Characterization of A re-designed clinical fluoroscopic portal imager

Jaffray, D.; Chawla, Kamal K.; Drake, Douglas G.; Wong, John W.

doi:10.1016/0167-8140(96)80676-1

Cited by 3 publications

(3 citation statements)

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“…For 1 MU per projection, it may be important to use a reference dosimeter like that in the water scans system to eliminate the dose rate fluctuation (c) map the fan beam projections into parallel ones since the current MLS-ART produces the best reconstruction accuracy for parallel beams (or alternatively, develop a fan beam MLS-ART algorithm by reordering the rays in each projection) (d) investigate the feasibility of using cone beams for 3D portal CT reconstruction using MLS-ART and the same EPID system as an alternative approach to the study of Jaffray et al (1996). This work represents an alternative feasibility study of MV CT to those using cone beams (Jaffray et al 1996, Midgley et al 1998. Since the real advantage of MV CT is in differentiating soft tissues by 1%, clinical use of the current portal CT is not reliable.…”

Section: Discussionmentioning

confidence: 99%

Feasibility of megavoltage portal CT using an electronic portal imaging device (EPID) and a multi-level scheme algebraic reconstruction technique (MLS-ART)

Guan

Zhu

1998

Phys. Med. Biol.

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Although electronic portal imaging devices (EPIDs) are efficient tools for radiation therapy verification, they only provide images of overlapped anatomic structures. We investigated using a fluorescent screen/CCD-based EPID, coupled with a novel multi-level scheme algebraic reconstruction technique (MLS-ART), for a feasibility study of portal computed tomography (CT) reconstructions. The CT images might be useful for radiation treatment planning and verification. We used an EPID, set it to work at the linear dynamic range and collimated 6 MV photons from a linear accelerator to a slit beam of 1 cm wide and 25 cm long. We performed scans under a total of approximately 200 monitor units (MUs) for several phantoms in which we varied the number of projections and MUs per projection. The reconstructed images demonstrated that using the new MLS-ART technique megavoltage portal CT with a total of 200 MUs can achieve a contrast detectibility of approximately 2.5% (object size 5 mm x 5 mm) and a spatial resolution of 2.5 mm.

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Section: Discussionmentioning

confidence: 99%

Feasibility of megavoltage portal CT using an electronic portal imaging device (EPID) and a multi-level scheme algebraic reconstruction technique (MLS-ART)

Guan

Zhu

1998

Phys. Med. Biol.

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“…Other researchers have demonstrated larger improvements to the efficiency of the optical chain of their prototype systems. 22,23 Such increases in the amount of light reaching the TV camera would alleviate the secondary quantum sink affecting video-based portal imagers 6 as well as increase the theoretical DQE of the video-based system by a factor as high as 9.6, depending on spatial frequency. Therefore, this experiment determines what increase in DQE is required to make noticeable visual impact.…”

Section: A Virtual Prototypesmentioning

confidence: 99%

Monte Carlo simulation of the image formation process in portal imaging

2003

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We have written Monte Carlo programs to simulate the formation of radiological images. Our code is used to propagate a simulated x-ray fluence through each component of an existing video-based portal imaging system. This simulated fluence consists of a 512 x 512 pixel image containing both contrast-detail patterns as well as checker patterns to assess spatial resolution of the simulated portal imager. All of the components of the portal imaging system were modeled as a cascade of eight linear stages. Using this code, one can assess the visual impact of changing components in the imaging chain by changing the appropriate probability density function. Virtual experiments were performed to assess the visual impact of replacing the lens and TV camera by an amorphous silicon array, and the effect of scattered radiation on portal images.

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“…A number of megavoltage (MV) computerized tomography (CT) systems have been engineered, based upon radiotherapy linear accelerator (LINAC) treatment beams operating in a fan beam scanning mode (see, for example, Simpson et al 1982, Swindell et al 1983, Brahme et al 1987, Lewis et al 1992. The recent availability of electronic portal imaging device (EPID) area detectors presents the possibility of expanding this work to cone beam scanning (Jaffray et al 1996). The reconstruction method for a circular orbit, cone beam scan (Feldkamp et al 1984, Webb et al 1987, Morton et al 1990 is similar to conventional filtered back-projection algorithms for single-slice fan beam CT.…”

Section: Introductionmentioning

confidence: 99%

A feasibility study for megavoltage cone beam CT using a commercial EPID

Midgley

Millar

1998

Phys. Med. Biol.

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This study used a standard commercial electronic portal imaging device (EPID) area detector attached to an isocentric linear accelerator and the Feldkamp algorithm to produce cone beam tomographic reconstructions. The EPID has a active area of 32.5 x 32.5 cm2, and can record 12-bit images using two monitor units (MU), with a resolution of 2.1 x 2.0 mm2 FWHM. Since the EPID was not large enough to record the full patient projection at about 1.5 geometric magnification, it was necessary to offset the detector to collect half-cone projections. Corrections are required to convert pixel values into units of exit dose and to realign the projections to overcome the +/- 4 mm support arm sag. With a geometric magnification of 1.5 the sensitive volume is a cylinder of radius 21 cm and length 17 cm. Unfortunately, the patient couch contains metal bed support rails that lie just outside this cylinder, and produce streak artefacts in the reconstruction. Using 90 views the system delivers a central dose of 90 cGy, and has a density resolution of 4%.

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Characterization of A re-designed clinical fluoroscopic portal imager

Cited by 3 publications

References 0 publications

Feasibility of megavoltage portal CT using an electronic portal imaging device (EPID) and a multi-level scheme algebraic reconstruction technique (MLS-ART)

Feasibility of megavoltage portal CT using an electronic portal imaging device (EPID) and a multi-level scheme algebraic reconstruction technique (MLS-ART)

Monte Carlo simulation of the image formation process in portal imaging

A feasibility study for megavoltage cone beam CT using a commercial EPID

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