Congress:
EuroSafe Imaging 2017
Keywords:
CT, Breast, Action 8 - Radiation protection training and learning material, Action 2 - Clinical diagnostic reference levels (DRLs), Action 6 - Education and training in medical radiation protection, Action 3 - Optimisation, diagnostic reference levels, image quality, Radiation safety, Dosimetric comparison
Authors:
D. Akata, M. R. Onur, M. G. Akpinar, G. Durhan, M. Ariyürek, O. Öcal, M. N. Özmen
DOI:
10.1594/esi2017/ESI-0046
Description of activity and work performed
In this presentation,
we summarized the breast dose reduction methods in chest CT.
Breast Dose Reduction Methods
1.
Bismuth shielding
2.
Organ-based tube current modulation
3.
Iterative reconstruction
4. Total dose reduction
1.
Bismuth Shielding
Bismuth shields (Figs.
1)
- Decrease dose: Reduces %30 breast dose in the absence of organ based tube current modulation
- Increase noise
- Increase artifacts (beam-hardening,
streak)
- Breast shields should not be applied before the scout planning image is acquired because pre-scout image bismuth shielding results in higher patient attenuation leading to increased tube current.
- Real-time automatic tube current modulation systems cause increased dose since they detect attenuation of the shield.
2.
Organ-based Tube Current Modulation (OBTCM)
- OBTCM decreases anterior current with respect to posterior (Fig.
2)
- 27–50% dose savings to the radiosensitive anterior organs
- OBTCM was found to be the best option in breast dose reduction
3.
Iterative reconstruction
- After acquiring CT images with low dose by decreasing kV and/or mAs,
iterative reconstruction techniques improve quality of images by decreasing noise (Fig.
3,4)
- Using iterative reconstruction techniques in chest CT decrease overall radiation dose.
Lowering radiation dose in chest CT mostly affects breast tissue as most radiosensitive tissue in thoracic region.
4.
Total Tube Current Reduction
Tube current reduction can be maintained with different ways.
- Detector thickness may be determined as 1.25 or 1.5 mm if thin-section MPRs and high-resolution 3-D images are not required
- Automatic tube current exposure control and automatic tube potential selection may be used if the patient is properly positioned in the gantry
- Increased pitch
Cranial breast displacement
- Cranial breast displacement reduces the radiation dose to the breast surface in coronary CT angiography (CTA) examinations.
- Breast displacement can be adequately achieved by dedicated radiolucent breast displacement devices which have adjustable straps and extension pieces to accomodate breast sizes.
- Breast surface dose can be reduced to 23% in coronary CTA examinations.
Breast Thickness (Fig.
6,7)
- Breast thickness can affect the efficiency of dose reduction options
- The most important dimension to consider for CT is breast thickness,
defined as the distance from the chest wall to the anterior breast tangency line in women lying supine for CT examination.
- Breast thickness < 4 cm is more susceptible to breast dose recuction techniques such as bismuth shielding,
OBTCM.