Abstract
The first MRIdian® MR linear accelerator (MR-Linac; ViewRay, Oakwood Village, Ohio) in the United Kingdom went live in December 2019 following a record installation time. Stereotactic MRI-guided Adaptive Radiotherapy (SMART) has since been implemented and has advantages of excellent soft tissue definition of both target and organs at risk (OARs), real-time target and OAR visualisation on cine-MRI, daily recontouring of target and critical OARs with live online plan adaptation/re-optimisation, and automatic respiratory-gated treatment delivery. We present a multi-disciplinary narrative and technical description of how this innovative technique was implemented for hepatobiliary (HPB) cancers. In particular, we explain how a collaborative approach and desire to push the boundaries and improve outcomes enabled 50 patients to be treated in the first five months, many with technically challenging tumours not always deliverable on other platforms. Physics, dosimetry, radiographer, and clinician perspectives on implementing SMART are presented. MRIdian® single fraction lung stereotactic ablative radiotherapy (SABR) will shortly be implemented along with innovative research in conjunction with our academic partners.
Highlights
MR linear accelerator (MR-Linac) technology holds great promise for patients with tumours in challenging anatomical locations, such as the liver, pancreas and upper abdomen, via a paradigm shift in image guidance combined with an online adaptation of target volumes and organs at risk (OARs) and a re-optimisation of treatment plans
There are currently two operational systems - Elekta’s Unity® (Elekta, Stockholm, Sweden) and ViewRay’s MRIdian® (ViewRay, Oakwood Village, Ohio) [1]. Whilst they are used for conventional radiotherapy or stereotactic ablative radiotherapy (SABR), we believe the greatest therapeutic yield derives from the latter and have used MRIdian® solely as a SABR platform
Treatment delivery is automatically breath-hold gated so the dose is only delivered when positioning is optimal, removing the need for an internal target volume (ITV), reducing the planning target volume (PTV) margin and volume of normal tissue irradiated
Summary
MR linear accelerator (MR-Linac) technology holds great promise for patients with tumours in challenging anatomical locations, such as the liver, pancreas and upper abdomen, via a paradigm shift in image guidance combined with an online adaptation of target volumes and organs at risk (OARs) and a re-optimisation of treatment plans. With the increased confidence given by the soft tissue definition of the MRIdian®, recontouring of targets and OARs and daily plan re-optimisation, and automatic respiratory gating with live cine-MRI, it has been possible to dose escalate primary pancreatic cancer from 33 Gy in five fractions to 50 Gy in five fractions [19] This has been achieved with all OARs in tolerance and to date, no acute >grade 3 toxicity has been observed. Adapting cases involving liver and pancreas tumours with their surrounding OARs requires a suitable accreditation process This included a specific radiological anatomy training day where consultants buddied up with clinicians of different site-specialisations and reviewed MRIdian® scans of both the abdomen and pelvis with radiologist supervision.
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