Author: Jeff Boob, Jaydev K. Dave, Tim Minch, Bhavyata Tanna 👨🔬
Affiliation: Dr. Ronald E. McNair Academic High School, Mayo Clinic, CurveBeam AI 🌍
Purpose: To compute effective doses associated with imaging of the extremities with a HiRise (CurveBeam AI, Hatfield, PA) cone-beam CBCT scanner specifically designed for weight-bearing imaging of the hip and lower extremities, in addition to hand/wrist.
Methods: Anthropomorphic sectional adult hand/wrist (Model XA231P), knee (Model XA245L), and foot/ankle (Model XA241R; The Phantom Laboratory, Salem, NY) phantoms were imaged using the HiRise scanner and 3 different protocols – Lite (100 kVp), Standard (120 kVp) and Large (120 kVp), with varying x-ray pulse duration and frequency. Screened OSL dosimeters (nanoDots, Landauer, Glenwood, IL) were placed in the slots within the sectional phantoms for dose measurements, and were read out using a calibrated microStar reader (Landauer Inc.). For the foot/ankle phantom two commonly used clinical positions were simulated – positioning the phantom in the center of the bore (bilateral imaging) and positioning the phantom at an offset with the “foot/ankle of interest” centered in the bore. For each imaging condition (phantom x protocol) 10 acquisitions were performed, and the dosimeters were read out 3 times to compute associated radiation dose. These dose readings were corrected based on free-in-air calibration, and energy-based depth-dependent correction factors. Average tissue-absorbed doses were calculated. Then utilizing the fraction of tissue irradiated and 2007 ICRP tissue weighting factors effective doses were computed.
Results: The effective doses for the Lite, Standard, and Large protocols were 2.4, 5.6 and 8.6 µSv for hand/wrist imaging, and 11.7, 17.8 and 21.4 µSv for knee imaging, respectively. For bilateral foot/ankle imaging, the effective doses for the 3 protocols were 10.8, 18.1 and 29.3 µSv, respectively. When the foot/ankle were placed at an offset, the computed effective doses were relatively higher (13.2, 21.5 and 42.4 µSv).
Conclusion: Effective dose values for extremity imaging with HiRise scanners ranged from 2.4 to 42.4 µSv under different conditions.