Patient positioning and immobilization procedures for hybrid MR-Linac systems

Abstract

Hybrid magnetic resonance (MR)-guided linear accelerators represent a new horizon in the field of radiation oncology. By harnessing the favorable combination of on-board MR-imaging with the possibility to daily recalculate the treatment plan based on real-time anatomy, the accuracy in target and organs-at-risk identification is expected to be improved, with the aim to provide the best tailored treatment. To date, two main MR-linac hybrid machines are available, Elekta Unity and Viewray MRIdian. Of note, compared to conventional linacs, these devices raise practical issues due to the positioning phase for the need to include the coil in the immobilization procedure and in order to perform the best reproducible positioning, also in light of the potentially longer treatment time. Given the relative novelty of this technology, there are few literature data regarding the procedures and the workflows for patient positioning and immobilization for MR-guided daily adaptive radiotherapy. In the present narrative review, we resume the currently available literature and provide an overview of the positioning and setup procedures for all the anatomical districts for hybrid MR-linac systems.

Implementation of Magnetic Resonance Imaging-Guided Radiation Therapy in Routine Care: Opportunities and Challenges in the United States

“… 17 , 19 The MR-Linac also allows therapy in fewer sessions with a higher dose of radiation therapy, also called hypofractionation, hence, permitting a shorter treatment. 20 , 21 This can be beneficial in a case like localized prostate cancer 22 , 23 , 24 because traditional external beam radiation therapy often varies from 5, 20, to 39 treatment sessions. 25 …”

Novel modified patient immobilisation device with an integrated coil support system for MR-guided online adaptive radiotherapy in the management of brain and head-and-neck tumours

“…There is a paucity of literature on immobilisation and support devices in the MRgRT setting. Many institutions use customised in-house developments to address this issue [9]. In addition, to our best knowledge, only one research group has published their initial experience in treating primary and recurrent head-and-neck cancers on the Viewray system [11,12].…”

“…The different patient treatment setups have been previously described [9]. Briefly, there are two different set-ups for treatment of brain and H&N. For treatments of brain targets, a posterior receiver coil is placed on the couch and the HeadSTEP (HS) system (IT-V Innsbruck, Austria) is positioned on top of the posterior coil and mounted on the table using an indexing bar.…”

“…Manufacturers are required to guarantee MRI compatibility. Our group recently published a multi-institutional joint review on patient and immobilisation procedures on MRgRT treatment platforms [9]. The Viewray MRIdian system has been in clinical use at our clinic since early 2020.…”

1.5T MR-Guided Daily Adaptive Stereotactic Body Radiotherapy for Prostate Re-Irradiation: A Preliminary Report of Toxicity and Clinical Outcomes

“…The same approach was used for daily online ‘adapt-to-shape’ (ATS) workflow. For the OARs, the following constraints were applied for baseline treatment planning and for all the daily-adapted sessions: V10<40%, V18<20% for rectum; V10<25%, V18<15% for bladder; Dmax<30Gy for urethra; V24<10% for femurs; V24<50% for penile bulb ( 14 ).…”