Ethical and Research Governance Approval was sought and obtained.
Eight DR rooms using equipment from three different manufacturers were investigated in one UK Trust.
This included three Siemens Ysio units,
two Carestream Evolution and three hybrid systems consisting of Shimadzu consoles and Canon detectors.
The methodology was divided into six phases.
1.
Initially the EI used by a variety of DR manufacturers was investigated to check if it was calibrated according the IEC standard.
Each manufacturer was contacted by email to ascertain how their EI was calibrated and identify their EIT per body part.
2.
A patient dose audit was undertaken for common patient examinations to document current EI and EIT values and benchmark exposure levels against local DRLs to assess the scope for patient dose optimisation.
This included 30 examinations per room for five body parts (n=1200).The exposure factors of kVp,
mAs,
EI and Dose Area Product (DAP) values were retrieved from the Dicom elements for each examination.
Inclusion criteria:
-X-ray examinations of Chest Postero-anterior (PA),
Antero-posterior (AP) Abdomen,
AP Pelvis,
AP knee and Lateral lumbar spine.
-Only PA chest projections were included to ensure the source to image detector distance (SID) was standardised at 180cm.
-Both in-hours and out-of-hours examinations
Exclusion criteria:
-Paediatrics under 16 years of age to reduce significant variation in size.
3.
Retake analysis was performed over three months prior to EI calibration checks to benchmark current repetition rates and categorise reasons for repeat exposures.
4.
Experimental studies were performed with the aid of Medical Physics to determine if the EI calibration was according to IEC standard.
;
5.
Where required,
the findings from the EI investigation in phase 4 were used to
i.
Calibrate the EI in the relevant equipment to IEC standard
ii.
Adjust EIT values as recommended by each manufacturer
iii.Adjust patient exposure factors to optimise clinical examinations to within local DRLs.
6.
After the corrective action was undertaken,
a repeat patient dose audit for each of the five body parts and a further retake analysis was undertaken to allow for comparison with baseline levels.
Results
The EIT from each manufacturer is illustrated in Table 1,
which is applied across all body parts.
Table 1.
Target Exposure (EIT) indices for each manufacturer.
Manufacturer 1
|
Manufacturer 2
|
Manufacturer 3
|
226.22
|
312
|
200
|
The exposure data from the dose audit are illustrated in Table 2.
These values are the average obtained over 30 examinations for each of the five body parts per manufacturer.
Table 2.
Mean kVp,
mAs,
DAP EI,
EI T, and DI values per five selected body parts for each manufacturer.
Manufacturer 1
|
|
|
|
|
|
|
|
|
kVp
|
mAs
|
DAP
dGycm²
|
DRL (dGycm²)
|
EI
|
EIT
|
DI Value
|
Abdomen AP
|
73.78
|
19.83
|
11.44
|
25
|
205.51
|
226.22
|
0
|
Chest PA
|
106.17
|
1.17
|
0.64
|
1
|
225.3
|
226.22
|
0
|
Lateral Lumbar spine
|
91.35
|
25.98
|
11.92
|
25
|
216.42
|
226.22
|
0
|
Pelvis AP
|
75.03
|
9.85
|
6.35
|
22
|
302.04
|
226.22
|
+1
|
Knee AP
|
64.23
|
2.1
|
0.42
|
none
|
277.72
|
226.22
|
+1
|
|
|
|
|
|
|
|
|
Manufacturer 2
|
|
|
|
|
|
|
|
|
kVp
|
mAs
|
DAP
dGycm²
|
DRL (dGycm²)
|
EI
|
EIT
|
DI Value
|
Abdomen AP
|
75.01
|
17.95
|
10.64
|
25
|
226.18
|
312
|
-1
|
Chest PA
|
125.34
|
1.11
|
0.51
|
1
|
128.42
|
312
|
-4
|
Lateral Lumbar spine
|
85.05
|
32.04
|
13.57
|
25
|
191.36
|
312
|
-2
|
Pelvis AP
|
71.85
|
14.38
|
8.87
|
22
|
313.49
|
312
|
0
|
Knee AP
|
59.8
|
2.03
|
0.5
|
none
|
165.33
|
312
|
-3
|
|
|
|
|
|
|
|
|
Manufacturer 3
|
|
|
|
|
|
|
|
|
kVp
|
mAs
|
DAP
dGycm²
|
DRL (dGycm²)
|
EI
|
EIT
|
DI Value
|
Abdomen AP
|
78.6
|
19.54
|
21.54
|
25
|
219.2
|
200
|
0
|
Chest PA
|
125
|
1.19
|
0.96
|
1
|
49.97
|
200
|
-6
|
Lateral Lumbar spine
|
84.98
|
71.58
|
41.17
|
25
|
245.56
|
200
|
+1
|
Pelvis AP
|
74.31
|
29.01
|
26.21
|
22
|
320.64
|
200
|
+2
|
Knee AP
|
68.02
|
2.19
|
0.52
|
none
|
350.71
|
200
|
+2
|
The average DI value was obtained by the following equation;
DI=10 log10(EI/EIT)
Dose levels from manufacturer 1 were below the DRLs,
the EI values achieved were close to the EIT thus DI values were acceptable (0 and +1).
Dose levels from manufacturer 2 were below DRLs but as EI values were significantly below EIT,
DI values were negative and indicating underexposure.
Only pelvis examinations had a DI of 0.
Dose levels from manufacturer 3 showed that the average DAP of 41.17 dGycm² for lateral lumbar spines (range 6-129 dGycm 2) and 26.21 dGycm² for Pelvis examinations (range 3-98dGycm 2) exceeded the DRL with 63% and 55% respectively of the sample receiving a dose above the DRL.
There was a great variation noted in DI with no direct correlation between DI and DAP.
Retake analysis identified retake rates of 5.9%,
6.2% and 12.1% for Manufacturers 1- 3 respectively.
On further analysis,
less than 1% of images from each manufacturer were exposure related.
The majority of reject reasons given by the radiographer were classed as “radiographer issues” i.e.
positioning and anatomy cut off.
Experimental studies were performed and EI values were recalibrated with the aid of medical physics. As Manufacturer 1 was calibrated optimally,
no further data was collected on that system,
the DAPs were below the DRLs and retake rate was the lowest of the 3 manufacturers.
DI appeared to correlate with DAP.
A repeat data collection (n= 900) and a further retake analysis was undertaken for Manufacturers 2 and 3 to establish if the corrective measures/recalibration had led to improvements in dose and image quality.
Further results are illustrated in table 3.
Table 3.
Mean kVp,
mAs,
DAP and EI values per five selected body parts for Manufacturer 2 and Manufacturer 3 post implementation of optimised calibration technique.
Manufacturer 2
|
|
|
|
|
|
|
|
|
kVp
|
mAs
|
DAP
dGycm²
|
DRL (dGycm²)
|
EI
|
EIT
|
DI Value
|
Abdomen AP
|
75.27
|
18.71
|
11.72
|
25
|
236.53
|
312
|
-1
|
Chest PA
|
124.9
|
1.188
|
0.622
|
1
|
95.24
|
312
|
-5
|
Lateral Lumbar spine
|
85.186
|
33.94
|
15.16
|
25
|
199.98
|
312
|
-2
|
PelvisAP
|
75.33
|
20.87
|
27.5
|
22
|
358.27
|
312
|
+1
|
Knee AP
|
60.03
|
2.11
|
0.5242
|
none
|
198.71
|
312
|
-2
|
|
|
|
|
|
|
|
|
Manufacturer 3
|
|
|
|
|
|
|
|
|
kVp
|
mAs
|
DAP dGycm²
|
DRL (dGycm²)
|
EI
|
EIT
|
DI Value
|
Abdomen AP
|
78.66
|
22.3
|
24.406
|
25
|
266.13
|
200
|
+1
|
Chest PA
|
125
|
1.077
|
1.056
|
1
|
52.28
|
200
|
-6
|
Lateral Lumbar spine
|
95
|
47.67
|
36.04
|
25
|
300.32
|
200
|
+2
|
PelvisAP
|
83.37
|
15.72
|
19.72
|
22
|
322.4
|
200
|
+2
|
Knee AP
|
67.93
|
2.04
|
0.629
|
none
|
371.22
|
200
|
+3
|
The second retake analysis identified retake rates of 7.98% and 10.12% on Manufacturer 2 and 3 respectively.
Previously Manufacturer 2 was 6.2% whereas Manufacturer 3 was 12.1%.
Again the number of images repeated due to inappropriate radiation exposure,
were very low with 0.22% and 0.35% for Manufacturers 2 and 3 respectively.