Introducing magnetic resonance imaging into the lung cancer radiotherapy workflow - An assessment of patient experience.

INTRODUCTION: Magnetic resonance imaging (MRI) offers superior soft tissue contrast to computed tomography (CT), the current standard imaging modality for planning radiotherapy treatment. Improved soft tissue contrast could reduce uncertainties in identifying tumour and surrounding healthy tissues, potentially leading to improved outcomes in patients with lung cancer. This study explored patient experience of MR treatment planning scans in addition to a CT scan. METHODS: Participants were recruited to the 'Magnetic Resonance Imaging for the Delineation of Organs At Risk and Target Volumes in Lung Cancer Patients (MR-Lung)' study at a UK specialist cancer centre. Participants completed their standard of care radiotherapy planning CT scan and two additional MRI scans. Baseline and post-scan questionnaires were completed assessing anxiety and claustrophobia. Motion artefact during MRI was assessed by a modified visual grading analysis. Sixteen participants completed semi-structured interviews; transcripts were analysed thematically. RESULTS: 29 people (66% female; aged 54-89 years) participated. Nineteen participants completed all imaging and 10 participants withdrew before completion. There was minimal adverse impact on state and scan-specific anxiety levels from completing the MRI scans. Completers experienced significantly less scan-specific anxiety during MRI 1 compared to non-completers (U = 33, z = -1.98, p < 0.05). 78% of those who withdrew during or post MRI 1 were positioned 'arms up'. Motion artefact negatively impacted image quality in 34% of scans. Participants commonly reported concerns during MRI; noise, claustrophobia and pain in upper limbs. CONCLUSION: Two thirds of participants tolerated two additional MR scans with minimal adverse impact on anxiety levels. IMPLICATIONS FOR PRACTICE: Patient arm positioning and comfort ought to be considered when introducing MR-Linac systems. A screening tool to identify those at high risk of non-completion should be developed.

Inter- and intra-fractional stability of rectal gas in pelvic cancer patients during MRIgRT.

PURPOSE: Due to the electron return effect (ERE) during magnetic resonance imaging guided radiotherapy (MRIgRT), rectal gas during pelvic treatments can result in hot spots of over-dosage in the rectal wall. Determining the clinical impact of this effect on rectal toxicity requires estimation of the amount and mobility (and stability) of rectal gas during treatment. We therefore investigated the amount of rectal gas and local inter- and intra-fractional changes of rectal gas in pelvic cancer patients. METHODS: To estimate the volume of gas present at treatment planning, the rectal gas contents in the planning computed tomography (CT) scans of 124 bladder, 70 cervical and 2180 prostate cancer patients were calculated. To estimate inter- and intra-fractional variations in rectal gas, 174 and 131 T2-w MRIs for six cervical and eleven bladder cancer patients were used. These scans were acquired during four scan-sessions (~20-25 min each) at various time-points. Additionally, 258 T2-w MRIs of the first five prostate cancer patients treated using MRIgRT at our center, acquired during each fraction, were analyzed. Rectums were delineated on all scans. The area of gas within the rectum delineations was identified on each MRI slice using thresholding techniques. The area of gas on each slice of the rectum was used to calculate the inter- and intra-fractional group mean, systematic and random variations along the length of the rectum. The cumulative dose perturbation as a result of the gas was estimated. Two approaches were explored: accounting or not accounting for the gas at the start of the scan-session. RESULTS: Intra-fractional variations in rectal gas are small compared to the absolute volume of rectal gas detected for all patient groups. That is, rectal gas is likely to remain stable for periods of 20-25 min. Larger volumes of gas and larger variations in gas volume were observed in bladder cancer patients compared with cervical and prostate cancer patients. For all patients, local cumulative dose perturbations per beam over an entire treatment in the order of 60 % were estimated when gas had not been accounted for in the daily adaption. The calculated dose perturbation over the whole treatment was dramatically reduced in all patients when accounting for the gas in the daily set-up image. CONCLUSION: Rectal gas in pelvic cancer patients is likely to remain stable over the course of an MRIgRT fraction, and also likely to reappear in the same location in multiple fractions, and can therefore result in clinically relevant over-dosage in the rectal wall. The over-dosage is reduced when accounting for gas in the daily adaption.

Delivering Functional Imaging on the MRI-Linac: Current Challenges and Potential Solutions.

Magnetic resonance imaging (MRI) is a highly versatile imaging modality that can be used to measure features of the tumour microenvironment including cell death, proliferation, metabolism, angiogenesis, and hypoxia. Mapping and quantifying these pathophysiological features has the potential to alter the use of adaptive radiotherapy planning. Although these methods are available for use on diagnostic machines, several challenges exist for implementing these functional MRI methods on the MRI-linear accelerators (linacs). This review considers these challenges and potential solutions.

The Potential Value of MRI in External-Beam Radiotherapy for Cervical Cancer.

The reference standard treatment for cervical cancer is concurrent chemoradiotherapy followed by magnetic resonance imaging (MRI)-guided brachytherapy. Improvements in brachytherapy have increased local control rates, but late toxicity remains high with rates of 11% grade ≥3. The primary clinical target volume (CTV) for external-beam radiotherapy includes the cervix and uterus, which can show significant inter-fraction motion. This means that generous margins are required to cover the primary CTV, increasing the radiation dose to organs at risk and, therefore, toxicity. A number of image-guided radiotherapy techniques (IGRT) have been developed, but motion can be random and difficult to predict prior to treatment. In light of the development of integrated MRI linear accelerators, this review discusses the potential value of MRI in external-beam radiotherapy. Current solutions for managing pelvic organ motion are reviewed, including the potential for online adaptive radiotherapy. The impacts of the use of MRI in tumour delineation and in the delivery of stereotactic ablative body radiotherapy (SABR) are highlighted. The potential role and challenges of using multi parametric MRI to guide radiotherapy are also discussed.