Congress:
EuroSafe Imaging 2020
Keywords:
Experimental, Not applicable, Quality assurance, Safety, CT, Radiation physics, Eyes, Breast, Action 7 - Radiation protection of children, Performed at one institution
Authors:
J. Damilakis, A. Papadakis
DOI:
10.26044/esi2020/ESI-04974
Description of activity and work performed
Four physical anthropomorphic phantoms that represent the average individual as neonate, 1-year-old, 5-year-old, and 10-year-old were used. Standard head and thorax acquisitions were performed with automatic tube current modulation (ATCM) and ATCM+OTCM using a 64-detector row CT scanner (Revolution GSI, GE Medical Systems). When OTCM is enabled, the mA is reduced by up to 30% across 900 anterior projections in head and up to 40% across 1800 anterior projections in body examinations (Figure 1).
The angular range of OTCM exposure window was determined for different tube rotation times (t) using a solid state radiation detector (Figure 2).
Dose calculations were performed by means of Monte Carlo simulations. Radiation dose was measured for major superficial and centrally located radiosensitive organs of the head and thorax (Figure 3, Table 1).
Image noise was measured as the standard deviation of the Hounsfield unit value at selected anatomical sites (Figure 4, Table 2).
Clinical image quality was not evaluated. This study was limited to an OTCM technique offered by a single only manufacturer.
Table 1. Organ doses measured in ATCM and ATCM+OTCM simulated acquisitions for each phantom.
|
Organ Dose (mGy), ATCM/ATCM+OTCM
|
|
Neonate
|
1-year-old
|
5-year-old
|
10-year-old
|
Head
|
|
|
|
|
Eye lens
|
3.6/3.1 (13%)
|
9.0/7.7 (14%)
|
18.7/17 (9%)
|
27.6/25.0 (9%)
|
Brain
|
3.5/3.3 (4%)
|
9.3/9.0 (2%)
|
22.6/22.0 (2%)
|
41.2/38.9 (5%)
|
Salivary Glands
|
3.7/3.4 (7%)
|
10.5/9.4 (10%)
|
24.6/22.2 (10%)
|
36.3/33.6 (7%)
|
Thorax
|
|
|
|
|
Breast Buds
|
0.55/0.53 (4%)
|
1.1/0.79 (28%)
|
1.3/0.95 (26%)
|
2.0/1.8 (10%)
|
Lung
|
0.53/0.47 (11%)
|
0.95/0.85 (10%)
|
1.5/1.4 (7%)
|
2.3/2.2 (4%)
|
Liver
|
0.43/0.39 (9%)
|
0.85/0.79 (7%)
|
0.63/0.61 (3%)
|
1.9/1.9 (0%)
|
Thyroid
|
0.25/0.22 (11%)
|
0.46/0.44 (4%)
|
0.27/0.25 (7%)
|
0.50/0.47 (6%)
|
Table 2. Measured image noise in ROIs drawn at selected anatomical sites in head and thorax of each phantom.
|
ATCM/ATCM+OTCM (%Diff)
|
ROI
|
Neonate
|
1-year-old
|
5-year-old
|
10-year-old
|
Head
|
|
|
|
|
1
|
4.21/4.47 (6%)
|
5.01/5.36 (7%)
|
5.04/4.85 (-3%)
|
5.58/5.66 (1%)
|
2
|
4.86/4.35 (-10%)
|
5.51/6.09 (10%)
|
5.23/5.83 (11%)
|
5.86/5.91 (1%)
|
3
|
4.96/4.64 (-6%)
|
6.24/6.86 (10%)
|
4.83/5.39 (11%)
|
7.42/7.68 (3%)
|
4
|
4.21/5.51 (30%)
|
6.38/6.02 (-5%)
|
5.66/6.03 (6%)
|
6.40/6.72 (5%)
|
5
|
6.07/7.34 (21%)
|
5.69/6.35 (11%)
|
5.24/5.58 (6%)
|
6.68/6.96 (4%)
|
6
|
5.60/6.78 (21%)
|
5.07/5.88 (16%)
|
4.98/5.49 (10%)
|
6.37/6.99 (9%)
|
7
|
6.12/5.74 (-6%)
|
4.745.42 (14%)
|
4.88/5.22 (7%)
|
5.97/6.58 (10%)
|
8
|
5.89/6.19 (5%)
|
4.95/5.17 (4%)
|
4.47/5.00 (11%)
|
6.37/7.22 (13%)
|
9
|
4.76/5.39 (13%)
|
4.87/5.71 (17%)
|
4.704.85 (3%)
|
5.87/6.84 (16%)
|
10
|
4.48/6.45 (43%)
|
4.49/4.91 (9%)
|
4.20/5.64 (34%)
|
7.117.25 (2%)
|
Mean
|
5.11 ± 0.74/5.68 ± 1.01
|
5.29 ± 0.63/5.77 ± 0.58
|
4.92 ± 0.41/5.39 ± 0.40
|
6.36 ± 0.58/6.78 ± 0.61
|
%Diff/P value
|
11%/0.061
|
9%/0.0021
|
9%/0.0062
|
8%/0.0082
|
|
|
|
|
|
Thorax
|
|
|
|
|
1
|
9.89/9.79 (-1%)
|
10.79/12.88 (19%)
|
10.99/12.50 (13%)
|
12.44/12.59 (1%)
|
2
|
10.69/10.05 (-6%)
|
12.54/12.79 (2%)
|
8.66/12.39 (43%)
|
12.64/13.01 (3%)
|
3
|
12.36/11.98 (-3%)
|
10.01/12.36 (23%)
|
13.29/15.34 (15%)
|
13.72/15.92 (16%)
|
4
|
12.33/13.61 (10%)
|
10.88/14.40 (32%)
|
12.90/17.59 (36%)
|
14.56/14.62 (0%)
|
5
|
12.43/11.97 (-3%)
|
12.72/14.85 (16%)
|
15.17/16.71 (10%)
|
14.36/16.54 (15%)
|
6
|
12.36/13.69 (10%)
|
12.77/14.90 (16%)
|
14.66/16.72 (14%)
|
16.37/16.45 (0%)
|
7
|
13.33/13.72 (3%)
|
12.36/13.88 (12%)
|
12.02/12.82 (6%)
|
14.00/14.87 (6%)
|
8
|
11.49/13.72 (19%)
|
12.93/14.13 (9%)
|
11.29/13.13 (16%)
|
14.72/15.69 (6%)
|
9
|
12.14/13.34 (9%)
|
12.70/14.10 (11%)
|
12.99/16.46 (26%)
|
15.80/16.55 (5%)
|
10
|
11.26/12.22 (8%)
|
13.53/15.91 (17%)
|
14.24/16.49 (15%)
|
16.01/17.05 (6%)
|
Mean
|
11.83 ± 1.00/12.41 ± 1.49
|
12.12 ± 1.14/14.02 ± 1.09
|
12.62 ± 1.95/15.01 ± 2.06
|
14.46 ± 1.33/15.33 ± 1.53
|
%Diff/P value
|
5%/0.087
|
15%/0.0001
|
19%/0.0001
|
6%/0.007
|