Two-and-a-half-year clinical experience with the world's first magnetic resonance image guided radiation therapy system

Fischer‐Valuck, Benjamin W.; Henke, Lauren E.; Green, Olga; Kashani, Rojano; Acharya, Sahaja; Bradley, Jeffrey D.; Robinson, Clifford G.; Thomas, Maria; Zoberi, Imran; Thorstad, Wade L.; Huang, Jiayi; Roach, Michael C.; Rodriguez, Vivian; Santanam, Lakshmi; Li, Harold; Li, Hua; Contreras, Jessica; Mazur, Thomas R.; Hallahan, Dennis E.; Olsen, Jeffrey R.; Parikh, Parag J.; Mutic, Sasa; Michalski, Jeff M.

doi:10.1016/j.adro.2017.05.006

Cited by 134 publications

(160 citation statements)

References 20 publications

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“…The use of magnetic resonance imaging (MRI) in radiation therapy (RT) has grown in recent years due to a desire to take advantage of the attractive properties of the modality, especially with the advent of MRI‐based delivery systems . Compared to x‐ray computed tomography (CT), MRI offers superior soft tissue contrast without exposing the patient to ionizing radiation .…”

Section: Introductionmentioning

confidence: 99%

“…Compared to x‐ray computed tomography (CT), MRI offers superior soft tissue contrast without exposing the patient to ionizing radiation . Taking full advantage of these attractive properties with MRI‐based therapy delivery systems allows for numerous applications including motion tracking and management as well as online adaptive therapy . The increasing use of MRI for tissue and target delineation makes an MRI‐only RT workflow, one in which MRI is the sole imaging modality employed for treatment planning and dose calculations, a favorable option for MR image‐guided RT (MR‐IGRT) applications.…”

Section: Introductionmentioning

confidence: 99%

“…In the conventional MR‐IGRT treatment planning workflow, the patient undergoes both MRI and CT simulation before planning commences . MRI is the primary imaging modality used to guide treatment, but the electron density information required for dose calculations necessitates that CT simulation be a component of the conventional workflow .…”

Section: Introductionmentioning

confidence: 99%

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Synthetic CT reconstruction using a deep spatial pyramid convolutional framework for MR‐only breast radiotherapy

et al. 2019

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Purpose The superior soft‐tissue contrast achieved using magnetic resonance imaging (MRI) compared to x‐ray computed tomography (CT) has led to the popularization of MRI‐guided radiation therapy (MR‐IGRT), especially in recent years with the advent of first and second generation MRI‐based therapy delivery systems for MR‐IGRT. The expanding use of these systems is driving interest in MRI‐only RT workflows in which MRI is the sole imaging modality used for treatment planning and dose calculations. To enable such a workflow, synthetic CT (sCT) data must be generated based on a patient’s MRI data so that dose calculations may be performed using the electron density information derived from CT images. In this study, we propose a novel deep spatial pyramid convolutional framework for the MRI‐to‐CT image‐to‐image translation task and compare its performance to the well established U‐Net architecture in a generative adversarial network (GAN) framework. Methods Our proposed framework utilizes atrous convolution in a method named atrous spatial pyramid pooling (ASPP) to significantly reduce the total number of parameters required to describe the model while effectively capturing rich, multi‐scale structural information in a manner that is not possible in the conventional framework. The proposed framework consists of a generative model composed of stacked encoders and decoders separated by the ASPP module, where atrous convolution is applied at increasing rates in parallel to encode large‐scale features. The performance of the proposed method is compared to that of the conventional GAN framework in terms of the time required to train the model and the image quality of the generated sCT as measured by the root mean square error (RMSE), structural similarity index (SSIM), and peak signal‐to‐noise ratio (PSNR) depending on the size of the training data set. Dose calculations based on sCT data generated using the proposed architecture are also compared to clinical plans to evaluate the dosimetric accuracy of the method. Results Significant reductions in training time and improvements in image quality are observed at every training data set size when the proposed framework is adopted instead of the conventional framework. Over 1042 test images, values of 17.7 ± 4.3 HU, 0.9995 ± 0.0003, and 71.7 ± 2.3 are observed for the RMSE, SSIM, and PSNR metrics, respectively. Dose distributions calculated based on sCT data generated using the proposed framework demonstrate passing rates equal to or greater than 98% using the 3D gamma index with a 2%/2 mm criterion. Conclusions The deep spatial pyramid convolutional framework proposed here demonstrates improved performance compared to the conventional GAN framework that has been applied to the image‐to‐image translation task of sCT generation. Adopting the method is a first step toward an MRI‐only RT workflow that enables widespread clinical applications for MR‐IGRT including online adaptive therapy.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Synthetic CT reconstruction using a deep spatial pyramid convolutional framework for MR‐only breast radiotherapy

et al. 2019

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“…Magnetic resonance image‐guided radiation therapy (MR‐IGRT) offers simultaneous tracking of the target during treatment delivery while taking advantage of the excellent soft tissue contrast of MRI . Even at low magnetic field strengths such as 0.35T, visualization of tissues and most critical structures is superior to cone beam CT (CBCT) .…”

Section: Introductionmentioning

confidence: 99%

“…Even at low magnetic field strengths such as 0.35T, visualization of tissues and most critical structures is superior to cone beam CT (CBCT) . Also, the use of MR‐IGRT can avoid the additional radiation exposure that is inherent to CBCT and therefore, can enable daily monitoring of intra‐fractional motion as well as treatment plan adjustments based on changes in anatomy . Recently, MRI has been coupled with a linear accelerator (MR‐linac) offering possibilities such as treatment of small brain metastases in an MR‐guided stereotactic radiosurgery (MRgSRS) setting .…”

Section: Introductionmentioning

confidence: 99%

Large field of view distortion assessment in a low‐field MR‐linac

Nejad-Davarani

Kim

et al. 2019

Medical Physics

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Purpose MR‐guided radiation therapy (RT) offers unparalleled soft tissue contrast for localization and target tracking. However, MRI distortions may be detrimental to high precision RT. This work characterizes the gradient nonlinearity (GNL) and total distortions over the first year of clinical operation of a 0.35T MR‐linac. Methods For GNL characterization, an in‐house large field of view (FOV) phantom (60 × 42.5 × 55 cm3, >6000 spherical landmarks) was configured and scanned at four timepoints with forward/reverse read polarities (Gradient Echo sequence, FA/TR/TE = 28°/30 ms/6 ms). GNL was measured in Anterior‐Posterior (AP), Left‐Right (LR), and Superior‐Inferior (SI) frequency‐encoding directions based on deviation of the auto‐segmented landmark centroids between rigidly registered MR and CT images and assessed based on radial distance from magnet isocenter. Total distortion was assessed using a 30 × 30 cm2 grid phantom oriented along the cardinal axes over >1 year of operation. Results The scanner's spatial integrity within the first ~10 months was stable (maximum total distortion variation = 10/6/8%, maximum distortion = 1.41/0.99/1.56 mm in Axial/Coronal/Sagittal planes, respectively). GNL distortions measured during this time period <10 cm from isocenter were (−0.74, 0.45), (−0.67, 0.53), and (−0.86, 0.70) mm in AP/LR/SI directions. In the 10‐20 cm range, <1.5% of the distortions exceeded 2 mm in the AP and LR axes while <4% of the distortions exceeded 2 mm for SI. After major repairs and magnet re‐shim, detectable changes were observed in total and GNL distortions (20% reduction in AP and 36% increase in SI direction in the 20–25 cm range). Across all timepoints and axes, 38–53% of landmarks in the 20–25 cm range were displaced by >1 mm. Conclusions GNL distortions were negligible within a 10 cm radius from isocenter. However, in the periphery, non‐negligible distortions of up to ~7 mm were observed, which may necessitate GNL corrections for MR‐IGRT for treatment sites distant from magnet isocenter.

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Development and evaluation of a novel MR‐compatible pelvic end‐to‐end phantom

Cunningham

Barberi²,

Miller³

et al. 2018

J Applied Clin Med Phys

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MR‐only treatment planning and MR‐IGRT leverage MRI's powerful soft tissue contrast for high‐precision radiation therapy. However, anthropomorphic MR‐compatible phantoms are currently limited. This work describes the development and evaluation of a custom‐designed, modular, pelvic end‐to‐end (PETE) MR‐compatible phantom to benchmark MR‐only and MR‐IGRT workflows. For construction considerations, subject data were assessed for phantom/skeletal geometry and internal organ kinematics to simulate average male pelvis anatomy. Various materials for the bone, bladder, and rectum were evaluated for utility within the phantom. Once constructed, PETE underwent CT‐SIM, MR‐Linac, and MR‐SIM imaging to qualitatively assess organ visibility. Scans were acquired with various bladder and rectal volumes to assess component interactions, filling capabilities, and filling reproducibility via volume and centroid differences. PETE simulates average male pelvis anatomy and comprises an acrylic body oval (height/width = 23.0/38.1 cm) and a cast‐mold urethane skeleton, with silicone balloons simulating bladder and rectum, a silicone sponge prostate, and hydrophilic poly(vinyl alcohol) foam to simulate fat/tissue separation between organs. Access ports enable retrofitting the phantom with other inserts including point/film‐based dosimetry options. Acceptable contrast was achievable in CT‐SIM and MR‐Linac images. However, the bladder was challenging to distinguish from background in CT‐SIM. The desired contrast for T1‐weighted and T2‐weighted MR‐SIM (dark and bright bladders, respectively) was achieved. Rectum and bone exhibited no MR signal. Inputted volumes differed by <5 and <10 mL from delineated rectum (CT‐SIM) and bladder (MR‐SIM) volumes. Increasing bladder and rectal volumes induced organ displacements and shape variations. Reproduced volumes differed by <4.5 mL, with centroid displacements <1.4 mm. A point dose measurement with an MR‐compatible ion chamber in an MR‐Linac was within 1.5% of expected. A novel, modular phantom was developed with suitable materials and properties that accurately and reproducibly simulate status changes with multiple dosimetry options. Future work includes integrating more realistic organ models to further expand phantom options.

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Two-and-a-half-year clinical experience with the world's first magnetic resonance image guided radiation therapy system

Cited by 134 publications

References 20 publications

Synthetic CT reconstruction using a deep spatial pyramid convolutional framework for MR‐only breast radiotherapy

Synthetic CT reconstruction using a deep spatial pyramid convolutional framework for MR‐only breast radiotherapy

Large field of view distortion assessment in a low‐field MR‐linac

Development and evaluation of a novel MR‐compatible pelvic end‐to‐end phantom

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