Radiation Dose Reduction of Unenhanced CT Limited to the Kidneys for Follow-Up of Patients With Known Nephrolithiasis Without Symptoms
Fananapazir G, Klimkiv L, Canvasser N, Lamba R, Loehfelm TW, Corwin MT
OBJECTIVE: The purpose of this study is to identify the landmarks and associated radiation dose reduction for limited CT of the kidneys of patients requiring follow-up for known nephrolithiasis.
MATERIALS AND METHODS: This retrospective study included all adult patients who underwent CT examination type "CT abdomen + pelvis renal stone" at our institution during 2017. Several exclusion criteria were identified, including scoliosis and congenital renal abnormalities. A total of 299 patients met the inclusion and exclusion criteria. The radiation dose and z-axis length associated with the original CT scan were recorded. The upper and lower limits of both kidneys in relation to the vertebral body endplates were recorded, to determine the z-axis length for a CT scan limited to the kidneys. A commercially available radiation dose analytics software package was used to provide estimates of whole-body-and individual organ-equivalent doses for the original CT scan and the limited range CT scan.
RESULTS: The superior endplate of T11 and the inferior endplate of L5 are landmarks that will include both kidneys on almost all scans. A limited z-axis range leads to a mean scan length reduction of 50%. The whole-body mean effective dose is reduced by 41.5%, and the doses to the breast and the gonadal and bladder organs are reduced by 71.7%, 73.8%, and 81.8%, respectively.
CONCLUSION: For patients without symptoms who are undergoing CT surveillance to evaluate renal calculi growth, new stone formation, or both, a limited-range scan extending from the superior endplate of T11 to the inferior endplate of L5 results in a significant reduction in radiation dose.
Read Full Article Here: https://doi.org/10.2214/AJR.18.20805