An Evaluation and Comparison of Beam Characteristics, Stray Radiation Room Surveys, Organ Dose, and Image Quality of Multiple Intra-Operative Imaging Devices for Orthopedic Lumbar Spinal Surgery
The overall purpose of this study was a comparison of radiation exposure for patients and staff during intra-operative imaging for orthopedic lumbar spine surgery. In order to achieve this, we: (1) Characterized each x-ray machine for physics performance, (2) Measured occupational radiation exposure inside the surgical suite for multiple intra-operative imaging devices utilizing currently in place clinical protocols for abdominal/spinal imaging, and (3) Measured specific organ doses for a phantom of three different Body Mass Indices (BMI) for each machine. We also compared the dose changes relative to changes in BMI as well as surgical image quality changes relative to BMI. This served as the majority of the first phase of a two phase project. The purpose of the second phase of the project will be to optimize scan parameters for surgical hardware placement in terms of image quality and organ dose for the devices that allow for modifications of scanner settings.
Materials and Methods:
(1) X-Ray quality control meters were used to verify particular beam characteristics and additional information was calculated from the beam data. Both a small volume ionization chamber as well as Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) dosimeters were used to validate linear response of new design X-Ray tubes. (2) Both handheld ionization chamber survey meters as well as Geiger-Muller based personal dose meters were used to measure stray radiation for room surveys in locations representative of typical radiation worker positions during intra-operative imaging. (3) MOSFET dosimeters were placed in an adult male anthropomorphic phantom representing a normal BMI. 20 MOSFETs were used in nine organs with two small volume ion chambers used for skin surface dosimetry. Two additional layers of adipose equivalent material were progressively added to the phantom to represent BMI values of overweight and obese.
(1) The maximum tube potential, half value layer (HVL), effective energy, and soft tissue f-factor for each machine is as follows: IMRIS VISIUS iCT: 118.4 kVp, 7.66 mm Al, 53.64 keV, and 0.934 cGy/R; Mobis Airo: 122.3 kVp, 7.21 mm Al, 51.31 keV, and 0.925 cGy/R; Siemens ARCADIS Orbic 3D: 83 kVp, 7.12 mm Al, 32.76 keV, and 0.914 cGy/R; GE OEC 9900 Elite: 75 kVp, 4.25 mm Al, 46.6 keV, and 0.920 cGy/R. (2) The highest exposure rates measured during clinically implemented protocols for each scanner are as follows: IMRIS VISIUS iCT: 800 mR/hr; Mobis Airo: 6.47 R/hr; Siemens ARCADIS Orbic 3D: 26.4 mR/hr. (3) The effective dose per scan of each device for a full lumbar spine scan are as follows, for normal, overweight, and obese BMI, respectively: IMRIS VISIUS iCT: 12.00 ± 0.30 mSv, 15.91 ± 0.75 mSv, and 23.23 ± 0.55 mSv; Mobius Airo: 5.90 ± 0.25 mSv, 4.97 ± 0.12 mSv, and 3.44 ± 0.21 mSv; Siemens ARCADIS Orbic 3D: 0.30 ± 0.03 mSv, 0.39 ± 0.02 mSv, and 0.28 ± 0.03 mSv; GE OEC 9900 Elite: 0.44 mSv, 0.77 mSv, and 1.14 mSv.
(1) The IMRIS VISIUS iCT i-Fluoro capable CT scanner and Mobius Airo mobile CT scanner have similar beam characteristics with significantly different tube parameter modulation protocols. Siemens ARCADIS Orbic 3D and GE OEC 9900 offer comparable beam characteristics but different imaging methods. All scanners performed within factory specifications. (2) The IMRIS VISIUS iCT should not be used in i-Fluoro mode for surgical procedures active during scanning due to the 1.42 cGy/s point dose rate in the beam field. The high exposure rate from the Mobius Airo is offset by short scan times and can be mitigated by ensuring enforcement of currently established radiation protection regulations and policies. Minimal stray radiation is measured from the Siemens ARCADIS Orbic 3D. (3) The differences in tube modulation of the CT scanners means the Mobius Airo offers a significantly reduced effective dose with increasing patient BMI over the IMRIS VISIUS iCT. Effective dose from the CT scanners varies as much as one to two orders of magnitude higher than the C Arms, but the Siemens ARCADIS Orbic 3D offers unusable image quality for patients with higher than normal BMI. Based off of physician reported usable surgical image quality of Mobius Airo, this device is recommended for continued integration and implementation during routine surgical procedures for patients of all BMI in orthopedic lumbar spine surgery.
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