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PURPOSE: To assess the value of glutamate chemical exchange saturation transfer (GluCEST) after whole-brain radiotherapy (WBRT) as an imaging marker of radiation-induced brain injury (RBI) and to preliminarily show the feasibility of multiparametric MRI-guided organ at risk (OAR) avoidance. METHODS: Rats were divided into two groups: the control (CTRL) group (n = 9) and the RBI group (n = 9). The rats in the RBI group were irradiated with an X­ray radiator and then subjected to a water maze experiment 4 weeks later. In combination with high-performance liquid chromatography (HPLC), we evaluated the value of GluCEST applied to glutamate changes for RBI and investigated the effect of such changes on glutamatergic neuronal function. RESULTS: The average GluCEST values were markedly lower in the hippocampus and cerebral cortex. Positive correlations were observed between GluCEST values and regional homogeneity (ReHo) values in both the hippocampus and the cerebral cortex. HPLC showed a positive correlation with GluCEST values in the hippocampus. GluCEST values were positively correlated with spatial memory. CONCLUSION: GluCEST MRI provides a visual assessment of glutamate changes in RBI rats for monitoring OAR cognitive toxicity reactions and may be used as a biomarker of OAR avoidance as well as metabolism to facilitate monitoring and intervention in radiation damage that occurs after radiotherapy.

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Introduction: At our department we have a dedicated 1.5 Tesla MRI/HDR brachytherapy suite, which provides the possibility of repeated MRI scanning before, during and after applicator insertion and before and/or after irradiation for patients with advanced cervical cancer. In this study we analysed the effect of this adaptive workflow. We investigated the number of interventions, their impact on organ doses (OAR) and the respective dose differences between total prescribed and total delivered doses. Materials and methods: Seventy patients with locally advanced cervical cancer FIGO2009 stages IB-IVA, treated from June 2016 till August 2020, were retrospectively analysed. The standard brachytherapy schedule consisted of two applicator insertions and delivery of three or four HDR fractions.OARs were recontoured on the repeated MRI scans. The D2cm3 dose difference between total prescribed and total delivered dose for bladder, rectum, sigmoid and bowel were calculated. Results: In total 153 interventions were performed, 3 replacements of the applicator, 23 adaptations of needle positions, bladder filling was changed 74 times and repeated rectal degassing 53 times. The impact of the rectal interventions was on average -1.2 Gy EQD23. Dose differences between total delivered and total prescribed D2cm3 for bladder, rectum, sigmoid and bowel were -0.6, 0.3, 2.2 and -0.6 Gy EQD23, respectively. Conclusions: An MRI scanner integrated into the brachytherapy suite enables multiple interventions based on the scans before treatment planning and dose delivery. This allows for customized treatment according to the changing anatomy of the individual patient and a better estimation of the delivered dose.

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Background and purpose: Lung cancer is a leading cause of cancer-related mortality, and stereotactic body radiotherapy (SBRT) has become a standard treatment for early-stage lung cancer. However, the heterogeneous response to radiation at the tumor level poses challenges. Currently, standardized dosage regimens lack adaptation based on individual patient or tumor characteristics. Thus, we explore the potential of delta radiomics from on-treatment magnetic resonance (MR) imaging to track radiation dose response, inform personalized radiotherapy dosing, and predict outcomes. Materials and methods: A retrospective study of 47 MR-guided lung SBRT treatments for 39 patients was conducted. Radiomic features were extracted using Pyradiomics, and stability was evaluated temporally and spatially. Delta radiomics were correlated with radiation dose delivery and assessed for associations with tumor control and survival with Cox regressions. Results: Among 107 features, 49 demonstrated temporal stability, and 57 showed spatial stability. Fifteen stable and non-collinear features were analyzed. Median Skewness and surface to volume ratio decreased with radiation dose fraction delivery, while coarseness and 90th percentile values increased. Skewness had the largest relative median absolute changes (22 %-45 %) per fraction from baseline and was associated with locoregional failure (p = 0.012) by analysis of covariance. Skewness, Elongation, and Flatness were significantly associated with local recurrence-free survival, while tumor diameter and volume were not. Conclusions: Our study establishes the feasibility and stability of delta radiomics analysis for MR-guided lung SBRT. Findings suggest that MR delta radiomics can capture short-term radiographic manifestations of the intra-tumoral radiation effect.

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BACKGROUND AND PURPOSE: Fast and automated generation of treatment plans is desirable for magnetic resonance imaging (MRI)-guided adaptive radiotherapy (MRIgART). This study proposed a novel patient-specific auto-planning method and validated its feasibility in improving the existing online planning workflow. MATERIALS AND METHODS: Data from 40 patients with prostate cancer were collected retrospectively. A patient-specific auto-planning method was proposed to generate adaptive treatment plans. First, a population dose-prediction model (M0) was trained using data from previous patients. Second, a patient-specific model (Mps) was created for each new patient by fine-tuning M0 with the patient's data. Finally, an auto plan was optimized using the parameters derived from the predicted dose distribution by Mps. The auto plans were compared with manual plans in terms of plan quality, efficiency, dosimetric verification, and clinical evaluation. RESULTS: The auto plans improved target coverage, reduced irradiation to the rectum, and provided comparable protection to other organs-at-risk. Target coverage for the planning target volume (+0.61 %, P = 0.023) and clinical target volume 4000 (+1.60 %, P < 0.001) increased. V2900cGy (-1.06 %, P = 0.004) and V1810cGy (-2.49 %, P < 0.001) to the rectal wall and V1810cGy (-2.82 %, P = 0.012) to the rectum were significantly reduced. The auto plans required less planning time (-3.92 min, P = 0.001), monitor units (-46.48, P = 0.003), and delivery time (-0.26 min, P = 0.004), and their gamma pass rates (3 %/2 mm) were higher (+0.47 %, P = 0.014). CONCLUSION: The proposed patient-specific auto-planning method demonstrated a robust level of automation and was able to generate high-quality treatment plans in less time for MRIgART in prostate cancer.

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OBJECTIVES: Image-guided adaptive brachytherapy (IGABT) is the standard of care for patients with cervical cancer. The objective of this study was to compare the treatment outcomes and adverse effects of computed tomography (CT)-guided and magnetic resonance imaging (MRI)-guided scenarios. MATERIALS AND METHODS: Data of patients with cervical cancer treated using external beam radiotherapy followed by IGABT from 2012 to 2016 were retrospectively reviewed. CT-guided IGABT was compared with the three modes of MRI-guided IGABT: pre-brachytherapy (MRI Pre-BT) without applicator insertion for fusion, planning MRI with applicator in-place in at least 1 fraction (MRI ≥1Fx), and MRI in every fraction (MRI EveryFx). Patient characteristics, oncologic outcomes, and late radiation toxicity were analyzed using descriptive, survival, and correlation statistics. RESULTS: Overall, 354 patients were evaluated with a median follow-up of 60 months. The 5-year overall survival (OS) rates were 61.5%, 65.2%, 54.4%, and 63.7% with CT-guided, MRI PreBT, MRI ≥1Fx, and MRI EveryFx IGABT, respectively with no significant differences (p = 0.522). The 5-year local control (LC) rates were 92.1%, 87.8%, 80.7%, and 76.5% (p = 0.133), respectively, with a significant difference observed between the CT-guided and MRI ≥1Fx (p = 0.018). The grade 3-4 late gastrointestinal toxicity rates were 6% in the CT-guided, MRI ≥1Fx, and MRI EveryFx, and 8% in MRI PreBT. The grade 3-4 late genitourinary toxicity rates were 4% in the CT-guided, 2% in MRI PreBT, 1% in MRI ≥1Fx, and none in MRI EveryFx. No significant differences were observed in the oncologic and toxicity outcomes among MRI PreBT, MRI ≥1Fx, and MRI EveryFx. CONCLUSIONS: CT-guided IGABT yielded an acceptable 5-year OS, LC, and toxicity profile compared with all MRI scenarios and is a potentially feasible option in resource-limited settings.

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INTRODUCTION: This work reports on a systematic approach to select MRI sequences, quantify inter-observer image registration variation and determine patient positioning for the clinical implementation of MR-guided adaptive radiotherapy (MRgRT) in patients with oropharyngeal (H&N) and lung cancer. METHODS: A total of 30 participants (N=10 H&N and N=10 lung cancer patients and N=10 healthy participants) were scanned on the Elekta Unity Magnetic Resonance Linear Accelerator (MRL). Participant experience questionnaires were used to determine the most appropriate positioning device for lung treatments and tolerability of H&N immobilization devices within the confined MR Linac environment. Visual guided assessments (VGAs) completed by three observers (one oncologist and two radiographers) were used to determine the most suitable tissue weighting (using vendor-provided 3D T1w and T2w sequences) for online image registration. Offline MRI to CT and MRI to MRI rigid registrations were undertaken by nine radiographers using bony and soft tissue matching. Single-factor ANOVA and paired t-tests were utilized to determine the interobserver variation. RESULTS: Based on oncologist and patient feedback, lung cancer patients would be treated in a vac-bag with their arms by their sides, while H&N cancer patients would be immobilized using a 5-point fixation device and 5-point personalized thermoplastic shell. There was no clear preference for T1w or T2w images in the H&N cohort. However, observers preferred T2w sequences for tumour and organ at risk (OAR) visualization in the lung images. When a bony match was conducted, single-factor ANOVA tests showed no statistically significant differences between all H&N image registration types (p=0.09). For the soft-tissue registrations, T1w-CT and T1w-T1w registrations showed a statistically significant (p=0.01) reduction in inter-observer variability over T2w-CT registrations. Paired t-tests showed no statistically significant differences for bony or soft tissue matches using T1w or T2w sequences to the planning CT in the lung cohorts (p=0.63 and p=0.52, respectively). CONCLUSION: We describe the systematic approach to the selection of strategies for imaging, immobilization, and online image registration we used for H&N and lung cancer treatments on the MRL. This has facilitated the selection of the most appropriate adaptive MRgRT strategies for treating these sites at our institution.

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PURPOSE: The technological advancements in surgical robots compatible with magnetic resonance imaging (MRI) have created an indispensable demand for real-time deformable image registration (DIR) of pre- and intra-operative MRI, but there is a lack of relevant methods. Challenges arise from dimensionality mismatch, resolution discrepancy, non-rigid deformation and requirement for real-time registration. METHODS: In this paper, we propose a real-time DIR framework called MatchMorph, specifically designed for the registration of low-resolution local intraoperative MRI and high-resolution global preoperative MRI. Firstly, a super-resolution network based on global inference is developed to enhance the resolution of intraoperative MRI to the same as preoperative MRI, thus resolving the resolution discrepancy. Secondly, a fast-matching algorithm is designed to identify the optimal position of the intraoperative MRI within the corresponding preoperative MRI to address the dimensionality mismatch. Further, a cross-attention-based dual-stream DIR network is constructed to manipulate the deformation between pre- and intra-operative MRI, real-timely. RESULTS: We conducted comprehensive experiments on publicly available datasets IXI and OASIS to evaluate the performance of the proposed MatchMorph framework. Compared to the state-of-the-art (SOTA) network TransMorph, the designed dual-stream DIR network of MatchMorph achieved superior performance with a 1.306 mm smaller HD and a 0.07 mm smaller ASD score on the IXI dataset. Furthermore, the MatchMorph framework demonstrates an inference speed of approximately 280 ms. CONCLUSIONS: The qualitative and quantitative registration results obtained from high-resolution global preoperative MRI and simulated low-resolution local intraoperative MRI validated the effectiveness and efficiency of the proposed MatchMorph framework.

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PURPOSE: To investigate whether MRI-guided transrectal laser ablation is safe and effective for the treatment of lower urinary tract symptoms caused by BPH. MATERIALS AND METHODS: This single-center retrospective cohort study evaluated men who underwent MRI-guided transrectal laser ablation for BPH between February 2017 and July 2021. Age, prostate-specific antigen, prostate volume, prior surgical BPH treatments if any, International Prostate Symptom Score (IPSS) and Sexual Health Inventory of Men (SHIM) were collected. The primary outcome measures assessed were change in IPSS and SHIM 6, 12 and 24 months after laser ablation and adverse events. RESULTS: Fifty-two patients were included, having completed at least one follow-up survey. The mean patient age was 62.9 ± 5.7 years, and mean prostate volume was 80.2 ± 39.2 cc. Eighteen patients (34.6%) had received a prior BPH treatment. The IPSS scores dropped an average of 16.7 ± 7.0 (p < 0.001), 16.9 ± 7.5 (p < 0.001) and 17.1 ± 7.2 (p < 0.001) points from baseline at 6, 12 and 24 months, respectively. There was no statistically significant difference in IPSS score drop between patients who had received a prior BPH procedure and those who had not (p = 0.628). The SHIM scores showed a statistically insignificant increase at all time points. Nineteen patients (36.5%) reported a complication. There were 12 grade II complications (23%) and seven grade I complications (13.5%). There were no grade III or higher complications. CONCLUSION: Transrectal MRI-guided focal laser ablation is safe and effective for the treatment of lower urinary tract symptoms caused by BPH, with a significant improvement in symptom severity after 2 years.

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Objective: This retrospective study aims to assess the role of pre-contrast sequences of an MRI-guided breast biopsy (MRIB) exam in confident and accurate lesion site localization based on tissue landmarks. Methods: The charts of all consecutives MRIB that were performed between January 2018 and December 2020 were reviewed. The images of the eligible exams were analyzed by 3 breast radiologists. Each radiologist independently attempted to identify lesion site on pre-contrast MRIB sequences, while blinded to the post-contrast MRIB images. Confidence levels (I-confident, II-not confident, and III-unknown) were assigned by each reviewer. A fourth radiologist assessed the accuracy (≤5 mm-accurate, >5 mm-inaccurate) in lesion site localization using the actual biopsied lesion site and the post-contrast MRIB images as reference. Descriptive statistics were used to calculate the percentage of confidence and accuracy categories for each reviewer, with Chi-square tests applied to analyze relationships between categorical variables. Results: There were 174 female patients with 181 lesions eligible for the trial. When the lesion site is confidently identified on the pre-contrast MRIB images (level 1 confidence), mean grade 1 accuracy was 93.8% (P < .001). Accuracy decreased with Level II and III confidence (55.3% and 34.2% respectively). Up to 61.4% improved accuracy was demonstrated when combining the performance of 2 reviewers. No correlation was found between breast density, lesion morphology, or biopsy positioning with confidence level or accuracy grade. Conclusion: Careful review of the pre-contrast MRIB images and familiarization with the surrounding tissue landmarks are important steps in confidently and accurately detecting lesion site.

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Purpose To compare diffusion-weighted imaging (DWI) with thermal dosimetry as a noncontrast method to predict ablation margins in individuals with prostate cancer treated with MRI-guided focused ultrasound (MRgFUS) ablation. Materials and Methods This secondary analysis of a prospective trial (ClinicalTrials.gov no. NCT01657942) included 17 participants (mean age, 64 years ± 6 [SD]; all male) who were treated for prostate cancer using MRgFUS in whom DWI was performed immediately after treatment. Ablation contours from computed thermal dosimetry and DWI as drawn by two blinded radiologists were compared against the reference standard of ablation assessment, posttreatment contrast-enhanced nonperfused volume (NPV) contours. The ability of each method to predict the ablation zone was analyzed quantitively using Dice similarity coefficients (DSCs) and mean Hausdorff distances (mHDs). Results DWI revealed a hyperintense rim at the margin of the ablation zone. While DWI accurately helped predict treatment margins, thermal dose contours underestimated the extent of the ablation zone compared with the T1-weighted NPV imaging reference standard. Quantitatively, contour assessment between methods showed that DWI-drawn contours matched postcontrast NPV contours (mean DSC = 0.84 ± 0.05 for DWI, mHD = 0.27 mm ± 0.13) better than the thermal dose contours did (mean DSC = 0.64 ± 0.12, mHD = 1.53 mm ± 1.20) (P < .001). Conclusion This study demonstrates that DWI, which can visualize the ablation zone directly, is a promising noncontrast method that is robust to treatment-related bulk motion compared with thermal dosimetry and correlates better than thermal dosimetry with the reference standard T1-weighted NPV. Keywords: Interventional-Body, Ultrasound-High-Intensity Focused (HIFU), Genital/Reproductive, Prostate, Oncology, Imaging Sequences, MRI-guided Focused Ultrasound, MR Thermometry, Diffusionweighted Imaging, Prostate Cancer ClinicalTrials.gov Identifier no. NCT01657942 Supplemental material is available for this article. © RSNA, 2024.

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INTRODUCTION: This work reports on an unusual finding observed during image quality assessment in the preparation for the clinical implementation of breast magnetic resonance image-guided radiotherapy (MRIgRT) on a 1.5 Tesla (T) magnetic resonance linear accelerator (MR-Linac) (Elekta AB, Stockholm, Sweden). CASE AND OUTCOMES: A patient with T2 N0 M0 right breast invasive ductal carcinoma, receiving adjuvant radiotherapy, underwent two imaging sessions on the MR-Linac. The imaging protocol included T1- and T2-weighted (W) turbo spin echo (TSE) sequences, a T1W mDixon, and a T2W TSE navigated sequence acquired on end-expiration. All images were reconstructed in the axial plane. Images were assessed for image quality and appropriateness for use within the treatment pathway using visual grading analysis (VGA). An artefact in the right breast was noted independently by all observers. The patient's skin and medical notes were reviewed for possible explanation. The findings were discussed with the patient's responsible clinician, and subsequent referral to the local multi-disciplinary team (MDT) for radiologist review was made. On further investigation, the patient's images demonstrated a signal void in the subareolar region of the right breast coinciding with the surgical site. This was distal from the tumour bed and deemed unlikely to be related to a Magseed marker or intraoperative clips. The patient reported no history of nipple tattoo or piercing. There was nothing on clothing that this could be attributed to. DISCUSSION: Following MDT review, where all potential sources of signal void were considered, it was concluded that the cause was Magtrace, a superparamagnetic iron oxide tracer, recommended for sentinel lymph node localisation in patients with breast cancer in the United Kingdom. The artefact was characteristic of a magnetic susceptibility artefact. These can arise from local magnetic field inhomogeneities caused by the presence of the metal compounds in MagTrace. For breast MRIgRT on the MR-Linac, treatment verification and the possibility of real-time replanning is a critical aspect. The magnetic susceptibility artefact significantly inhibited plan adaption and confidence in the online image registration process making the patient ineligible for treatment on the MR-Linac. CONCLUSION: As part of ongoing work-up for breast MRIgRT, the screening of patients for Magtrace is now included. Optimisation of MR imaging sequences for radiotherapy planning and image review to minimise distortion are being developed.

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Magnetic resonance imaging is a novel imaging technique for guiding electrophysiology based ablation operations for atrial flutter and typical atrial fibrillation. When compared to standard electrophysiology ablation, this innovative method allows for better outcomes. Intra-procedural imaging is important for following the catheter in real time throughout the ablation operation while also seeing cardiac architecture and determining whether the ablation is being completed appropriately utilizing oedema sequences. At the same time, intra-procedural imaging allows immediate visualization of any complications of the procedure. We describe a case of a 67 year old male underwent an isthmus-cavo-tricuspid magnetic resonance-guided thermoablation procedure for atrial flutter episodes. During the procedure we noted an atypical focal thinning of the right atrial wall at the isthmus cava-tricuspidal zone. The post-procedural Black Blood T2 STIR showed an area of hyperintensity at the hepatic dome and glissonian capsule, which was consistent with intraparenchymal hepatic oedema, in close proximity to the atrial finding. Given the opportunity to direct monitoring of adjacent tissues, we aim to highlight with our case the ability of magnetic resonance-guided cardiac ablation to immediately detect peri-procedural complications in the ablative treatment of atrial fibrillation.

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Objective.To develop and validate a dose-of-the-day (DOTD) treatment plan verification procedure for liver and pancreas cancer patients treated with an magnetic resonance (MR)-Linac system.Approach.DOTD was implemented as an automated process that uses 3D datasets collected during treatment delivery. Particularly, the DOTD pipeline's input included the adapt-to-shape (ATS) plan-i.e. 3D-MR dataset acquired at beginning of online session, anatomical contours, dose distribution-and 3D-MR dataset acquired during beam-on (BON). The DOTD automated analysis included (a) ATS-to-BON image intensity-based deformable image registration (DIR), (b) ATS-to-BON contours mapping via DIR, (c) BON-to-ATS contours copying through rigid registration, (d) determining ATS-to-BON dosimetric differences, and (e) PDF report generation. The DIR process was validated by two expert reviewers. ATS-plans were recomputed on BON datasets to assess dose differences. DOTD analysis was performed retrospectively for 75 treatment fractions (12-liver and 5-pancreas patients).Main results.The accuracy of DOTD process relied on DIR and mapped contours quality. Most DIR-generated contours (99.6%) were clinically acceptable. DICE correlated with depreciation of DIR-based region of interest mapping process. The ATS-BON plan difference was found negligible (<1%). The duodenum and large bowel exhibited highest variations, 24% and 39% from fractional values, for 5-fraction liver and pancreas. For liver 1-fraction, a 62% variation was observed for duodenum.Significance.The DOTD methodology provides an automated approach to quantify 3D dosimetric differences between online plans and their delivery. This analysis offers promise as a valuable tool for plan quality assessment and decision-making in the verification stage of the online workflow.

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BACKGROUND: MR-integrated proton therapy is under development. It consists of the unique challenge of integrating a proton pencil beam scanning (PBS) beam line nozzle with an magnetic resonance imaging (MRI) scanner. The magnetic interaction between these two components is deemed high risk as the MR images can be degraded if there is cross-talk during beam delivery and image acquisition. PURPOSE: To create and benchmark a self-consistent proton PBS nozzle model for empowering the next stages of MR-integrated proton therapy development, namely exploring and de-risking complete integrated prototype system designs including magnetic shielding of the PBS nozzle. MATERIALS AND METHODS: Magnetic field (COMSOL Multiphysics ${\text{Multiphysics}}$ ) and radiation transport (Geant4) models of a proton PBS nozzle located at OncoRay (Dresden, Germany) were developed according to the manufacturers specifications. Geant4 simulations of the PBS process were performed by using magnetic field data generated by the COMSOL Multiphysics ${\text{Multiphysics}}$ simulations. In total 315 spots were simulated which consisted of a 40 × 30 cm 2 $40\times 30\,{\text{cm}}^{2}$ scan pattern with 5 cm spot spacings and for proton energies of 70, 100, 150, 200, and 220 MeV. Analysis of the simulated deflection at the beam isocenter plane was performed to determine the self-consistency of the model. The magnetic fringe field from a sub selection of 24 of the 315 spot simulations were directly compared with high precision magnetometer measurements. These focused on the maximum scanning setting of ± $\pm$  20 cm beam deflection as generated from the second scanning magnet in the PBS for a proton beam energy of 220 MeV. Locations along the beam line central axis (CAX) were measured at beam isocenter and downstream of 22, 47, 72, 97, and 122 cm. Horizontal off-axis positions were measured at 22 cm downstream of isocenter ( ± $\pm$  50, ± $\pm$  100, and ± $\pm$  150 cm from CAX). RESULTS: The proton PBS simulations had good spatial agreement to the theoretical values in all 315 spots examined at the beam line isocenter plane (0-2.9 mm differences or within 1.5 % of the local spot deflection amount). Careful analysis of the experimental measurements were able to isolate the changes in magnetic fields due solely to the scanning magnet contribution, and showed 1.9  ± $\pm$  1.2 µ T $\bf{\mu} {\text{T}}$ -9.4 ± $\pm$  1.2 µ T $\bf{\mu} {\text{T}}$ changes over the range of measurement locations. Direct comparison with the equivalent simulations matched within the measurement apparatus and setup uncertainty in all but one measurement point. CONCLUSIONS: For the first time a robust, accurate and self-consistent model of a proton PBS nozzle assembly has been created and successfully benchmarked for the purposes of advancing MR-integrated proton therapy research. The model will enable confidence in further simulation based work on fully integrated designs including MRI scanners and PBS nozzle magnetic shielding in order to de-risk and realize the full potential of MR-integrated proton therapy.

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AIMS: Prognosis of locally advanced pancreatic cancer (LAPC) remains poor with limited therapeutic options. Radiation therapy in pancreatic cancer has been restricted by the disease's proximity to radiosensitive organs at risk (OAR). However, stereotactic magnetic resonance-guided adaptive radiation therapy (SMART) has demonstrated promise in delivering ablative doses safely. We sought to report clinical outcomes from a UK-based Compassionate Access Programme that provided access to SMART to patients with LAPC. MATERIALS AND METHODS: This was a registry retrospective study conducted at a single centre with access to SMART. Patients with LAPC were treated with prescription dose of 40 Gy in 5 fractions. The planning objective was that 98% of PTV received ≥95% of the prescribed dose, prioritising duodenal, stomach and bowel UK SABR consortium constraints. Daily online adaptation was performed using magnetic resonance guidance and on-table re-optimisation. 0-3 months and > 3-month post-treatment-related toxicities, local progression-free survival, metastatic-free survival and overall survival were evaluated. RESULTS: 55 patients were treated with SMART at our institution from 2020 to 2022. Median follow-up from date of diagnosis was 17 months (range 5-37 months). Median age was 69.87% of patients underwent induction chemotherapy. 71% of patients reported 0-1 grade acute toxicity only. No grade >3 acute toxicity was reported. 5 patients (9%) reported a grade 3 toxicity (fatigue, nausea, abdominal pain, duodenal stricture). No grade >3 toxicity after 3 months was reported. 6 (10%) of patients had grade 3 toxicity (fatigue, nausea, abdominal pain, duodenal haemorrhage). Median local PFS post diagnosis was 17 months (95% CI 15.3-18.7). Median OS post diagnosis was 19 months (95% CI 15.9-22.1). One-year local control post SMART was 65%. CONCLUSION: This is the first UK-reported experience of MR-guided daily adaptive pancreatic SABR. SMART shows promise in delivering ablative doses with acceptable toxicity rates and good clinical outcomes.

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INTRODUCTION: Magnetic resonance guided focused ultrasound (MRgFUS) thalamotomy is an effective treatment for drug-resistant tremor. The most frequent side effects are ataxia, gait disturbance, paresthesias, dysgeusia, and hemiparesis. Here, we report the first case of thalamic hand dystonia rapidly occurring after MRgFUS thalamotomy of the ventral intermediate nucleus (V.im). CASE PRESENTATION: MRgFUS thalamotomy was performed in a 60-year-old left-handed patient for his disabling medically refractory essential tremor. The intervention resulted in a marked reduction of his action tremor. However, the patient developed an unvoluntary abnormal posture in his left hand a few days after the procedure with difficulty holding a cigarette between his fingers. Brain MRI revealed the expected MRgFUS lesion within the right V.im as well as an extension of the lesion anteriorly to the V.im in the ventro-oralis nucleus. Tractography showed that the lesion disrupted the dentato-rubro-thalamic tract as expected with a lesion suppressing tremor. However, the lesion also was interrupted fibers connecting to the superior frontal and pre-central cortices (primary motor cortex, premotor cortex, and supplementary area). We hypothesized that the interventional MRgFUS thalamotomy was slightly off target, which induced a dysfunction within the cortico-striato-thalamo-cortical network and the cerebello-thalamo-cortical pathway reaching a sufficient threshold of basal ganglia/cerebellum circuitry interference to induce dystonia. CONCLUSION: This rare side effect emphasizes the risk of imbalance within the dystonia network (i.e., basal ganglia-cerebello-thalamo-cortical circuit) secondary to V.im thalamotomy.

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BACKGROUND: The advantages of proton therapy can be further enhanced with online magnetic resonance imaging (MRI) guidance. One of the challenges in the realization of MRI-guided proton therapy (MRPT) is accurately calculating the radiation dose in the presence of magnetic fields. PURPOSE: This study aims to develop an efficient and accurate proton dose calculation algorithm adapted to the presence of magnetic fields. METHODS: An analytical-numerical radiation dose calculation algorithm, Proton and Ion Dose Engine (PRIDE), was developed. The algorithm combines the pencil beam algorithm (PBA) with a novel iterative voxel-based ray-tracing algorithm. The new ray-tracing method uses fewer assumptions and ensures broader applicability for proton beam trajectory prediction in magnetic fields, and has been compared to Wolf's method and Schellhammer's method. The accuracy of PRIDE algorithm was validated on three phantoms and two practical plans (one single-field water plan and one prostate tumor plan) in different magnetic field strengths up to 3.0 T. The validation was performed by comparing the results against the Monte Carlo (MC) simulations, using the global gamma index criteria of 2%/2 mm and 3%/3 mm with a 10% threshold. RESULTS: PRIDE showed good agreement with MC in homogeneous and slab heterogeneous phantom, achieving gamma passing rates (%GPs) above 99% for 2%/2 mm criteria when magnetic field strength is not greater than 1.5 T. Although the agreement decreased for scenarios involving high proton energy (240 MeV) and strong magnetic field (3.0 T), the 2%/2 mm %GPs still remained above 98%. In lateral heterogeneous phantom, the accuracy of PRIDE decreased due to the PBA's limitation. For the two practical plans in different magnetic fields, %GPs exceeded 98% and 99% for 2%/2 mm and 3%/3 mm criteria, respectively. CONCLUSIONS: PRIDE can perform efficient and accurate proton dose calculation in magnetic fields up to 3.0 T, and is expected to work as a useful tool for proton dose calculation in MRPT.

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HERMES is a phase II trial of MRI-guided daily-adaptive radiotherapy (MRIgART) randomising men with localised prostate cancer to either 2-fractions of SBRT with a boost to the tumour or 5-fraction SBRT. In the context of this highly innovative regime the dose delivered must be carefully considered. The first ten patients recruited to HERMES were analysed in order to establish the dose received by the targets and organs at risk (OARS) in the context of intrafraction motion. A regression analysis was performed to measure how the volume of air within the rectum might further impact rectal dose secondary to the electron return effect (ERE). One hundred percent of CTV target objectives were achieved on the MRI taken prior to beam-on-time. The post-delivery MRI showed that high-dose CTV coverage was achieved in 90% of sub-fractions (each fraction is delivered in two sub-fractions) in the 2-fraction cohort and in 88% of fractions the 5-fraction cohort. Rectal D1 cm3 was the most exceeded constraint; three patients exceeded the D1 cm3 < 20.8 Gy in the 2-fraction cohort and one patient exceeded the D1 cm3 < 36 Gy in the 5-fraction cohort. The volume of rectal gas within 1 cm of the prostate was directly proportional to the increase in rectal D1 cm3, with a strong (R = 0.69) and very strong (R = 0.90) correlation in the 2-fraction and 5-fraction cohort respectively. Dose delivery specified in HERMES is feasible, although for some patients delivered doses to both target and OARs may vary from those planned.

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Contrast-enhanced breast MRI has an established role in aiding in the detection, evaluation, and management of breast cancer. This article discusses MRI sequences, the clinical utility of MRI, and how MRI has been evaluated for use in breast radiotherapy treatment planning. We highlight the contribution of MRI in the decision-making regarding selecting appropriate candidates for breast conservation therapy and review the emerging role of MRI-guided breast radiotherapy.

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Introduction: Magnetic resonance imaging (MRI)-guided wire localization can be applied to assist to remove suspected breast lesions accurately. This study aimed to evaluate the clinical application value of this technique in Chinese women. Methods: A total of 126 patients (131 lesions) who had underwent such technique in our hospital from April 2017 to June 2023 were enrolled. 1.5T MRI system and a wire localization device were used. Image characteristics, clinical features and postoperative pathology were collected and analyzed. Results: All of 126 patients (131 lesions) were successfully localized by MRI and excised for biopsy. There were 39 malignant lesions (29.77%) and 92 benign lesions (70.23%). There was no significant correlation between the morphology of DCE-MRI and the ratio of malignant lesions (P=0.763), while there was a statistical correlation between the BPE, TIC curve and the malignancy rate (P<0.05). All the lesions were assessed according to BI-RADS category of MRI (C4A=77, C4B=40, C4C=12, C5=2). The malignancy rates were as follows: 16.88% for 4A lesions (13/77), 37.50% for 4B lesions (15/40), 75.00% for 4C lesions (9/12) and 100% for 5 lesions (2/2). There was a significant correlation between the BI-RADS category and the incidence of benign-to-malignant lesions (P<0.001). Conclusion: MRI-guided wire localization can assist to remove suspected breast lesions early, safely and accurately. This technique makes up for the deficiency of X-ray and ultrasound, improves the accuracy of diagnosis and resection therapy in intraductal carcinoma and early invasive carcinoma, and helps to improve the the prognosis of breast cancer.