![]() ![]() (Fig.1) 1) to avoid radiation‐induced damage to its sensitive electronics. When not in use, the AIRO is stored in the maze (Fig. The AIRO's small footprint (W × L × H: 1.94 × 1.54 × 1.90 m) occupies 1.28 m 2 of treatment floor space (in scan mode). Our institution is the first to acquire and clinically implement the AIRO Mobile CT System (AIRO) for IGPT. The AIRO Mobile CT System (Mobius Imaging LLC, Shirley, MA, USA) is a large bore (107 cm) helical 32 slice CT scanner historically utilized for intra‐operative imaging for spinal surgeries. 12 For these reasons, a small‐footprint mobile CT scanner, commonly used for image‐guided surgery, could be of great value for 3D image‐guided proton therapy (IGPT). To date, stand‐alone in‐room CT scanners utilized have had large footprints and are either not amenable to or cumbersome to use in the more compact proton therapy centers, such as the S250 (Mevion Medical Systems, Littleton, MA, USA). 9, 10, 11 Some proton vendors are developing technologies for CBCT (Proteus ®ONE, IBA, Belgium, HITACHI, Tokyo, Japan). 8 Recently, people have reported on the use of in‐room CT scanners for proton beam radiation therapy localization. Unfortunately, due to the size and geometry of proton therapy units, imaging has largely been limited to orthogonal kV/kV x‐ray systems. Patient localization accuracy is particularly important in proton beam radiation therapy due to the sharp dose fall‐off compared to conventional x‐ray therapy. 1, 2, 3, 4, 5, 6, 7 These imagers provide improved treatment accuracy over conventional orthogonal imaging allowing for increased precision in radiation delivery. It may be of a concern for a complicated orthopedic procedure.Advances in in‐room computed tomography (CT) scanners and cone‐beam technology have led to the proliferation of CT localization for image guided radiation therapy (IGRT). The use of a bowtie filter can homogenize the photon flux at the detectors and reduce radiation to the patient in those peripheral regions of the body.Ĭonclusion: The Airo with a flat filter delivers relatively more radiation to patient especially to the skin. The dose distribution across the body phantom is more homogeneous in the Confidence than the Airo. The P/C ratio for the Confidence is 2.11 at 120kV. ![]() For the Airo, the P/C ratios are 4.83, 4.03, 3.64 for 80kV, 100kV, and 120kV, respectively. ![]() The higher P/C ratio in the Airo is due to the beam-shaping filter where a flat filter is applied, while a bowtie filter is used for the Siemens Confidence. Results: The x-ray quality is comparable (6.85 vs. For comparison the same experiment was repeated in a Siemens Confidence. The image uniformity between the center and edge was analyzed. The center and peripheral CTDIs were measured with a 32-cm body phantom for 80kV, 100kV, and 120kV. All measurements were normalized to the measurement at the iso-center. The measurements were made with 2cm intervals between them for 120kV, 192mAs using service mode. For the assessment of the beam-shaping filter, exposure was measured under service mode with a RaySafe R/F detector in 14 lateral positions starting from the iso-center. Methods: We measured the HVL at the iso-center to verify the x-ray beam quality. This study is to investigate what causes the ratio difference and how it impacts radiation dose and image quality. For the Airo mobile CT, the P/C ratio is approximately 4. Purpose: For a conventional CT with a 32 cm body phantom, the ratio between the peripheral and the center CTDI measurement (the P/C ratio) is close to 2.
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