The cumulative verification image analysis tool for offline evaluation of portal images

Wong, John W.; Yan, Di; Michalski, Jeff M.; Graham, M.L.; Halverson, Karen J.; Harms, William B.; Purdy, James A.

doi:10.1016/0360-3016(95)00270-7

Cited by 15 publications

(5 citation statements)

References 42 publications

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“…These images are quantitatively aligned to the reference digitally reconstructed radiograph ͑DRR͒ from the planning CT using a template based on bony land-marks. 7,16,17 The portal image alignment for each patient is done by a single user. Translations along two orthogonal axes are derived from the matching on each electronic portal image.…”

Section: A Patient Datamentioning

confidence: 99%

Effect of the first day correction on systematic setup error reduction

Lockman

Wong

et al. 2007

Medical Physics

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Treatment simulation is usually performed with a conventional simulator using kV X-rays or with a computed tomography (CT) simulator before the treatment course begins. The purpose is to verify patient setup under the same conditions as for treatment planning. Systematic (preparation) setup errors can be introduced by this process. The purpose of this study is to characterize the setup errors using electronic portal image (EPI) analyses and to propose a method to reduce the systematic component by performing simulation and patient preparation on the treatment machine. In this study, the first four or five days EPIs were analyzed from a total of 533 prostate cancer patients who were simulated on conventional simulators. We characterized setup errors using four parameters: {M(microi), Sigma (microi), RMS(microi), sigma (sigmai)}, where microi and sigmai are individual patient mean and standard deviation, M, Sigma, and RMS are the mean, standard deviation, and root-mean-square of underlying variables (microi and sigmai). We have performed a simulation of removing systematic components by correcting the first day setup error. As a comparison, we also carried out a similar analyses for patients simulated on a CT simulator and patients treated on a linac with an on-board kV CT imaging system, although a limited number of patients were available in these two samples. We found that Sigma (/ui)=(2.6,3.4,2.4) mm, and RMS(sigmai)=(1.5,1.9,1.0) mm in lateral, anterior/posterior, and cranial/caudal directions, indicating that systematic errors are much larger than random errors. Strong correlations were found between measurement on the first day and microi, implying the first day's measurement is a good predictor for microi. The same parameters were also computed for days 2-4, with and without the first day correction. Without correction, M(microi)2-4=(0.7,1.6,-1.0) mm, and Sigma(microi)2-4=(2.6,3.5,2.4) mm. With correction, M(microi)2-4=(0.0,0.4,0.4) mm, much closer to zero, and Sigma(microi)2-4=(1.8,2.2, 1.2) mm, also much smaller. While the use of a CT simulator can reduce the systematic errors, the benefits of first day correction can still be observed, although at a smaller magnitude. Therefore, the systematic setup error can be significantly reduced if the patient is marked and fields are verified on the treatment machine on the first fraction, preferably with an on-board kV imaging system.

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Section: A Patient Datamentioning

confidence: 99%

Effect of the first day correction on systematic setup error reduction

Lockman

Wong

et al. 2007

Medical Physics

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“…A variety of methods have been reported for monitoring the interfraction setup variation, including the isocenter dose reproducibility [1], repeated radiographs [2], and repeated CT examinations [3]. A variety of methods have also been reported for monitoring intrafraction breathing movements, including electronic portal images [2], fluoroscopy [4], tumor movement from CT [5], dose-volume histograms [6], and the calculation of the geometric error based on respiratory motion data [7].…”

Section: Introductionmentioning

confidence: 99%

“…A variety of methods have also been reported for monitoring intrafraction breathing movements, including electronic portal images [2], fluoroscopy [4], tumor movement from CT [5], dose-volume histograms [6], and the calculation of the geometric error based on respiratory motion data [7]. Moreover, not only interfraction setup variations and intrafraction breathing movements can alter the dose distribution, but also the changes in Hounsfield units 6 (HU) during breathing [8], mechanical response delays [7], and tumor volume changes during the treatment course.…”

Section: Introductionmentioning

confidence: 99%

Verification of beam delivery using fibrosis after proton beam irradiation to the lung tumor

et al. 2012

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“…The setup error correction in prostate radiotherapy has been covered by many studies. The setup error can be measured by comparing the MV portal images obtained by an electronic portal-imaging device (EPID) with reference to a simulation film or digital reconstructed radiograph (DRR) based on a bony structure (Wong et al 1995, de Boer and Heijmen 2001, Herman et al 2001, Ghilezan et al 2005. Both online and offline strategies have been proposed and implemented to correct setup error (Wu et al 2006).…”

Section: Introductionmentioning

confidence: 99%

A hybrid strategy of offline adaptive planning and online image guidance for prostate cancer radiotherapy

Yu¹,

Wu²

2010

Phys. Med. Biol.

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The offline adaptive radiotherapy (ART) has been used to effectively correct and compensate the prostate motion and reduce the required margin. The efficacy depends on the characteristics of the patient setup error and interfraction motion through the whole treatment, specifically, the systematic errors are corrected and random errors are compensated through the margins. In online image-guided radiation therapy (IGRT) of prostate cancer, the translational setup error and interfractional prostate motion are corrected through pre-treatment imaging and couch correction at each fraction. However, the rotation and deformation of target are not corrected and only accounted for with margins in treatment planning. The purpose of this study was to investigate whether the offline ART strategy is necessary for an online IGRT protocol and to evaluate the benefit of the hybrid strategy. First, to investigate the rationale of the hybrid strategy, 592 conebeam computed tomography (CBCT) images taken before and after each fraction for an online IGRT protocol from 16 patients were analyzed. Specifically the characteristics of prostate rotation were analyzed. It was found that there exist systematic inter-fractional prostate rotations, and they are patient-specific. These rotations, if not corrected, are persistent through the treatment fraction, and rotations detected in early fractions are representative of those in later fractions. These findings suggest that the offline adaptive re-planning strategy is beneficial to the online IGRT protocol with further margin reductions. Second, to quantitatively evaluate the benefit of the hybrid strategy, 412 repeated helical CT scans from 25 patients during treatment course were included in the replanning study. Both low risk patients (LRP, clinical target volume, CTV = prostate) and intermediate risk patients (IRP, CTV = prostate + seminal vesicles) were included in simulation. Contours of prostate and seminal vesicles were delineated on each CT. The benefit of margin reduction to compensate for both rotation and deformation in hybrid strategy was evaluated geometrically. With the hybrid strategy, the planning margins can be reduced by 1.4 mm for LRP, and 2.0 mm for IRP, compared with the standard online IGRT only, to maintain the same 99% target volume coverage. The average relative reduction in planning target volume (PTV) based on internal target volume (ITV) from PTV based on CTV is 19% for LRP, and 27% for IRP, respectively.

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The cumulative verification image analysis tool for offline evaluation of portal images

Cited by 15 publications

References 42 publications

Effect of the first day correction on systematic setup error reduction

Effect of the first day correction on systematic setup error reduction

Verification of beam delivery using fibrosis after proton beam irradiation to the lung tumor

A hybrid strategy of offline adaptive planning and online image guidance for prostate cancer radiotherapy

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