Abstract
In recent years, we have seen the integration of magnetic resonance imaging (MRI) simulators into radiotherapy centres and the emergence MR linear accelerators (MR‐linac). Currently, there are limited studies to demonstrate the clinical effectiveness of MRI guided radiotherapy (MRIgRT) treatment for breast cancer patients. The objective of this scoping review was to identify and map the existing evidence surrounding the clinical implementation of MRIgRT for breast cancer patients. We also identified the challenges and knowledge gaps in the literature. The scoping review was reported in accordance with the Preferred Reporting Items for Systematic reviews and Meta‐Analysis (PRISMA) extension for Scoping Reviews reporting guidelines. Titles and abstracts were screened by two independent reviewers. Quantitative and qualitative data were extracted and summarised using thematically organised tables. Results identify that accelerated partial breast irradiation (APBI) is the most common form of treatment for MRIgRT. The presence of the magnet does not affect target coverage or violate organ at risk (OAR) constraints compared to standard radiotherapy methods. Consideration is advised for skin and chest wall (CW) due to the electron return effect (ERE) and areas such as armpit and chin due to the electron stream effect (ESE). Clinically, bolus has been used to protect and prevent unwanted dose in these areas. Overall treatment for APBI on the MR‐linac is feasible.
Highlights
The development of magnetic resonance imaging-guided radiation therapy (MRIgRT) has greatly improved imaging visibility in the radiation therapy (RT) domain
Magnetic resonance imaging (MRI) uses a strong magnetic field to provide superior soft tissue delineation and an increased sensitivity for tumour detection compared to CBCT.[1]
Studies were divided between MR planning dosimetry, MR treatment studies and one quality assurance study.[32]
Summary
The development of magnetic resonance imaging-guided radiation therapy (MRIgRT) has greatly improved imaging visibility in the radiation therapy (RT) domain. The system has since evolved into the Elekta Unity system.[3] The MRIdian (ViewRay Inc., Mountain View, CA, USA) is an alternative system, initially designed with three 60Co sources 120 degrees apart and equipped with a 0.35 T static MRI system.[4] A more recent generation has replaced this system, with a 6 MV flattening filter free linac and a 0.35 T superconducting magnet.[5] These machines acquire intrafractional images with increased target and organ at risk (OAR) visibility, making online planning adaptations possible and enabling a more personalised treatment approach for patients.[6] To improve the integration of MR-linacs within departments, MR simulators are being used for preliminary planning scans These machines include flat table tops, localisation for stabilisation equipment and external localising lasers.[7] Imaging on the MR simulator or MR-linac do not contribute any extra dose to the patient compared to CBCT, which is desirable when considering the ‘as low as reasonably achievable’ (ALARA) principle.
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