Modeling scintillator‐photodiodes as detectors for megavoltage CT

Monajemi, T; Steciw, S; Fallone, B. G.; Rathee, S

doi:10.1118/1.1710733

Cited by 31 publications

(37 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…5 Several studies have investigated models of detector performance for megavoltage photons for radiotherapy applications. [6][7][8][9][10] These studies focus on single-or segmented-crystal scintillators and have been used to simulate light output as well as symmetric detector spread via the modulation transfer function ͑MTF͒. Experimental validation of both light output and symmetric detector response has been reported in the cited works.…”

Section: Introductionmentioning

confidence: 99%

Experimental validation of Monte Carlo (MANTIS) simulated x‐ray response of columnar CsI scintillator screens

Freed

Miller²,

Tang

et al. 2009

Medical Physics

View full text Add to dashboard Cite

Purpose: MANTIS is a Monte Carlo code developed for the detailed simulation of columnar CsI scintillator screens in x-ray imaging systems. Validation of this code is needed to provide a reliable and valuable tool for system optimization and accurate reconstructions for a variety of x-ray applications. Whereas previous validation efforts have focused on matching of summary statistics, in this work the authors examine the complete point response function ͑PRF͒ of the detector system in addition to relative light output values. Methods: Relative light output values and high-resolution PRFs have been experimentally measured with a custom setup. A corresponding set of simulated light output values and PRFs have also been produced, where detailed knowledge of the experimental setup and CsI:Tl screen structures are accounted for in the simulations. Four different screens were investigated with different thicknesses, column tilt angles, and substrate types. A quantitative comparison between the experimental and simulated PRFs was performed for four different incidence angles ͑0°, 15°, 30°, and 45°͒ and two different x-ray spectra ͑40 and 70 kVp͒. The figure of merit ͑FOM͒ used measures the normalized differences between the simulated and experimental data averaged over a region of interest. Results: Experimental relative light output values ranged from 1.456 to 1.650 and were in approximate agreement for aluminum substrates, but poor agreement for graphite substrates. The FOMs for all screen types, incidence angles, and energies ranged from 0.1929 to 0.4775. To put these FOMs in context, the same FOM was computed for 2D symmetric Gaussians fit to the same experimental data. These FOMs ranged from 0.2068 to 0.8029. Our analysis demonstrates that MANTIS reproduces experimental PRFs with higher accuracy than a symmetric 2D Gaussian fit to the experimental data in the majority of cases. Examination of the spatial distribution of differences between the PRFs shows that the main reason for errors between MANTIS and the experimental data is that MANTIS-generated PRFs are sharper than the experimental PRFs. Conclusions: The experimental validation of MANTIS performed in this study demonstrates that MANTIS is able to reliably predict experimental PRFs, especially for thinner screens, and can reproduce the highly asymmetric shape seen in the experimental data. As a result, optimizations and reconstructions carried out using MANTIS should yield results indicative of actual detector performance. Better characterization of screen properties is necessary to reconcile the simulated light output values with experimental data.

show abstract

Section: Introductionmentioning

confidence: 99%

Experimental validation of Monte Carlo (MANTIS) simulated x‐ray response of columnar CsI scintillator screens

Freed

Miller²,

Tang

et al. 2009

Medical Physics

View full text Add to dashboard Cite

show abstract

“…chemically etched surfaces as well as for various attached reflector materials, and reflections are therefore generally assumed to be either purely specular or purely diffuse (Lambertian) [1][2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

“…ONTE Carlo simulation is often used to predict and optimize the light collection from scintillation crystals [1][2][3][4][5]. To accurately predict and optimize the light collection, e.g.…”

Section: Introductionmentioning

confidence: 99%

Design of an Instrument to Measure Optical Reflectance of Scintillating Crystal Surfaces

Janecek

Moses

2008

IEEE Trans. Nucl. Sci.

View full text Add to dashboard Cite

Abstract-In order for a Monte Carlo simulation to be accurate in predicting and optimizing the light collection in scintillation detectors, the light reflectance off an internal surface within the scintillating crystal must be understood well. We present design studies for an instrument that will accurately measure the reflectance distribution within a scintillating crystal. A laser is aimed towards the center of a 50.8-mm diameter scintillating crystal hemisphere. The laser can be positioned at any arbitrary angle. The laser beam is reflected off the flat surface of the hemisphere and the light distribution is measured by a movable array of photodiodes that can measure the reflected light over the entire 2! solid angle. Thirty-six PIN photodiodes, mounted in two rows and offset to each other by half the length of a photodiode, measure the reflected light. The currents from the photodiodes are switched through a multiplexer to a digital multimeter, where the current is recorded. The current measurements give a dynamic range of 10 5 :1. A LabVIEW program controls the motion of the laser and photodiodes, the switch, and the data collection. The mechanical set-up is placed inside of a light-tight glove box. By flowing dry nitrogen gas through the glove box we can control the water content in the atmosphere and so measure hydroscopic scintillators.

show abstract

“…6,9,[12][13][14][15][23][24][25] Such modeling should account for both radiation and optical effects and an obvious approach would involve Monte Carlo based, event-by-event simulation of both radiation and optical transport so as to account for the most important physical effects. 13,23 However, since scintillation yields range from ∼8000 to 54 000 optical photons per MeV of deposited x-ray energy for the most promising scintillators for this application (Bi 4 4 and CsI:Tl), 26, 27 the computational demands related to optical transport can greatly exceed those related to radiation transport. This, plus the fact that the number of x-ray histories required for such studies is itself often very large (so as to achieve clinically realistic doses or a desired level of statistical precision), means that studies can become too computationally burdensome to be carried out on practical timescales.…”

mentioning

confidence: 99%

Optimization of the design of thick, segmented scintillators for megavoltage cone-beam CT using a novel, hybrid modeling technique

et al. 2014

View full text Add to dashboard Cite

Purpose: Active matrix flat-panel imagers (AMFPIs) incorporating thick, segmented scintillators have demonstrated order-of-magnitude improvements in detective quantum efficiency (DQE) at radiotherapy energies compared to systems based on conventional phosphor screens. Such improved DQE values facilitate megavoltage cone-beam CT (MV CBCT) imaging at clinically practical doses. However, the MV CBCT performance of such AMFPIs is highly dependent on the design parameters of the scintillators. In this paper, optimization of the design of segmented scintillators was explored using a hybrid modeling technique which encompasses both radiation and optical effects. Methods: Imaging performance in terms of the contrast-to-noise ratio (CNR) and spatial resolution of various hypothetical scintillator designs was examined through a hybrid technique involving Monte Carlo simulation of radiation transport in combination with simulation of optical gain distributions and optical point spread functions. The optical simulations employed optical parameters extracted from a best fit to measurement results reported in a previous investigation of a 1.13 cm thick, 1016 μm pitch prototype BGO segmented scintillator. All hypothetical designs employed BGO material with a thickness and element-to-element pitch ranging from 0.5 to 6 cm and from 0.508 to 1.524 mm, respectively. In the CNR study, for each design, full tomographic scans of a contrast phantom incorporating various soft-tissue inserts were simulated at a total dose of 4 cGy. Results: Theoretical values for contrast, noise, and CNR were found to be in close agreement with empirical results from the BGO prototype, strongly supporting the validity of the modeling technique. CNR and spatial resolution for the various scintillator designs demonstrate complex behavior as scintillator thickness and element pitch are varied-with a clear trade-off between these two imaging metrics up to a thickness of ∼3 cm. Based on these results, an optimization map indicating the regions of design that provide a balance between these metrics was obtained. The map shows that, for a given set of optical parameters, scintillator thickness and pixel pitch can be judiciously chosen to maximize performance without resorting to thicker, more costly scintillators. Conclusions: Modeling radiation and optical effects in thick, segmented scintillators through use of a hybrid technique can provide a practical way to gain insight as to how to optimize the performance of such devices in radiotherapy imaging. Assisted by such modeling, the development of practical designs should greatly facilitate low-dose, soft tissue visualization employing MV CBCT imaging in external beam radiotherapy.

show abstract

Modeling scintillator‐photodiodes as detectors for megavoltage CT

Cited by 31 publications

References 32 publications

Experimental validation of Monte Carlo (MANTIS) simulated x‐ray response of columnar CsI scintillator screens

Experimental validation of Monte Carlo (MANTIS) simulated x‐ray response of columnar CsI scintillator screens

Design of an Instrument to Measure Optical Reflectance of Scintillating Crystal Surfaces

Optimization of the design of thick, segmented scintillators for megavoltage cone-beam CT using a novel, hybrid modeling technique

Contact Info

Product

Resources

About