A cone-beam megavoltage CT scanner for treatment verification in conformal radiotherapy

Mosleh-Shirazi, Mohammad Amin; Evans, Philip; Swindell, W.; Webb, Steve; Partridge, Mike

doi:10.1016/s0167-8140(98)00042-5

Cited by 127 publications

(86 citation statements)

References 22 publications

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“…They include mobile in‐room computed tomography (CT) scanners, (4) CT on rails, 5 , 6 B‐mode ultrasound systems, (6) tomotherapy, (6) and kilovoltage 7 , 8 and megavoltage 2 , 9 cone‐beam CT scanners (CBCT), widely in use currently.…”

Section: Introductionmentioning

confidence: 99%

Adaptive optimization by 6 DOF robotic couch in prostate volumetric IMRT treatment: rototranslational shift and dosimetric consequences

Chiesa

Placidi

Azario

et al. 2015

J Applied Clin Med Phys

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The purpose of this study was to investigate the magnitude and dosimetric relevance of translational and rotational shifts on IGRT prostate volumetric‐modulated arc therapy (VMAT) using Protura six degrees of freedom (DOF) Robotic Patient Positioning System. Patients with cT3aN0M0 prostate cancer, treated with VMAT simultaneous integrated boost (VMAT‐SIB), were enrolled. PTV2 was obtained adding 0.7 cm margin to seminal vesicles base (CTV2), while PTV1 adding to prostate (CTV1) 0.7 cm margin in all directions, except 1.2 cm, as caudal margin. A daily CBCT was acquired before dose delivery. The translational and rotational displacements were corrected through Protura Robotic Couch, collected and applied to the simulation CT to obtain a translated CT (tCT) and a rototranslated CT (rtCT) on which we recalculated the initial treatment plan (TP). We analyzed the correlation between dosimetric coverage, organs at risk (OAR) sparing, and translational or rotational displacements. The dosimetric impact of a rototranslational correction was calculated. From October 2012 to September 2013, a total of 263 CBCT scans from 12 patients were collected. Translational shifts were <5mm in 81% of patients and the rotational shifts were <2∘ in 93% of patient scans. The dosimetric analysis was performed on 172 CBCT scans and calculating 344 VMAT‐TP. Two significant linear correlations were observed between yaw and the V20 femoral heads and between pitch rotation and V50 rectum (p<0.001); rototranslational correction seems to impact more on PTV2 than on PTV1, especially when margins are reduced. Rotational errors are of dosimetric significance in sparing OAR and in target coverage. This is relevant for femoral heads and rectum because of major distance from isocenter, and for seminal vesicles because of irregular shape. No correlation was observed between translational and rotational errors. A study considering the intrafractional error and the deformable registration is ongoing.PACS number: 87.55.de

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Section: Introductionmentioning

confidence: 99%

Adaptive optimization by 6 DOF robotic couch in prostate volumetric IMRT treatment: rototranslational shift and dosimetric consequences

Chiesa

Placidi

Azario

et al. 2015

J Applied Clin Med Phys

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“…However, MVCT imaging is being investigated as a three-dimensional ͑3D͒ alternative. Many systems have been proposed for multislice cone beam CT using purpose-built detectors [2][3][4] or using commercial EPIDs such as fluoroscopic systems, [5][6][7] liquid-filled ionization chamber 8 or an amorphous silicon flat-panel detector. 9 The first tomotherapy prototype utilises an arc-shaped one-dimensional detector array for fan-beam megavoltage CT. [10][11][12] Two approaches combining the treatment unit with an onboard kilovoltage CT system are under development.…”

Section: Introductionmentioning

confidence: 99%

“…The mentioned detector uses a 2D array of scintillation crystal detector elements made of CsI͑Tl͒, thallium-doped cesium iodide, instead of the phosphor screen of conventional metal/phosphor screen devices. [2][3][4] The thickness of the scintillation crystals was chosen to yield a relatively high quantum efficiency of 18%, however, further increasing the thickness of the crystals has its limitations. 3 The work of this paper is intended to make some steps towards an optimized detector for megavoltage CT imaging using a different concept of improving efficiency.…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo study of a highly efficient gas ionization detector for megavoltage imaging and image-guided radiotherapy

et al. 2002

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The imaging characteristics of an arc-shaped xenon gas ionization chamber for the purpose of megavoltage CT imaging were investigated. The detector consists of several hundred 320 m thick gas cavities separated by thin tungsten plates of the same thickness. Dose response, efficiency and resolution parameters were calculated using Monte Carlo simulations. The calculations were compared to measurements taken in a 4 MV photon beam, assuming that the measured signal in the chambers corresponds to the therein absorbed dose. The measured response profiles for narrow and broad incident photon beams could be well reproduced with the Monte Carlo calculations. They show, that the quantum efficiency is 29.2% and the detective quantum efficiency at zero frequency DQE͑0͒ is 20.4% for the detector arc placed in focus with the photon source. For a detector placed out of focus, these numbers even increase. The efficiency of this kind of radiation detector for megavoltage radiation therefore surpasses the reported efficiency of existing detector technologies. The resolution of the detector is quantified with calculated and measured line spread functions. The corresponding modulation transfer functions were determined for different thicknesses of the tungsten plates. They show that the resolution is only slightly dependent on the plate thickness but is predominantly determined by the cell size of the detector. The optimal plate thickness is determined by a tradeoff between quantum efficiency, total signal generation and resolution. Thicker plates are more efficient but the total signal and the resolution decrease with plate thickness. In conclusion, a gas ionization chamber of the described type is a highly efficient megavoltage radiation detector, allowing to obtain CT images with very little dose for a sufficient image quality for anatomy verification. This kind of detector might serve as a model for a future generation of highly efficient radiation detectors.

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“…Nakagawa et al proposed to use a pre-treatment MV CT slice to verify the patient set-up for stereotactic radiosurgery of the lung [22]. To overcome the problem of table indentation Mosleh-Shirazi et al [23] reported a feasibility study on 3D MV CBCT using a scintillation detector Á CCD camera based EPID on the linac, with the image frame acquisition synchronized with the radiation pulses. A first prototype required approximately 40 cGy and 2h reconstruction time on a Sun SPARC 2 to obtain a density resolution of 2% and spatial resolution of 2.5 mm.…”

Section: Cbctmentioning

confidence: 99%

An overview of volumetric imaging technologies and their quality assurance for IGRT

Verellen¹,

Ridder²,

Tournel³

et al. 2008

Acta Oncologica

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A cone-beam megavoltage CT scanner for treatment verification in conformal radiotherapy

Cited by 127 publications

References 22 publications

Adaptive optimization by 6 DOF robotic couch in prostate volumetric IMRT treatment: rototranslational shift and dosimetric consequences

Adaptive optimization by 6 DOF robotic couch in prostate volumetric IMRT treatment: rototranslational shift and dosimetric consequences

Monte Carlo study of a highly efficient gas ionization detector for megavoltage imaging and image-guided radiotherapy

An overview of volumetric imaging technologies and their quality assurance for IGRT

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