Per the authors, non-contrast Computed Tomography of the kidneys, ureters, and bladder (CT KUB) is the favored imaging technique to confirm a diagnosis of urinary tract calculi – and indeed, it has the highest sensitivity and specificity for urolithiasis, compared to KUB or renal ultrasound alone. According to the Virtual Radiologic Standard Imaging Protocol, the anatomical scanning region of the KUB starts at the top of the liver on inspiration and ends at the pubis symphysis. If this protocol is not followed, patients have a higher risk of being exposed to unnecessary amounts of radiation. This is especially concerning because breast tissue, multiple mediastinal organs, and gonadal tissue are likely to be at risk if this field is extended above or below the recommended margins. In this study, the authors aim to find the correlation between adherence to the established protocol of CT KUB scanning and patient overexposure to radiation.
This was a retrospective CT KUB review performed on 173 patients from 2 National Health Service (NHS, UK’s nationalized healthcare system) sites for the month of January 2018. Patient distribution was equal across both sites. Patient data was accessed using the clinical database manager. Distance measurements were taken from the CT scan images in the coronal view using the appropriate tool. For each patient, they recorded the gender, age, hospital site, time of CT, position, field of view (FoV), radiation dose, and measured the distance of the anatomical regions exposed in millimeters.
Full demographics of the study group were not provided. Median age appeared to be between 48-57 on the diagram demonstrating age distribution. 60% of the patients were male. 71% of the studies were completed in the prone position.
Of the 173 patients that were scanned, only 9% were appropriately exposed! 3% were overexposed to radiation above the liver alone, 49% below the pubis symphysis alone and 39% for both. This is demonstrated below:
Looking specifically at positioning, although 29% of patients were scanned in the supine position, the median dose of radiation in this population was greater than that of patients in the prone position.
Even though data shows that male patients were over scanned across sites, the dose of radiation across gender appears to be insignificant.
Though medical professionals and radiology technicians scanned patients outside working hours, this did not correlate with increased overexposure to radiation.
This study demonstrates, that despite well documented recommendations for a non-contrast CT scan, a substantial amount of patients are still being exposed to avoidable radiation doses during a CT KUB because the Virtual Radiologic Standard Imaging protocol is not being followed diligently. More patients were over scanned inferior to the pubis symphysis than superior to the top of the liver.
It is concerning that there is this much over-exposure even for a non-contrast CT. We can only imagine it is even higher in patients undergoing contrast axial imaging – with multiple rounds of scanning. It is imperative that radiologists remain in the appropriate anatomical regions to avoid undesirable radiation exposure to patients.
Presented by: Karlisa Crooks, Epsom, United Kingdom
Co-authors: Victoria Durojaiye, Ben Horsburgh
Written by: Thenappan Chandrasekar, MD (Clinical Instructor, Thomas Jefferson University) (twitter: @tchandra_uromd, @JEFFUrology) at the American Urological Association's 2019 Annual Meeting (AUA 2019), May 3 – 6, 2019 in Chicago, Illinois