At this week’s ASTRO 2026 meeting in Boston, MA, researchers shared the results of clinical trials addressing important and longstanding questions in cancer care. In a dedicated news briefing highlighting noteworthy research studies, two speakers presented new evidence that could help inform how we deliver care to patients with brain metastases.

Brain metastases – cancerous cells that spread to the brain from another site in the body – are typically removed surgically or treated with radiotherapy. For most types of cancer, the preferred approach is stereotactic radiosurgery (SRS), in which high-dose radiation is precisely directed to individual lesions while limiting dose to surrounding healthy brain tissue.

Randomized trials have shown that SRS results in superior cognitive preservation and quality-of-life compared with whole-brain radiotherapy (WBRT), where the entire brain is irradiated to ensure treatment of both visible tumours and microscopic disease. There’s an exception, however. Historically, for brain metastases arising from small cell lung cancer (SCLC), a rare, fast-growing cancer, WBRT remains the standard-of-care. Results of a new trial challenge this approach.

Chad Rusthoven from the University of Colorado Anschutz School of Medicine shared the findings of the first phase III randomized trial to compare SRS versus WBRT for brain metastases from SCLC. The trial found that after adjusting for patient and disease characteristics, SRS was associated with a 40% lower risk of death than WBRT.

Rusthoven noted that recent advances have improved outcomes for patients receiving WBRT. “This includes addition of memantine [a drug that helps protect cognitive function], as well as hippocampal avoidance techniques,” he explained. “As a result, HA-WBRT plus memantine is now the preferred whole-brain treatment strategy for cognitive preservation.”

As such, the NRG-CC009 trial – which included 151 patients in the US and Canada – randomly assigned participants to receive either focused SRS to visible metastases or HA-WBRT plus memantine. All subjects had a median of two SCLC metastases, although some had more than 20.

For the primary endpoint – the time before a patient experienced cognitive decline – the study found no significant difference between the two treatment groups. However, patients treated with SRS had a median overall survival of 17.4 months, compared with 8.6 months for those in the HA-WBRT group. Rates of serious treatment-related side effects or death from neurologic causes were similar for the two cohorts.

Although no differences in neurocognitive failure were observed, the superior overall survival with SRS addresses a fundamental historical objection to SRS alone for small cell lung cancer brain metastases. That is, the concern that omission of WBRT would lead to worse overall survival in this population. Overall these findings support SRS as a treatment option for patients with brain metastases from small cell lung cancer,” Rusthoven concluded.

The power of fractionation

Speaking at the same briefing, Ayal Aizer from Mass General Brigham/Dana-Farber Cancer Institute explained how fractionated radiosurgery can reduce the risk of cancer recurrence after surgery for large brain metastases, without significantly increasing side effects. Fractionation – in which the radiation dose is divided into several treatments – gives healthy tissue time to recover between doses while still effectively treating the surgical cavity.

Large metastases, which can cause pressure on the brain leading to symptoms such as seizures, headaches or difficulties with speech or movement, can be removed via surgery. This is usually followed by radiotherapy to destroy any microscopic cancer cells left behind in the surgical cavity. Aizer explained that current guidelines recommend treating the cavity with SRS, following two pivotal trials demonstrating favourable outcomes for SRS compared with postoperative WBRT and observation.

For larger surgical cavities, however, the challenge, is how to deliver enough dose to eliminate any remaining cancer cells without exposing too much surrounding healthy brain to radiation. “In both of these trials where single-fraction SRS was utilized, the one-year surgical bed recurrence rates were high: 40% in one trial, 28% in the other,” he explained. “Meanwhile, alternative approaches such as fractionated SRS to the surgical bed had been emerging.”

Aizer described Alliance A071801, the first randomized phase III trial to directly compare single-fraction versus fractionated SRS for resected brain metastases. The multi-centre trial enrolled 242 patients with one to four brain metastases, one of which was larger than 2 cm and surgically removed. The metastases arose from different primary tumour types, the most common being lung cancer.

The team randomly assigned patients to receive either a single session of SRS, with dose based on target size, or fractionated SRS: 27 Gy in three fractions for smaller targets or 30 Gy in five fractions (9%) for larger ones.

One year after treatment, 87% of patients who received fractionated SRS were free from recurrence at the surgical site, compared with 81% of those who received single-session radiosurgery. Side effects such as radiation necrosis and cerebral oedema were low in both treatment groups, with no significant differences between the two.

The overall survival was also improved after fractionated SRS, with patients surviving a median of 29 months, compared with 20 months for those treated in a single session. The researchers note that this survival difference was unexpected and it is not yet clear why this occurred.

“In conclusion, we can say that fractionated SRS improved surgical bed control compared with single-fraction SRS after resection of a brain metastasis,” said Aizer. “The improvement in surgical control was achieved without an apparent increase in toxicity. For patients undergoing resection of a larger brain metastasis, postoperative fractionated SRS should be considered the standard-of-care.”

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The annual meeting of the American Society for Radiation Oncology is the place to be to discover the latest radiotherapy technology developments and new product launches. And this year was no exception. The ASTRO 2026 meeting, held this week in Boston, MA, saw Siemens Healthineers unveil its newest radiotherapy system – Accela – which combines precision delivery with speeds fast enough to enable stereotactic treatments in a single breath-hold.

Accela achieves this by implementing a new delivery technique known as NeoArc, or dynamic modulated arc therapy (DMAT). DMAT is a type of arc therapy, in which the treatment beam rotates continuously around the patient during treatment, with the beam shape and intensity controlled to deliver the prescribed treatment plan.

But while conventional arc-based approaches such as volumetric-modulated arc therapy (VMAT) primarily optimize treatment plans for the dose distribution, DMAT evaluates dosimetric objectives and delivery efficiency simultaneously. This enables clinicians to tailor treatments for both speed and precision, to optimize the balance between them and, ultimately, to reduce the patient time on the treatment table.

Sasa Mutic, head of radiation oncology solutions at Siemens Healthineers, tells Physics World that the product launch at ASTRO was a great success. “The response to Accela from customers and the medical community has been overwhelming and overwhelmingly positive,” he says. “It was extremely gratifying to see that the ASTRO audience instantly grasped the significance of what we’ve accomplished and the impact it will have on clinicians and patients.”

Done in 60 seconds

Accela integrates high-speed gantry rotation of up to 2.5 rpm, dose rates of up to 40 Gy/min and a dual-layer multileaf collimator (MLC) with leaf speeds of up to 6.5 cm/s. This combination means that, as well as single breath-hold stereotactic treatments, Accela can deliver multi-site stereotactic body radiotherapy (SBRT) in as little as 60 s and go from imaging to beam-off in as low as 90 s – including on-couch imaging with a large HyperSight cone-beam CT panel, couch shifts and the treatment delivery.

An additional benefit of ultrafast radiotherapy is the potential to actually alter the body’s biological response.

“Because the treatment times are potentially as quick as a single breath hold, there is much less blood irradiated,” explains Dee Khuntia, chief medical officer at Varian, the Siemens Healthineers cancer-care business. “This allows for preservation of lymphocytes, which are necessary for helping the body heal, fight infection and fight cancer. It is also well documented that patients undergoing radiation or chemo-radiation who have lymphopenia [not enough lymphocytes in the blood] have lower survival rates.”

The first patient treatments with Accela are scheduled for December in Europe. By this time, the system will have the CE mark, with FDA clearance expected early next year. One of the first centres to use Accela will be Maastro in the Netherlands, which plans to initially treat small lung tumours, lung metastases, brain tumours and metastases in the vertebrae – sites that require a high radiation dose administered extremely precisely, while sparing healthy tissue and nearby vulnerable organs.

• Updated on 6 October 2026 to amend the imaging to beam-off time and add a clarification from Siemens Healthineers: Accela and NeoArc are 510(k) pending. Not available for sale or quotation. No guarantee of commercialization or feature availability.

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Patient-specific quality assurance (PSQA) plays an essential role in the safe and effective delivery of radiotherapy to cancer patients. Enabling a “dry run” in which the treatment plan is delivered to a physical device before the patient enters the room, PSQA provides a final safety net before treatment. The aim: to ensure that the correct dose is delivered to the correct location for every patient and every single fraction.

That said, measurement-based PSQA is not sensitive enough to catch all errors – some still slip through. What’s more, pre-treatment measurements are not feasible in online adaptive radiotherapy, where treatment is re-planned and delivered within minutes. There’s simply no time to deliver the new plan to a phantom while the patient waits on the couch

And as clinics increasingly adopt adaptive workflows, incorporate artificial intelligence (AI) into the treatment chain and deliver more complex, more automated and faster radiotherapy than ever before – is it time to rethink radiotherapy QA? Could properly commissioned delivery techniques render routine measurement-based PSQA obsolete?

This was the question discussed at the QA & Dosimetry Symposium (QADS) hosted earlier this year by Sun Nuclear. In an animated debate, Victor Hernandez of Hospital Universitari Sant Joan de Reus in Spain and Dirk Verellen of the University of Antwerp and Iridium Netwerk in Belgium, considered the options.

Far fewer PSQA measurements

“We are debating today because we have a problem,” said Hernandez. “Measurement-based PSQA is not sensitive, not efficient and just not working.” The good news, however, is that a simple independent dose calculation – as provided by software-based PSQA – is an order of magnitude better at detecting failures than measurements.

Hernandez emphasized that to make this shift, it’s essential to commission and standardize the whole radiotherapy process, including not just the linac and treatment planning system (TPS) but the PSQA system itself, to optimize how it is used and understand its limitations. Perhaps the most important step is commissioning the treatment planning process – or “QAing” the plan characteristics. “Less complex plans tend to be more accurate and more robust to uncertainties,” Hernandez explained. “So you need to evaluate and minimize plan complexity during treatment planning.”

He proposed a simple process for QA of treatment planning, based on class solutions (pre-defined dosimetric objectives and geometric parameters) that incorporate complexity metrics in their definition. These class solutions are validated using measurements and used to standardize treatment planning. If a final plan falls outside of the class solution, it will require verification using both measurements and software. But most clinical plans will be within a class solution, where software-based verification will suffice.

Hernandez noted that if you’re performing less PSQA, then machine QA becomes more important and must be reinforced. This could, for example, involve measurements of a fixed set of complex plans every few weeks to make sure that the linac is stable. “But that’s no longer PSQA – it’s part of your machine QA programme,” he emphasized.

“You can perform treatment planning without controlling or evaluating the plan parameters, but then there’s no consistency in your plans and you need pre-treatment measurements of all plans because you’re not in control,” he explained. “Or you can control the plan parameters. Then you reduce variability, improve robustness and quality, and you don’t really need PSQA measurements anymore because that’s part of QA, which is of course, much more efficient.”

“That’s my vision for enhancing safety and advancing QA,” Hernandez concluded.

The unknown errors

Verellen was less convinced that measurement-based PSQA is obsolete. Contemplating Hernandez’s arguments, he agreed that phantom-based pre-treatment PSQA is “just recommissioning over and over again”, noting that “you won’t see any errors in your PSQA unless you have done your commissioning wrong.”

He concurred that accurate commissioning should pick up any mechanical or dosimetric errors, dose tracking can account for anatomical variations, and surface- and image-guided radiotherapy can address positioning errors. “And we also have in vivo dosimetry,” he added. “So in principle, we are covered.”

But sometimes, the things that go wrong are the things nobody thought to look for. “You might have a very good plan, but are you really sure that everything is covered?” he said.

One obstacle is knowing which metrics to use to define a complex plan. Another problem lies in the onslaught of new technologies such as online adaptive that create and deliver a plan in minutes. Verellen pointed out that companies are selling complex adaptive systems as a plug-and-play option that can be commissioned and treating patients in just a few weeks. “Your department is not ready for that. You don’t have the procedures. People are not trained for that,” he emphasized.

And as software is updated, hardware is upgraded and AI is rapidly becoming inherent in ever more stages of the radiotherapy workflow, it becomes challenging to rely on existing procedures. “With this large-scale introduction of AI and automation, we really start to rethink our role as humans in monitoring that process,” said Verellen.

The big challenge is to anticipate each and every kind of error that could possibly occur. And as Verellen pointed out, radiotherapy is much more than just the treatment machine. “There are a lot of people [involved] and they may make mistakes,” he said. “The interactions of the different system components make things so complicated that it’s very difficult to really anticipate all the things that might go wrong.”

What’s needed is a way to evaluate, validate and monitor the entire treatment chain, and a way to detect and avoid catastrophic events. Currently, pre-treatment PSQA is still an important safety barrier in this respect, he emphasized, by detecting the small, unexpected errors that could add up to create a catastrophic event. Moreover, in vivo dosimetry (IVD) will become even more important as a final safeguard of quality that, in the case of online adaptive radiotherapy, will need to evolve into real-time IVD.

“We need rigorous commissioning, but we need to realise that this cannot predict every situation,” said Verellen. “That’s my main point: as my father used to say, ‘don’t throw away your old shoes before you have the new pair’  – this is why we still need pre-treatment patient-specific QA at this stage … until we’ve figured out how to deal with the new developments.”

Near agreement

Remarkably for a conference debate, Hernandez and Verellen agreed on many points – in particular, that the field requires a redefinition of radiotherapy QA. “AI and automation are like a tsunami coming over us and we are not prepared for it,” said Verellen. “We have to step back and rethink the QA of the process.”

Where they differed, however, was on whether it is safe to abandon current PSQA measurement practices right now. “We know where we want to go, but we’re not there yet,” said Verellen.

“I agree with Dirk about many things,” said Hernandez. “But pre-treatment verification to a phantom is not patient safety. That’s why we need to make sure that our plans are accurate and robust, then you can verify it in every single fraction.”

“That works if the flow goes according to plan,” Verellen countered. “But unpredictable things happen.” He likened the risk to that of skydiving, where sky divers spend much time meticulously folding the parachute to guarantee that it will open. “But I’ve never seen a sky diver jumping without a reserve parachute,” he said. “For me, pre-treatment PSQA is my backup, until we have a solution that’s more or less watertight. And at this moment, it is not.”

Both agreed that the way forward is to focus, not just on the machine or the plan, but on understanding and verifying the entire treatment process – particularly the treatment planning and delivery processes. Treatment verifications such as real-time beam monitoring systems and IVD are also crucial for patient safety. “We need to think about how to better monitor all these processes to really advance QA and improve safety for patients,” said Hernandez.

The next frontier

While the QADS debate was framed as “measurement versus calculation”, Greg Robinson from Sun Nuclear reiterates that the real evolution is the shift from checking a device to monitoring the entire process, driven by the introduction of automation and AI.

“The debate was interesting because they were arguing for both extremes, but I think the field is going to land somewhere in the middle,” Robinson tells Physics World. “It’s not that physical measurements are going away, but the frequency by which clinics are doing these measurements is dropping.”

Verellen pointed out that to enable the uptake of software-only PSQA, “we need QA tools that monitor the process”. One option for completely virtual pre-treatment QA is the DoseCHECK secondary 3D dose calculation algorithm and PerFRACTION, both part of SunCHECK from Sun Nuclear.

“SunCHECK brings machine and patient QA together in a single platform,” explains Robinson. “[This] lets a clinic see relationships that isolated tools miss; for instance, when a change in machine performance begins to show up in patient results.” Meanwhile, for adaptive online radiotherapy, AdaptCHECK provides an independent secondary check of the adapted plan within the session time frame.

Looking further ahead, Robinson predicts that the next frontier will be “turning connected QA data into understanding”. In other words, ensuring that errors are not just detected, but can be understood and prevented. “It isn’t enough to tell a physicist that a result passed or failed – the value is in the why: what’s trending, what’s related, what’s likely to drift next,” he explains. “Sun Nuclear is developing new solutions to help physicists untangle the meaning behind all of this data, and make connections across machine and patient data much more seamless.”

Robinson concludes that measurement-based PSQA is not obsolete, but can no longer stand alone. “The future is an independent, connected, insight-driven QA layer that spans machine and patient, works where measurement can’t, and explains the results it produces,” he says. “Quality first, delivered by automation and intelligence rather than replaced by them. That’s exactly where Sun Nuclear is investing.”

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