Low‐dose megavoltage cone‐beam computed tomography using a novel multi‐layer imager (MLI)

Abstract

Purpose: The feasibility of low-dose megavoltage cone-beam acquisition (MVCBCT) using a novel, high detective quantum efficiency (DQE) multi-layer imager (MLI) was investigated. The aim of this work was to reconstruct MVCBCT images using the MLI at different total dose levels, and assess Hounsfield Unit (HU) accuracy, noise and contrast-to-noise ratio (CNR) for low-dose megavoltage cone-beam acquisition. Methods: The MLI has four stacked layers; each layer contains a combination of copper filter/converter, gadolinium oxysulfide (GOS) scintillator and a-Si detector array. In total, 720 projections of a CATPHAN â phantom were acquired over 360°at 2.5, 6, and 6 MV flattening filter free (FFF) beam energies on a Varian TrueBeam LINAC. The dose per projection was 0.01, 0.0167, and 0.05 MU for 2.5, 6, and 6 MV FFF, respectively. MVCBCT images were reconstructed with varying numbers of projections to provide a range of doses for evaluation. Hounsfield Unit uniformity, accuracy, noise and CNR were estimated. Improvements were quantified relative to the standard AS1200 single-layer imager. Results: Average HU uniformity for the MLI reconstructions was within a range of 95%-99% for all of the energies studied. Relative electron density estimation from HU values was within 0.4% AE 1.8% from nominal values. The CNR for MVCBCT based on MLI projections was 2-49 greater than from AS1200 projections. The 2.5 MV beam acquisition with the MLI exhibited the lowest noise and the best balance between CNR and dose for low-dose reconstructions. Conclusions: Megavoltage cone-beam acquisition imaging with a novel MLI prototype mounted on a clinical linear accelerator demonstrated substantial improvement over the standard AS1200 EPID. Further optimization of MVCBCT reconstruction, particularly for 2.5 MV acquisitions, will improve image metrics. Overall, the MLI improves CNR at substantially lower doses than currently required by conventional detectors. This new high DQE detector could provide high-quality MVCBCT at

Investigation of image quality of MV and kV CBCT with low‐Z beams and high DQE detector

“…CWO was noted to have a 20‐fold efficiency improvement over GOS with significantly higher stability and light yield than BGO 10 . Likewise, image quality improvement was seen using multilayer GOS imagers with two to four times greater CNR than an equivalent single layer GOS detector 11 …”

“…10 Likewise, image quality improvement was seen using multilayer GOS imagers with two to four times greater CNR than an equivalent single layer GOS detector. 11 Currently, these two approaches to improving MV imaging, the amelioration of detector efficiencies and introduction of low-Z targets, have remained largely separate. Likewise, direct comparison of the benefit of different imaging strategies in the literature remains challenging as different works have different combi-nations of voxel size, cone-beam size, phantom dose, focal-spot size, and other imaging variables.…”

Full modulation transfer functions of thick parallel‐ and focused‐element scintillator arrays obtained by a Monte Carlo optical transport model

“…[1][2][3][4][5][6][7] The low quantum efficiency (QE) of megavoltage (MV) photons, has been challenging. Different approaches have been implemented to increase the detective quantum efficiency (DQE), from using multilayer imagers, 8 bidirectional flat panel detectors, 9 and scintillating fibers with different septa materials. 10,11 Thick segmented crystalline scintillators have also been investigated as the x-ray converter, [12][13][14][15][16][17][18][19][20][21] whilst usually some improvement in signal-to-noise ratio is also offered by frame averaging.…”

Improving image quality and reducing dose with 2.5 MV diamond target volume‐of‐interest cone beam CT imaging

“…Kilovoltage x-ray image guidance offers favorable image quality and dose characteristics, but kV onboard imaging incurs increased cost, maintenance, and introduces its own uncertainties 1 ;while for planar imaging,lacks the advantageous perspective of the treatment beams-eyeview. 2 Numerous efforts have focused on improvement of MV imaging systems with regard to both detectors and beam production, including the ongoing development of efficient multilayer detectors 3,4 and the recent installation of the 2.5 MV imaging beam on the modern TrueBeam (Varian Medical Systems, Palo Alto, CA) treatment unit.…”

“…Consequently, this 2.5 MV diamond target beam demonstrates improved contrast-to-noise ratio (CNR) versus dose characteristics compared to the commercial 2.5 MV copper target beam, by factors of up to 1.7 times in planar imaging. 5 This study examines the feasibility of MV conebeam CT (CBCT) with this novel 2.5 MV diamond target beam.Although low-dose MV CBCT with standard MV therapy beams has been explored in experimental benchtop settings 4,[7][8][9] the 1%-2% detective quantum efficiency 10 of commercial detectors in combination with these beams has limited translation to the clinic. Due to its unique energy spectrum, the sintered diamond target beam permits 2.5 MV image acquisition with doses on the order of mGy per frame 5 and therefore may be comparatively advantageous for CBCT acquisition.…”