Retrospective self-sorted 4D-MRI for the liver

Lindt, Tessa N. van de; Fast, Martin F.; Heide, Uulke A. van der; Sonke, Jan‐Jakob

doi:10.1016/j.radonc.2018.05.006

Cited by 25 publications

(20 citation statements)

References 22 publications

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“…is that they can fail to properly synchronize with the pulse sequence start and end acquisition time points, lose coherence with k-space acquired data, as well as suffer from the uncertainties in correlation between external measurements with actual internal anatomical motion. [13][14][15][16][17][18][19][20][21][22][23]96,97,104,105 For internal surrogates, there are two main approaches of either extracting the signal directly from the acquired imaged data 95,[106][107][108][109][110][111][112][113][114] or with a navigator, 115,116 which is a fast 1D MRI acquisition of a selected anatomical interface of moving structures (preferably with high contrast), most commonly the lung-liver interface. 97 The advantage of using a navigator over image-derived surrogates is the ability to minimize image artifacts, 117 as well as better represent variabilities within the breathing cycles captured throughout the image acquisition.…”

Section: B 4d-mrimentioning

confidence: 99%

A modern review of the uncertainties in volumetric imaging of respiratory‐induced target motion in lung radiotherapy

Vergalasova

Cai

2020

Medical Physics

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Radiotherapy has become a critical component for the treatment of all stages and types of lung cancer, often times being the primary gateway to a cure. However, given that radiation can cause harmful side effects depending on how much surrounding healthy tissue is exposed, treatment of the lung can be particularly challenging due to the presence of moving targets. Careful implementation of every step in the radiotherapy process is absolutely integral for attaining optimal clinical outcomes. With the advent and now widespread use of stereotactic body radiation therapy (SBRT), where extremely large doses are delivered, accurate, and precise dose targeting is especially vital to achieve an optimal risk to benefit ratio. This has largely become possible due to the rapid development of image-guided technology. Although imaging is critical to the success of radiotherapy, it can often be plagued with uncertainties due to respiratory-induced target motion. There has and continues to be an immense research effort aimed at acknowledging and addressing these uncertainties to further our abilities to more precisely target radiation treatment. Thus, the goal of this article is to provide a detailed review of the prevailing uncertainties that remain to be investigated across the different imaging modalities, as well as to highlight the more modern solutions to imaging motion and their role in addressing the current challenges.

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Section: B 4d-mrimentioning

confidence: 99%

A modern review of the uncertainties in volumetric imaging of respiratory‐induced target motion in lung radiotherapy

Vergalasova

Cai

2020

Medical Physics

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“…While slice‐based 4D‐MRI sequences may use any slice orientation, we are focusing on two in‐house developed 4D‐MRI sequences based on coronal or axial 2D slices . Both methods are based on repeatedly sampling the 3D VOI with an interleaved, multislice turbo‐spin echo (TSE) or gradient echo acquisition over the course of 3–5 min.…”

Section: Methodsmentioning

confidence: 99%

“…The time series of rigid registration shifts in cranial‐caudal (CC) direction then forms the respiratory self‐sorting signal, and can be used to assign each 2D slice to its appropriate respiratory phase bin in the 4D‐MRI. In case of the coronal 4D‐MRI sequence, sorting was based on the respiratory amplitude, whereas for the axial 4D‐MRI sequence, phase binning was used . In contrast to many 3D‐based 4D‐MRI solutions, the image reconstruction only takes seconds and does not require any dedicated reconstruction hardware.…”

Section: Methodsmentioning

confidence: 99%

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Correcting geometric image distortions in slice‐based 4D‐MRI on the MR‐linac

et al. 2019

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Purpose: The importance of four-dimensional-magnetic resonance imaging (4D-MRI) is increasing in guiding online plan adaptation in thoracic and abdominal radiotherapy. Many 4D-MRI sequences are based on multislice two-dimensional (2D) acquisitions which provide contrast flexibility. Intrinsic to MRI, however, are machine-and subject-related geometric image distortions. Full correction of slice-based 4D-MRIs acquired on the Unity MR-linac (Elekta AB, Stockholm, Sweden) is challenging, since through-plane corrections are currently not available for 2D sequences. In this study, we implement a full three-dimensional 3D correction and quantify the geometric and dosimetric effects of machine-related (residual) geometric image distortions. Methods: A commercial three-dimensional (3D) geometric QA phantom (Philips, Best, the Netherlands) was used to quantify the effect of gradient nonlinearity (GNL) and static-field inhomogeneity (B0I) on geometric accuracy. Additionally, the effectiveness of 2D (in-plane, machine-generic), 3D (machine-generic), and in-house developed 3D þ (machine-specific) corrections was investigated. Corrections were based on deformable vector fields derived from spherical harmonics coefficients. Three patients with oligometastases in the liver were scanned with axial 4D-MRIs on our MR-linac (total: 10 imaging sessions). For each patient, a step-and-shoot IMRT plan (3 9 20 Gy) was created based on the simulation mid-position (midP)-CT. The 4D-MRIs were then warped into a daily midP-MRI and geometrically corrected. Next, the treatment plan was adapted according to the position offset of the tumor between midP-CT and the 3D-corrected midP-MRIs. The midP-CT was also deformably registered to the daily midP-MRIs (different corrections applied) to quantify the dosimetric effects of (residual) geometric image distortions. Results: Using phantom data, median GNL distortions were 0.58 mm (no correction), 0.42-0.48 mm (2D), 0.34 mm (3D), and 0.34 mm (3D þ ), measured over a diameter of spherical volume (DSV) of 200 mm. Median B0I distortions were 0.09 mm for the same DSV. For DSVs up to 500 mm, through-plane corrections are necessary to keep the median residual GNL distortion below 1 mm. 3D and 3D þ corrections agreed within 0.15 mm. 2D-corrected images featured uncorrected through-plane distortions of up to 21.11 mm at a distance of 20-25 cm from the machine's isocenter. Based on the 4D-MRI patient scans, the average external body contour distortions were 3.1 mm (uncorrected) and 1.2 mm (2D-corrected), with maximum local distortions of 9.5 mm in the uncorrected images. No (residual) distortions were visible for the metastases, which were all located within 10 cm of the machine's isocenter. The interquartile range (IQR) of dose differences between planned and daily dose caused by variable patient setup, patient anatomy, and online plan adaptation was 1.37 Gy/Fx for the PTV D95%. When comparing dose on 3D-corrected with uncorrected (2D-corrected) images, the IQR was 0.61 (0.31) Gy/Fx. Conclusions: GNL is the ma...

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“…For radiotherapy contouring this may however be inappropriate if the treatment is done under deep inspiration breath-hold (the maximum inhale phase of the breathing cycle), or during free breathing, taking the mid-ventilation or mid-position of the tumor as reference. While standard solutions are not readily available, 4D-MRI solutions have been proposed that map multiple phases of the breathing motion and allow contouring in a mid-ventilation or mid-position phase that is more representative of the mean position during free breathing [37] , [38] , [39] .…”

Section: Image Artifactsmentioning

confidence: 99%

MRI basics for radiation oncologists

Heide

Frantzen-Steneker

Astreinidou

et al. 2019

Clinical and Translational Radiation Oncology

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Highlights Issues of MRI that are relevant for radiation oncologists are addressed. Radiation oncology requires dedicated scan protocols. Use of diagnostic protocols is not recommended for radiotherapy. MR images must be made in treatment position with the standard positioning devices. Safety screening prior to entering the MRI room is crucial.

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Retrospective self-sorted 4D-MRI for the liver

Cited by 25 publications

References 22 publications

A modern review of the uncertainties in volumetric imaging of respiratory‐induced target motion in lung radiotherapy

A modern review of the uncertainties in volumetric imaging of respiratory‐induced target motion in lung radiotherapy

Correcting geometric image distortions in slice‐based 4D‐MRI on the MR‐linac

MRI basics for radiation oncologists

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