1. CT dose optimization software synergy – A clinical perspective
LEE O’HORA BSc msc
DR.SHANE FOLEY BSc PgDip PhD
Mater misericordiae university hospital
UNIVERSITY COLLEGE DUBLIN

2. ACKNOWLEDGEMENTS
Irish Institute Radiographers and Radiation Therapist University College Dublin Mater Misericordiae University Hospital, Dublin
ECR 2015

3. CT CONTRIBUTION TO POPULATION DOSE
As a result of in increased availability and use of CT and the relatively high doses associated with CT, CT is now the widely accepted as the largest contributor to population dose from medical exposures internationally.
52%(Europe 2014¹) - 75%(USA 2009²)
1. DDM2 (2014). Study on European Population Doses from Medical Exposure. Dose Data Med 2 Project Report Part 1
2. NCRP (2009). Ionizing radiation exposure of the population of the United States. Report No 160.
ECR 2015

4. LEGISLATIVE FRAMEWORK
ICRP 103, 2007¹
COUNCIL DIRECTIVE 13/59, 2013²
Optimization
Technological advances in CT
Automatic Tube Current modulation (ATCM)
Iterative Reconstruction (IR)
Automatic Tube Voltage Modulation (ATVM)
Euratom Council Directive 13/59. Basic safety standards for protection against the dangers arising from exposure to ionising radiation.
ICRP Recommendations of the International Commission on Radiological Protection. ICRP Publication 103.
ECR 2015

5. THE CURRENT STUDY-EQUIPMENT, SOFTWARE AND PROCEDURES
2 Siemens Somatom AS 64 slice CT Scanners Both had ATCM (Baseline) Scanner 1 – ACTM plus IR Scanner 2 – ACTM plus IR plus ATVM Sampled 4 most common procedures done; Brain, CTPA (CT Pulmonary Angiogram), Abdomen and TAP (Thorax Abdomen and Pelvis)
Variance between scanner outputs for standard phantoms within acceptable limits.
CTDI accuracy and consistency within acceptable limits for all scanners
ECR 2015

6. THE CURRENT STUDY-PARAMETERS
Consistency of;
Scanners
Protocols
Radiologists
Radiographers
Patients/Patient Size
Image Quality
Statistical analysis was performed using SPSS software (PASW 18, Chicago, IL). CT dose, image quality and patient size data was first checked for normality using Kolmogorov-Smirnov tests and appropriate statistical tests were then applied.
One way analysis of variance testing was used to compare the mean values between groups
No differences were found when comparing patient size measures between groups (p=0.927), but objective noise measures improved when iterative reconstruction was used (p<0.05).
ECR 2015

7. THE CURRENT STUDY-PATIENTS
Large clinical cohort (4011 patients) GROUP ACTM GROUP ACTM + IR GROUP ACTM + IR + ATVM Dose length product (DLP) was retrospectively collected via the hospital PACS system
ECR 2015

8. Dose length product (mGycm)
RESULTS
Dose length product (mGycm)
Examination
Protocol: Group N
Range
Mean
Standard deviation
Brain 1
649
995.2
95.6 2
270
689.7*
80.6 3
348
662.6*
78.8
CTPA
260
73-552
154.3
62.7
267
38-333
123.0*
48.7
286
41-350
117.1*
59.5
Abdomen
427
584.3
314.7
420.1*
211.7
320
337.4*
164.6
TAP
307
651.7
256.5
545.8*
245.9
337
397.5*
136.1
Total
4011
* indicates p<0.01 when compared to Group 1 using ANOVA
Results of the ANOVA analysis showed that there were statistically significant differences between the DLP measures for each of the groups across all examinations (p<0.001) except between group two and three (p=0.68) in the CTPA category
ECR 2015

9. Dose length product (mGycm)
Dose length product (mGycm)
Examination
Protocol: Group
Mean
% Dose Reduction
Brain 1
995.2 2
689.7
30.7 3
662.6
33.4
CTPA
154.3
123.0
20.3
117.1
24.1
Abdomen
584.3
420.1
28.1
337.4
42.3
TAP
651.7
545.8
16.2
397.5 39
RESULTS
Dose reductions of 16-31% were achieved using iterative reconstruction alone
Reductions of 24-42% when both iterative reconstruction and automatic tube voltage selection were combined
ECR 2015

10. RESULTS
Typical DLP reduction (mGycm)
Effective dose reduction (mSv)
Annual Examination Frequency
Annual Effective dose saving (mSv)
Brain
332
0.7
4482
3124
CTPA 37
0.5
813
421
Abdomen
247
3.7
2022
7492
TAP
254
3.8
1341
5109
Annual Saving:
16146
When the dose savings were calculated out to annual figures, the influence of these software optimisation features, for this institution alone would yield a saving of approximately 16 man-Sieverts per year for the four CT examinations
ECR 2015

11. DISCUSSION
Large clinical cohort Little variation in conditions Actual improved image quality for groups 2 and 3 AVTM, Synergistic benefits vary depending on procedure Limitations: Retrospective design: did not account for patient height differences – although AP diameter measurements as a surrogate for patient size, indicated no differences across groups
ECR 2015

12. CONCLUSION
The application of optimisation software confers significant dose savings during routine clinical CT examinations and should be used where available.
When used together, iterative reconstruction and automatic kV modulation have a synergistic benefit with dose reductions of up to 42% and reductions in image noise.
This has potential to stem the growing and sizeable contribution of CT scanning to the collective population dose from medical imaging.
ECR 2015