Clinical assessment and characterization of a dual‐tube kilovoltage X‐ray localization system in the radiotherapy treatment room

Abstract

Although flat‐panel kilovoltage X‐ray imaging devices have been well tested for clinical use in diagnostic radiology, their use as a part of an image‐guided radiation therapy (IGRT) system in a treatment room is new and requires systematic assessment.We used the Novalis IGRT system (BrainLAB, Feldkirchen, Germany) for the present study. The system consists of two floor‐mounted kilovoltage X‐ray tubes projecting obliquely onto two flat‐panel detectors mounted on the ceiling. The system can automatically fuse two‐dimensional localization images with three‐dimensional simulation computed tomography images to provide positioning guidance. We evaluated these system parameters: Overall performance of the IGRT system, including isocenter correlation between the IGRT system and the linear accelerator (LINAC)Image quality of the systemExposure received by patients for a pair of imagesLinearity, uniformity, and repeatability of the system The Novalis system uses a daily isocenter calibration procedure to ensure consistency of isocenters between the IGRT and the LINAC systems. The localization accuracy was about 1 mm. We measured the relative modulation transfer function (RMTF) to quantify the spatial resolution of the imaging device, with f50 being 0.7 – 0.9 line pairs per millimeter. The maximal exposure of an image was 95 mR. We derived an empirical relationship between the exposure and the X‐ray technical settings. The other parameters of the system were quantitatively measured and generally met the requirements.The IGRT system is safe and reliable for clinical use as a target localization device. The measured data can be used as a benchmark for a quality assurance procedure.PACS number: 87.56‐v

Clinical commissioning and use of the Novalis Tx linear accelerator for SRS and SBRT

“…The image quality and quality assurance programs for the OBI (planar and CBCT) have been detailed in the studies by Yoo et al (70) and Bissonnette et al (71,72) Hyer et al (73) compared the qualities of two volumetric CBCT imaging systems, as well as the organ doses. Lee et al (74) assessed the image quality of the ETX system. Table 1 lists the technical specifications of the imaging detectors mounted on the NTX.…”

“…The phantom contains 21 groups of line pairs with spatial frequencies ranging from 0.5 to 5.0 lp/mm. The spatial resolution can be quantified by visually determining the resolvable line pairs, or by plotting a relative modulation transfer function (RMTF) for more quantitative analysis, (74)(75)(76) as shown in Figure 1 Figure 1(c) shows an MV portal image of an aluminum phantom, known as the "Las Vegas" phantom (Varian Medical Systems, Palo Alto, CA), which contains circular discs of different sizes and thicknesses. The visible circles are marked qualitatively.…”

Clinical accuracy of ExacTrac intracranial frameless stereotactic system

“…1. (See Chen et al 18 or Lee et al 21 for a description of the kilovolt x-ray system). As the x-ray system is nonorthogonal, it is possible that the spatial accuracy is reduced along the axis that bisects the kV beam axes.…”

A review of image-guided radiotherapy

“…The Novalis system consists of two X-ray tubes and digital imaging plates that provide 3D coordinates of the target. System characterization and clinical applications have been reported [59][60][61][62][63][64][65][66][67]. In a comparative study between ultrasound localization of the prostate and radiographic 3D imaging of radio-opaque markers, Fuller et al [68] found significant differences between the two methods.…”