Quality assurance and long‐term stability of a novel 3‐in‐1 X‐ray system for brachytherapy

Abstract

Purpose: A novel, mobile 3-in-1 X-ray system featuring radiography, fluoroscopy, and cone-beam computed tomography (CBCT) has been launched for brachytherapy recently. Currently, there is no quality assurance (QA) procedure explicitly applicable to this system equipped with innovative technologies such as dynamic jaws and motorized lasers. We developed a dedicated QA procedure and, based on its performance for a duration of 6 months, provide an assessment of the device's stability over time. Methods: With the developed QA procedure, we assessed the system's planar and CBCT-imaging performance by investigating geometric accuracy, CTnumber stability, contrast-noise-ratio, uniformity, spatial resolution, low-contrast detectability, dynamic range, and X-ray exposure using dedicated phantoms. Furthermore, we evaluated geometric stability by using the flexmap-approach and investigated the device's laser-and jaw-positioning accuracy with an in-house test phantom. CBCT-and planar-imaging protocols for pelvis, breast, and abdomen imaging were examined. Results: Planar-and CBCT-imaging performances were widely stable with a geometric accuracy ≤1 mm, CT-number stability of up to 46 HU, and uniformity variations of up to 48 HU over time. For planar imaging, low-contrast detectability and dynamic range exceeded current recommendations. Although geometric stability was considered tolerable, partly substantial positioning inaccuracies of up to more than 120 mm and −13 mm were obtained for lasers and jaws, respectively. X-ray exposure showed small variations of ≤0.56 µGy and ≤0.76 mGy for planar-and CBCT-imaging, respectively. The conductance of the QA procedure allowed a smooth evaluation of the system's overall performance. Conclusion:We developed a QA workflow for a novel 3-in-1 X-ray system allowing to assess the device's imaging and hardware performance. The system showed in general a reasonable imaging performance and stability over time, whereas improvements regarding laser and jaw accuracy are strictly required.

Cone‐beam CT imaging with laterally enlarged field of view based on independently movable source and detector

“…We think that these effects were not observed for higher-frequency line-pairs, since in these cases additional effects as scatter or beam hardening within the structures have to be considered as well. The reduced resolution characteristics for EnFOV180 may be affected by the unbalanced scatter profiles reported above, but also by a corresponding scanner misalignment 8,23 and imperfect image stitching due to non-overlapping projections resulting in blurring and circular artifacts as shown by Chang et al 34 Note that these artifacts may also be an additional factor for the decreased noise obtained for EnFOV180, due to the difference image approach in noise assessment.…”

“…The ImagingRing m (IRm; medPhoton, Austria) is a mobile O‐arm CBCT system that features independent source and detector rotations. The system was clinically operated for the first time in 2021 22 and technical characterizations were published recently 8,23 . The IRm gantry consists of two rings, where the source rotates along the outer (source‐axis‐distance [SAD]: 74 cm) and the 43 × 43 cm 2 detector along the inner (detector‐axis‐distance [DAD]: 52 cm) ring around the common isocenter (Figure 1a).…”

“…The system was clinically operated for the first time in 2021 22 and technical characterizations were published recently. 8,23 The IRm gantry consists of two rings, where the source rotates along the outer (source-axis-distance [SAD]: 74 cm) and the 43 × 43 cm 2 detector along the inner (detector-axis-distance [DAD]: 52 cm) ring around the common isocenter (Figure 1a). Four dynamic jaws allow for collimating the X-ray cone-beam and enable a beam aperture of up to 55 • .…”

First implementation of an innovative infra‐red camera system integrated into a mobile CBCT scanner for applicator tracking in brachytherapy—Initial performance characterization

“…In the current state, it is necessary to perform tracking with a fixed gantry position, as established during calibration, to ensure optimal tracking precision. During gantry rotations, wobbling of the CBCT scanner 22,23 or mechanical hysteresis effects 22 might result in varying stress to the system, which is transferred to the camera mounting due to its rigid assembly. A further calibration procedure similar to the ImagingRing's flexmap calibration, 26 which measures tracked marker positions as a function of the gantry angle and accounts for occurring spatial deviations during live-tracking, could be beneficial to improve system performance.…”

“…The stability of calibrations is important to ensure an accurate tracking over time. In the following, the CBCT coordinate system is considered to be fixed due to the previously observed 23 good long‐term stability of the ImagingRing. Therefore, tracking errors may arise mainly from variations in the camera coordinate system.…”