Impact of a contouring atlas on radiographer inter-observer variation in male pelvis radiotherapy.

PURPOSE/OBJECTIVE: To determine the impact of a MR-based contouring atlas for male pelvis radiotherapy delineation on inter-observer variation to support radiographer led real-time magnetic resonance image guided adaptive radiotherapy (MRgART). MATERIAL/METHODS: Eight RTTs contoured 25 MR images in the Monaco treatment planning system (Monaco 5.40.01), from 5 patients. The prostate, seminal vesicles, bladder, and rectum were delineated before and after the introduction of an atlas developed through multi-disciplinary consensus. Inter-observer contour variations (volume), time to contour and observer contouring confidence were determined at both time-points using a 5-point Likert scale. Descriptive statistics were used to analyse both continuous and categorical variables. Dice similarity coefficient (DSC), Dice-Jaccard coefficient (DJC) and Hausdorff distance were used to calculate similarity between observers. RESULTS: Although variation in volume definition decreased for all structures among all observers post intervention, the change was not statistically significant. DSC and DJC measurements remained consistent following the introduction of the atlas for all observers. The highest similarity was found in the bladder and prostate whilst the lowest was the seminal vesicles. The mean contouring time for all observers was reduced by 50% following the introduction of the atlas (53 to 27 minutes, p=0.01). For all structures across all observers, the mean contouring confidence increased significantly from 2.3 to 3.5 out of 5 (p=0.02). CONCLUSION: Although no significant improvements were observed in contour variation amongst observers, the introduction of the consensus-based contouring atlas improved contouring confidence and speed; key factors for a real-time RTT-led MRgART.

Geometric distortion caused by metallic femoral head prosthesis in prostate cancer imaging on an MR Linac: in-vivo measurements of spatial deformation.

OBJECTIVES: Metallic implants cause artefacts and distortion on MRI. To ensure accurate dose delivery and plan adaptation on an MR Linac, there is a need to evaluate distortion caused. METHODS: Participants were imaged on an MR Linac (Elekta Unity, Elekta AB Stockholm). Three sequences were evaluated. Two vendor supplied (T2W TSE 3D), and one T2W TSE 3D optimized to reduce metal artefact distortions. Images were rigidly registered to CT images by a single observer, using bony anatomy. Three coronal and three axial images were selected, and six paired, adjacent, bony landmarks were identified on each slice. Images bisecting treatment isocentre were included. Difference between landmark coordinates was taken to be measure of distortion. RESULTS: Five observers participated. Thirty six pairs of bony landmarks were identified. Median difference in position of landmarks was ≤3 mm (range 0.3-4.4 mm). One-way analysis of variance (ANOVA) between observer means showed no significant variation between sequences or patients (P = 1.26 in plane, P = 0.11 through plane). Interobserver intra class correlation (ICC) was 0.70 in-plane and 0.78 through-plane. Intra-observer ICC for three observers was 0.76, 0.81, 0.83, showing moderate to good reliability on this small cohort. CONCLUSIONS: This in-vivo feasibility study suggests distortion due to metallic hip prosthesis is not an obstacle for pelvic radiotherapy on an MR Linac. Research on the impact on plan quality is warranted. ADVANCES IN KNOWLEDGE: This work supports feasibility of treating patients with metallic hip prosthesis on an MR Linac.

Sorting lung tumor volumes from 4D-MRI data using an automatic tumor-based signal reduces stitching artifacts.

PURPOSE: To investigate whether a novel signal derived from tumor motion allows more precise sorting of 4D-magnetic resonance (4D-MR) image data than do signals based on normal anatomy, reducing levels of stitching artifacts within sorted lung tumor volumes. METHODS: (4D-MRI) scans were collected for 10 lung cancer patients using a 2D T2-weighted single-shot turbo spin echo sequence, obtaining 25 repeat frames per image slice. For each slice, a tumor-motion signal was generated using the first principal component of movement in the tumor neighborhood (TumorPC1). Signals were also generated from displacements of the diaphragm (DIA) and upper and lower chest wall (UCW/LCW) and from slice body area changes (BA). Pearson r coefficients of correlations between observed tumor movement and respiratory signals were determined. TumorPC1, DIA, and UCW signals were used to compile image stacks showing each patient's tumor volume in a respiratory phase. Unsorted image stacks were also built for comparison. For each image stack, the presence of stitching artifacts was assessed by measuring the roughness of the compiled tumor surface according to a roughness metric (Rg). Statistical differences in weighted means of Rg between any two signals were determined using an exact permutation test. RESULTS: The TumorPC1 signal was most strongly correlated with superior-inferior tumor motion, and had significantly higher Pearson r values (median 0.86) than those determined for correlations of UCW, LCW, and BA with superior-inferior tumor motion (p < 0.05). Weighted means of ratios of Rg values in TumorPC1 image stacks to those in unsorted, UCW, and DIA stacks were 0.67, 0.69, and 0.71, all significantly favoring TumorPC1 (p = 0.02-0.05). For other pairs of signals, weighted mean ratios did not differ significantly from one. CONCLUSION: Tumor volumes were smoother in 3D image stacks compiled using the first principal component of tumor motion than in stacks compiled with signals based on normal anatomy.

First-in-human technique translation of oxygen-enhanced MRI to an MR Linac system in patients with head and neck cancer.

BACKGROUND AND PURPOSE: Tumour hypoxia is prognostic in head and neck cancer (HNC), associated with poor loco-regional control, poor survival and treatment resistance. The advent of hybrid MRI - radiotherapy linear accelerator or 'MR Linac' systems - could permit imaging for treatment adaptation based on hypoxic status. We sought to develop oxygen-enhanced MRI (OE-MRI) in HNC and translate the technique onto an MR Linac system. MATERIALS AND METHODS: MRI sequences were developed in phantoms and 15 healthy participants. Next, 14 HNC patients (with 21 primary or local nodal tumours) were evaluated. Baseline tissue longitudinal relaxation time (T1) was measured alongside the change in 1/T1 (termed ΔR1) between air and oxygen gas breathing phases. We compared results from 1.5 T diagnostic MR and MR Linac systems. RESULTS: Baseline T1 had excellent repeatability in phantoms, healthy participants and patients on both systems. Cohort nasal concha oxygen-induced ΔR1 significantly increased (p < 0.0001) in healthy participants demonstrating OE-MRI feasibility. ΔR1 repeatability coefficients (RC) were 0.023-0.040 s-1 across both MR systems. The tumour ΔR1 RC was 0.013 s-1 and the within-subject coefficient of variation (wCV) was 25% on the diagnostic MR. Tumour ΔR1 RC was 0.020 s-1 and wCV was 33% on the MR Linac. ΔR1 magnitude and time-course trends were similar on both systems. CONCLUSION: We demonstrate first-in-human translation of volumetric, dynamic OE-MRI onto an MR Linac system, yielding repeatable hypoxia biomarkers. Data were equivalent on the diagnostic MR and MR Linac systems. OE-MRI has potential to guide future clinical trials of biology guided adaptive radiotherapy.

To see or not to see: Evaluation of magnetic resonance imaging sequences for use in MR Linac-based radiotherapy treatment.

BACKGROUND/PURPOSE: This work evaluated the suitability of MR derived sequences for use in online adaptive RT workflows on a 1.5 Tesla (T) MR-Linear Accelerator (MR Linac). MATERIALS/METHODS: Non-patient volunteers were recruited to an ethics approved MR Linac imaging study. Participants attended 1-3 imaging sessions in which a combination of DIXON, 2D and 3D volumetric T1 and T2 weighted images were acquired axially, with volunteers positioned using immobilisation devices typical for radiotherapy to the anatomical region being scanned. Images from each session were appraised by three independent reviewers to determine optimal sequences over six anatomical regions: head and neck, female and male pelvis, thorax (lung), thorax (breast/chest wall) and abdomen. Site specific anatomical structures were graded by the perceived ability to accurately contour a typical organ at risk. Each structure was independently graded on a 4-point Likert scale as 'Very Clear', 'Clear', 'Unclear' or 'Not visible' by observers, consisting of radiographers (therapeutic and diagnostic) and clinicians. RESULTS: From July 2019 to September 2019, 18 non-patient volunteers underwent 24 imaging sessions in the following anatomical regions: head and neck (n=3), male pelvis (n=4), female pelvis (n=5), lung/oesophagus (n=5) abdomen (n=4) and chest wall/breast (n=3). T2 sequences were the most preferred for perceived ability to contour anatomy in both male and female pelvis. For all other sites T1 weighted DIXON sequences were most favourable. CONCLUSION: This study has determined the preferential sequence selection for organ visualisation, as a pre-requisite to our institution adopting MR-guided radiotherapy for a more diverse range of disease sites.

Radiotherapy respiratory motion management in hepatobiliary and pancreatic malignancies: a systematic review of patient factors influencing effectiveness of motion reduction with abdominal compression.

BACKGROUND: The effectiveness of abdominal compression for motion management in hepatobiliary-pancreatic (HPB) radiotherapy has not been systematically evaluated. METHODS & MATERIALS: A systematic review was carried out using PubMed/Medline, Cochrane Library, Web of Science, and CINAHL databases up to 1 July 2021. No date restrictions were applied. Additional searches were carried out using the University of Manchester digital library, Google Scholar and of retrieved papers' reference lists. Studies conducted evaluating respiratory motion utilising imaging with and without abdominal compression in the same patients available in English were included. Studies conducted in healthy volunteers or majority non-HPB sites, not providing descriptive motion statistics or patient characteristics before and after compression in the same patients or published without peer-review were excluded. A narrative synthesis was employed by tabulating retrieved studies and organising chronologically by abdominal compression device type to help identify patterns in the evidence. RESULTS: The inclusion criteria were met by 6 studies with a total of 152 patients. Designs were a mix of retrospective and prospective quantitative designs with chronological, non-randomised recruitment. Abdominal compression reduced craniocaudal respiratory motion in the majority of patients, although in four studies there were increases seen in at least one direction. The influence of patient comorbidities on effectiveness of compression, and/or comfort with compression was not evaluated in any study. CONCLUSION: Abdominal compression may not be appropriate for all patients, and benefit should be weighed with potential increase in motion or discomfort in patients with small initial motion (<5 mm). Patient factors including male sex, and high body mass index (BMI) were found to impact the effectiveness of compression, however with limited evidence. High-quality studies are warranted to fully assess the clinical impact of abdominal compression on treatment outcomes and toxicity prospective in comparison to other motion management strategies.

The impact of gadolinium-based MR contrast on radiotherapy planning for oropharyngeal treatment on the MR Linac.

PURPOSE: Gadolinium-based contrast agents (GBCAs) may add value to magnetic resonance (MR)-only radiotherapy (RT) workflows including on hybrid machines such as the MR Linac. The impact of GBCAs on RT dose distributions however have not been well studied. This work used retrospective GBCA-enhanced datasets to assess the dosimetric effect of GBCAs on head and neck plans. METHODS: Ten patients with oropharyngeal squamous cell carcinoma receiving RT from November 2018 to April 2020 were included in this study. RT planning included contrast-enhanced computed tomography (CT) and MR scans. A contrast agent "contour" was defined by delineating GBCA-enhanced regions using an agreed window/level threshold, transferred to the planning CT and given a standardized electron density (ED) of 1.149 in the Monaco treatment planning system (Elekta AB). Four plans were per patient calculated and compared using two methods: (1) optimized without contrast (Plan A) then recalculated with ED (Plan B), and (2) optimized with contrast ED (Plan C) then without (Plan D). For target parameters minimum and maximum doses to 1cc of PTVs, D95 values, and percent dose differences were calculated. Dose differences for organs-at-risk (OARs) were calculated as a percentage of the clinical tolerance value. For the purposes of this study, ±2% over the whole treatment course was considered to be a clinically acceptable dose deviation. Wilcoxon-signed rank tests were used to determine any dose differences within and between the two methods of optimization and recalculation (p < 0.05). Pearson's correlations were used to establish the relationship between gadolinium uptake volume in a structure (i.e., proportion of structure covered by a density override) and the resulting dose difference. RESULTS: The median percent dose differences for key reportable dosimetric parameters between non-contrast and simulated contrast plans were <1.2% over all fractions over all patients for reportable target parameters (mean 0.34%, range 0.22%-1.02%). The percent dose differences for maximum dose to 1cc of both PTV1 and PTV2 were significantly different after application of density override (p < 0.05) but only in method 2 (Plan C vs. Plan D). For D95 PTV1, there was a statistically significant effect of density override (p < 0.01), however only in method 1 (Plan A vs. Plan B). There were no significant differences between calculation methods of the impact of contrast in most target parameters with the exception of D95 PTV1 (p < 0.01) and for D95 PTV2 (p < 0.05). The median percent dose differences for reportable OAR parameters as a percentage of clinical planning tolerances were <2.0% over a full treatment course (mean 0.65%, range 0.27%-1.62%). There were no significant differences in dose to OARs within or between methods for contrast impact assessment. CONCLUSIONS: Dose differences to targets and OARs in oropharyngeal cancer treatment due to the presence of GBCA were minimal, and this work suggests that prospective in vivo evaluations of impact may not be necessary in this clinical site. Accounting for GBCAs may not be needed in daily adaptive workflows on the MR Linac.

Developing electronic learning to deliver MR safety training in a radiotherapy department.

INTRODUCTION/BACKGROUND: Magnetic Resonance Imaging (MRI) is used in radiotherapy planning, and increasingly in on-treatment guidance. The potential for the MR environment to be hazardous, without stringent safe working practices, is real. Guidance suggests all workers in MRI undergo annual safety training. To facilitate a tangible MR safety program, an electronic learning module was created and evaluated. METHODS: An existing presentation, normally delivered face-to-face, was modified and questions added to test knowledge. The module was delivered and feedback collected, together with answers to the questions, over three phases to ensure deliverability, clarity, and robustness. These comprised an initial pilot phase for non-MR personnel, an evaluation phase for staff renewing annual MR safety training, and finally for new therapeutic radiographer graduates, a test-retest methodology. RESULTS: Seven participants took part in the initial pilot phase, followed by thirty-one in the evaluation phase. Participants included radiographers (therapeutic and diagnostic), play specialists, clinical oncologists and anaesthetists, physicists and nursing staff. Within the evaluation group, 74.2% achieved a score >80%. Incorrect responses were principally related to questions regarding expected levels of responsibility and working practices, rather than the physics of high magnetic field strengths. The test-retest phase (n = 5) followed. Mean scores prior to learning were 59%, improving to 79% following learning, with the weakest sections mirroring those highlighted within the evaluation phase. DISCUSSION: Transferring MR safety training into an electronic format has provided a standardised, tangible tool that provides evidence of compliance with recommended guidance. CONCLUSIONS: This work illustrates the transition of MR safety learning for radiotherapy staff from passive presentation, to an interactive teaching methodology. The e-learning module has now been implemented within the department.

MRI and CBCT for lymph node identification and registration in patients with NSCLC undergoing radical radiotherapy.

PURPOSE: This study compared MRI to CBCT for the identification and registration of lymph nodes (LN) in patients with locally advanced (LA)-NSCLC, to assess the suitability of targeting LNs in future MR-image guided radiotherapy (MRgRT) workflows. METHOD: Radiotherapy radiographers carried out Visual Grading Analysis (VGA) assessment of image quality, LN registration and graded their confidence in registration for each of the 24 LNs on CBCT and two MR sequences, MR1 (T2w Turbo Spin Echo) and MR2 (T1w DIXON water only image). RESULTS: Pre-registration image quality assessment revealed MR1 and MR2 as significantly superior to CBCT in terms of image quality (p ≤ 0.01). No significant differences were noted in interobserver variability for LN registration between CBCT, MR1 and MR2. Observers were more confident in their MR registrations compared to their CBCT based LN registrations (p ≤ 0.02). SUMMARY: Interobserver setup correction variability was not found to be significantly different between CBCT and MR. Image quality and registration confidence were found to be superior for MRI sequences. This is a promising step towards MR-guided radiotherapy for the treatment of LA-NSCLC.

IPEM Topical Report: an international IPEM survey of MRI use for external beam radiotherapy treatment planning.

Introduction/Background. Despite growing interest in magnetic resonance imaging (MRI), integration in external beam radiotherapy (EBRT) treatment planning uptake varies globally. In order to understand the current international landscape of MRI in EBRT a survey has been performed in 11 countries. This work reports on differences and common themes identified.Methods. A multi-disciplinary Institute of Physics and Engineering in Medicine working party modified a survey previously used in the UK to understand current practice using MRI for EBRT treatment planning, investigate how MRI is currently used and managed as well as identify knowledge gaps. It was distributed electronically within 11 countries: Australia, Belgium, Denmark, Finland, France, Italy, the Netherlands, New Zealand, Sweden, the UK and the USA.Results. The survey response rate within the USA was <1% and hence these results omitted from the analysis. In the other 10 countries the survey had a median response rate of 77% per country. Direct MRI access, defined as either having a dedicated MRI scanner for radiotherapy (RT) or access to a radiology MRI scanner, varied between countries. France, Italy and the UK reported the lowest direct MRI access rates and all other countries reported direct access in ≥82% of centres. Whilst ≥83% of centres in Denmark and Sweden reported having dedicated MRI scanners for EBRT, all other countries reported ≤29%. Anatomical sites receiving MRI for EBRT varied between countries with brain, prostate, head and neck being most common. Commissioning and QA of image registration and MRI scanners varied greatly, as did MRI sequences performed, staffing models and training given to different staff groups. The lack of financial reimbursement for MR was a consistent barrier for MRI implementation for RT for all countries and MR access was a reported important barrier for all countries except Sweden and Denmark.Conclusion. No country has a comprehensive approach for MR in EBRT adoption and financial barriers are present worldwide. Variations between countries in practice, equipment, staffing models, training, QA and MRI sequences have been identified, and are likely to be due to differences in funding as well as a lack of consensus or guidelines in the literature. Access to dedicated MR for EBRT is limited in all but Sweden and Denmark, but in all countries there are financial challenges with ongoing per patient costs. Despite these challenges, significant interest exists in increasing MR guided EBRT planning over the next 5 years.

IPEM topical report: guidance on the use of MRI for external beam radiotherapy treatment planning.

This document gives guidance for multidisciplinary teams within institutions setting up and using an MRI-guided radiotherapy (RT) treatment planning service. It has been written by a multidisciplinary working group from the Institute of Physics and Engineering in Medicine (IPEM). Guidance has come from the experience of the institutions represented in the IPEM working group, in consultation with other institutions, and where appropriate references are given for any relevant legislation, other guidance documentation and information in the literature. Guidance is only given for MRI acquired for external beam RT treatment planning in a CT-based workflow, i.e. when MRI is acquired and registered to CT with the purpose of aiding delineation of target or organ at risk volumes. MRI use for treatment response assessment, MRI-only RT and other RT treatment types such as brachytherapy and gamma radiosurgery are not considered within the scope of this document. The aim was to produce guidance that will be useful for institutions who are setting up and using a dedicated MR scanner for RT (referred to as an MR-sim) and those who will have limited time on an MR scanner potentially managed outside of the RT department, often by radiology. Although not specifically covered in this document, there is an increase in the use of hybrid MRI-linac systems worldwide and brief comments are included to highlight any crossover with the early implementation of this technology. In this document, advice is given on introducing a RT workload onto a non-RT-dedicated MR scanner, as well as planning for installation of an MR scanner dedicated for RT. Next, practical guidance is given on the following, in the context of RT planning: training and education for all staff working in and around an MR scanner; RT patient set-up on an MR scanner; MRI sequence optimisation for RT purposes; commissioning and quality assurance (QA) to be performed on an MR scanner; and MRI to CT registration, including commissioning and QA.

An unusual case of oedematous prostate volumetric changes observed over the course of radiotherapy on the MR linear accelerator.

INTRODUCTION: The integration of magnetic resonance (MR) imaging into radiotherapy through new technology, including the MR -linear accelerator (MRL), has allowed further advancements into image guided radiotherapy (IGRT). Better soft tissue visualisation has led to some unusual findings. CASE AND OUTCOMES: A patient with T1c N0 M0 prostate adenocarcinoma received 60Gy in 20# radiotherapy on the MRL. Radiotherapy planning (RTP) scans were completed on both CT and MR (using T2 and T1 weighted three-dimensional turbo spin echo sequences, reconstructed transaxially (TRA). The MR scans revealed atypical oedema in the right peripheral zone, visualised on T2-weighted (T2w) MR Images as an accumulation of high signal intensity fluid. Daily MRL treatment includes a (T2w 3D Tra) sequence with which oedematous changes could be monitored. The images demonstrated an increase in oedematous volume over fractions 1-10 causing the prostate contour variations from the initial planning scans. Despite the prostate volume variations PTV coverage was never breached and dose constraints were always met for both PTV and surrounding organs at risk (OAR's), excluding the need for oncologist input. A single Therapeutic Radiographer (RTT) experienced in MRL delivery, contoured the prostate and oedematous volumes on the radiotherapy plan (RTP) MR and all on-treatment MR images to assess change over the radiotherapy course. The initial volumes were 53.4 cm3 and 8.3 cm3 for the prostate plus oedema and oedema alone respectively. The most significant change was seen for both the prostate and oedema on fraction nine (68.0 cm3 and 10.1 cm3, respectively). Reductions were noted after this with final (fraction 20) volumes of 55.2 cm3 and 0.58 cm3 respectively. DISCUSSION: The ability to visualise prostatic oedema was new to the radiotherapy treatment team due to better soft tissue visualisation than standard radiotherapy. The results from contouring the prostate and oedema volumes confirmed radiographer observations and demonstrated how oedema impacted the overall prostate volume by quantifying the oedematous variations over time. The changes in oedema volume are presumed to be in response to radiotherapy. CONCLUSION: Further adaptive radiotherapy work-flow developments, utilising an "Adapt to Shape" model will allow real-time re-contouring of the prostate to ensure tumour control is not compromised. Further work investigating the frequency and impact of oedemotous changes to external beam prostate patients will help to inform practice.

Therapeutic Radiographers at the Helm: Moving Towards Radiographer-Led MR-Guided Radiotherapy.

INTRODUCTION: Magnetic resonance-guided adaptive radiotherapy (MRgART) has the potential to improve treatment processes and outcomes for a variety of tumour sites; however, it requires significant clinical resources. Magnetic resonance linear accelerator (MR-linac) treatments require a daily multidisciplinary presence for delivery. To facilitate sustainable MRgART models, agreed protocols facilitating therapeutic radiographer (RTT)-led delivery must be developed to establish a service similar to conventional image-guided radiotherapy (IGRT). This work provides a clinical perspective on the implementation of a protocol-driven 'clinician-lite' MRgART workflow at one institution. METHODS: To identify knowledge, skills, and competence required at each step in the MRgART workflow, an interdisciplinary informal survey and needs assessment were undertaken to identify additional or enhanced skills required for MRgART, over and above those required for conventional cone-beam computed tomography-based IGRT. The MRgART pathway was critically evaluated by relevant professionals to encourage multidisciplinary input and discussion, allowing an iterative development of the RTT-led workflow. Starting with the simplest online adaptation strategy, consisting of a virtual couch shift and online replanning, clear guidelines were established for the delivery of radical prostate radiotherapy with a reduction in staff numbers present. RESULTS: The MRgART-specific skills identified included MRI safety and screening, MR image acquisition, MRI-based anatomy, multimodality image interpretation and registration, and treatment plan evaluation. These skills were developed in RTTs via tutorials, workshops, focussed self-directed reading, teaching of colleagues, and end-to-end workflow testing. After initial treatments and discussions, roles and responsibilities of the three professional groups (clinicians, RTTs, and physicists) have evolved to achieve a 'clinician-lite' workflow for simple radical prostate treatments. DISCUSSION: Through applying a definitive framework and establishing agreed threshold and action levels for action within anticipated treatment scenarios similar to those in cone-beam computed tomography-based IGRT, we have implemented a 'clinician-lite' workflow for simple adaptive treatments on the MR-linac. The responsibility for online plan evaluation and approval now rests with physicists and RTTs to streamline MRgART. Early evaluation of the framework after treatment of 10 patients has required minimal online clinician input (1.5% of 200 fractions delivered). CONCLUSION: A 'clinician-lite' prostate treatment workflow has been successfully introduced on the MR-linac at our institution and will serve as a model for other tumour sites, using more complex adaptive strategies. Early indications are that this framework has the potential to improve patient throughput and efficiency. Further identification and validation of roles and responsibilities such as online contouring, and more interactive online planning, will facilitate RTTs to fully lead in the online workflow as adaptive radiotherapy becomes ever more complex.

Comparison of radiographer interobserver image registration variability using cone beam CT and MR for cervix radiotherapy.

OBJECTIVES: The aim of this study was to assess the consistency of therapy radiographers performing image registration using cone beam computed tomography (CBCT)-CT, magnetic resonance (MR)-CT, and MR-MR image guidance for cervix cancer radiotherapy and to assess that MR-based image guidance is not inferior to CBCT standard practice. METHODS: 10 patients receiving cervix radiation therapy underwent daily CBCT guidance and magnetic resonance (MR) imaging weekly during treatment. Offline registration of each MR image, and corresponding CBCT, to planning CT was performed by five radiographers. MR images were also registered to the earliest MR interobserver variation was assessed using modified Bland-Altman analysis with clinically acceptable 95% limits of agreement (LoA) defined as ±5.0 mm. RESULTS: 30 CBCT-CT, 30 MR-CT and 20 MR-MR registrations were performed by each observer. Registration variations between CBCT-CT and MR-CT were minor and both strategies resulted in 95% LoA over the clinical threshold in the anteroposterior direction (CBCT-CT ±5.8 mm, MR-CT ±5.4 mm). MR-MR registrations achieved a significantly improved 95% LoA in the anteroposterior direction (±4.3 mm). All strategies demonstrated similar results in lateral and longitudinal directions. CONCLUSION: The magnitude of interobserver variations between CBCT-CT and MR-CT were similar, confirming that MR-CT radiotherapy workflows are comparable to CBCT-CT image-guided radiotherapy. Our results suggest MR-MR radiotherapy workflows may be a superior registration strategy. ADVANCES IN KNOWLEDGE: This is the first publication quantifying interobserver registration of multimodality image registration strategies for cervix radical radiotherapy patients.

Magnetic resonance-guided radiation therapy: A review.

Magnetic resonance-guided radiation therapy (MRgRT) is a promising approach to improving clinical outcomes for patients treated with radiation therapy. The roles of image guidance, adaptive planning and magnetic resonance imaging in radiation therapy have been increasing over the last two decades. Technical advances have led to the feasible combination of magnetic resonance imaging and radiation therapy technologies, leading to improved soft-tissue visualisation, assessment of inter- and intrafraction motion, motion management, online adaptive radiation therapy and the incorporation of functional information into treatment. MRgRT can potentially transform radiation oncology by improving tumour control and quality of life after radiation therapy and increasing convenience of treatment by shortening treatment courses for patients. Multiple groups have developed clinical implementations of MRgRT predominantly in the abdomen and pelvis, with patients having been treated since 2014. While studies of MRgRT have primarily been dosimetric so far, an increasing number of trials are underway examining the potential clinical benefits of MRgRT, with coordinated efforts to rigorously evaluate the benefits of the promising technology. This review discusses the current implementations, studies, potential benefits and challenges of MRgRT.

IPEM Topical Report: A 2018 IPEM survey of MRI use for external beam radiotherapy treatment planning in the UK.

The benefits of integrating MRI into the radiotherapy pathway are well published, however there is little consensus in guidance on how to commission or implement its use. With a view to developing consensus guidelines for the use of MRI in external beam radiotherapy (EBRT) treatment planning in the UK, a survey was undertaken by an Institute of Physics and Engineering in Medicine (IPEM) working-party to assess the current landscape of MRI use in EBRT in the UK. A multi-disciplinary working-party developed a survey to understand current practice using MRI for EBRT treatment planning; investigate how MRI is currently used and managed; and identify knowledge gaps. The survey was distributed electronically to radiotherapy service managers and physics leads in 71 UK radiotherapy (RT) departments (all NHS and private groups). The survey response rate was 87% overall, with 89% of NHS and 75% of private centres responding. All responding centres include EBRT in some RT pathways: 94% using Picture Archiving and Communication System (PACS) images potentially acquired without any input from RT departments, and 69% had some form of MRI access for planning EBRT. Most centres reporting direct access use a radiology scanner within the same hospital in dedicated (26%) or non-dedicated (52%) RT scanning sessions. Only two centres reported having dedicated RT MRI scanners in the UK, lower than reported in other countries. Six percent of radiotherapy patients in England (data not publically available outside of England) have MRI as part of their treatment, which again is lower than reported elsewhere. Although a substantial number of centres acquire MRI scans for treatment planning purposes, most centres acquire less than five patient scans per month for each treatment site. Commissioning and quality assurance of both image registration and MRI scanners was found to be variable across the UK. In addition, staffing models and training given to different staff groups varied considerably across the UK, reflecting the current lack of national guidelines. The primary barriers reported to MRI implementation in EBRT planning included costs (e.g. lack of a national tariff for planning MRI), lack of MRI access and/or capacity within hospitals. Despite these challenges, significant interest remains in increasing MRI-assisted EBRT planning over the next five years.

Keeping Up with the Hybrid Magnetic Resonance Linear Accelerators: How Do Radiation Therapists Stay Current in the Era of Hybrid Technologies?

The benefits of integrating magnetic resonance imaging (MRI) into radiotherapy planning have long been extolled, first appearing in the literature as early as 1986. Most often described as a tool to be used when registered to a planning computed tomography to improve target and organ at risk delineation, the use of MRI for on-board image guidance and as a sole imaging modality throughout the entire radiotherapy pathway is quickly becoming a reality for appropriately selected patient populations in academic centres throughout the world. With the commercialization of these integrated magnetic resonance - radiotherapy delivery systems, an MRI-only workflow will prove beneficial, with MRI being used for treatment planning, localization, and on-treatment plan adaptation. Despite these technological advancements, recent surveys indicate uptake of MRI in radiotherapy as a routine practice has proven challenging. Reasons cited for this slow uptake were primarily related to health economics and/or accessibility. Furthermore, these surveys, like much of the academic literature, shy away from focusing on safe, sustainable staffing models enabled by comprehensive and appropriate education and training. In stark contrast to conebeam computed tomography guided therapy, magnetic resonance - radiotherapy systems are currently being operated by teams of physicians, radiographers, and physicists because of the diverse and complex tasks required to deliver treatment. The pace of innovation in RT remains high and unfortunately the window of opportunity to implement appropriate education continues to narrow. It is vital that we establish a framework to future-proof our profession. In the era of magnetic resonance-guided radiotherapy, we have yet to address the question of how to devise a consensus on the requisite knowledge, skills, and competence for radiation therapists and therapy radiographers using and/or operating MRI that provides guidance, without becoming prohibitively costly or time consuming.

Comparison of prostate delineation on multimodality imaging for MR-guided radiotherapy.

OBJECTIVE:: With increasing incorporation of MRI in radiotherapy, we investigate two MRI sequences for prostate delineation in radiographer-led image guidance. METHODS:: Five therapeutic radiographers contoured the prostate individually on CT, T2 weighted (T2W) and T2* weighted (T2*W) imaging for 10 patients. Contours were analysed with Monaco ADMIRE (research v. 2.0) to assess interobserver variability and accuracy by comparison with a gold standard clinician contour. Observers recorded time taken for contouring and scored image quality and confidence in contouring. RESULTS:: There is good agreement when comparing radiographer contours to the gold-standard for all three imaging types with Dice similarity co-efficient 0.91-0.94, Cohen's κ 0.85-0.91, Hausdorff distance 4.6-7.6 mm and mean distance between contours 0.9-1.2 mm. In addition, there is good concordance between radiographers across all imaging modalities. Both T2W and T2*W MRI show reduced interobserver variability and improved accuracy compared to CT, this was statistically significant for T2*W imaging compared to CT across all four comparison metrics. Comparing MRI sequences reveals significantly reduced interobserver variability and significantly improved accuracy on T2*W compared to T2W MRI for DSC and Cohen's κ. Both MRI sequences scored significantly higher compared to CT for image quality and confidence in contouring, particularly T2*W. This was also reflected in the shorter time for contouring, measuring 15.4, 9.6 and 9.8 min for CT, T2W and T2*W MRI respectively. Conclusion: Therapeutic radiographer prostate contours are more accurate, show less interobserver variability and are more confidently and quickly outlined on MRI compared to CT, particularly using T2*W MRI. Advances in knowledge: Our work is relevant for MRI sequence choice and development of the roles of the interprofessional team in the advancement of MRI-guided radiotherapy.

Intravenous contrast-enhanced cone beam computed tomography (IVCBCT) of intrahepatic tumors and vessels.

PURPOSE: Liver tumors are challenging to visualize on cone beam computed tomography (CBCT) without intravenous (IV) contrast. Image guidance for liver cancer stereotactic body ablative radiation therapy (SABR) could be improved with the direct visualization of hepatic tumors and vasculature. This study investigated the feasibility of the use of IV contrast-enhanced CBCT (IV-CBCT) as a means to improve liver target visualization. METHODS AND MATERIALS: Patients on a liver SABR protocol underwent IV-CBCT before 1 or more treatment fractions in addition to a noncontrast CBCT. Image acquisition was initiated 0 to 30 seconds following injection and acquired over 60 to 120 seconds. "Stop and go" exhale breath-hold CBCT scans were used whenever feasible. Changes in mean CT number in regions of interest within visible vasculature, tumor, and adjacent liver were quantified between CBCT and IV-CBCT. RESULTS: Twelve pairs of contrast and noncontrast CBCTs were obtained in 7 patients. Intravenous-CBCT improved hepatic tumor visibility in breath-hold scans only for 3 patients (2 metastases, 1 hepatocellular carcinoma). Visible tumors ranged in volume from 124 to 564 mL. Small tumors in free-breathing patients did not show enhancement on IVCBT. CONCLUSIONS: Intravenous-CBCT may enhance the visibility of hepatic vessels and tumor in CBCT scans obtained during breath hold. Optimization of IV contrast timing and reduction of artifacts to improve tumor visualization warrant further investigation.