Presentation Authors: Noah Canvasser*, Liliya Klimkiv, Michael Corwin, Ramit Lamba, Thomas Loehfelm, Ghaneh Fananapazir, Sacramento, CA
Introduction: Unenhanced computed tomography (CT) is considered the gold-standard modality for kidney stone detection. Multiple scenarios, including pre-operative planning, assessing post-operative success, and asymptomatic follow-up, might allow for a limited scanning field as the standard &[Prime]abdomen and pelvis&[Prime] often extends well beyond the kidneys. The goal of this study was to identify the bony landmarks and associated radiation dose reduction for a limited CT scan of the kidneys in patients with nephrolithiasis.
Methods: This IRB-approved, HIPAA-compliant, retrospective study included all adult patients who underwent a CT under the exam description &[Prime]CT abdomen + pelvis renal stone&[Prime] during 2017. The total z-axis length of the original CT scan and the radiation dose was recorded. The upper and lower limits of the kidneys on each scan was recorded based on the sagittal scout vertebral body endplates, and the new reduced z-axis length was measured. A commercially available software package was used to provide whole body estimates and individual organ equivalent dose for both the original CT scan as well as the limited CT scan with the new prescribed z-axis.
Results: Our final cohort consisted of 299 patients, average age 55 years (range 18-89 years), 152 male, and 147 female. The average length of the original CT scans was 46.93 cm (range 30.90 to 60.10). Using the superior endplate of T10 as the upper limit of the scan, the superior portion of all (299/299) patients&[prime] kidneys were included in the scan field. Using the superior endplate of T11, 99.7% (298/299) of the patients&[prime] kidneys were included, and using the superior endplate of T12, 87.0% (260/299) of the patients&[prime] kidneys were included.Using the inferior endplate of L4 as the lower limit of the scan, the inferior portion of 93.0% (278/299) of the patients&[prime] kidneys were included, and using the inferior endplate of L5, the inferior portion of all (299/299) patients&[prime] kidneys were included.The new prescribed upper and lower limits of the CT scan to include the kidneys was the superior endplate of T11 and the inferior endplate of L5. This led to an average scan length reduction of approximately 50%. The whole body mean effective dose was reduced by 41%, and the breast, gonadal, and bladder reduction was 72%, 74%, and 82%, respectively.
Conclusions: In patients who warrant limited CT imaging of the kidneys only, the prescribed upper and lower limits of superior endplate of T11 and inferior endplate of L5, respectively, provide a sizeable reduction in scan length and radiation dose.