While the clinical utility and use of CT in this situation is a bit controversial, it is good to understand that excellent diagnostic CT information can be obtained in the very low radiation dose sub-millisievert range. Particularly in times of poor PCR test availability or delayed PCR results, very low dose Chest CT is quick and may have a valuable clinical function. [See this article in Radiology: Cardiothoracic Imaging or Aunt Minnie]
In a recent article published online (1), the authors investigated CT utilization and cumulative radiation dose in adult stone patients over a period of 3 years. In their analysis, patients were classified as “active” (≥ 2 diagnosis codes for nephrolithiasis, or receipt of stone surgery) or “inactive” (one stone diagnosis) and compared to age- and gender-matched controls. The authors concluded that CT use and non-surgical radiation exposure for active stone patients is significant, with over 10% estimated to exceed occupational limits (50 mSv annually) in the first year. They further mentioned that for active stone patients, mean 3-year estimated cumulative CT-related radiation was 28.3 ± 28.5 mSv for operative patients and 22.0 ± 24.4 mSv for non-operative patients. As has been previously mentioned in a blog I wrote in 2016 (2), there is support for tracking cumulative dose (3) as well as thought that cumulative dose should not be given any importance when making decisions about individual patients (4, 5). The linear no-threshold relationship implies that irrespective of which CT scan a patient is receiving, the absolute risk is the same. There is no increase in sensitivity from the increasing dose received from repeated CT scans, only an accumulation of probability. The linear no-threshold model would break down and not make any sense if there was an increase in sensitivity from repeated scans. Low dose techniques should be used for repeated CT scans to minimize dose to the patients. Educating our colleagues about the benefits of CT as well as its utilization and use of low dose KUB scans for repeat stone assessment would reduce dose to these patients, but using cumulative dose as a reason for not using CT is not appropriate.
Jessica C. Dai, Helena C. Chang , Sarah K. Holt , Jonathan D. Harper , National trends in CT utilization and estimated CT-related radiation exposure in the evaluation and follow-up of stone patients, Urology (2019), doi: https://doi.org/10.1016/j.urology.2019.07.030.
The compound annual growth rate for CT of the abdomen and pelvis in the emergency department setting for a diagnosis of suspected urolithiasis was studied to help determine factors influencing decision makers. Such factors included geographic location, socioeconomic variances, hospital type (academic vs private), as well as private payer insurance vs Medicare and other payer sources.
As the authors in this article state, ” … efforts to optimize appropriate imaging use, particularly in the growing ED setting, could be beneficial.”
Researchers at Virginia Mason Medical Center in Seattle launched a hospital-wide quality improvement project, resulting in lowering CT radiation dose by nearly 20%.
In this article, they detailed three initiatives which enabled them to achieve this dose reduction:
“(1) More frequent use of existing low-dose protocols; (2) Development of new protocols specific to patient body size; and (3) Improved patient positioning.”
The combined efforts of radiologists, residents, and CT technologists at this institution “to promote the use of low-dose protocols and improve patient positioning led to statistically significant reductions in radiation dose for all types of CT exams they assessed. On average, the reduction in radiation dose was 18.3% for contrast-enhanced chest, abdomen, and pelvis CT scans and 11.8% for CT pulmonary angiograms, as reported in this article on AuntMinnie.
This article discusses how researchers assessed the use of low tube potentials for CCTA in worldwide clinical practice and the resulting influence on radiation exposure and image quality.
As reported by AuntMinnie staff writer Abraham Kim, “CCTA exams performed using low tube voltages (either 90 to 100 kVp or ≤ 80 kVp) were associated with reductions exceeding 50% for CT dose index (CTDIvol) and dose-length product, compared with the conventional tube-voltage range of 110 kVp to 120 kVp. These reductions led to statistically significant decreases in median radiation dose and volume of contrast agent required.”
GIGO applies here, but with much greater consequences. Conversely, good information in results in more valuable consultation out in the form of the Radiology reports. See this article for how the authors “found improvement in quality of histories provided on requisitions for unenhanced head CT after a fairly simple intervention in the ED. In addition to aiding interpretation, improved clinical information significantly reduced time in receiving payment for the studies.” This results in a “win” for all, including likely improved quality of care for patients.