MR-LINAC, a New Partner in Radiation Oncology: Current Landscape.
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ABSTRACT:
SUBMITTER: Ocanto A
PROVIDER: S-EPMC10813892 | biostudies-literature | 2024 Jan
REPOSITORIES: biostudies-literature
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MR-LINAC, a New Partner in Radiation Oncology: Current Landscape.
Ocanto Abrahams A Torres Lisselott L Montijano Miguel M Rincón Diego D Fernández Castalia C Sevilla Beatriz B Gonsalves Daniela D Teja Macarena M Guijarro Marcos M Glaría Luis L Hernánz Raúl R Zafra-Martin Juan J Sanmamed Noelia N Kishan Amar A Alongi Filippo F Moghanaki Drew D Nagar Himanshu H Couñago Felipe F
Cancers 20240108 2
Technological advances in radiation oncology are oriented towards improving treatment precision and tumor control. Among these advances, magnetic-resonance-image-guided radiation therapy (MRgRT) stands out, with technological advances to deliver targeted treatments adapted to a tumor's anatomy on the day while minimizing incidental exposure to organs at risk, offering an unprecedented therapeutic advantage compared to X-ray-based IGRT delivery systems. This new technology changes the traditional ...[more]
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Project description:Background and objectiveMagnetic resonance guided radiotherapy (MRgRT) is an emerging technological innovation with more and more institutions gaining clinical experience in this new field of radiation oncology. The ability to better visualize both tumors and healthy tissues due to excellent soft tissue contrast combined with new possibilities regarding motion management and the capability of online adaptive radiotherapy might increase tumor control rates while potentially reducing the risk of radiation-induced toxicities. As conventional computed tomography (CT)-based image guidance methods are insufficient for adaptive workflows in abdominal tumors, MRgRT appears to be an optimal method for this tumor site. The aim of this narrative review is to outline the opportunities and challenges in magnetic resonance guided radiation therapy in gastrointestinal cancers.MethodsWe searched for studies, reviews and conceptual articles, including the general technique of MRgRT and the specific utilization in gastrointestinal cancers, focusing on pancreatic cancer, liver metastases and primary liver cancer, rectal cancer and esophageal cancer.Key content and findingsThis review is highlighting the innovative approach of MRgRT in gastrointestinal cancer and gives an overview of the currently available literature with regard to clinical experiences and theoretical background.ConclusionsMRgRT is a promising new tool in radiation oncology, which can play off several of its beneficial features in the specific field of gastrointestinal cancers. However, clinical data is still scarce. Nevertheless, the available literature points out large potential for improvements regarding dose coverage and escalation as well as the reduction of dose exposure to critical organs at risk (OAR). Further prospective studies are needed to demonstrate the role of this innovative technology in gastrointestinal cancer management, in particular trials that randomly compare MRgRT with conventional CT-based image-guided radiotherapy (IGRT) would be of high value.
| S-EPMC11399841 | biostudies-literature
Project description:PurposeAdaptive stereotactic body radiation therapy (SBRT) for prostate cancer (PC) by the 1.5 T MR-linac currently requires online planning by an expert user. A fully automated and user-independent solution to adaptive planning (mCycle) of PC-SBRT was compared with user's plans for the 1.5 T MR-linac.Methods and materialsFifty adapted plans on daily magnetic resonance imaging scans for 10 patients with PC treated by 35 Gy (prescription dose [Dp]) in 5 fractions were reoptimized offline from scratch, both by an expert planner (manual) and by mCycle. Manual plans consisted of multicriterial optimization (MCO) of the fluence map plus manual tweaking in segmentation, whereas in mCycle plans, the objectives were sequentially optimized by MCO according to an a-priori assigned priority list. The main criteria for planning approval were a dose ≥95% of the Dp to at least 95% of the planning target volume (PTV), V33.2 (PTV) ≥ 95%, a dose less than the Dp to the hottest cubic centimeter (V35 ≤ 1 cm3) of rectum, bladder, penile bulb, and urethral planning risk volume (ie, urethra plus 3 mm isotropically), and V32 ≤ 5%, V28 ≤ 10%, and V18 ≤ 35% to the rectum. Such dose-volume metrics, plus some efficiency and deliverability metrics, were used for the comparison of mCycle versus manual plans.ResultsmCycle plans improved target dose coverage, with V33.2 (PTV) passing on average (±1 SD) from 95.7% (±1.0%) for manual plans to 97.5% (±1.3%) for mCycle plans (P < .001), and rectal dose sparing, with significantly reduced V32, V28, and V18 (P ≤ .004). Although at an equivalent number of segments, mCycle plans consumed moderately more monitor units (+17%) and delivery time (+9%) (P < .001), whereas they were generally faster (-19%) in terms of optimization times (P < .019). No significant differences were found for the passing rates of locally normalized γ (3 mm, 3%) (P = .059) and γ (2 mm, 2%) (P = .432) deliverability metrics.ConclusionsIn the offline setting, mCycle proved to be a trustable solution for automated planning of PC-SBRT on the 1.5 T MR-linac. mCycle integration in the online workflow will free the user from the challenging online-optimization task.
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Project description:BackgroundGadolinium-based contrast is often used when acquiring MR images for radiation therapy planning for better target delineation. In some situations, patients may still have residual MRI contrast agents in their tissue while being treated with high-energy radiation. This is especially true when MRI contrast agents are administered during adaptive treatment replanning for patients treated on MR-Linac systems.PurposeThe purpose of this study was to analyze the molecular stability of MRI contrast agents when exposed to high energy photons and the associated secondary electrons in a 1.5T MR-Linac system. This was the first step in assessing the safety of administering MRI contrast agents throughout the course of treatment.Materials and methodsTwo common MRI contrast agents were irradiated with 7 MV photons to clinical dose levels. The irradiated samples were analyzed using liquid chromatography-high resolution mass spectrometry to detect degradation products or conformational alterations created by irradiation with high energy photons and associated secondary electrons.ResultsNo significant change in chemical composition or displacement of gadolinium ions from their chelates was discovered in samples irradiated with 7 MV photons at relevant clinical doses in a 1.5T MR-Linac. Additionally, no significant correlation between concentrations of irradiated MRI contrast agents and radiation dose was observed.ConclusionThe chemical composition stability of the irradiated contrast agents is promising for future use throughout the course of patient treatment. However, in vivo studies are needed to confirm that unexpected metabolites are not created in biological milieus.
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Project description:Background and purposeDiffusion-weighted imaging (DWI) for treatment response monitoring is feasible on hybrid magnetic resonance linear accelerator (MR-linac) systems. The MRI scanner of the Elekta Unity system has an adjusted design compared to diagnostic scanners. We investigated its impact on measuring the DWI-derived apparent diffusion coefficient (ADC) regarding three aspects: the choice of b-values, the spatial variation of the ADC, and scanning during radiation treatment. The aim of this study is to give recommendations for accurate ADC measurements on Unity systems.Materials and methodsSignal-to-noise ratio (SNR) measurements with increasing b-values were done to determine the highest bvalue that can be measured reliably. The spatial variation of the ADC was assessed on six Unity systems with a cylindrical phantom of 40 cm diameter. The influence of gantry rotation and irradiation was investigated by acquiring DWI images before and during treatment of 11 prostate cancer patients.ResultsOn the Unity system, a maximum b-value of 500 s/mm2 should be used for ADC quantification, as a trade-off between SNR and diffusion weighting. Accurate ADC values were obtained within 7 cm from the iso-center, while outside this region ADC values deviated more than 5%. The ADC was not influenced by the rotating linac or irradiation during treatment.ConclusionWe provide Unity system specific recommendations for measuring the ADC. This will increase the consistency of ADC values acquired in different centers on the Unity system, enabling large cohort studies for biomarker discovery and treatment response monitoring.
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Project description:Purpose Resident physicians use social media (SM) for many reasons. We sought to characterize current SM use by radiation oncology (RO) trainees for education and professional development. Methods and Materials An anonymous 40-question survey was sent by e-mail to RO residents in the 2018 to 2019 academic year. SM platform use, time spent on SM, professional use, and opinions regarding SM use were assessed. Descriptive statistics and a univariate logistic regression analysis were performed to identify factors associated with perceptions of SM and spending >25% of SM time for academic or professional purposes. Results Of the 615 residents surveyed, 149 responded (24% response rate). Facebook (73%), theMednet (62%), Instagram (59%), Twitter (57%), and Doximity (50%) were the top SM platforms used. Most respondents (53%) reported <25% of overall SM time on professional/academic purposes, and 21% reported using SM >60 minutes per day over the past week. Residents with an RO mentor on SM (n = 35; 24%; odds ratio [OR]: 2.79; 95% confidence interval [CI], 1.29-6.08; P = .010), those participating in RO discussions on SM (n = 71; 48%; OR: 2.85; 95% CI, 1.42-5.72; P = .003), and those interacting with professional societies (n = 69; 46%; OR: 7.11; 95% CI, 3.32-15.24; P < .001) were more likely to spend >25% of their SM time on professional/academic purposes. The vast majority of respondents agreed that SM exposed them to novel educational content (82%) and was helpful for career development (65%). In addition, 69% agreed that SM can improve clinical skills and knowledge. A substantial minority agreed that SM distracts them from studying (38%) or they felt pressure to have a SM presence (29%). Conclusions Most RO residents reported that SM provides novel educational content and can help with career development. Potential disadvantages of SM for trainees may include distraction and pressure to maintain a SM presence. SM use by RO trainees merits further research to optimize its potential for education and professional development.
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| S-EPMC11759539 | biostudies-literature
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| S-EPMC8518312 | biostudies-literature
Project description:PurposeThis study analyzes assessments within radiation oncology (RO) to determine characteristics of existing assessment methods and then report resident perceptions of these methods. We hypothesize familiarity with evaluation methods is predictive of the perceived utility of evaluations and behavioral changes.Methods and materialsThis study was conducted in 2 phases. Phase 1 involved requesting resident evaluation forms from RO residency programs to assess the Accreditation Council for Graduate Medical Education 6 Core Competencies. Analysis of variance was used to determine any significant differences between institutions or categories of questions. In phase 2, RO residents were surveyed about familiarity with the Accreditation Council for Graduate Medical Education Milestones and their perceptions about the current methods. Responses to questions were further analyzed using linear regression models.ResultsIn phase 1, forms were obtained from 13 institutions, and they were based on the 6 Core Competencies with an average of 19 questions (standard deviation, 11; range, 5-47) in total. Analysis of variance did not show significant variation in the number of questions between the categories (F = 0.78, P = .6). A significant difference in the mean number of questions used for assessing each of the competencies was found between institutions (F = 6.6, P < .01). In phase 2, a majority of surveyed residents reported being "not" or only "slightly familiar" with the competencies (59.6%) and the factors used to assess them (73.1%). Resident-reported familiarity with the evaluation methods was not found to be a significant predictor of likelihood of changing postevaluation (coefficient = 0.41, P = .204), intimidation from receiving evaluations (coefficient = -0.06, P = .792), stress of receiving evaluations (coefficient = -0.11, P = .62), or usefulness of evaluations (coefficient = -0.02, P = .83).ConclusionsFamiliarity with evaluation methods is not correlated with perceptions or behavioral changes necessitating further investigation of alternative predictor variables. Despite the low familiarity with evaluation tools, most residents reported that evaluations were useful and likely to elicit changes in their behaviors and practice, highlighting the value of current evaluation methods.
| S-EPMC10172714 | biostudies-literature
Project description:The purpose of this study was to describe our experience with 1.0T MR-SIM including characterization, quality assurance (QA) program, and features necessary for treatment planning. Staffing, safety, and patient screening procedures were developed. Utilization of an external laser positioning system (ELPS) and MR-compatible couchtop were illustrated. Spatial and volumetric analyses were conducted between CT-SIM and MR-SIM using a stereotactic QA phantom with known landmarks and volumes. Magnetic field inhomogeneity was determined using phase difference analysis. System-related, in-plane distortion was evaluated and temporal changes were assessed. 3D distortion was characterized for regions of interest (ROIs) 5-20 cm away from isocenter. American College of Radiology (ACR) recommended tests and impact of ELPS on image quality were analyzed. Combined ultrashort echotime Dixon (UTE/Dixon) sequence was evaluated. Amplitude-triggered 4D MRI was implemented using a motion phantom (2-10 phases, ~ 2 cm excursion, 3-5 s periods) and a liver cancer patient. Duty cycle, acquisition time, and excursion were evaluated between maximum intensity projection (MIP) datasets. Less than 2% difference from expected was obtained between CT-SIM and MR-SIM volumes, with a mean distance of < 0.2 mm between landmarks. Magnetic field inhomogeneity was < 2 ppm. 2D distortion was < 2 mm over 28.6-33.6 mm of isocenter. Within 5 cm radius of isocenter, mean 3D geometric distortion was 0.59 ± 0.32 mm (maximum = 1.65 mm) and increased 10-15 cm from isocenter (mean = 1.57 ± 1.06 mm, maximum = 6.26 mm). ELPS interference was within the operating frequency of the scanner and was characterized by line patterns and a reduction in signal-to-noise ratio (4.6-12.6% for TE = 50-150 ms). Image quality checks were within ACR recommendations. UTE/Dixon sequences yielded detectability between bone and air. For 4D MRI, faster breathing periods had higher duty cycles than slow (50.4% (3 s) and 39.4% (5 s), p < 0.001) and ~fourfold acquisition time increase was measured for ten-phase versus two-phase. Superior-inferior object extent was underestimated 8% (6 mm) for two-phase as compared to ten-phase MIPs, although < 2% difference was obtained for ≥ 4 phases. 4D MRI for a patient demonstrated acceptable image quality in ~ 7 min. MR-SIM was integrated into our workflow and QA procedures were developed. Clinical applicability was demonstrated for 4D MRI and UTE imaging to support MR-SIM for single modality treatment planning.
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