Background CT coronary angiography CTCA now has an established role in the investigation of patients with chest pain. Under the IRMER regulations radiation doses to patients should be kept as low as reasonably practical (ALARP). Previous publications have used a chest conversion factor to calculate the effective dose (mSv) from CTCA. We have previously demonstrated that chest conversion factors significantly under-estimate the effective dose to the patient when applied to CTCA and have calculated a cardiac specific conversion factor of 0.028 mSv (mGy.cm)-1. Our department follows the ALARP ethos and has implemented new technologies together with physician training to reduce the radiation dose from CTCA. We aimed to investigate what impact the implementation of new technologies has had on the radiation dose of CTCA.
Method All patients who were coded as attending for a cardiac CT scan on the PACS and CRIS systems were included in the analysis. Scan indication included: rule out coronary artery disease, CABG assessment, pre-EP studies and problem solving. CT scanning between September 2007 and August 2010 was included; the total dose for the whole examination is used including the scout and non-enhanced scan (calcium score). Scans were performed on a Lightspeed VCT or HD750 (GE Healthcare). To calculate the effective dose a conversion factor was applied to the dose length product of each examination. The DLP is the radiation dose in one CT slice multiplied by the length of the scan. A cardiac specific conversion factor was used rather than a chest conversion factor (0.014) which significantly underestimates the effective dose from CTCA. Data was transformed and expressed as a geometric mean with 99% CI. For each analysis period all scans were included; retrospective, prospective, low kV and zero padding.
Results In the 3-year period 1736 scans were performed. The mean radiation dose in the first 6 months of the study (retrospective gating) was 29.6 mSv; using the accepted conversion factor at the time the mean dose was 14.9 mSv. In March 2008 prospective ECG gating was installed; this resulted in a halving of the mean radiation dose to 13.6 mSv. In March 2009 the scanner parameters was set to zero padding and 100 KV reducing the dose to 7.4 mSv. For the final 6 months the mean radiation dose for a cardiac scan was 5.9 mSv; this Abstract 114 figure 1 incorporates scans performed with standard filtered back projection, iterative reconstruction, high definition scanning and retrospective ECG gating for a variety of differing clinical scenarios.
Conclusion The introduction of dose saving strategies and appropriate physician training has lead to a significant reduction in the radiation dose from cardiac CT. As CTCA programmes become established in hospitals around the UK it is important that clinicians have the appropriate training and experience to keep the radiation dose to the patients as low as reasonably practical.
- Cardiac CT
- Radiation dose