A Self-Sorting Coronal 4D-MRI Method for Daily Image Guidance of Liver Lesions on an MR-LINAC

Lindt, T. Van de; Sonke, Jan‐Jakob; Nowee, Marlies E.; Jansen, E.P.M.; Pelt, V. van; Heide, Uulke A. van der; Fast, Martin F.

doi:10.1016/j.ijrobp.2018.05.029

Cited by 41 publications

(32 citation statements)

References 30 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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“…Combining liver SBRT with real-time magnetic resonance (MR) guidance has been demonstrated to be an accurate and reproducible treatment modality for these tumors, allowing for superior soft tissue visualization and tumor tracking [9,[11][12][13][14]. The MRIdian Linac system (ViewRay, Oakwood Village, OH) offers the ability for real-time target tracking and adaptive treatment using MR imaging (MRI) and is the first MR linear accelerator (MR-Linac) system to receive pre-market safety and efficacy clearance from the U.S. Food and Drug Administration [15].…”

Section: Introductionmentioning

confidence: 99%

Real-time Magnetic Resonance-guided Liver Stereotactic Body Radiation Therapy: An Institutional Report Using a Magnetic Resonance-Linac System

Feldman¹,

Modh²,

Glide-Hurst³

et al. 2019

Cureus

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BackgroundStereotactic body radiation therapy (SBRT) is a proven and effective modality for treatment of hepatic primary and metastatic tumors. However, these lesions are challenging for planning and treatment execution due to natural anatomic changes associated with respiration. Magnetic resonance imaging (MRI) offers superior soft tissue contrast resolution and the ability for real-time image-guided treatment delivery and lesion tracking.ObjectiveTo evaluate the plan quality, treatment delivery, and tumor response of a set of liver SBRT cancer treatments delivered with magnetic resonance (MR)-guided radiotherapy on a MR-linear accelerator (MR-linac).MethodsTreatment data from 29 consecutive patients treated with SBRT were reviewed. All treatments were performed using a step and shoot technique to one or more liver lesions on an MR-linac platform. Patients received 45 to 50 Gy prescribed to at least 95% of the planning target volume (PTV) in five fractions except for two patients who received 27-30 Gy in three fractions. Computed tomography and MRI simulation were performed in the supine position prior to treatment in the free-breathing, end exhalation, and end inhalation breath-hold positions to determine patient tolerability and potential dosimetric advantages of each technique. Immobilization consisted of using anterior and posterior torso MRI receive coils embedded in a medium-sized vacuum cushion. Gating was performed using sagittal cine images acquired at 4 frames/second. Gating boundaries were defined in the three major axes to be 0.3 to 0.5 cm. An overlapping region of interest, defined as the percentage volume allowed outside the boundary for beam-on to occur, was set between 1 and 10%. The contoured target was assigned a 5-mm PTV expansion. Organs at risk constraints adopted by the American Association of Physicists in Medicine Task Group 101 were used during optimization.ResultsTwenty-nine patients, with a total of 34 lesions, successfully completed the prescribed treatment with minimal treatment breaks or delays. Twenty-one patients were treated at end-exhale, and six were treated at end-inhale. Two patients were treated using a free-breathing technique due to poor compliance with breath-hold instructions. The reported mean liver dose was 5.56 Gy (1.39 - 10.43; STD 2.85) and the reported mean liver volume receiving the prescribed threshold dose was 103.1 cm3 (2.9 - 236.6; STD 75.2). Follow-up imaging at one to 12 months post treatment confirmed either stable or decreased size of treated lesions in all but one patient. Toxicities were mild and included nausea/vomiting, abdominal pain and one case of bloody diarrhea. Four patients died due to complications from liver cirrhosis unrelated to radiation effect.ConclusionSBRT treatment using a gated technique on an MR-linac has been successfully demonstrated. Potential benefits of this modality include decreased liver dose leading to decreased toxicities. Further studies to identify the benefits and risks associated with MR-guided SBRT are necessary.

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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%

“…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. Liver imaging specifically benefits from T2‐weighted contrast, which is achievable with TSE sequences . A high enough number of repeats (“dynamics”) ensures that the respiratory signal is sufficiently sampled in each slice position.…”

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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A Self-Sorting Coronal 4D-MRI Method for Daily Image Guidance of Liver Lesions on an MR-LINAC

Cited by 41 publications

References 30 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

Real-time Magnetic Resonance-guided Liver Stereotactic Body Radiation Therapy: An Institutional Report Using a Magnetic Resonance-Linac System

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

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