This study compared patient dose and image quality of a mobile O-arm TM cone beam imaging system in the 3D scan acquisition mode to those of a 64 slice Computed Tomography (CT) imaging system. The investigation included patient dose, scattered radiation, and image quality measurements. The patient dose was measured using a 0.6cc Farmer ion chamber and 30 cm long Computed Tomography (CT) head and body polymethylmethacrylate (PMMA) phantoms. The results show that under identical radiographic techniques (kVp, mAs, etc.) and with the same scan length, the O-arm TM in 3D scan acquisition mode delivers approximately half the radiation dose of a 64 slice CT scanner. Scattered radiation was measured at several locations around the O-arm TM , at 1 m, 2 m and 3 m distances in 3D CT scan acquisition mode with a RadCal 10 × 5-180 pancake ion chamber using a 30cm long CT body phantom as the source of scatter. Similar measurements were made in a 64 slice CT scanner. The data demonstrate that scattered radiation from the O-arm TM to personnel involved in a clinical procedure is comparable to that from a 64 slice CT scanner. Image quality was compared by exposing a CATPHAN phantom to comparable doses in both the O-arm TM and the CT scanner. The resultant images were then evaluated for modulation transfer function (MTF), high-contrast spatial resolution, and low contrast sensitivity for clinical application purpose. The O-arm TM shows comparable high contrast to the CT (7 lp/cm vs. 8 lp/cm). The low contrast in the O-arm TM is not visible due to fixed pattern noise. For image guided surgery applications where the location of a structure is emphasized over a survey of all image details, the O-arm TM has some advantages due to wide radiation beam coverage and lower patient dose. The image quality of the O-arm TM needs significant improvement for other clinical applications where high image quality is desired.

Radiation performance characteristics of a dedicated intraoperative accelerator were determined to prepare the unit for clinical use. The linear accelerator uses standing wave X‐band technology (wavelength approximately 3 centimeters) in order to minimize the mass of the accelerator. The injector design, smaller accelerator components, and low electron beam currents minimize radiation leakage. The unit may be used in a standard operating room without additional shielding. The mass of the accelerator gantry is 1250 Kg (weight approximately 2750 lbs) and the unit is transportable between operating rooms. Nominal electron energies are 4, 6, 9, and 12 MeV, and operate at selectable dose rates of 2.5 or 10 Gray per minute. Dmax depths in water for a 10 cm applicator are 0.7, 1.3, 1.7, and 2.0 for these energies, respectively. The depths of 80% dose are 1.2, 2.1, 3.1, and 3.9 cm, respectively. Absolute calibration using the American Association of Physicists in Medicine TG‐51 protocol was performed for all electron energies using the 10 cm applicator. Applicator sizes ranged from 3 to 10 cm diameter for flat applicators, and 3 to 6 cm diameter for 30° beveled applicators. Output factors were determined for all energies relative to the 10 cm flat applicator. Central axis depth dose profiles and isodose plots were determined for every applicator and energy combination. A quality assurance protocol, performed each day before patient treatment, was developed for output and energy constancy.PACS number(s): 87.53.–j, 87.52.–g

Purpose: The O‐arm is a cone beam imaging system designed primarily to support orthopedic surgery as well as for image‐guided and vascular surgery. Using a gantry that can be opened or closed, the O‐arm can function as a 2D fluoroscopy device or collect 3D volumetric imaging data like a CT system. Our clinical applications of the O‐arm in spine surgical procedures, assessment of pedicle screw position, kyphoplasty procedures, and etc show that the O‐arm 3D mode provides enhanced imaging information in the surgical procedure compared to radiographs or fluoroscopy alone. However, the radiation dose of the O‐arm has remained uninvestigated. This study is to investigate patient dose and scatter radiation from an O‐arm and compare the results to those from a CT scanner and a conventional C‐arm. Method and Materials: The patient dose was measured using a 0.6 cc Farmer ion chamber and 30 cm long CT head and body phantoms. Scatter radiation was measured at several locations around the O‐arm, at 1m, 2m and 3m distances from the iso‐center of the O‐arm, in both the 2D fluoroscopic mode and the 3D mode with a Radcal 10×5−180 pancake ion chamber using a 30 cm long CTDI body phantom as the source of scatter. The same measurements were made for an OEC C‐arm and a 64 slice CT scanner, respectively. Results: The results show that under identical technical conditions and with the same scan length, the O‐arm 3D mode delivers radiation dose to patients and scatter dose to personnel that is comparable to that of the 64 slice CT scanner. The O‐arm 2D mode produces similar scatter radiation as a conventional GE OEC fluoroscopic C‐arm system. Conclusion: Our study demonstrated that the O‐arm had comparable radiation dose to patients and radiologists as CT and C‐arm systems.