Research paper
A prospective national survey of coronary CT angiography radiation doses in the United Kingdom

https://doi.org/10.1016/j.jcct.2017.05.002Get rights and content

Abstract

Background

Little real-world radiation dose data exist for the majority of cardiovascular CT. Some data have been published for coronary CT angiography (coronary CTA) specifically, but they invariably arise from high-volume centres with access to the most recent technology.

Objective

The aim of this study was to document real-world radiation doses for coronary CTA in the United Kingdom, and to establish their relationship to clinical protocol selection, acquisition heart rate, and scanner technology.

Methods

A dose survey questionnaire was distributed to members of the British Society of Cardiovascular Imaging and other UK cardiac CT units. All participating centres collected data for consecutive coronary CTA cases over one month. The survey captured information about the exam conducted, patient demographics, pre-scan details such as beta-blocker administration, acquisition heart rate and scan technique, and post-scan dose indicators – series volumetric CT dose index (CTDIvol), series dose-length product (DLP), and exam DLP.

Results

Fifty centres provided data on a total of 1341 coronary CTA exams. Twenty-nine centres (58%) performed at least 20 coronary CTA scans in the collection period. The median BMI, acquisition heart rate and exam DLP were 28 kg/m2, 60 bpm and 209 mGycm respectively. The corresponding effective dose was estimated as 5.9 mSv using a conversion factor of 0.028 mSv/mGycm. There was no statistically significant difference in radiation dose between low and high-volume centres. Median exam DLP increased with the acquisition heart rate due to the selection of wider temporal windows. The highest exam DLPs were obtained on the older scanner technology.

Conclusion

This study provides baseline data for benchmarking practice, optimizing radiation dose and improving service quality locally.

Introduction

The demand for cardiovascular CT in the United Kingdom (UK) continues to increase: coronary CT angiography (coronary CTA) was incorporated into National Guidelines in 20101 for the assessment of coronary artery disease burden in stable chest pain, and cardiovascular CT is becoming an established technique in the assessment of patients with other forms of cardiovascular disease.2, 3, 4, 5, 6, 7, 8 Nevertheless concerns remain about the associated radiation dose,9 in particular with potentially high-dose techniques such as retrospective ECG gating.

There is little evidence documenting real-world radiation dose data for the majority of cardiovascular CT; however some data does exist for coronary CTA specifically. The PROTECTION studies10, 11, 12 report median exam dose-length products (DLP) for coronary CTA of 885 mGycm (interquartile range 568–1259 mGycm) in 2009.10 Subsequently, advances in technology have led to lower doses with the PROTECTION III study demonstrating DLPs of 252 (±147) mGycm for a standard coronary CTA in 2012.12

Whilst the scientific literature suggests that recent technological developments13 and the availability of optimisation guidelines14, 15 for coronary CTA have resulted in significant dose reductions, the data presented may be biased as these data invariably arise from high-volume centres, often with access to the most recent technology. Therefore these results probably do not represent real-world practice or doses. The objective of this pilot observational study was therefore to establish typical radiation doses for coronary CTA practice in the UK, and the relationship of these doses to clinical protocol decisions, including the choice of ECG gating technique and acquisition heart rate, and scanner technology.

Section snippets

Data capture

Members of the British Society of Cardiovascular Imaging (BSCI), which incorporates the British Society of Cardiovascular CT (BSCCT), were invited to take part in a coronary CTA radiation dose survey. A spreadsheet questionnaire was distributed to approximately 200 members and to other UK cardiac CT centres that expressed an interest in taking part. This approach targeted the majority of cardiac CT departments in the UK. The questionnaire was completed for all coronary CTA exams performed

Results

Data on a total of 1341 exams were provided by 50 centres. For comparison, there are 154 acute National Health Service trusts in England and 15 Health Boards in Scotland, although not all provide a cardiovascular CT service. It is therefore likely that at least one third of cardiovascular CT centres contributed to the survey. Four out of 50 centres did not provide weight or BMI but the exam data were otherwise complete; their responses have been retained in the data set.

Discussion

Cardiovascular CT has become an established technique for the assessment of native coronary arteries for a variety of clinical conditions. It has the potential to give high radiation doses if scans are not acquired using all the available tools to optimise the dose. There is evidence of significant variation in the volume of cardiovascular CT performed between organisations in the UK,21 and concern that this might result in an equal variation in the associated radiation exposure. It has

Conclusions

The median BMI, acquisition heart rate and exam DLP for coronary CTA acquisition are 28 kg/m2, 60 bpm and 209 mGycm respectively in the UK. This compares favourably with published contemporary studies. Radiation dose increases with acquisition heart rate across all scanner technologies, reiterating the need for heart rate control. Cardiac CT practitioners now have a clearer understanding of the doses achieved by their peers.

Conflicts of interest

None.

Acknowledgements

The authors would like to acknowledge all the participating centres, including the radiologists, radiographers, physicists and cardiologists who supported this initiative. Additionally thanks should go to the BSCI/BSCCT committee who worked to design, edit, advertise and promulgate the survey.

References (26)

Cited by (28)

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    The results of the UK nationwide dose audit were presented and discussed. This showed that using real world data and an even more severe k-factor of 0.028, a median dose of 5.9 mSv was observed across 50 centres.30 That this would equate to 2.95 mSv using the historic conversion factor truly shows that significant advances are being made in translating the theoretical dose reduction derived from reduced coverage, reduced kV and iterative reconstruction produced in the academic literature out into routine clinical practice.

  • Image reconstruction in cardiovascular CT: Part 2 – Iterative reconstruction; potential and pitfalls

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    This review reported a mean reduction in CCTA acquisition dose from 4.2 mSv to 2.2 mSv. It is interesting to note that the median dose for CCTA in a subsequent UK national survey was a DLP of 200mGycm,11 equivalent to 2.8 mSv, using the same conversion factor (k = 0.014), again raising the question of whether lower dose acquisition without IR may be equally acceptable and that the addition of IR is maybe not what facilitates the dose reduction. Furthermore, a critical assessment of published manuscripts in this field reveals that many studies have compared a “high dose” acquisition, with a “low dose” acquisition with IR in different patients (with inherent bias) and in these studies; those where FBP and IR is compared in the same patients, IR is often analysed with no adequate control arm i.e. against low dose acquisition without IR.8,12–15

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