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. 2020 Oct 2;20:112. doi: 10.1186/s12880-020-00510-2

Repeatability of small lung nodule measurement in low-dose lung screening: a phantom study

Yu Du 1, Gao-Feng Shi 1,✉, Ya-Ning Wang 1, Qi Wang 1, Hui Feng 1
PMCID: PMC7532632  PMID: 33008318

Abstract

Background

Lung cancer screening revealed that people with small pulmonary nodules are mostly asymptomatic and that some of these people are at risk of developing lung cancer, so we intended to explore the repeatability of small lung nodule measurement in low-dose lung screening.

Methods

We scanned eight ground-glass nodules (GGNs) and solid nodules, with diameters of 3, 5, 8, and 10 mm. They were divided according to the different combination schemes of tube voltage (KV) and tube current (mA) as 70, 80, 100, and 120 KV, and currents of nine tubes were divided as 20, 30, 40, 50, 60, 70, 80, 90, and 100 mAs.

Results

Compared with the conventional dose group (120 kVp, 100 mAs), the nodule diameter and solid nodule volume measured by all scanning combinations were more consistent (P > 0.05), the volumes of 10 mm GGNs combinations were consistent (P > 0.05), the volumes of 8 mm GGNs were consistent (P > 0.05), the volumes of 5 mm GGNs combinations were consistent (P > 0.05), and the volumes of 3 mm were consistent (P > 0.05).

Conclusion

In lung cancer screening, CT parameters should be as follows: tube voltage is more than 80 kVp, and tube current is 80 mAs in order to meet the requirements for the accurate measurement of the diameter and volume of pulmonary nodules.

Keywords: Computer tomography, Low dose, Pulmonary nodules, Body model, Lung cancer

Background

With the increasing popularity of lung cancer screening, the detection rate of small pulmonary nodules has increased. Lung cancer screening revealed that people with small pulmonary nodules are mostly asymptomatic and that some of these people are at risk of developing lung cancer [1]. Since the detection rate of small pulmonary nodules has increased, the subsequent problem is to determine how to deal with this as early as possible, and additional examination and treatment measures should be avoided. For malignant nodules, early diagnosis can provide a safer and clearer treatment plan. Considering the possibility of false positives, the computed tomography (CT) follow-up and monitoring of small nodules is very important. In addition, the possible radiation risk and economic cost of follow-up should also be comprehensively considered [2]. According to the International Lung Nodule Screening Guidelines, the size and growth rate of nodules are still well-recognized as important indicators to distinguish benign and malignant nodules [3, 4]. Compared with the nodule size in the first examination, the growth rate of the nodule can be calculated, in order to determine its benign and malignant nature. At present, the measurement of nodule size mainly includes diameter measurement, and the latest guidelines take volume measurement as a measurement standard [4, 5].

In the lung cancer screening guidelines, such as the Lung Reporting and Data System (Lung-RADS) and the National Comprehensive Cancer Network (NCCN) guidelines, the mean diameter is used as the size standard for nodal follow-up and treatment [6, 7]. In the Dutch-Belgian Nelson test, volumes serve as a similar standard [5]. Indeed, the determination of the nodule follow-up and treatment plan during the lung cancer screening is not based on the actual size of the nodule in the surgical specimen, but on the size measured on the CT image and the changes before and after the follow-up [8]. Therefore, the present study focuses on the measurement accuracy of low-dose CT for small nodules and determines how to consistently measure the average diameter and volume, in order to determine its size and change, rather than the measurement accuracy of the actual nodule size.

The national lung screening test (NLST) revealed that the use of low-dose CT screening in high-risk groups could reduce lung cancer mortality [9, 10]. According to the size and changes of nodules, lung cancer screening guidelines provide different treatment options. Therefore, in addition to the detection of pulmonary nodules, the repeatability of pulmonary nodule measurement is also an important factor in the follow-up and risk assessment of pulmonary nodules in CT screening. Since annual CT screening increases the risk of radiation-related cancer, the principle of minimizing the CT screening dose is also important [11]. Therefore, it is important to keep the accuracy of the screening image while reducing the radiation dose and avoiding large errors in the detection or measurement of pulmonary nodules.

In lung nodule screening, when using 120 kVp of tube voltage, the tube current can be reduced to less than 100 mAs, on the premise that the image quality can meet the diagnostic requirements. In some studies, the tube current was reduced to 80, 70, 60, or even 10 mAs, and the radiation dose was reduced by 50–84% [12, 13]. Some studies have also reduced the tube current threshold to 20 mAs for pulmonary nodules, including ground-glass nodules screening [14]. Another approach to reducing the radiation dose is to reduce the tube voltage. At present, the most common tube voltage is 100–140 kVp. However, some studies have considered that 80 kVp is feasible for lung nodule screening [15]. Furthermore, few studies have concurrently reduced the tube current and tube voltage in carrying out the lung nodule screening. The phantom experiment is a very helpful method to avoid the extra radiation on patients. Therefore, the present study aimed to investigate the effect of different tube current and voltage combinations in low-dose scanning on the consistency of measurement of the pulmonary small nodule size using phantom. The conventional scanning dose (120 kVp, 100 mAs) was used as the control group.

Methods

Chest phantom

The chest model used in the present study (Lungman, Kyoto Kagaku, Tokyo, Japan) was a model that could accurately simulate the human anatomy. The model has a size of 43 × 40 × 48 cm and was designed based on an adult male with a weight of 70 kg. The body model was a male torso model with an artificial mediastinum and trachea, including the pulmonary vessels (right and left) and upper abdomen (diaphragm). The thickness of the chest wall was determined according to the clinical data. The X-ray absorptivity of the substitute material for simulating human soft tissue (polyurethane) and the simulated bone (epoxy resin) were both similar to that of the human tissue. The upper arm was in an abduction position to ensure that the trunk position is suitable for the CT examination. The use of this model can track the direction of the pulmonary vessels in space.

Simulated pulmonary nodules

For the simulated pulmonary nodules used in the present study, the solid nodules (S, + 100 HU) were made of polyurethane resin, and non-solid nodules (NS, − 800 HU) were made of polyurethane foam resin. In the present study, eight spherical simulated nodules with a smooth surface were used. The diameters were 3, 5, 8, and 10 mm, respectively, the volumes were 14.10, 65.00, 268.00, and 523.00 mm3, respectively, and the CT attenuation values were 100 HU and − 800 HU (tube voltage: 120 kVp).

Image acquisition

A GE Revolution CT scanner [General Electric Co. (GE), USA] was used, and the combined scanning schemes of different tube voltages (kV) and tube currents (MA) were adopted for the phantom. Combinations of tube voltage and tube currents were used. Four tube voltages (70, 80, 100, and 120 KV, respectively) and nine tube currents (40, 60, 80, 100, 120, 140, 160, 180, and 200 mA, respectively) were used. The CT scanning pitch was 0.992:1.000, and the rotation time of the rack was 0.5 s. During the scanning, eight nodules were fixed on the vascular bundle in the phantom with double-sided adhesive tapes. The placement positions were the upper, middle, and lower lungs. The scans were separately performed, and six nodules could be placed for one scan. Each nodule and site were scanned three times, and these were placed in the left and right lungs, respectively. The scanning scope included the whole model from the thoracic entrance to the costophrenic angle. During the scanning process, it was ensured that the scope of each scan was the same. When collecting the images, the Stand and Bone algorithms were used to carry out the adaptive statistical iterative reconstruction (ASIR), in order to obtain the axial image, in which the ASIR ratio was 40%, and both the slice thickness and interval of the reconstruction was 0.625 mm.

Measurement methods

After the end of the scan, all images were imported into the Lung VCAR Single Lesion analysis software AW4.7 workstation (Advantage Workstation, GE, USA), and image processing was performed by a professional imaging physician (8 years of experience in chest imaging diagnosis). The software for pulmonary nodule analysis provided quantitative information on the pulmonary nodule size through volume segmentation for semi-automatic measurement. Apart from clicking again when the software system failed to segment the pulmonary nodules, a manual correction was not performed. The software calculated the diameter (anterior-posterior, left-right, and upper-lower diameters) and the volume of each pulmonary nodule, according to the lesion segmentation (Fig. 1). The average diameter obtained by calculating the average value of three diameter lines has been used in the Lung Cancer Screening Guidelines [16].

Fig. 1.

Fig. 1

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CT images of pulmonary nodules of different sizes

Radiation dose

The radiation dose parameters for the different scanning combinations were recorded: volume CT dose index (CTDIvol) and dose length product (DLP). The unit of CTDIvol was mGy. DLP = CTDIvol (mGy) × scan length (cm), and the unit was mGy.cm. An effective dose (ED) meant that the patient received an effective radiation dose during the examination. This was calculated using the following formula: ED = DLP × kn, in which the unit was mSv, and k was the tissue weight factor. According to the European Union’s “CT image quality standard guidelines,” the appropriate weighted tissue factor of a standard chest is 0.017. The CTDIvol and DLP of the different combinations were respectively recorded and calculated, and the ED was calculated.

Statistics analysis

All experimental data were statistically analyzed using Statistic Package for Social Science 21.0. Measurement data were expressed as mean ± standard deviation (x ± SD). Count data were expressed in percentages (%). The test of normality was conducted using W-tests. The homogeneity of variance was tested using F-tests. The multi-group comparison was conducted using a univariate analysis of variance. The backtesting was conducted using the least significant difference (LSD). Non-normally distributed means of multiple samples or normally distributed means of multiple samples with a heterogeneity of variance were compared using nonparametric tests. Count data were compared using Chi-square tests. P < 0.05 was considered statistically significant.

Results

Comparison of nodule diameters measured by different scanning combinations

In the present study, a total of 864 scans were completed. The results revealed that compared with the conventional dose group, the measured nodule diameters were in good agreement in all the other groups (all P > 0.05, Table 1), and the measured nodule diameters were in good agreement in all the other groups (all P > 0.05, Table 2).

Table 1.

Mean diameter of 10 mm nodules

Diameter Diameter
kV mAs 10 mm sd P 10 mm sd P
GGN S
70 20 9.57 0.21 0.898 9.60 0.20 1.000
70 30 10.90 0.61 0.837 9.60 0.20 .830
70 40 12.55 0.64 0.982 9.53 0.21 .056
70 50 9.33 0.15 0.985 10.37 0.86 .079
70 60 9.77 0.31 0.906 10.43 0.80 .830
70 70 10.80 0.44 0.939 9.67 0.12 .747
70 80 10.37 0.68 0.967 9.70 0.10 1.000
70 90 10.00 0.26 0.951 9.60 0.20 .200
70 100 10.20 0.75 0.800 10.00 0.36 .915
80 20 12.20 0.89 0.953 9.63 0.15 .592
80 30 10.70 0.40 0.987 9.77 0.29 .110
80 40 9.73 0.50 0.901 10.10 0.46 .392
80 50 10.87 0.35 0.902 9.87 0.38 .166
80 60 10.67 0.47 0.951 10.03 0.59 .285
80 70 10.20 0.10 0.959 9.93 0.49 .044
80 80 10.10 0.46 0.944 10.23 0.71 .285
80 90 10.30 0.70 0.949 9.93 0.35 .520
80 100 10.23 0.87 0.974 9.80 0.26 .453
100 20 9.90 0.36 0.964 9.83 0.32 .592
100 30 10.03 0.38 0.990 9.77 0.15 .520
100 40 9.70 0.10 0.959 9.80 0.26 .056
100 50 10.10 0.44 0.949 10.20 0.87 .520
100 60 10.23 0.35 0.934 9.80 0.26 .915
100 70 10.43 0.31 0.944 9.63 0.15 .392
100 80 10.30 0.56 0.990 9.87 0.25 .336
100 90 9.70 0.10 0.969 9.90 0.30 .915
100 100 9.97 0.31 0.962 9.63 0.15 .240
120 20 10.07 0.42 0.918 9.97 0.32 .453
120 30 10.63 0.42 0.977 9.83 0.32 .166
120 40 9.87 0.38 0.918 10.03 0.40 .453
120 50 10.63 0.49 0.959 9.83 0.25 .668
120 60 10.10 0.40 0.982 9.73 0.15 .747
120 70 9.80 0.10 0.977 9.70 0.10 .747
120 80 9.87 0.21 0.972 9.70 0.10 .747
120 90 9.93 0.25 0.967 9.70 0.10 .747
120 100 10.00 0.26 – 9.70 0.10 –
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Table 2.

Mean diameter of 8 mm nodules

Diameter Diameter
kV mAs 8 mm sd sd P 8 mm sd P
GGN S
70 20 9.10 0.10 .070 8.10 0.70 .068
70 30 8.53 0.91 .068 8.83 0.74 .058
70 40 8.47 0.95 .857 8.00 1.41 .078
70 50 7.97 0.25 .418 8.20 0.56 .058
70 60 8.70 0.75 .753 8.83 0.31 .365
70 70 7.87 0.35 .140 8.50 0.56 .192
70 80 8.20 0.40 .787 8.63 0.72 .420
70 90 7.90 0.30 .892 7.93 0.15 .420
70 100 8.00 0.20 .027 7.93 0.25 .091
80 20 8.77 1.46 .033 8.33 0.12 .840
80 30 8.70 0.10 .964 8.13 0.40 .420
80 40 8.07 0.15 .964 7.93 0.15 .762
80 50 8.07 0.15 .964 8.10 0.40 .687
80 60 8.13 0.21 .097 8.07 0.38 .097
80 70 8.77 0.15 .080 8.90 0.10 .545
80 80 8.73 0.15 1.000 8.00 0.26 .614
80 90 8.10 0.20 .857 8.03 0.31 .481
80 100 7.97 0.12 .210 7.97 0.21 .269
100 20 9.03 0.80 .118 7.83 0.25 .762
100 30 9.07 0.67 .262 8.10 0.20 .365
100 40 8.93 1.36 .323 7.90 0.20 .315
100 50 8.83 0.75 .822 7.87 0.35 .481
100 60 7.93 0.25 .822 7.97 0.12 .365
100 70 7.93 0.15 .964 7.90 0.10 .420
100 80 8.13 0.21 .857 7.93 0.15 .365
100 90 7.97 0.21 .369 7.90 0.26 .687
100 100 8.77 0.74 .822 8.07 0.15 .315
120 20 7.93 0.15 1.000 7.87 0.35 .420
120 30 8.10 0.20 .822 7.93 0.15 .315
120 40 7.93 0.15 .892 7.87 0.21 .481
120 50 8.00 0.26 .928 8.43 0.21 .420
120 60 8.17 0.15 .472 7.93 0.15 .269
120 70 8.63 0.12 .892 7.83 0.06 .420
120 80 8.00 0.10 .822 7.93 0.25 .614
120 90 7.93 0.06 .857 8.03 0.12 .133
120 100 7.97 0.06 – 7.70 0.20 –
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Also, compared with the conventional dose group, the measured nodule diameters were in good agreement in all the other groups (all P > 0.05, Table 3), and the measured nodule diameters were in good agreement in all the other groups (all P > 0.05, Table 4).

Table 3.

Mean diameter of 5 mm nodules

Diameter Diameter
kV mAs 5 mm sd P 5 mm sd P
GGN S
70 20 5.27 0.38 .061 5.07 0.06 1.000
70 30 4.67 0.67 .294 5.07 0.06 1.000
70 40 4.93 0.21 .143 5.07 0.06 1.000
70 50 4.80 0.44 .344 5.07 0.06 .471
70 60 5.57 0.31 .916 5.17 0.12 1.000
70 70 5.23 0.61 .294 5.07 0.06 1.000
70 80 4.93 0.21 .294 5.07 0.06 1.000
70 90 4.93 0.21 .143 5.07 0.06 1.000
70 100 4.80 0.44 .095 5.07 0.06 .151
80 20 4.73 0.35 .143 4.87 0.40 1.000
80 30 4.80 0.44 .294 5.07 0.06 1.000
80 40 4.93 0.21 .294 5.07 0.06 1.000
80 50 4.93 0.21 .294 5.07 0.06 1.000
80 60 4.93 0.21 .673 5.07 0.06 1.000
80 70 5.13 0.67 .294 5.07 0.06 1.000
80 80 4.93 0.21 .294 5.07 0.06 1.000
80 90 4.93 0.21 .294 5.07 0.06 1.000
80 100 4.93 0.21 .143 5.07 0.06 1.000
100 20 4.80 0.44 .294 5.07 0.06 1.000
100 30 4.93 0.21 .143 5.07 0.06 1.000
100 40 4.80 0.44 .117 5.07 0.06 1.000
100 50 5.77 0.76 .248 5.07 0.06 1.000
100 60 5.63 0.51 .143 5.07 0.06 1.000
100 70 4.80 0.44 .294 5.07 0.06 .151
100 80 4.93 0.21 .294 4.87 0.40 1.000
100 90 4.93 0.21 .294 5.07 0.06 1.000
100 100 4.93 0.21 .173 5.07 0.06 1.000
120 20 5.70 0.87 .294 5.07 0.06 1.000
120 30 4.93 0.21 .095 5.07 0.06 .151
120 40 4.73 0.35 .248 4.87 0.40 .000
120 50 4.90 0.20 .344 5.83 0.64 1.000
120 60 4.97 0.15 .143 5.07 0.06 .630
120 70 4.80 0.26 .294 5.00 0.10 1.000
120 80 4.93 0.21 .294 5.07 0.06 1.000
120 90 4.93 0.21 .344 5.07 0.06 .471
120 100 4.97 0.23 – 5.17 0.12 –
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Table 4.

Mean diameter of 3 mm nodules

Diameter Diameter
kV mAs 3 mm sd P 3 mm sd P
GGN S
70 20 3.80 0.87 .062 3.23 0.23 .202
70 30 4.53 0.67 .028 2.87 0.21 .202
70 40 4.67 1.12 .034 2.87 0.21 .352
70 50 4.63 0.50 .074 2.97 0.23 .202
70 60 3.10 0.40 .042 3.60 0.26 .352
70 70 3.00 0.44 .074 3.50 0.40 1.000
70 80 3.10 0.40 .089 3.23 0.23 .641
70 90 3.13 0.35 .042 3.10 0.40 .907
70 100 3.00 0.44 .042 3.20 0.44 .641
80 20 3.00 0.44 .391 3.37 0.23 .001
80 30 4.13 0.29 .074 4.20 0.62 .641
80 40 3.10 0.40 .042 3.10 0.40 .641
80 50 3.00 0.44 .042 3.10 0.40 .352
80 60 3.00 0.44 .265 2.97 0.23 .641
80 70 3.37 0.23 .074 3.37 0.23 .641
80 80 3.10 0.40 .042 3.10 0.40 .641
80 90 3.00 0.44 .074 3.10 0.40 .415
80 100 3.10 0.40 .051 3.00 0.44 .641
100 20 3.03 0.50 .089 3.10 0.40 1.000
100 30 3.13 0.35 .023 3.23 0.23 .641
100 40 2.90 0.53 .023 3.10 0.40 .352
100 50 2.90 0.53 .074 2.97 0.23 .641
100 60 3.10 0.40 .074 3.10 0.40 .202
100 70 3.10 0.40 .074 2.87 0.21 .641
100 80 3.10 0.40 .147 3.10 0.40 .202
100 90 3.23 0.23 .147 2.87 0.21 1.000
100 100 3.23 0.23 .147 3.23 0.23 .641
120 20 3.23 0.23 .074 3.10 0.40 .641
120 30 3.10 0.40 .023 3.10 0.40 .641
120 40 2.90 0.53 .074 3.10 0.40 .726
120 50 3.10 0.40 .863 3.33 0.21 .641
120 60 3.73 0.59 .074 3.10 0.40 .815
120 70 3.10 0.40 .074 3.17 0.35 .415
120 80 3.10 0.40 .074 3.00 0.44 .726
120 90 3.10 0.40 .074 3.13 0.35 .641
120 100 3.10 0.40 – 3.10 0.40 –
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Comparison of nodule volumes measured by different scanning combinations

Compared with the conventional dose group, the difference between the combination of 80 kVp and 50 mAs and their combinations were not statistically significant in the 10-mm NS group (P > 0.05). The measured nodule volumes were in good agreement between the combination of 70 kVp and 20 mAs, and the above combinations in the 10-mm S group (all P > 0.05, Table 5).

Table 5.

the volume of 10 mm nodules

Volume Volume
kV mAs 10 mm sd P 10 mm sd P
GGN S
70 20 293.00 48.75 .000 495.00 13.23 .662
70 30 343.00 37.32 .000 492.33 8.39 .009
70 40 386.33 37.02 .015 511.33 10.02 .000
70 50 371.67 11.06 .840 535.67 26.27 .000
70 60 345.33 6.66 .003 521.33 17.56 .027
70 70 378.33 10.97 .000 508.67 2.89 .001
70 80 387.00 5.57 .000 515.33 6.66 .016
70 90 411.33 6.03 .000 510.00 2.65 .014
70 100 402.00 3.00 .228 510.33 1.53 .585
80 20 357.00 17.06 .000 498.33 3.21 .129
80 30 408.67 4.04 .357 504.33 3.06 .093
80 40 353.67 2.52 .000 505.33 1.53 .093
80 50 521.00 5.29 .000 505.33 2.08 .129
80 60 460.00 5.29 .000 504.33 2.08 .158
80 70 424.67 1.53 .000 503.67 2.08 .074
80 80 434.33 8.02 .000 506.00 6.56 .007
80 90 460.00 7.55 .000 512.00 8.19 .003
80 100 496.00 13.11 .000 513.67 7.64 .093
100 20 393.33 7.09 .000 505.33 5.69 .002
100 30 407.33 15.18 .000 514.33 5.86 .093
100 40 425.67 5.86 .000 505.33 6.11 .001
100 50 437.00 2.00 .000 515.67 5.51 .031
100 60 462.67 6.11 .000 508.33 3.51 .036
100 70 472.00 7.00 .000 508.00 2.65 .007
100 80 488.33 3.21 .000 512.00 5.29 .104
100 90 477.00 3.61 .000 505.00 6.00 .014
100 100 506.67 4.73 .000 510.33 1.53 .007
120 20 416.33 5.13 .000 512.00 3.61 .008
120 30 449.00 17.78 .000 511.67 5.03 .000
120 40 430.33 5.86 .000 517.33 6.11 .007
120 50 463.33 4.51 .000 512.00 4.00 .104
120 60 490.33 4.16 .000 505.00 4.58 .211
120 70 507.33 7.02 .000 502.67 3.21 .009
120 80 499.33 3.51 .000 511.33 2.08 .083
120 90 497.33 3.21 .000 505.67 4.73 .008
120 100 502.33 6.51 511.67 3.21
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Compared with the conventional dose group, the difference between the combination of 80 kVp and 50 mAs and the above combinations was not statistically significant in the 8-mm NS group (P > 0.05). The measured nodule volumes were in good agreement between the combination of 70 kVp and 20 mAs, and the above combinations in the 8-mm S group (all P > 0.05, Table 6).

Table 6.

the volume of 8 mm nodules

Volume Volume
kV mAs 8 mm sd P 8 mm sd P
GGN S
70 20 183.67 25.42 .001 255.00 1.00 .569
70 30 202.67 9.45 .026 252.33 6.43 .320
70 40 196.67 7.64 .015 250.33 7.02 .137
70 50 198.00 6.56 .000 248.00 13.08 .137
70 60 227.33 15.63 .001 262.00 9.54 .887
70 70 203.67 2.08 .000 255.67 4.04 .393
70 80 239.00 3.00 .000 251.00 7.21 .000
70 90 216.00 3.61 .298 238.00 5.29 .042
70 100 189.67 5.03 .030 245.33 9.50 .434
80 20 196.33 7.09 .004 258.67 4.04 .010
80 30 200.67 3.06 .013 242.67 6.66 .078
80 40 198.33 4.16 .000 246.67 6.81 .007
80 50 209.00 2.00 .000 242.00 2.65 .669
80 60 218.33 3.51 .000 253.00 3.61 .049
80 70 261.33 2.08 .000 264.33 1.53 .943
80 80 268.00 4.00 .000 255.33 5.86 .776
80 90 244.00 7.21 .000 256.33 6.11 .569
80 100 228.00 5.57 .000 257.67 7.51 .067
100 20 217.67 3.06 .000 246.33 4.16 .042
100 30 235.67 5.03 .000 245.33 5.13 .049
100 40 236.33 1.53 .000 245.67 6.66 .057
100 50 261.33 2.08 .000 246.00 7.94 .202
100 60 250.00 12.77 .000 249.00 4.00 .256
100 70 226.67 3.79 .000 249.67 4.16 .355
100 80 235.33 3.21 .000 250.67 1.53 .887
100 90 266.67 3.06 .000 254.33 4.73 1.000
100 100 316.00 4.58 .326 255.00 3.61 .434
120 20 189.33 4.93 .000 251.33 4.93 .943
120 30 237.33 4.73 .000 254.67 4.04 .104
120 40 227.67 8.08 .000 247.33 2.08 .042
120 50 262.67 3.21 .000 264.67 6.66 .202
120 60 255.67 2.89 .000 249.00 2.00 .522
120 70 282.67 4.04 .000 252.00 4.00 .569
120 80 250.33 2.52 .000 252.33 4.16 .887
120 90 255.00 2.00 .000 254.33 4.73 .831
120 100 254.00 5.00 – 254.00 1.73
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Compared with the conventional dose group, the difference between the combination of 80 kVp and 50 mAs and the above combinations was not statistically significant in the 5-mm NS group (P > 0.05). The measured nodule volumes were in good agreement between the combination of 70 kVp and 20 mAs, and the above combinations in the 5-mm S group (all P > 0.05, Table 7).

Table 7.

the volume of 5 mm nodules

Volume Volume
kV mAs 5 mm sd P 5 mm sd P
GGN S
70 20 33.67 1.53 .709 60.67 4.51 .059
70 30 34.33 3.06 .001 63.67 1.53 .022
70 40 40.00 2.00 .576 64.33 1.53 .396
70 50 34.67 2.52 .000 62.00 2.00 .204
70 60 43.33 2.52 .000 62.67 2.08 .036
70 70 43.67 1.53 .000 64.00 2.00 .004
70 80 44.00 1.00 .000 65.33 1.53 .013
70 90 43.67 2.08 .000 64.67 1.53 .036
70 100 44.33 2.08 .004 64.00 2.00 .671
80 20 39.00 3.61 .138 60.00 1.00 .204
80 30 36.33 1.53 .028 62.67 2.08 .139
80 40 37.67 1.53 .000 63.00 1.00 .092
80 50 42.00 1.00 .000 63.33 1.53 .036
80 60 45.00 1.00 .000 64.00 1.00 .059
80 70 53.00 1.00 .000 63.67 1.53 .000
80 80 49.00 6.56 .000 66.67 1.53 .000
80 90 47.33 1.53 .000 67.00 2.65 .000
80 100 48.67 2.08 .000 69.00 3.61 .013
100 20 43.67 1.53 .000 64.67 1.53 .001
100 30 44.33 1.53 .000 66.33 2.08 .000
100 40 46.33 1.53 .000 66.67 2.08 .036
100 50 49.00 3.61 .000 64.00 3.61 .004
100 60 45.67 3.51 .000 65.33 2.08 .000
100 70 46.67 1.53 .000 67.33 2.08 .092
100 80 48.00 1.00 .000 63.33 1.53 .000
100 90 56.33 1.53 .000 66.67 1.53 .000
100 100 57.67 0.58 .000 66.67 0.58 .002
120 20 51.67 0.58 .000 65.67 1.15 .002
120 30 44.67 0.58 .000 65.67 1.53 .524
120 40 45.33 1.15 .000 61.67 1.15 .289
120 50 55.67 2.08 .000 62.33 0.58 .000
120 60 56.33 2.52 .000 67.33 0.58 .001
120 70 56.33 0.58 .000 66.00 1.00 .000
120 80 57.00 1.73 .000 67.67 0.58 .000
120 90 56.33 2.08 .000 66.67 1.53 .001
120 100 55.67 1.15 66.33 2.08
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Compared with the conventional dose group, the measured nodule volumes were in good agreement between the combination of 80 kVp and 80 mAs, and the above combinations in the 10-mm S group (all P > 0.05). The measured nodule volumes were in good agreement between the combination of 70 kVp and 20 mAs, and the above combinations in the 3-mm S group (all P > 0.05, Table 8).

Table 8.

the volume of 3 mm nodules

Volume Volume
kV mAs 5 mm sd P 5 mm sd P
GGN S
70 20 16.00 1.00 .003 15.00 1.00 .013
70 30 18.33 0.58 .191 12.00 3.00 .003
70 40 17.00 1.00 .083 11.33 2.52 .003
70 50 17.33 1.53 .000 11.33 1.53 1.000
70 60 15.67 1.15 .000 15.00 1.00 .398
70 70 8.67 0.58 .000 14.00 2.00 .161
70 80 8.67 1.53 .000 13.33 1.53 .398
70 90 8.57 1.15 .000 16.00 1.00 .161
70 100 8.20 1.00 .000 13.33 1.53 .261
80 20 6.33 1.15 .031 13.67 1.53 .000
80 30 15.33 1.15 .000 12.33 1.53 .051
80 40 15.13 0.58 .000 12.67 1.53 .013
80 50 8.67 0.58 .000 12.00 1.00 .003
80 60 8.47 1.53 .000 11.33 1.15 .398
80 70 8.33 1.15 .000 14.00 1.00 .051
80 80 9.00 1.00 .000 12.67 2.08 .093
80 90 10.00 0.00 .000 13.00 2.00 .261
80 100 9.67 1.53 .000 13.67 2.52 .001
100 20 9.00 1.00 .000 11.00 1.00 .013
100 30 9.67 0.58 .000 12.00 1.00 .000
100 40 9.33 0.58 .000 10.67 0.58 .000
100 50 9.67 1.53 .000 10.67 1.53 .000
100 60 10.33 1.15 .000 10.33 1.53 .000
100 70 9.33 0.58 .000 11.33 0.58 .006
100 80 10.67 0.58 .000 11.67 0.58 .000
100 90 11.67 0.58 .000 10.33 0.58 .161
100 100 12.33 0.58 .000 13.33 0.58 .000
120 20 10.33 0.58 .000 10.67 0.58 .001
120 30 9.67 0.58 .000 11.00 1.00 .000
120 40 9.67 0.58 .000 10.00 1.00 .051
120 50 11.67 0.58 .000 12.67 0.58 .006
120 60 12.33 0.58 .000 11.67 0.58 .026
120 70 11.33 0.58 .000 12.33 0.58 .006
120 80 12.67 0.58 .000 11.67 1.53 .026
120 90 12.33 0.58 .000 12.33 1.53 .093
120 100 12.67 0.58 13.00 2.00
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Discussion

The results of the present study revealed that compared with the conventional dose group (120 kVp and 100 mAs), the measured nodule diameters were in good agreement in all scanning combination groups, but the differences were not all statistically significant. The measured nodule volumes were in good agreement between all scanning combination groups and the conventional dose group, but the differences were not all statistically significant.

Different scanning doses can be obtained by changing the combination of tube voltage and tube current. In the present study, the lowest scanning dose (70 kVp and 20 mAs) was 0.17 mSv, which was only 3.98% of the conventional dose (120 kVp and 100 mAs; 4.24 mSv). For solid and ground-glass small nodules, the difference in the mean diameter of nodules measured by various scanning doses was not statistically significant, the measurement result of the lower scanning dose was in good agreement with that of the conventional dose, and the results revealed that the decrease in scanning dose in a certain range has little impact on the measurement of the mean diameter of nodules.

Compared with the measurement of the nodule diameter, changes in nodule volumes measured by different scanning combinations were relatively complex. For solid nodules with different diameters, even with a lower scanning dose, the results were consistent. For 10-mm ground-glass nodules, better consistency could be obtained by using the scanning combination of more than 80 kVp and 50 mAs. For 8-mm and 5-mm ground-glass nodules, better consistency could be obtained by using the scanning combination of more than 80 kVp and 70 mAs. For 3-mm ground-glass nodules, better consistency could be obtained by using the scanning combination of more than 80 kVp and 80 mAs. With the decrease in scanning dose, the signal-to-noise ratio (SNR) also decreased. In the present study, the segmentation and volume measurement of ground-glass nodules using the pulmonary nodule analysis software was significantly affected, with a decrease in nodule diameter, and this effect was more obvious. Therefore, better consistency could only be obtained by using the scanning combinations of higher tube voltage and tube current. The reason may be because as the tube voltage and tube current decreased, the software had more difficulty accurately segmenting the boundary of the ground-glass nodules. In particular, this was difficult to distinguish from the surrounding vascular structure, resulting in significant differences in volume measurement results. The scanning dose of the combination of 100 kVp and 20 mAs was 0.53 mSv, while the scanning dose of the combination of 80 kVp and 40 mAs was 0.54 mSv. The scanning doses of these two combinations were similar. However, the consistency of the measurement results of the latter to the ground-glass nodule volume was poor. This suggests that compared with the reduction in tube current, the effect of reducing the tube voltage on the measurement of the volume of ground-glass nodules may be greater.

The present study has the following limitations. First, in the present study, the phantom was used for the experiment. Therefore, the conclusion needs to be verified through further clinical applications. The phantom used in the present study was designed based on a 70 kg adult male. Therefore, further studies are needed to determine whether this is suitable for populations with other body types. Second, in the present study, a CT scanner and its supporting software were used to scan and measure the simulated pulmonary nodules. Therefore, further verification is needed to determine whether this is suitable for other types of CT scanners and computer-aided design software. Third, in the present study, the diameters of the simulated pulmonary nodules were 3, 5, 8, and 10 mm, respectively. Although these simulated the solid nodules and ground-glass nodules with the CT attenuation values of 100 HU and − 800 HU (tube voltage: 120 kVp), these could not completely simulate the pulmonary nodules encountered in clinical work, and there were great differences in size, shape, CT attenuation value, and other aspects [6, 17–19]. Therefore, further in-depth studies are needed to verify the conclusions of the present study. Finally, in the present study, the detection rate of small nodules in different combinations of scanning conditions and different doses was not analyzed. Hence, further follow-up studies are needed.

Conclusion

In lung cancer screening, CT parameters should be as follows: tube voltage is more than 80 kVp, and tube current is 80 mAs, in order to meet the requirements for the accurate measurement of the diameter and volume of pulmonary nodules.

Acknowledgements

We would like to acknowledge the hard and dedicated work of all the staff that implemented the intervention and evaluation components of the study.

Abbreviations

CT

The computed tomography

Lung-RADS

The lung Reporting and Data System

NCCN

The National Comprehensive Cancer Network

NLST

The national lung screening test

ASIR

The adaptive statistical iterative reconstruction

CTDIvol

CT dose index

DLP

Dose length product

ED

EFFECTIVE dose

LSD

The least significant difference

SNR

The signal-to-noise ratio

Authors’ contributions

YD and GS conceived the idea and conceptualised the study. YW and QW collected the data. HF analysed the data. YD and GS drafted the manuscript, then QW and HF reviewed the manuscript. All authors read and approved the final draft. The author(s) declare(s) that they had full access to all of the data in this study and the author(s) take(s) complete responsibility for the integrity of the data and the accuracy of the data analysis.

Funding

No external funding received to conduct this study.

Availability of data and materials

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Ethics approval and consent to participate

I confirm that I have read the Editorial Policy pages. This study was conducted with approval from the Ethics Committee of the Fourth Hospital of Hebei Medical University. This study was conducted in accordance with the declaration of Helsinki. Consent is not applicable as there were no human participants.

Consent for publication

Not applicable.

Competing interests

All the authors declare that they have no competing interest.

Footnotes

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

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