Tumours are prone to move relative to healthy tissue and organs-at-risk (OARs) as a cancer patient undergoes a course of radiotherapy – and can even change position during an individual treatment session. The ability of MR-guided radiotherapy (MRgRT) systems like the Elekta Unity MR-Linac to detect that target motion and adapt therapy accordingly – in effect, helping clinicians to “see what they treat” in real time – points the way to a more personalized radiation oncology tailored to the unique requirements of each patient. That end game, it seems, is edging ever closer with the clinical roll-out of Elekta’s Comprehensive Motion Management (CMM) upgrade for the Unity treatment system, with real-time tumour tracking and automatic gating as the underpinnings for online plan adaptation.

Among the early-adopting clinical customers for CMM is US-based University of Iowa Health Care. At its main radiation oncology clinic in Iowa City, this integrated cancer centre treats around 1600 patients each year using an all-Elekta suite of five external-beam radiotherapy systems: an Elekta Unity MR-Linac; three Versa HD machines (all with onboard imaging; one with HexaPOD robotic table); and a Leksell Gamma Knife Icon (for stereotactic radiosurgery of brain lesions). “We’ve been treating a range of indications with the Unity system over the past four-and-a-half years – mostly prostate, liver, pancreas as well as oligometastatic cancers,” explains Daniel Hyer, professor of radiation oncology and director of clinical physics at University of Iowa Health Care.

A catalyst for clinical innovation

Fast forward to September 2023 and the University of Iowa’s introduction of the CMM upgrade on its Elekta Unity MR-Linac – a clinical innovation that yielded immediate and significant impacts for Hyer and the multidisciplinary care team. “During our first week live with CMM,” he notes, “the system gated the beam during unexpected motion of a pelvic node. On another patient, we were able to perfectly track a target next to the heart despite cardiac and respiratory motion. Ultimately, we expect that CMM will enable us to treat many of our lung cases on the Elekta Unity system.”

It’s not hard to see why. Put simply, CMM’s motion-management features – tracking the tumour target automatically and responding to any movement in real-time – are fundamental to improving the accuracy of beam delivery and, in turn, enhancing therapeutic outcomes. “The core innovation with CMM,” notes Hyer, “is that the Unity system now actively tracks the tumour target on the live imaging and shuts the beam off automatically if the target moves outside its planned envelope of motion. These automated gating techniques can be free-breathing or when the patient is in breath-hold.”

Operationally, CMM supports three workflows to manage the treatment of tumour targets subject to periodic breathing motion. There are two free-breathing workflows (free-breathing exhale and free-breathing average) that avoid the need for the patient to hold their breath during radiation delivery – a challenging proposition for many – while predictive algorithms ensure precise motion management with virtually zero latency on target tracking.

In contrast, the breath-hold technique sees the patient coached to hold their breath while the Unity system acquires the daily 3D MR image in a single breath-hold (with automatic gating to ensure the treatment is delivered only during subsequent breath-holds). For unexpected non-respiratory motion – owing to rectal gas, say, or bladder-filling – the so-called exception gating strategy is used to track the tumour target in real-time, with the radiation being paused if the target moves out of tolerance.

In this way, CMM has already opened up new treatment pathways for the Iowa radiation oncology team, with five lung cancer cases treated on the upgraded Unity system in December alone (versus two lung patients on the MR-Linac in the preceding four years). “Previously with lung lesions,” notes Hyer, “we didn’t want to treat the entire motion envelope.” In the case of a lung tumour that moves 15–20 mm, for example, all of that motion had to be accommodated prior to CMM – which means a lot of healthy tissue being irradiated. “Now we can cut that volume down thanks to CMM,” Hyer adds. “If the patient is free-breathing, but we only want to treat a subset of that motion – say 5 mm – we can design the treatment plan accordingly and ensure the treatment beam turns on and off automatically as required.”

Another area of clinical innovation with the MR-Linac relates to the treatment of pelvic and prostate nodes. In this case, CMM enables Hyer and colleagues to rapidly shift the plan to account for systematic changes in target position that might occur during the treatment session – thereby circumventing the delay and workflow inefficiencies associated with reimaging and replanning.

“Before the introduction of CMM, we basically had to start over if the patient moved on the table,” notes Hyer. “Now, with CMM active tracking, we can do what’s called a baseline shift and recentre the treatment on the new target position.” This baseline shift plan typically takes around a minute, which means that clinicians are already becoming a lot less hesitant about tightening their margins on pelvic and prostate tumours in treatment planning.

Forward motion

So what does the CMM roadmap look like at University of Iowa Health Care through 2024? According to Hyer, preclinical testing is already underway using breath-hold sequences to enhance Elekta Unity’s anatomy-specific MR imaging of difficult-to-visualize structures like the pancreas. “We’re developing a whole strategy around breath-hold,” he says. “The imaging sequences so far have yielded exquisite visualizations of the duodenum, stomach and bowel with clear potential to help us with treatments in challenging locations like the pancreas.”

Technical innovation is also in the pipeline, including plans to introduce real-time visual feedback to help the patient on the treatment couch see how the tumour target is lining up versus where it’s supposed to be. “Right now, we provide that feedback via audio coaching,” says Hyer, “so the next step is a visual representation on the inside of the MRI bore – an innovation that will effectively make the patient an active participant in their own treatment.”

Meanwhile, Hyer and the University of Iowa medical physics team are working closely with the two other sites involved in Elekta’s CMM pilot release: UMC Utrecht in the Netherlands and the IRCCS Ospedale Sacro Cuore Don Calabria in Negrar, Italy. “We’re collaborating on the physics side and comparing best practice on a range of issues including liver tracking,” Hyer concludes.