Magnetic Resonance Imaging In Radiotherapy Research Articles

Narrative review of the utility of magnetic resonance imaging in radiotherapy for cervical cancer.

In radiotherapy (RT) for locally advanced cervical cancer, high soft tissue contrast on magnetic resonance imaging (MRI) can ensure accurate delineation of target volumes (TVs) and optimal dose distribution to the RT target and organs at risk (OAR). MRI-guided adaptive RT (MRIgART) is a novel technology that revises RT plans according to anatomical changes occurring throughout the treatment to improve target coverage and minimise OAR toxicity. This review aims to assess the evidence and gaps of MRI use in RT planning and MRIgART in the treatment of cervical cancer, as well as challenges in its clinical implementation. Ovid Medline and PubMed were searched using keywords for MRI in RT for cervical cancer. After applying the inclusion and exclusion criteria, the initial search was deduced to 32 studies. A total of 37 final studies were reviewed, including eight additional articles from references. In the primary studies, TVs and organ motion were assessed before, during, and after treatment. MRI was used to investigate dose distribution and therapeutic response to the treatment in association with its outcome. Lastly, rationales for MRIgART were evaluated. It was concluded that MRI enables accurate target delineation, assessment of organ motion and interfraction changes, and monitoring of treatment response through dynamic parameters. Enhanced target coverage and reduced OAR irradiation through MRIgART can improve local control and the overall outcome, although its rationales against the logistical challenges need to be evaluated on further research.

Comparison of compressed sensing and controlled aliasing in parallel imaging acceleration for 3D magnetic resonance imaging for radiotherapy preparation

Magnetic resonance imaging (MRI) for radiotherapy is often based on 3D acquisitions, but suffers from low signal-to-noise ratio due to immobilization device and flexible coil use. The aim of this study was to investigate if Compressed Sensing (CS) improves image quality for 3D Turbo Spin Echo acquisitions compared with Controlled Aliasing k-space-based parallel imaging in equivalent acquisition time for intracranial T1, T2-Fluid-Attenuated Inversion Recovery (FLAIR) and pelvic T2 imaging. Qualitative ratings suffered from large inter-rater variability. CS-T1 brain MRI was superior numerically and qualitatively. CS-T2-FLAIR brain MRI was numerically superior, but rater equivalent. CS-T2 pelvic MRI was equivalent without gain.

Audit feasibility for geometric distortion in magnetic resonance imaging for radiotherapy.

Background and purposeMagnetic Resonance Imaging (MRI) is increasingly being used in radiotherapy (RT). However, geometric distortions are a known challenge of using MRI in RT. The aim of this study was to demonstrate feasibility of a national audit of MRI geometric distortions. This was achieved by assessing large field of view (FOV) MRI distortions on a number of scanners used clinically for RT.Materials and methodsMRI scans of a large FOV MRI geometric distortion phantom were acquired on 11 MRI scanners that are used clinically for RT in the UK. The mean and maximum distortions and variance between scanners were reported at different distances from the isocentre.ResultsFor a small FOV representing a brain (100–150 mm from isocentre) all distortions were < 2 mm except for the maximum distortion of one scanner. For a large FOV representing a head and neck/pelvis (200–250 mm from isocentre) mean distortions were < 2 mm except for one scanner, maximum distortions were > 10 mm in some cases. The variance between scanners was low and was found to increase with distance from isocentre.ConclusionsThis study demonstrated feasibility of the technique to be repeated in a country wide geometric distortion audit of all MRI scanners used clinically for RT. Recommendations were made for performing such an audit and how to derive acceptable limits of distortion in such an audit.

Sensitivity analysis of different quality assurance methods for magnetic resonance imaging in radiotherapy.

Background and purposeThere are currently no standard quality assurance (QA) methods for magnetic resonance imaging (MRI) in radiotherapy (RT). This work was aimed at evaluating the ability of two QA protocols to detect common events that affect quality of MR images under RT settings.Materials and methodsThe American College of Radiology (ACR) MRI QA phantom was repeatedly scanned using a flexible coil and action limits for key image quality parameters were derived. Using an exploratory survey, issues that reduce MR image quality were identified. The most commonly occurring events were introduced as provocations to produce MR images with degraded quality. From these images, detection sensitivities of the ACR MRI QA protocol and a commercial geometric accuracy phantom were determined.ResultsMachine-specific action limits for key image quality parameters set at were comparable with the ACR acceptable values. For the geometric accuracy phantom, provocations from uncorrected gradient nonlinearity effects and a piece of metal in the bore of the scanner resulted in worst distortions of 22.2 mm and 3.4 mm, respectively. The ACR phantom was sensitive to uncorrected signal variations, electric interference and a piece of metal in the bore of the scanner but could not adequately detect individual coil element failures.ConclusionsThe ACR MRI QA phantom combined with the large field-of-view commercial geometric accuracy phantom were generally sensitive in identifying some common MR image quality issues. The two protocols when combined may provide a tool to monitor the performance of MRI systems in the radiotherapy environment.

Clinical application of diffusion-weighted magnetic resonance imaging in radiotherapy for nasopharyngeal carcinoma.

To explore the clinical application of diffusion-weighted magnetic resonance imaging (DWI) in nasopharyngeal carcinoma (NPC) diagnosis, detection of lymph node metastasis, radiotherapy and prognosis. Twenty patients with diagnosed NPC in an early stage of radiotherapy were enrolled in our department between May 2010 and May 2013. T1 and T2 weighted magnetic resonance imaging and DWI of the nasopharynx and neck were performed 1 week before radiotherapy, during radiotherapy at a dose of 60 Gy, and 1 month after radiotherapy. Pertinent measurements and related data were recorded. In comparison with that before radiotherapy, the ADC value of the nasopharyngeal primary lesion increased significantly during radiotherapy at a dose of 60 Gy and at 1 month after radiotherapy (F = 187.160, P = 0.000). When the dose of radiotherapy reached 60 Gy, the DWI signals from both the neck and the retropharyngeal lymph nodes were significantly lower than those before radiotherapy. DWI can be used for sensitive and accurate diagnosis of lymph node metastasis in the neck and retropharyngeal space, monitoring of the radiotherapy effect in early stages of NPC and development of new medical treatment strategies.

Basic concepts and applications of functional magnetic resonance imaging for radiotherapy of prostate cancer.

Recently, the interest to integrate magnetic resonance imaging (MRI) in radiotherapy for prostate cancer has increased considerably. MRI can contribute in all steps of the radiotherapy workflow from diagnosis, staging, and target definition to treatment follow-up. Of particular interest is the ability of MRI to provide a wide range of functional measures. The complexity of MRI as an imaging modality combined with the growing interest of the application to prostate cancer radiotherapy, emphasize the need for dedicated education within the radiation oncology community. In this context, an overview of the most common as well as a few upcoming functional MR imaging techniques is presented: the basic methodology and measurement is described, the link between the functional measures and the underlying biology is established, and finally relevant applications of functional MRI useful for prostate cancer radiotherapy are given.

P269] Absorbed dose calculation based on CBCT data for head and neck cancer patients

Purpose In a radiotherapy magnetic resonance imaging (MRI) only workflow, a synthetic CT (sCT) data set is generated from the MRI data as a substitute to the computed tomography (CT). Since no CT scan will be acquired, no such data is available for quality control (QC) of the sCT. It has been suggested to use kV-cone beam CT (CBCT) data for QC in the head region [1] . The aim of this study is to evaluate the possibility to use CBCT for QC of the sCT for head and neck (H&N) cancer by comparing H&N treatment plans calculated using the CT and CBCT data, respectively. Methods Five patients with one CT and two CBCT data sets each, were evaluated. All CBCT data sets were deformably registered to the CT data, remediating errors originating from repositioning and/or anatomical changes between the imaging sessions. The CBCT and CT data were adjusted to the same field of view (FOV) in the longitudinal direction. A clinical treatment plan was created based on the CT data for each patient. Treatment volumes, organs-at-risk (OAR) and treatment plan were copied from the CT to the deformable registered CBCT. The treatment plan was then recalculated, with the standard CT HU-RED conversion curve. Dosimetric differences between the dose distributions for the treatment plans were calculated and evaluated by comparing dose-volume constrains. Results The mean local difference for the mean absorbed dose to the clinical target volume (CTV) was 0.41% with a maximum and minimum value of 1.37% and 0.15% respectively. The CTV D 98 % criteria had a difference of 0.19% and CTV D 2 % criteria a difference of 0.38%. The planning OAR volume (PRV) of the spinal cord had a difference of 0.39% and the parotid right and left a difference of 0.36% and 0.08%, respectively. Conclusions The dosimetric difference between the dose distributions for treatment plans calculated based on CT and CBCT data were minor. This indicates that CBCT data could be a good candidate for QC of sCT data in an MRI only workflow for H&N cancer patients.

What are the current and future requirements for magnetic resonance imaging interpretation skills in radiotherapy? A critical review

AbstractPurposeIncreasing usage of magnetic resonance imaging (MRI) in radiotherapy (RT) and the advent of MRI-based image-guided radiotherapy (IGRT) suggests a need for additional training within the RT profession. This critical review aimed to identify potential gaps in knowledge by evaluating the current skill base in MRI among therapeutic radiographers as evidenced by published research.MethodsPapers related to MRI usage were retrieved. Topic areas included outlining, planning and IGRT; diagnosis, follow-up and staging-related papers were excluded. After selection and further text analysis, papers were grouped by tumour site and year of publication.ResultsThe literature search and filtering resulted in a total of 123 papers, of which 66 were related to ‘outlining’, 37 to ‘planning’ and 20 to ‘IGRT’. The main sites of existing MRI expertise in RT were brain, central nervous system, prostate, and head and neck tumours. Expertise was clearly related to regions where MRI offered improved soft-tissue contrast. MRI studies within RT have been published from 2007 onwards at a steadily increasing rate.ConclusionCurrent use of MRI in RT is mainly restricted to sites where MRI offers a considerable imaging advantage over computed tomography. Given the changing use of MRI for image guidance, emerging therapeutic radiographers will require training in MRI interpretation across a wider range of anatomical regions.

Research progress of diffusion-weighted magnetic resonance imaging in radiotherapy of pancreatic cancer

In recent years, the incidence of pancreatic cancer shows rising trend and higher mortality. Pancreatic cancer lacks early diagnostic methods with high sensitivity and specificity, and the surgical resection rate is 10 %-20 % with high operation mortality, poor long-term curative effect and less than 5 % survival rate within 5 years. At present, researchers indicate that radiotherapy can improve the quality of life, increase tumor local control rate and prolong the overall survival time of patients with pancreatic cancer in different levels. Diffusion weighted imaging (DWI), as a functional imaging technology of magnetic resonance imaging (MRI), is the only way to react cell levels. This paper will summarize the application of DWI in radiotherapy of pancreatic cancer. Key words: Pancreatic neoplasms; Diffusion magnetic resonance imaging; Apparent diffusion coefficient; Radiotherapy

Applications of magnetic resonance imaging in radiotherapy of nasopharyngeal carcinoma

Magnetic resonance imaging (MRI)has apparent dominance in nasopharyngeal carcinoma (NPC) diagnosis,staging,the plan of radiotherapy target and assessment of efficacy because of its high-contrast of parenchyma and muli-parameters imaging.Especially diffusion-weighted imaging (DWI) developed in several years,it can provide qualitative and quantitative information at the cellular level about tumor cellularity and the integrity of cell membranes,which is valuable for tumor detection,cervical lymph nodes metastases,systemic transfer,monitoring and predicting the treatment response of nasopharyngeal carcinoma. Key words: Magnetic resonance imaging; Nasopharyngeal neoplasms; Radiotherapy

940 POSTER The prognostic significance of volumetric evaluation by magnetic resonance imaging in radiotherapy for patients with cervical cancer

940 POSTER The prognostic significance of volumetric evaluation by magnetic resonance imaging in radiotherapy for patients with cervical cancer

The Prognostic Significance of Volumetric Evaluation by Magnetic Resonance Imaging in Radiotherapy for Patients with Cervical Cancer

The Prognostic Significance of Volumetric Evaluation by Magnetic Resonance Imaging in Radiotherapy for Patients with Cervical Cancer