Non-contrast CT KUB in the assessment of acute ureteric colic - are we over-scanning and over-radiating our patients? A closed loop audit
BAUS ePoster online library. Ahmad A.
Jun 26, 2018; 217784
Mr. Adnan Ahmad
Mr. Adnan Ahmad
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Abstract
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Introduction
Non-contrast CT KUB is the gold standard investigations for the assessment of acute ureteric colic (Tsiotras et al 2018). The ionising radiation and medical exposure regulations (IRMER) (DoH 2000) is a government legislation that provides a framework to reduce patient exposure to cumulative ionising radiation through the 'as low as reasonably achievable' (ALARA) principle. As clinicians, we are 'duty holders' and bound by the law to ensure the risk of exposure and stochastic effects of radiation are balanced against the benefit.
Aims
The Royal College of Radiologists (RCR) state that all patients undergoing non-contrast CT KUB should not exceed more than 10% scan length above the upper pole of the highest kidney - this is documented at the superior endplate of T12 (Twemlow et al 2015).
Given the anatomical variations of the renal tract, the RCR suggest that scans should be commenced between T10-T12 and no higher than the upper border of T10 (Maguire et al 2016).
Furthermore, a public health review in England (Shrimpton et al 2014) of typical radiation doses from diagnostic tests estimated an average dose for non-contrast CT KUB to be 355mGy.cm. This converts into an effective absorbed dose equivalent to 31.8 months of background radiation.
This audit aims to evaluate current practice against the above standards.

Methods
- Retrospective analysis of 100 patients undergoing non-contrast CT KUB between July and August 2017 for acute ureteric colic - any contrast scans or non-ureteric colic scans were excluded.
- Data collection included the following parameters: total scan slices, slices above upper pole of kidney - the difference is expressed as a percentage of total scan length to determine if the patient was 'over-scanned'.
- We also audited the vertebral level of scan commencement and vertebral level where the entire urinary tract was included.
NB: Scan levels will henceforth be expressed as vertebral levels with their corresponding borders in parenthesis e.g. T9 (upper) would be indicative of the upper border of T9 etc.
- Total radiation dose was expressed as dose length product (DLP) - this is the amalgamation of the dose required for one slice of the scan multiplied by the total scan length - calculated automatically by CT scanner.
- Tissue co-efficient was used to convert DLP to the effective dose absorbed by the patient (Huda et al 2011)
- Data analysis and primary conclusions were presented at the local audit meeting with an agreed change and implemented in November 2017
- Prospective analysis of 50 patients undergoing non-contrast CT KUB between January and February 2018 was carried out.

Results
First cycle:
Retrospective data on n=100 patients undergoing non-contrast CT KUB for acute ureteric colic.
58% of patients were male and the average age of cohort was 49.57 years.
76% of the cohort was 'over-scanned'. Of the over-scan group 68.5% (n=52) had a 10-20% over-scan and 31.5% (n=24) had a >20% over-scan. The range was between 10.39-30.72%.
N=1 had a significant finding on the over-scan of bilateral pleural effusion and consolidation - this was also visible on a CXR done prior to the CT KUB.
N=45 patients had a scan commenced above T10 (upper). Of these, n=44 had an associated over-scan.
The vertebral levels of scan commencement ranged between T5 (lower) and L1 (upper). The median level of scan commencement was T10 (upper).
The vertebral level of the upper pole of the highest kidney ranged from T10 (lower) to L2 (upper). The median vertebral level of the highest kidney was T12 (mid).
The average DLP for this cycle was 232+/-171 (48.6-1198). This equates to an average effective dose of 3.48mSv or the equivalent of 21 months of background radiation.
Analysis and Implementation of change
The results of the first audit demonstrated that significant portions of patients were being over-scanned. There was a clear link between the vast range of vertebral levels from which scans were commenced and the associated over-scan.
Completely preventable scans were defined as scans commenced above T10 (upper) where there was an associated over-scan. N=44 patients had a completely preventable over-scan.
Potentially preventable scans were defined as scans commenced between T10 (upper) - T12 (lower) with an associated over-scan. This would mostly be due to low lying kidneys and perhaps the greatest challenge to overcome.
The results were presented at the local radiology audit meeting and below changes were agreed:
- All radiographers across all sites should limit the scans to no higher than the upper border of T10.
- Where the shadow of the upper pole of the highest kidney can be seen on scout films, scans should be commenced from there provided it is no higher than the upper border of T10.
The radiographer superintendents communicated the agreed changes to the radiographers of their respected sites. A month was allowed for implementation of changes and the results re-audited.

Second cycle:
Following implementation of the above, prospective analysis was carried out on n=50 patients undergoing non-contrast CT KUB for acute ureteric colic.
52% of patients were male with an average age of 48.18 years.
84% of scans adhered to the agreed change.
In contrast to the first cycle, 46% (n=23) of the cohort was 'over-scanned'. Of the 'over-scanned' group 82% (n=19) had a 10-20% over-scan and 18% (n=4) had a >20% over-scan. The over-scan range was 10.37-24.42%.
No patients had any significant findings on their over-scan.
16% (n=8) patients had their scans commenced above T10 (upper). Of these, 100% of the patients had an associated over-scan. The vertebral level of scans commencement ranged from T7 (mid) to L1 (mid). The median level of scan commencement was T10 (lower)
The vertebral level of the upper pole of the highest kidney ranged from T10 (lower) - L2 (upper). The median level of the upper pole of the kidney was T12 (upper).
The average DLP for the re-audit was 212+/-236 (23-1575). This equates to an average effective dose of 3.18mSv or 19 months of background radiation.

Discussion With a relatively simple cost-neutral and time-effective method, we were able to demonstrate improvement in almost all domains measured (see table 2).
Over-scan rates improved from 76% to 46%. The proportion of patients with >20% over-scan improved from 24% to 8%. The variability in the range of vertebral level of scan commencement has also been reduced significantly.
The average effective dose imparted to patient improved from 3.48mSv to 3.18mSv. This difference is equivalent to 2 months of background radiation per scan. Our DLP standard of 355mGy.cm was bested in both the initial audit and the re-audit and our average DLP improved from 232mGy.cm to 212mGy.cm. This is in keeping with current rates quoted in literature (table 3) and significantly better than our international counterparts.
Of note, both cycles featured a similar cohort with near identical age and gender distribution.
Whilst we were able to demonstrate significant improvement in most domains, some remained equivocal.
Potentially preventable over-scans became the main issue in the re-audit, representing 65%(n=15) of all over-scan patients in comparison to 42% (n=32) in the first cycle. Furthermore, the range of DLP was much broader in the re-audit due to one spurious result which resulted in an excessive dose of imparted radiation.
Limitations of this audit cycle include the lower number of patients for the re-audit cycle (n=50) compared to the initial cycle (n=100). The first and second author collected all data independently and thus variability in data collection e.g. determining vertebral levels etc cannot be excluded. Finally, the health-board operates 4 sites. Whilst two hospitals maintain identical scanners and software protocols, variability amongst the other sites could have impacted on results from a radiation point of view as mentioned above.
Perhaps our greatest limitation is reflected in the stone detection rate of 48% in the first cycle and 40% in our re-audit cycle. This would suggest that a majority of patients have been improperly assessed and put through ionising radiation or assuming that all patients were assessed correctly and had clinical signs, symptoms and urine tests suggestive of ureteric colic, that we may need further delineation and stratification of symptomology or biochemical patterns before a non-contrast CT KUB is undertaken.

Conclusion and Recommendations
Non-contrast CT KUB's are used frequently in the assessment of acute ureteric colic and indeed for follow-up purposes for patients with radiolucent ureteric stones.
In this closed loop audit, we have demonstrated a significant improvement in our over-scan rates by 30% and an effective dose reduction equivalent to 2 months of background radiation per scan for patients undergoing non-contrast CT KUB.
Whilst we are currently not over-radiating our patients, relative to the set standard, we must aim to maintain ALARA principles and where possible reduce exposure to ionising radiation. By simply limiting the level of scan commencement to the upper border of T10, we can reduce the percentage of 'over-scan' and thus the overall radiation that patients are exposed to.
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