Hypofractionation: pushing the boundaries of MLC performance

The clinical upside of hypofractionated radiation therapy has been evident for some time, with cancer patients benefiting from increased dose per fraction such that they can complete their course of radiotherapy much faster than is possible with conventional treatment schedules – and just as safely and effectively. Think fewer hospital visits, a speedier return to family and, for some indications, enhanced treatability and outcomes. Equally compelling is the long-term opportunity for healthcare providers, with higher dose per fraction (and fewer fractions) translating into significant workflow efficiencies, lower cost of care and, ultimately, increased patient throughput – all of which looks even more compelling against a backdrop of growing cancer incidence worldwide and the perfect storm of the coronavirus pandemic.

Right now, though, the challenge for radiotherapy OEMs and the wider supply chain is to come up with the enabling technologies and treatment protocols to realize these clinical and economic outcomes at scale. For starters, the radiation oncology team needs the ability to maintain submillimetre accuracy and precision throughout treatment delivery – identifying the target location in the body; automatically detecting, tracking and correcting for target motion (due to breathing and peristalsis, for example); and accurately repointing the beam in real-time to support the clinical use of smaller margins to reduce the side-effects of treatment.

With this in mind, a German R&D initiative is aiming to realize a “new gold standard” in the performance of the so-called multileaf collimator (MLC), a core building block of the radiotherapy linacs used for cutting-edge cancer treatments like hypofractionation and ultrahypofractionation. The industry–academia joint venture, which earlier this year received backing from the Bavarian regional government, brings together laser and radiotherapy QA specialist LAP with the Institute for Medical Engineering of the Ostbayerische Technische Hochschule (OTH) Amberg-Weiden. Their goal: a next-generation drive and control unit that promises an order-of-magnitude improvement in the speed and precision of the MLC subsystem – and specifically the array of independently controlled tungsten “leaves” (typically between 120 and 160) used to shape and vary the intensity of the treatment beam as it addresses the tumour volume.

Innovation meets pragmatism

The commercial imperative for MLC development is a mix of technology push and market pull, claims Stefan Ueltzhöffer, who heads up LAP’s MLC and radiotherapy QA business. “We follow the market closely,” he explains, “and maintain an ongoing dialogue with the radiotherapy equipment supply chain, the clinical user base and our academic partners. It’s clear from those conversations that emerging treatment modalities like hypofractionation and MR-guided radiotherapy (MR/RT) will benefit from MLC innovation, creating opportunities for subsystem suppliers like us to set new standard in terms of MLC performance.”

From that starting point, argues Ueltzhöffer, two questions inform the development roadmap for LAP’s MLC product line. First, how does LAP address the evolving needs of its customers (the radiotherapy OEMs) and customers’ customer (the radiation oncology clinics)? Second, what does differentiation of that MLC offering look like to enable LAP to gain market-share versus its competition? The answer, it seems, is a next-generation MLC that will consolidate the outcomes of various in-house development projects with the efforts of this latest collaboration with OTH. “Ultimately,” adds Ueltzhöffer, “I believe we will be talking about multiples of improvement in terms of MLC speed and precision, after pretty much only incremental changes in the technology over the past 20 years.”

Yet while LAP is clearly pushing for a step-function breakthrough in MLC performance, it’s also a given that any advanced capabilities must deliver against strict cost/performance criteria. “Pragmatism is key – the MLC is no longer a toy only for physicists,” notes Ueltzhöffer. “From a commercial and clinical perspective, we want MLCs that are more stable, more serviceable and easier to manufacture. As such, the innovations we are evaluating will enhance performance without sacrificing the considerable progress made on cost and machinability over the past decade.”

Play to your strengths

If that’s the commercial context, what of the technical progress to date? According to Ueltzhöffer, several advanced MLC technologies are already in the works and shaping up well in proof-of-concept demonstrators at LAP. One particular area of focus right now is the MLC drive, with a simplified set-up expected to yield significant outcomes in terms of reduced footprint, weight and designed-in MR compatibility (to minimize the need for shielding in MR/RT treatment systems).

“The MLC drive has always been quite cumbersome in terms of the size of the motors and associated sensors,” says Ueltzhöffer. “As such, we are looking at easier-to-integrate modules that could lead to a lot more degrees of freedom in designing the MLC subsystem – and maybe even make it possible to get rid of some of the transmission mechanisms.”

Another development track is evaluating the use of laser-based sensors to provide optical encoding and tracking of the MLC leaves – a traditional pain-point for today’s MLC designs which rely on cameras, other optical sensors or potentiometers to do that job. “It’s a no-brainer,” says Ueltzhöffer. “We’re applying diverse laser technologies and specialist domain knowledge from the wider LAP group to support our MLC innovation programme.”

If the technology end-point is clear – a new generation of MLCs and a “big leap forward” in capability – the commercial outcome appears more fluid and nuanced. On the one hand, LAP intends to grow its market-share by supplying turnkey MLC units for OEM equipment vendors to integrate directly into their radiotherapy machines. Equally, Ueltzhöffer also plans to license key MLC technologies – for example, drives, sensors and controllers – to those OEM equipment vendors who prefer to build their own MLC subsystems.

“More broadly,” concludes Ueltzhöffer, “LAP remains focused on delivering the enabling technologies for next-generation radiotherapy – in particular, emerging modalities like hypofractionation and MR/RT – through ongoing innovation across its MLC, QA and laser positioning product lines.”