Minimising Radiation Dose in Computerised Tomography in the Investigation of Renal Stone Disease: A Teaching Hospital Audit

Background: CTKUB is a commonly performed scan as the gold standard investigation for renal stone disease. However, CT exposes a patient to ionising radiation. The radiation delivered to the patient increases in importance given the young demographic and often need for interval imaging. To minimise exposure, low dose scanning techniques are employed, and image field is reduced to only scan relevant anatomy. A common starting point for CT KUB is often the T10 vertebra however many scans are performed starting at higher levels exposing the patient to unnecessary radiation. Methods: A list of 100 patients who underwent CTKUB for renal stone disease at a teaching hospital was created. Following exclusion of duplicates and application of exclusion criteria 51 scans were included. Each scan was individually analysed to assess vertebral level of upper limit of kidney and vertebral level at which the CTKUB scan was started. Percentage overshoot was calculated as number of axial slices cranial to the upper aspect of the kidneys. Results: 22% of scans included in the study were started proximal to T10, these scans had a mean percentage overshoot of 19.6% exposing the patient to excess radiation. Of the CT KUB scans started at T10 or below mean percentage overshoot was improved to 8.6%. At the level of T10 all analysed scans would avoid undershooting. Conclusions: Implementation of a CTKUB imaging protocol which starts at T10 will minimise ionising radiation exposure whilst allowing visualisation of the complete renal tract. Keywords: CT KUB, Radiation safety, Minimise radiation