Monte Carlo modeling of the origin of contaminant electrons on a 0.5T bi-planar Linac-MR.

Introduction: In the last decade, hybrid linear accelerator magnetic resonance imaging (Linac-MR) devices have evolved into FDA-cleared clinical tools, facilitating magnetic resonance guided radiotherapy (MRgRT). The addition of a magnetic field to radiation therapy has previously demonstrated dosimetric and electron effects regardless of magnetic field orientation.

Purpose: This study uses Monte Carlo simulations to investigate the importance and efficacy of the magnetic field design in mitigating surface dose enhancement in the Aurora-RT, focusing specifically on contaminant electrons, their origin, and energy spectrum.

A hybrid PCA acceleration method for rapid real-time 2D MRI.

To develop a 2D MR acceleration method utilizing principal component analysis (PCA) in a hybrid fashion for rapid real-time applications.Retrospective testing was performed on 10 lung, 10 liver and 10 prostate 3T MRI data sets for image quality and target contourability. Sampling of k-space is performed by acquiring central (low-frequency) data in every frame while the high-frequency data is incoherently undersampled such that all of k-space is acquired in a pre-determined number of frames.

Dose perturbations at tissue interfaces during parallel linac-MR treatments: The "Lateral Scatter Electron Return Effect" (LS-ERE).

Background: Magnetic resonance (MR) imaging devices have been integrated with medical linear accelerators (linac) in radiation therapy. Both perpendicular linac-MR (LMR-B⊥) and parallel (LMR-B∥) systems exist, where due to the MR's magnetic field dose can be perturbed in the patient. Dose perturbations from the electron return effect (ERE) and electron streaming effects (ESEs) are present in LMR-B⊥ systems, where a dose collimating effect has been observed in LMR-B∥ systems .

Skin dose investigations on a 0.5 T parallel rotating biplanar linac-MR using Monte Carlo simulations and measurements.

Background: The Alberta rotating biplanar linac-MR has a 0.5 T magnetic field parallel to the beamline. When developing a new linac-MR system, interactions of charged particles with the magnetic field necessitate careful consideration of skin dose and tissue interface effects.

Clinical reference dosimetry for the 0.5 T inline rotating biplanar Linac-MR.

Background: The world's first clinical 0.5 T inline rotating biplanar Linac-MR system is commissioned for clinical use. For reference dosimetry, unique features to device, including an SAD = 120 cm, bore clearance of 60 cm × 110 cm, as well as 0.

MRI-Guided Radiation Therapy Systems.

MR-Guided Radiation Therapy (MRIgRT) has been made possible only due to the ingenuity and commitment of commercial radiation therapy system vendors. Unlike conventional linear accelerator systems, MRIgRT systems have had to overcome significant and previously untested techniques to integrate the MRI systems with the radiation therapy delivery systems. Each of these three commercial systems has developed different approaches to integrating their MR and Linac functions.

Stationary-to-migratory transition in glioblastoma stem-like cells driven by a fatty acid-binding protein 7-RXRα neurogenic pathway.

Background: Glioblastoma (GBM) stem-like cells (GSCs) are crucial drivers of treatment resistance and tumor recurrence. While the concept of "migrating" cancer stem cells was proposed a decade ago, the roles and underlying mechanisms of the heterogeneous populations of GSCs remain poorly defined.

Methods: Cell migration using GBM cell lines and patient-derived GSCs was examined using Transwell inserts and the scratch assay.

Conventional Versus Hypofractionated Radiation for High-Risk Prostate Cancer Patients (CHIRP): 24-Month Patient-Reported Outcomes of the Randomized Phase 2 CHIRP Trial.

Purpose: In this study, we report the 24-month patient-reported outcomes of the randomized phase 2 CHIRP trial that compared conventional and hypofractionated radiation therapy (RT) in the treatment of high-risk prostate cancer.

Methods And Materials: Men with high-risk localized prostate cancer were randomized to either conventional (78 Gy/39 fractions) or hypofractionated RT (68 Gy/25 fractions). All patients received pelvic nodal RT and adjuvant androgen deprivation therapy.

Time domain principal component analysis for rapid, real-time 2D MRI reconstruction from undersampled data.

Purpose: A rapid real-time 2D accelerated method was developed for magnetic resonance imaging (MRI) using principal component analysis (PCA) in the temporal domain. This method employs a moving window of previous dynamic frames to reconstruct the current, real-time frame within this window. This technique could be particularly useful in real-time tracking applications such as in MR-guided radiotherapy, where low latency real-time reconstructions are essential.

Findings of the AAPM Ad Hoc committee on magnetic resonance imaging in radiation therapy: Unmet needs, opportunities, and recommendations.

The past decade has seen the increasing integration of magnetic resonance (MR) imaging into radiation therapy (RT). This growth can be contributed to multiple factors, including hardware and software advances that have allowed the acquisition of high-resolution volumetric data of RT patients in their treatment position (also known as MR simulation) and the development of methods to image and quantify tissue function and response to therapy. More recently, the advent of MR-guided radiation therapy (MRgRT) - achieved through the integration of MR imaging systems and linear accelerators - has further accelerated this trend.

Clinical Outcomes of the CHIRP Trial: A Phase II Prospective Randomized Trial of Conventionally Fractionated Versus Moderately Hypofractionated Prostate and Pelvic Nodal Radiation Therapy in Patients With High-Risk Prostate Cancer.

Purpose: Hypofractionated radiation therapy (HFRT) may offer treatment advantages for patients with prostate cancer. However, HFRT may also increase the risk of gastrointestinal (GI) or genitourinary (GU) toxicity compared with conventionally fractionated radiation therapy (CFRT). Several large trials have found that HFRT is well tolerated in mixed risk population studies.

Impact of a parallel magnetic field on radiation dose beneath thin copper and aluminum foils.

Purpose: The RF coils for magnetic resonance image guided radiotherapy (MRIgRT) may be constructed using thin and/or low-density conductors, along with thinner enclosure materials. This work measures the surface dose increases for lightweight conductors and enclosure materials in a magnetic field parallel to a 6 MV photon beam.

Methods: Aluminum and copper foils (9-127 μm thick), as well as samples of polyimide (17 μm) and polyester (127 μm) films are positioned atop a polystyrene phantom.

How thin can you go? Performance of thin copper and aluminum RF coil conductors.

Purpose: To evaluate the impact of emerging conductor technology on RF coils. Performance and resulting image quality of thin or alternate conductors (eg, aluminum instead of copper) and thicknesses (9-600 μm) are compared in terms of SNR.

Methods: Eight prototype RF coils (15 cm × 15 cm square loops) were constructed and bench-tested to measure quality factor.

Real-Time Lung Tumor Tracking Using a CUDA Enabled Nonrigid Registration Algorithm for MRI.

Objective: This study intends to develop an accurate, real-time tumor tracking algorithm for the automated radiation therapy for cancer treatment using Graphics Processing Unit (GPU) computing. Although a previous moving mesh based tumor tracking approach has been shown to be successful in delineating the tumor regions from a sequence of magnetic resonance image, the algorithm is computationally intensive and its computation time on standard Central Processing Unit (CPU) processors is too slow to be used clinically especially for automated radiation therapy system.

Method: A re-implementation of the algorithm on a low-cost parallel GPU-based computing platform is utilized to accelerate this computation at a speed that is amicable to clinical usages.

Single patient convolutional neural networks for real-time MR reconstruction: coherent low-resolution versus incoherent undersampling.

Accelerated MRI involves undersampling k-space, creating unwanted artifacts when reconstructing the data. While the strategy of incoherent k-space acquisition is proven for techniques such as compressed sensing, it may not be optimal for all techniques. This study compares the use of coherent low-resolution (coherent-LR) and incoherent undersampling phase-encoding for real-time 3D CNN image reconstruction.

PRESS timings for resolving C -glutamate H signal at 9.4 T: Demonstration in rat with uniformly labelled C-glucose.

MRS of C -labelled glutamate ( C -Glu) during an infusion of a carbon-13 ( C)-labelled substrate, such as uniformly labelled glucose ([U- C ]-Glc), provides a measure of Glc metabolism. The presented work provides a single-shot indirect C detection technique to quantify the approximately 2.51 ppm C -Glu satellite proton ( H) peak at 9.

Single patient convolutional neural networks for real-time MR reconstruction: a proof of concept application in lung tumor segmentation for adaptive radiotherapy.

Investigate 3D (spatial and temporal) convolutional neural networks (CNNs) for real-time on-the-fly magnetic resonance imaging (MRI) reconstruction. In particular, we investigated the applicability of training CNNs on a patient-by-patient basis for the purpose of lung tumor segmentation. Data were acquired with our 3 T Philips Achieva system.

Technical Note: Sensitive volume effects on ion chamber responses in longitudinal magnetic fields.

Purpose: It has been shown that ion chamber dose response Monte Carlo simulations, in transverse magnetic fields, are susceptible to small changes in the scored sensitive volume. Changes in sensitive volumes have been investigated as a surrogate for modeling the true collection volume governed by the electric field. This work has not been fully extended to longitudinal fields.

Technical Note: EPID's response to 6 MV photons in a strong, parallel magnetic field.

Purpose: Electronic portal imaging devices (EPIDs) are potentially useful for dosimetric verification in integrated MRI-linac systems. This work presents the reproducibility, linearity, image lag, and radiation field profiles in a conventional EPID, with and without a 0.5 T parallel magnetic field present in a 6 MV photon beam.

Tracking tumor boundary using point correspondence for adaptive radio therapy.

Background And Objective: Tracking mobile tumor regions during the treatment is a crucial part of image-guided radiation therapy because of two main reasons which negatively affect the treatment process: (1) a tiny error will lead to some healthy tissues being irradiated; and (2) some cancerous cells may survive if the beam is not accurately positioned as it may not cover the entire cancerous region. However, tracking or delineation of such a tumor region from magnetic resonance imaging (MRI) is challenging due to photometric similarities of the region of interest and surrounding area as well as the influence of motion in the organs. The purpose of this work is to develop an approach to track the center and boundary of tumor region by auto-contouring the region of interest in moving organs for radiotherapy.

Technical Note: Experimental verification of EGSnrc calculated depth dose within a parallel magnetic field in a lung phantom.

Purpose: The calculation of depth doses from a 6 MV photon beam in polystyrene using EGSnrc Monte Carlo, within a parallel magnetic field, has been previously verified against measured data. The current work experimentally investigates the accuracy of EGSnrc calculated depth doses in lung within the same parallel magnetic field.

Methods: Two cylindrical bore electromagnets produced a magnetic field parallel to the central axis of a Varian Silhouette beam.

Correction to: LyP-1 Conjugated Nanoparticles for Magnetic Resonance Imaging of Triple Negative Breast Cancer.

This article was updated to correct the spelling of B. Gino Fallone's name; it is correct as displayed above. Correction to: Mol Imaging Biol (2017).

Corrigendum to "Stability analysis of a deterministic dose calculation for MRI-guided radiotherapy".

Modern effort in radiotherapy to address the challenges of tumor localization and motion has led to the development of MRI guided radiotherapy technologies. Accurate dose calculations must properly account for the effects of the MRI magnetic fields. Previous work has investigated the accuracy of a deterministic linear Boltzmann transport equation (LBTE) solver that includes magnetic field, but not the stability of the iterative solution method.