A bench‐top megavoltage fan‐beam CT using ‐photodiode detectors. I. System description and detector characterization

Rathee, S; Tu, Dongsheng; Monajemi, T; Rickey, Daniel W.; Fallone, B. G.

doi:10.1118/1.2181290

Cited by 24 publications

(62 citation statements)

References 57 publications

(78 reference statements)

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“…23 For indirect detection, some of the detectors considered include thick optical fibers detecting Cerenkov radiation, 24 2D polymer matrices filled with Gd 2 O 2 S : Tb phosphor, 25 as well as 1D and 2D crystalline scintillators ͑e.g., CsI:Tl, Bi 4 Ge 3 O 12 , CdWO 4 , and ZnWO 4 ͒, employing the concept of segmentation. [26][27][28][29][30][31][32][33][34] A series of theoretical and empirical studies has been previously reported on 2D segmented crystalline scintillators, which consists of matrices of scintillating crystals separated by septal walls to limit the lateral spread of optical photons. 25,[35][36][37][38][39][40] Monte Carlo simulations of radiation and optical transport have suggested that EPIDs employing segmented CsI:Tl and Bi 4 Ge 3 O 12 ͑BGO͒ detectors up to 40 mm thick can offer DQE values of up to 29% and 42%, respectively.…”

Section: Introductionmentioning

confidence: 99%

High‐DQE EPIDs based on thick, segmented BGO and CsI:Tl scintillators: Performance evaluation at extremely low dose

et al. 2009

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Purpose: Electronic portal imaging devices ͑EPIDs͒ based on active matrix, flat-panel imagers ͑AMFPIs͒ have become the gold standard for portal imaging and are currently being investigated for megavoltage cone-beam computed tomography ͑CBCT͒ and cone-beam digital tomosynthesis ͑CBDT͒. However, the practical realization of such volumetric imaging techniques is constrained by the relatively low detective quantum efficiency ͑DQE͒ of AMFPI-based EPIDs at radiotherapy energies, ϳ1% at 6 MV. In order to significantly improve DQE, the authors are investigating thick, segmented scintillators, consisting of 2D matrices of scintillating crystals separated by septal walls. Methods: A newly constructed segmented BGO scintillator ͑11.3 mm thick͒ and three segmented CsI:Tl scintillators ͑11.4, 25.6, and 40.0 mm thick͒ were evaluated using a 6 MV photon beam. X-ray sensitivity, modulation transfer function, noise power spectrum, DQE, and phantom images were obtained using prototype EPIDs based on the four scintillators. Results: The BGO and CsI:Tl prototypes were found to exhibit improvement in DQE ranging from ϳ12 to 25 times that of a conventional AMFPI-based EPID at zero spatial frequency. All four prototype EPIDs provide significantly improved contrast resolution at extremely low doses, extending down to a single beam pulse. In particular, the BGO prototype provides contrast resolution comparable to that of the conventional EPID, but at 20 times less dose, with spatial resolution sufficient for identifying the boundaries of low-contrast objects. For this prototype, however, the BGO scintillator exhibited an undesirable radiation-induced variation in x-ray sensitivity. Conclusions: Prototype EPIDs based on thick, segmented BGO and CsI:Tl scintillators provide significantly improved portal imaging performance at extremely low dose ͑i.e., down to 1 beam pulse corresponding to ϳ0.022 cGy͒, creating the possibility of soft-tissue visualization using MV CBCT and CBDT at clinically practical dose.

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Section: Introductionmentioning

confidence: 99%

High‐DQE EPIDs based on thick, segmented BGO and CsI:Tl scintillators: Performance evaluation at extremely low dose

et al. 2009

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“…4 However, conventional MV AMFPIs suffer from very low x ray quantum efficiency (QE) and, as a result, very low detective quantum efficiency (∼2% and 1% at 6 MV, respectively), 5 necessitating the use of relatively high imaging doses (e.g., ∼50-200 cGy) in order to achieve soft tissue visualization using MV CBCT. 6,7 To address this challenge, various approaches for increasing the QE of MV imagers have been investigated or implemented, such as xenon gas ion chambers arranged in a fan-beam geometry, 8 and thick, segmented scintillating crystals arranged in the form of a linear array [9][10][11][12] or a 2D matrix. [13][14][15][16][17][18][19][20][21][22][23][24] In particular, the approach involving a 2D matrix of segmented scintillator elements (based on CsI:Tl, Bi 4 SiO 5 [LYSO]) has been explored both theoretically and empirically.…”

Section: Introductionmentioning

confidence: 99%

Theoretical investigation of the design and performance of a dual energy (kV and MV) radiotherapy imager

et al. 2015

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Purpose: In modern radiotherapy treatment rooms, megavoltage (MV) portal imaging and kilovoltage (kV) cone-beam CT (CBCT) imaging are performed using various active matrix flat-panel imager (AMFPI) designs. To expand the clinical utility of MV and kV imaging, MV AMFPIs incorporating thick, segmented scintillators and, separately, kV imaging using a beam's eye view geometry have been investigated by a number of groups. Motivated by these previous studies, it is of interest to explore to what extent it is possible to preserve the benefits of kV and MV imaging using a single AMFPI design, given the considerably different x ray energy spectra used for kV and MV imaging. In this paper, considerations for the design of such a dual energy imager are explored through examination of the performance of a variety of hypothetical AMFPIs based on x ray converters employing segmented scintillators. Methods: Contrast, noise, and contrast-to-noise ratio performances were characterized through simulation modeling of CBCT imaging, while modulation transfer function, Swank factor, and signal performance were characterized through simulation modeling of planar imaging. The simulations were based on a previously reported hybrid modeling technique (accounting for both radiation and optical effects), augmented through modeling of electronic additive noise. All designs employed BGO scintillator material with thicknesses ranging from 0.25 to 4 cm and element-to-element pitches ranging from 0.508 to 1.016 mm. A series of studies were performed under both kV and MV imaging conditions to determine the most advantageous imager configuration (involving front or rear x ray illumination and use of a mirror or black reflector), converter design (pitch and thickness), and operating mode (pitch-binning combination). Results: Under the assumptions of the present study, the most advantageous imager design was found to employ rear illumination of the converter in combination with a black reflector, incorporate a BGO converter with a 0.508 mm pitch and a 2 cm thickness, and operate at full resolution for kV imaging and 2 × 2 binning mode for MV imaging. Such a dual energy imager design should provide soft tissue visualization at low, clinically practical doses under MV conditions, while helping to preserve the high spatial resolution and high contrast offered by kV imaging. Conclusions: The authors' theoretical investigation suggests that a dual energy imager capable of largely preserving the desirable characteristics of both kV and MV imaging is feasible. Such an imager, when coupled to a dual energy radiation source, could facilitate simplification of current treatment room imaging systems (as well as their associated quality assurance), and facilitate more precise integration of kV and MV imaging information by virtue of reduced geometric uncertainties. C 2015 American Association of Physicists in Medicine. [http://dx

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“…These detectors are based on concepts involving high pressure gas ͑e.g., xenon͒ chambers employing tungsten walls, [10][11][12] thick optical fibers detecting Cerenkov radiation, 13 thick HgI 2 photoconductors, 14 segmented phosphors based on photopolymer matrices, 15 and segmented crystalline scintillators which consist of 2D matrices ͑or 1D arrays͒ of scintillator crystals separated by optically opaque septal walls. 7,[16][17][18][19] Among these approaches, segmented crystalline scintillators offer significantly improved QE, with only limited loss in spatial resolution, and possibly no substantial increase in noise compared to conventional AMFPIs. In order to examine this strategy, 1D segmented arrays incorporating zinc tungstate ͑ZnWO 4 ͒ and cadmium tungstate ͑CdWO 4 ͒ scintillators, [17][18][19] as well as 2D segmented matrices employing bismuth germanate ͑BGO͒, thallium-doped cesium iodide ͑CsI:Tl͒ and CdWO 4 scintillators, 7,[20][21][22] have been investigated by different research groups.…”

Section: Introductionmentioning

confidence: 99%

“…7,[16][17][18][19] Among these approaches, segmented crystalline scintillators offer significantly improved QE, with only limited loss in spatial resolution, and possibly no substantial increase in noise compared to conventional AMFPIs. In order to examine this strategy, 1D segmented arrays incorporating zinc tungstate ͑ZnWO 4 ͒ and cadmium tungstate ͑CdWO 4 ͒ scintillators, [17][18][19] as well as 2D segmented matrices employing bismuth germanate ͑BGO͒, thallium-doped cesium iodide ͑CsI:Tl͒ and CdWO 4 scintillators, 7,[20][21][22] have been investigated by different research groups. Recently, a 40 mm thick segmented CsI:Tl detector, with an element-toelement pitch of 1.016 mm and an area of 16.25 ϫ 16.25 cm 2 , has been developed and evaluated by our group.…”

Section: Introductionmentioning

confidence: 99%

A Monte Carlo investigation of Swank noise for thick, segmented, crystalline scintillators for radiotherapy imaging

et al. 2009

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Thick, segmented scintillating detectors, consisting of 2D matrices of scintillator crystals separated by optically opaque septal walls, hold considerable potential for significantly improving the performance of megavoltage ͑MV͒ active matrix, flat-panel imagers ͑AMFPIs͒. Initial simulation studies of the radiation transport properties of segmented detectors have indicated the possibility of significant improvement in DQE compared to conventional MV AMFPIs based on phosphor screen detectors. It is therefore interesting to investigate how the generation and transport of secondary optical photons affect the DQE performance of such segmented detectors. One effect that can degrade DQE performance is optical Swank noise ͑quantified by the optical Swank factor I opt ͒, which is induced by depth-dependent variations in optical gain. In this study, Monte Carlo simulations of radiation and optical transport have been used to examine I opt and zero-frequency DQE for segmented CsI:Tl and BGO detectors at different thicknesses and element-to-element pitches. For these detectors, I opt and DQE were studied as a function of various optical parameters, including absorption and scattering in the scintillator, absorption at the top reflector and septal walls, as well as scattering at the side surfaces of the scintillator crystals. The results indicate that I opt and DQE are only weakly affected by absorption and scattering in the scintillator, as well as by absorption at the top reflector. However, in some cases, these metrics were found to be significantly degraded by absorption at the septal walls and scattering at the scintillator side surfaces. Moreover, such degradations are more significant for detectors with greater thickness or smaller element pitch. At 1.016 mm pitch and with optimized optical properties, 40 mm thick segmented CsI:Tl and BGO detectors are predicted to provide DQE values of ϳ29% and 42%, corresponding to improvement by factors of ϳ29 and 42, respectively, compared to that of conventional MV AMFPIs.

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A bench‐top megavoltage fan‐beam CT using ‐photodiode detectors. I. System description and detector characterization

Cited by 24 publications

References 57 publications

High‐DQE EPIDs based on thick, segmented BGO and CsI:Tl scintillators: Performance evaluation at extremely low dose

High‐DQE EPIDs based on thick, segmented BGO and CsI:Tl scintillators: Performance evaluation at extremely low dose

Theoretical investigation of the design and performance of a dual energy (kV and MV) radiotherapy imager

A Monte Carlo investigation of Swank noise for thick, segmented, crystalline scintillators for radiotherapy imaging

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