Author: Jeff Boob, Jaydev K. Dave, Tim Minch, Bhavyata Tanna 👨🔬
Affiliation: Dr. Ronald E. McNair Academic High School, Mayo Clinic, CurveBeam AI 🌍
Purpose: To estimate effective doses associated with different imaging protocols for hip imaging with a cone beam CT (CBCT) scanner specifically designed for weight-bearing acquisitions.
Methods: An ATOM 701-G (CIRS, Norfolk, VA) adult hip phantom was imaged using a HiRise (CurveBeam AI, Hatfield, PA) CBCT scanner. The phantom consists of 14 sections and 70 slots for OSL dosimeters covering different anatomical organs. A calibrated microStar reader (Landauer Inc., Glenwood, IL) and OSL dosimeters (screened nanoDots, Landauer Inc.) were used for measuring doses. Three scanning protocols (Lite, Standard, Large) were used for imaging the phantom. A double-orbit scanning protocol was also used to capture the hip and pelvis. Acquisitions with ‘Large’ protocol were repeated after covering the phantom with tissue mimicking material (Super-Flex Bolus; Radiation Products Design, Inc., Albertville, MN) to simulate a large patient. For dosimetry, 10 acquisitions were performed for each scanning protocol/condition, nanoDots were read out 3 times and averaged values were used in the analysis. These values were corrected based on free-in-air calibration and energy-based depth-dependent correction factors. Resulting average tissue-absorbed dose values were used with tissue-weighting factors (ICRP 2007) to compute effective dose values, not considering and considering the fraction of irradiated tissue in the field-of-view.
Results: The effective dose values for Lite, Standard and Large protocols were 2.5, 4.0 and 7.5 mSv, respectively, using the standard phantom. The effective dose value for the Standard double-orbit protocol was 7.3 mSv When the scanning was repeated with Super-Flex Bolus and Large protocol, the effective dose values with single- and double-orbit protocols were 3.8 and 7.2 mSv, respectively. Considering the fraction of the tissue irradiated in the field-of-view, the effective dose reduces by 29 to 70%.
Conclusion: Effective dose values for weight-bearing imaging of the hip with HiRise scanners ranged from 1.9 to 7.5 mSv under different conditions.