Treatment Verification Using Digital Imaging

Shalev, Shlomo

doi:10.1007/978-3-662-03107-0_8

Cited by 9 publications

(4 citation statements)

References 99 publications

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“…The host PC runs a dedicated windows application, which was developed in our hospital. The program supports a patient database, configurable image acquisition procedures, display enhancement and quantitative image analysis tools, EPID performance quality assurance procedures and fully integrated decision protocols for off-line and on-line patient set-up corrections (Shalev 1995). The image processing functions make use of the library of routines (Matrox imaging library) that comes with the frame grabber.…”

Section: Epid Software and Image Acquisition Procedurementioning

confidence: 99%

Characterization of a high-elbow, fluoroscopic electronic portal imaging device for portal dosimetry

et al. 1999

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The application of a newly developed fluoroscopic (CCD-camera based) electronic portal imaging device (EPID) in portal dosimetry is investigated. A description of the EPID response to dose is presented in terms of stability, linearity and optical cross-talk inside the mechanical structure. The EPID has a relatively large distance (41 cm on-axis) between the fluorescent screen and the mirror (high-elbow), which results in cross-talk with properties quite different from that of the low-elbow fluoroscopic EPIDs that have been studied in the literature. In contrast with low elbow systems, the maximum cross-talk is observed for points of the fluorescent screen that have the largest distance to the mirror, which is explained from the geometry of the system. An algorithm to convert the images of the EPID into portal dose images (PDIs) is presented. The correction applied for cross-talk is a position dependent additive operation on the EPID image pixel values, with a magnitude that depends on a calculated effective field width. Deconvolution with a point spread function, as applied for low-elbow systems, is not required. For a 25 MV beam, EPID PDIs and ionization chamber measurements in the EPID detector plane were obtained behind an anthropomorphic phantom and a homogeneous absorber for various field shapes. The difference in absolute dose between the EPID and ionization chamber measurements, averaged over the four test fields presented in this paper, was 0.1 +/- 0.5% (1 SD) over the entire irradiation field, with no deviation larger than 2%.

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Section: Epid Software and Image Acquisition Procedurementioning

confidence: 99%

Characterization of a high-elbow, fluoroscopic electronic portal imaging device for portal dosimetry

et al. 1999

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“…The availability of portal imaging devices in modern linear accelerators has become routine for detection of geometrical uncertainties. 40 ICRU reports recommend estimating the magnitude of those uncertainties in every radiotherapy unit in order to apply appropriate margins to CTV. Diverse margin recipes have been published assuming different statistical goals.…”

Section: Discussionmentioning

confidence: 99%

Prospective observational study to estimate set-up errors and optimise PTV margins in patients undergoing IMRT for head and neck cancers from a Government cancer centre of Eastern India

Biswas

Lahiri

et al. 2019

J Radiother Pract

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Background:The head and neck cancers as a whole are the most common cancers among males in India. Technological advancements have led to an improvement in radiation therapy (RT) techniques with subsequent reduction in normal tissue complications. To correct patient set-up errors, an off-line correction method like no action level (NAL) protocol may be used as a preferred protocol particularly for a busy department. The objectives of the study were to measure the translational set-up errors using kV cone-beam computed tomography (CBCT) in patients undergoing intensity modulated radiotherapy (IMRT) in head and neck cancers and also to optimise clinical target volume (CTV) to planning target volume (PTV) margin using NAL protocol.Material and methods:On the first 5 days of RT, patient’s position was verified by kV-CBCT and then weekly during the course of treatment. The comparison between the reference and kV-CBCT images was performed, and the shifts measured and recorded. The mean error from the initial five consecutive fractions was corrected on the sixth daily fraction. Displacements in all the directions were measured. The population systematic and random errors were determined and used to estimate PTV margins according to the van Herk formula.Results:A total of 322 images were analysed. Before correction, 15, 12 and 9% patients had systematic error ≥3 mm on X, Y and Z axes, but after correction this was reduced to 9, 0 and 0%. The total percentage of patients whose set-up margin was ≥5 mm before correction was 5, 6·25, 3·75%, but after correction it reduced to 1·88, 0, and 0·63%. The margins of total population were reduced to 63, 65 and 56% after correction on X, Y and Z axes, respectively.Conclusion:A simple off-line NAL protocol can correct the set-up errors without daily on-line imaging in patients undergoing IMRT and hence acting as a resource sparing alternative. Five millimetre margin to CTVs was adequate and safe to overcome the problem of set-up errors in head and neck IMRT.

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“…They can be separated into ''off-line'' and ''on-line'' SCPs. 11,17 This classification refers to the moment at which setup corrections are performed. For off-line SCPs 16,18,19 the information from EPIs obtained in a certain treatment fraction is not applied to improve the setup of that fraction but, if necessary, a setup correction is performed in subsequent fractions.…”

Section: Introductionmentioning

confidence: 99%

A new approach to off‐line setup corrections: Combining safety with minimum workload

Boer

Heijmen

2002

Medical Physics

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Off-line patient setup correction protocols based on electronic portal images are an effective tool to reduce systematic patient setup errors. Recently, we have introduced the no action level (NAL) protocol which establishes a significant error reduction at a very small workload. However, this protocol did not include an explicit verification of the applied setup corrections. Systematic mistakes in the execution of setup corrections (e.g., a setup correction is always executed in the +X direction whereas a correction in the -X direction was prescribed) may introduce large systematic setup errors (irrespective of the setup protocol) and may seriously impair treatment outcome. We have therefore extended the NAL protocol with a correction verification (COVER) stage, solely aimed at detecting such mistakes. In short, COVER tests the magnitude of the postcorrection setup error in each relevant direction. If these residue errors are below the acceptance threshold T, no more electronic portal images are required and the protocol has finished. If not, the origin of this result should be investigated; if no obvious mistakes are present, the procedure is repeated for one more treatment fraction. If the residue setup errors are confirmed to be larger than T, the entire protocol is restarted. Using both Monte Carlo simulations and analytical calculations, we performed a risk analysis and evaluated the workload for various choices of T. A threshold T = 3 x sigma(r), where sigma(r) is the mean standard deviation of the random setup errors, ensured that (1) COVER introduces only a small additional workload (1.05 measurement per patient, while the absolute minimum is 1.0) and (2) serious correction mistakes are detected with high probability. Even if setup corrections are wrongly applied in each patient (worst case scenario), COVER ensures that the final distribution of systematic errors is not wider than the precorrection distribution of systematic errors; for realistic frequencies of correction mistakes (<< 1 per patient) this distribution becomes much more narrow. The combination of NAL and COVER thus provides a highly efficient as well as safe method to reduce systematic setup errors.

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Treatment Verification Using Digital Imaging

Cited by 9 publications

References 99 publications

Characterization of a high-elbow, fluoroscopic electronic portal imaging device for portal dosimetry

Characterization of a high-elbow, fluoroscopic electronic portal imaging device for portal dosimetry

Prospective observational study to estimate set-up errors and optimise PTV margins in patients undergoing IMRT for head and neck cancers from a Government cancer centre of Eastern India

A new approach to off‐line setup corrections: Combining safety with minimum workload

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