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Francisco J Reynoso, Austen Curcuru, Olga Green, Sasa Mutic, Indra J Das, Lakshmi Santanam
PURPOSE: Magnetokinetic changes may affect crystal orientation and polymerization within the active layer of radiochromic film (RCF). This effect is investigated in a magnetic resonance image-guided radiotherapy unit within the context of film dosimetry. METHODS: Gafchromic EBT2 RCF was irradiated in a 30 × 30 × 30 cm(3) solid water phantom using a Co-60 MRI guided radiotherapy system (B = 0.35 T) under normal operating conditions, and under the exact conditions and setup without a magnetic field...
December 2016: Medical Physics
Chang Heon Choi, So-Yeon Park, Jung-In Kim, Jin Ho Kim, Kyubo Kim, Joel Carlson, Jong Min Park
OBJECTIVES: To investigate the plan quality of tri-Co-60 intensity-modulated radiation therapy (IMRT) plans for spine stereotactic ablative radiotherapy (SABR). METHODS: A total of 20 patients with spine metastasis were retrospectively selected. For each patient, a tri-Co-60 IMRT plan and a volumetric modulated arc therapy (VMAT) plan were generated. The spinal cords were defined based on magnetic resonance images for the tri-Co-60 IMRT, while isotropic 1 mm margins were added to the spinal cords for the VMAT plans...
October 26, 2016: British Journal of Radiology
Shi Liu, Yu Wu, H Omar Wooten, Olga Green, Brent Archer, Harold Li, Deshan Yang
A software tool is developed, given a new treatment plan, to predict treatment delivery time for radiation therapy (RT) treatments of patients on ViewRay magnetic resonance image-guided radiation therapy (MR-IGRT) delivery system. This tool is necessary for managing patient treatment scheduling in our clinic. The predicted treatment delivery time and the assessment of plan complexities could also be useful to aid treatment planning. A patient's total treatment delivery time, not including time required for localization, is modeled as the sum of four components: 1) the treatment initialization time; 2) the total beam-on time; 3) the gantry rotation time; and 4) the multileaf collimator (MLC) motion time...
2016: Journal of Applied Clinical Medical Physics
Yuan Feng, Iwan Kawrakow, Jeff Olsen, Parag J Parikh, Camille Noel, Omar Wooten, Dongsu Du, Sasa Mutic, Yanle Hu
On-board magnetic resonance (MR) image guidance during radiation therapy offers the potential for more accurate treatment delivery. To utilize the real-time image information, a crucial prerequisite is the ability to successfully segment and track regions of interest (ROI). The purpose of this work is to evaluate the performance of different segmentation algorithms using motion images (4 frames per second) acquired using a MR image-guided radiotherapy (MR-IGRT) system. Manual con-tours of the kidney, bladder, duodenum, and a liver tumor by an experienced radiation oncologist were used as the ground truth for performance evaluation...
2016: Journal of Applied Clinical Medical Physics
Yingli Yang, Minsong Cao, Ke Sheng, Yu Gao, Allen Chen, Mitch Kamrava, Percy Lee, Nzhde Agazaryan, James Lamb, David Thomas, Daniel Low, Peng Hu
PURPOSE: To demonstrate the preliminary feasibility of a longitudinal diffusion magnetic resonance imaging (MRI) strategy for assessing patient response to radiotherapy at 0.35 T using an MRI-guided radiotherapy system (ViewRay). METHODS: Six patients (three head and neck cancer, three sarcoma) who underwent fractionated radiotherapy were enrolled in this study. A 2D multislice spin echo single-shot echo planar imaging diffusion pulse sequence was implemented on the ViewRay system and tested in phantom studies...
March 2016: Medical Physics
Daniel L Saenz, Yue Yan, Neil Christensen, Margaret A Henzler, Lisa J Forrest, John E Bayouth, Bhudatt R Paliwal
ViewRay is a novel MR-guided radiotherapy system capable of imaging in near real-time at four frames per second during treatment using 0.35T field strength. It allows for improved gating techniques and adaptive radiotherapy. Three cobalt-60 sources (~ 15,000 Curies) permit multiple-beam, intensity-modulated radiation therapy. The primary aim of this study is to assess the imaging stability, accuracy, and automatic segmentation algorithm capability to track motion in simulated and in vivo targets. Magnetic resonance imaging (MRI) characteristics of the system were assessed using the American College of Radiology (ACR)-recommended phantom and accreditation protocol...
November 8, 2015: Journal of Applied Clinical Medical Physics
Camille E Noel, Parag J Parikh, Christopher R Spencer, Olga L Green, Yanle Hu, Sasa Mutic, Jeffrey R Olsen
BACKGROUND: Onboard magnetic resonance imaging (OB-MRI) for daily localization and adaptive radiotherapy has been under development by several groups. However, no clinical studies have evaluated whether OB-MRI improves visualization of the target and organs at risk (OARs) compared to standard onboard computed tomography (OB-CT). This study compared visualization of patient anatomy on images acquired on the MRI-(60)Co ViewRay system to those acquired with OB-CT. MATERIAL AND METHODS: Fourteen patients enrolled on a protocol approved by the Institutional Review Board (IRB) and undergoing image-guided radiotherapy for cancer in the thorax (n = 2), pelvis (n = 6), abdomen (n = 3) or head and neck (n = 3) were imaged with OB-MRI and OB-CT...
2015: Acta Oncologica
Y Yang, D Low, M Cao, K Sheng, J Lamb, D Thomas, M Kamrava, P Hu
PURPOSE: To develop a diffusion MRI pulse sequence on the 0.35T MRI in a commercially available MRI-guided tri-Cobalt 60 radiotherapy system (Viewray), and demonstrate the initial utility of this pulse sequence on a patient undergoing radiation therapy. METHODS: The pulse sequence is a diffusion-weighted spin echo (SE) single-shot echo planar imaging (EPI) sequence. The pulse sequence parameters included: flip angle=90°, repetition time (TR) = 1500ms, echo time (TE) = 140ms, EPI factor = 128, b values = 0, 300, 500 s/mm2, 5 averages, and total scan time of 27sec...
June 2015: Medical Physics
O Green, S Goddu, H Li, S Mutic, I Kawrakow
PURPOSE: To evaluate the effect of ionization chamber volume size and orientation on dosimetric accuracy in the presence of a magnetic field. METHODS: The magnetic resonance image-guided radiotherapy (MR-IGRT) system (ViewRay, Inc., Oakwood, OH) was placed into clinical use after extensive calibration measurements with ionization chambers and verification tests using thermo-and opti-luminescent dosimeters. To further investigate the effect of the magnetic field on the ionization chamber results, measurements were made using four orientations and two different chambers with significantly different volumes: the Standard Imaging (Middleton, WI) A18 and the PTW N30013 Farmer chamber, with collecting volumes of 0...
June 2015: Medical Physics
O Green, L Rankine, B Cai, L Santanam, R Kashani, A Sharma, L Senadheera, C Mahaffey, S Mutic
PURPOSE: To develop a methodology for commissioning the real-time tumor tracking and beam control capabilities of a magnetic resonance imaging radiation therapy (MR-IGRT) system. METHODS: The MRIdian (ViewRay, Inc., Oakwood Village, OH) MR-IGRT machine consists of a 0.35-T magnet and a three-head Co-60 delivery system capable of real-time sagittal plane acquisition at 4 frames per second (fps). After obtaining a volumetric MR image, a "target" is chosen by contouring an area of interest with different signal intensity than the surrounding medium...
June 2015: Medical Physics
H Wan, R Pless, P Parikh
PURPOSE: ViewRay's MRIdian system acquires cine-MR images during treatment, allowing for real-time visualization of the tumor without additional dose. We propose a novel method for tracking the tumor target on these cine-MR images in real-time. METHODS: 9 patients with mobile abdominal tumors (3 stomach, 1 pancreas, 1 adrenal, 2 mesenteric, 2 peritoneal) were imaged on ViewRay (0.3T, open-bore; TrueFISP). Sagittal slice cine-MR images (3.5×3.5mm pixels) were acquired at 4 frames per second...
June 2015: Medical Physics
S Ellefson, W Culberson, B Bednarz, L DeWerd, J Bayouth
PURPOSE: Discrepancies in absolute dose values have been detected between the ViewRay treatment planning system and ArcCHECK readings when performing delivery quality assurance on the ViewRay system with the ArcCHECK-MR diode array (SunNuclear Corporation). In this work, we investigate whether these discrepancies are due to errors in the ViewRay planning and/or delivery system or due to errors in the ArcCHECK's readings. METHODS: Gamma analysis was performed on 19 ViewRay patient plans using the ArcCHECK...
June 2015: Medical Physics
D Thomas, D O'Connell, J Lamb, M Cao, Y Yang, N Agazaryan, P Lee, D Low
PURPOSE: To demonstrate real-time dose calculation of free-breathing MRI guided Co-60 treatments, using a motion model and Monte-Carlo dose calculation to accurately account for the interplay between irregular breathing motion and an IMRT delivery. METHODS: ViewRay Co-60 dose distributions were optimized on ITVs contoured from free-breathing CT images of lung cancer patients. Each treatment plan was separated into 0.25s segments, accounting for the MLC positions and beam angles at each time point...
June 2015: Medical Physics
P Hill, Z Labby, R A Bayliss, M Geurts, J Bayouth
PURPOSE: To develop a plan comparison tool that will ensure robustness and deliverability through analysis of baseline and online-adaptive radiotherapy plans using similarity metrics. METHODS: The ViewRay MRIdian treatment planning system allows export of a plan file that contains plan and delivery information. A software tool was developed to read and compare two plans, providing information and metrics to assess their similarity. In addition to performing direct comparisons (e...
June 2015: Medical Physics
S Liu, H Wooten, Y Wu, D Yang
PURPOSE: An algorithm is developed in our clinic, given a new treatment plan, to predict treatment delivery time for radiation therapy (RT) treatments of patients on ViewRay magnetic resonance-image guided radiation therapy (MR-IGRT) delivery system. This algorithm is necessary for managing patient treatment appointments, and is useful as an indicator to assess the treatment plan complexity. METHODS: A patient's total treatment delivery time, not including time required for localization, may be described as the sum of four components: (1) the treatment initialization time; (2) the total beam-on time; (3) the gantry rotation time; and (4) the multileaf collimator (MLC) motion time...
June 2015: Medical Physics
Y Wang, T Mazur, O Green, Y Hu, H Wooten, D Yang, T Zhao, S Mutic, H Li
PURPOSE: To build a fast, accurate and easily-deployable research platform for Monte-Carlo dose calculations. We port the dose calculation engine PENELOPE to C++, and accelerate calculations using GPU acceleration. Simulations of a Co-60 beam model provided by ViewRay demonstrate the capabilities of the platform. METHODS: We built software that incorporates a beam model interface, CT-phantom model, GPU-accelerated PENELOPE engine, and GUI front-end. We rewrote the PENELOPE kernel in C++ (from Fortran) and accelerated the code on a GPU...
June 2015: Medical Physics
D P O'Connell, D H Thomas, T H Dou, J M Lamb, L Yang, D A Low
PURPOSE: A respiratory motion model previously used to generate breathing-gated CT images was used with cine MR images. Accuracy and predictive ability of the in-plane models were evaluated. METHODS: Sagittalplane cine MR images of a patient undergoing treatment on a ViewRay MRI/radiotherapy system were acquired before and during treatment. Images were acquired at 4 frames/second with 3.5 × 3.5 mm resolution and a slice thickness of 5 mm. The first cine frame was deformably registered to following frames...
June 2015: Medical Physics
B Paliwal, W Asprey, Y Yan, D Saenz, J Bayouth
PURPOSE: In order to take advantage of the high resolution soft tissue imaging available in MR images, we investigated 3D images obtained with the low field 0.35 T MR in ViewRay to serve as an alternative to CT scans for radiotherapy treatment planning. In these images, normal and target structure delineation can be visualized. Assessment is based upon comparison with the CT images and the ability to produce comparable contours. METHODS: Routine radiation oncology CT scans were acquired on five patients...
June 2015: Medical Physics
Y Yan, D Saenz, J Bayouth, B Paliwal
PURPOSE: ViewRay is a novel image-guided radiotherapy approach with an integrated 0.35 T MR unit and three Cobalt-60 heads. In order to continuously ensure the high resolution and high soft tissue contrast available in MR images, we quantified a multitude of relevant imaging parameters over a period of six months to establish its stability and imaging quality. In the assessment process, consideration is also given to the need to establish the number of tests required to have confidence in the performance of the system for radiation therapy planning applications...
June 2015: Medical Physics
J Lamb, M Kamrava, N Agazaryan, M Cao, D Low, D Thomas, Y Yang
PURPOSE: Even in the IMRT era, bowel toxicity and bone marrow irradiation remain concerns with pelvic irradiation. We examine the potential gain from an adaptive radiotherapy workflow for post-operative gynecological patients treated to pelvic targets including lymph nodes using MRI-guided Co-60 radiation therapy. METHODS: An adaptive workflow was developed with the intent of minimizing time overhead of adaptive planning. A pilot study was performed using retrospectively analyzed images from one patient's treatment...
June 2015: Medical Physics
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