The brainchild of two self-professed math geeks who met in high school, biology-guided radiotherapy (BgRT) was introduced at ASTRO 2018 in San Antonio, Texas, as the first platform to harness the unique biology of a patient’s cancer to guide RT delivery, even in moving tumors. The system uses anatomic data from computed tomography (CT) and functional imaging data from positron emission tomography (PET) to detect cancer cells and guide radiation treatment in real time. Specifically, the system uses PET emissions – not images – to guide RT delivery directly to the tumor itself without the use of fiducials, gating or other motion management techniques.
BgRT is the culmination of a 10-year collaboration between Sam Mazin, PhD, and Akshay Nanduri, co-founders of RefleXion Medical, a biotargeting oncology company based in Hayward, California. Dr. Mazin is also the company’s chief technology officer, and Nanduri is vice president of strategy and business development.
“With BgRT, we are using the PET signal in real-time to track [tumors], and do that not just for one site, but for all sites of disease,” says Dr. Mazin. “The idea is that while the patient is in the machine, we’re essentially hitting all of those targets in that treatment session.”
This approach moves RT from single-tumor therapy to treatment of multiple targets in the same treatment session in cancers that have metastasized, with the primary goal of prolonging survival.
“The question we want to ask is, ‘First, can we make that efficient to do?’ because to treat several sites of disease is very complex and difficult for most centers,” he says. “But can one push the envelope there? Can one treat more sites of disease, which is commonly done with the brain, for example? Can we do that with the whole body, and have another treatment option for these patients? The answer is yes.”
Major components of the machine—the linear accelerator, a PET system with two arcs, and a CT scanner—rotate at a high speed of 60 RPM or 1 revolution per second. “The reason why we rotate so fast is to respond to PET emissions generated by the tumor quickly enough to automatically compensate for motion,” Dr. Mazin explains. “So now, each tumor site has inherent motion management. We can track not just one tumor site, but multiple tumor sites regardless of how they’re moving and we don’t have to predict that motion.”
In fact, the system’s multileaf collimator is the fastest in the industry by a significant margin—by roughly a factor of 5, running at 100 Hz, says Todd Powell, RefleXion’s president and CEO. Additionally, the gantry spins approximately 60 times faster than most machines. “We’re rotating at very, very fast speeds,” he says, “so that in itself is a fundamental innovation in the field.”
Also noteworthy is the system’s footprint, which was designed to fit into a standard linear accelerator vault. “Unlike many of the latest innovations throughout the industry that require new construction to accommodate a much larger device, this system is specifically designed to fit into existing vaults,” says Powell.
Patient comfort was factored in as well, with features such as customized lighting and speakers, and an 85-cm bore to help prevent claustrophobia.
Powell adds that the system will likely be used as a companion treatment to systemic therapy, which is part of the reason why pharmaceutical companies such as Pfizer and Johnson & Johnson have invested in the technology. “Drugs only work so well, and many times they fail in a patient, but radiation can change that equation,” he says. “This is a really exciting approach that can potentially improve the efficacy of systemic therapies for stage 4 patients.”
In addition to treating metastatic cancer patients, oncologists can use the system for standard CT-guided treatment, intensity-modulated radiation therapy (IMRT) or stereotactic body radiation therapy without using PET.
“We think this is a very attractive option for most centers in that they can use it to treat their conventional cases as well as really push the frontier in metastatic disease,” says Dr. Mazin. “We made a machine that treats every stage of disease.”
Powell adds that the BgRT is a platform (vs. just a machine), whose PET scanning byproducts will help position the system for research inroads. “We have the gold standard of cancer visualization and assessment as a natural byproduct every single time the patient is treated,” he says. “With that wealth of data about the cancer, the patient’s state of disease and the point of treatment, it’s a natural opportunity for us to gather and collect that data among all RefleXion sites and look for ways to further optimize treatment plans.
“In many ways,” he adds, “we are going to be gathering information about patients that is presently completely unavailable.”
Several initial research findings were presented at ASTRO 2018, including:
As for availability, Dr. Mazin says they plan to submit for 510(k) clearance later this year, with the goal of gaining approval by mid-2019, and shipping systems in the second half of next year.
Getting the word out about BgRT’s treatment potential was a key goal at ASTRO 2018, adds Powell. “Part of what we are trying to do is to get people to realize that we’re building a machine where the tumors themselves talk to the machine,” he says. “That unlocks the potential for shrinking the margin around an individual tumor, and also tracking multiple tumors. And that really opens up the door to metastatic patients who today don’t get radiation therapy at all.”
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