Study Population
A total of 126 people who underwent Xp and CT lung cancer screening from April 1,
2016 to March 31,
2018 were included in this study. The collected data were dose [mAs] of Xp,
CTDIvol,
and body mass index (BMI).
Calculation of SSDE
SSDE was calculated according to the AAPM report No.
204 and was set as SSDE(Calc.,
CT) (the upper portion in Fig. 1).
SSDE(Calc.,
CT) = CTDIvol × CF(CT Axi.)
CF(CT Axi.) was calculated based on the body thickness measured using the axial CT image.
The effective diameter was calculated and converted to CF using the conversion table.
In addition,
SSDE estimate was calculated from Xp examination and set as SSDE(Est.,
Xp) (the lower portion in Fig. 1).
SSDE(Est.,
Xp) = CTDIvol(Est.,
Xp) × CF(Est.,
Xp)
To calculate SSDE(Est.,
Xp), CTDIvol(Est.,
Xp) was estimated from the dose [mAs] of Xp based on the results of regression analysis (Fig. 3). CF(Est.,
Xp) was calculated based on the body thickness measured using Xp.
Statistical Analysis
Regression analysis was performed to evaluate the correlations between BMI and dose [mAs] of Xp/CTDIvol,
between dose [mAs] of Xp and CTDIvol,
and between SSDE(Calc.,
CT) and SSDE(Est.,
Xp).
The slope value,
intercept value,and correlation coefficient R were calculated,
respectively.
All data were analyzed using multivariable analysis ver.
2.0 made by Esumi.