SSDEs, and SSDE/CTDIvol according to BMI.BMI = body mass index, CTDIvol = volume CT dose index, SSDE = size-specific dose estimate, SSDE/CTDIvol = ratio of SSDE to CTDIvol

• 

  Fig. 3 Comparison of radiation dose estimates according to BMI and use of AEC.A. Radiation dose estimate based on 32-cm diameter reference phantom (CTDIvol). B. SSDEs. C. SSDE/CTDIvol according to BMI and AEC. AEC = automatic exposure control, 1 = underweight and normal, 2 = overweight and obese

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