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Delivering radiotherapy to twice the number of patients as Belgium’s second largest service, the Iridium Network – operating 10 linear accelerators in four of its eight hospitals – was driven to excel in all facets of radiation therapy, including patient setup and motion monitoring.


To treat 500 patients every month demands an efficient, accurate, patient- and user-friendly workflow. The radiotherapy group found an elegant solution in the C-RAD Catalyst HD™ system, which enables Surface Guided Radiation Therapy (SGRT). SGRT is a non-ionizing imaging technique to guide patient positioning during setup, monitor intra-fraction motion and manage gated treatment deliveries. After a methodical internal training program, Iridium staff began clinically implementing Catalyst HD, linac-by-linac, throughout the entire network.

The Way Forward in Radiation Therapy 

According to Iridium Network medical physicist An Sprangers, she and her colleagues, including the radiotherapy department head, appreciated that SGRT exemplifies recent radiation therapy advancements aimed at increased accuracy, more personalized treatments and greater patient comfort.

“We believe that SGRT will be the standard of care in the future for every hospital,” Sprangers says. “In addition to avoiding an ionizing radiation dose, SGRT eliminates the need for skin tattoos to confirm the patient’s position and facilitates a more precise, tailored treatment, all of which contribute to the patients’ physical comfort and peace of mind. Radiation therapists also find SGRT techniques easy to perform after suitable training, which is critical as they are the principal users of the technology.”

Iridium Network radiotherapists (RTTs) evaluated the C-RAD Catalyst HD system with their medical physicist colleagues. The group collectively agreed that C-RAD’s SGRT solution was user-friendly, efficient and increased patient safety, in addition to an optimal level of operational automation that would be vital in a department with many linacs and high patient throughput.

“As RTTs we wanted an SGRT product that was functionally ergonomic and straightforward to use and that would enable us to position the patient in a rapid, accurate fashion,” says Iridium RTT Ann Vermylen. “Furthermore, we wanted to be able to track the patient’s movement during treatment, improve our DIBH setup and become a markerless and tattoo-less environment for our patients. The main driver for the physics team was standardization and automation of the SGRT workflow. Catalyst HD fulfilled all of the RTT and physicist requirements.”

An Sprangers adds that from the Iridium staff’s point-of-view, C-RAD was the best company to develop the kind of process automation they were looking for. “C-RAD was very willing to collaborate with us to implement and help us optimize the new SGRT workflow. Moreover, the detailed information that is generated on patient set-up information during treatment in combination with the department’s solution for extensive in vivo dosimetry creates a large database, which is perfect for exploring data mining and AI-solutions in improving treatment quality.”

Super Users Spearhead Implementation 

Because Catalyst HD would present Iridium RTTs with a radically different patient positioning and motion monitoring workflow compared to what they were accustomed to, C-RAD recommended that the radiotherapy service select and train a small group of Iridium RTTs and physicists. These super users would then train the rest of the network’s RTTs on the solution.

“C-RAD first provided a theoretical course on Catalyst HD and then we formed the super user group, which trained comprehensively on the product over three days without a connection to a linac,” Vermylen says. “The super user concept was the best tactic to implement Catalyst, because the RTT super users could get practical, hands-on experience with the system, not only becoming trained themselves, but also gaining insight on how to train our other RTTs.”

Iridium physicists in the super user group worked closely with the RTT super users to ensure the project’s success, according to Iridium medical physicist Hannelore Van Dyck.

“The RTTs and physicists had excellent communication throughout the project,” she recalls. “The physicists did all the QA testing and calculation of table parameters to enable rapid, accurate positioning, while the RTTs focused on understanding how Catalyst HD worked and how it changed the workflow. It was a great idea to have a very dedicated team for those first few months. But in the end, while we physicists were available for support, it was the RTTs that we relied on to educate their colleagues.”

The experienced super user RTTs introduced Catalyst HD to the main clinic’s RTTs, enabling the technologists to acquire the same skills and processes for the system, to practice integrating them and to know when to apply what they have learned with a super user RTT beside them.

“It is not until the various skills are combined and practiced in complex situations that the apprentice RTT develops a deeper understanding of the system,” Vermylen explains. “Our goal was to systematically reduce the cognitive load for the RTTs and augment their decision-making process based on this new technology.”

After this phase was accomplished, a subset of the initial super user group moved on to another hospital in the network to repeat the process, while the other super users remained at the main clinic for backup and troubleshooting support. Super users subsequently trained users in the other two hospitals.

“We gave extra theoretical workshops during linac maintenance time to get everyone on board,” she says. “In addition, we recorded SGRT lessons that the RTTs could view at their own pace and have the opportunity to ask questions.”

In just seven months the implementation phase was complete and the Iridium Network’s RTTs were using Catalyst HD for patients on all ten linacs as of late February 2022, of which two linacs are used for stereotactic radiation.

Catalyst HD In Action at Iridium

Iridium Network RTTs are now using Catalyst HD for all patient setups, including those requiring a thermoplastic mask, Sprangers says.

“We don’t use tattoos on patients anymore,” she notes. “We are also using Catalyst HD to monitor patient motion in preparation for performing DIBH treatments for patients with left-sided breast cancer, as well as stereotactic cases.”

Both Sprangers and Vermylen place a high value on the C-RAD system’s deformable registration algorithm, an effective solution for registering two 3D images.

“It accounts for changes to elastic surfaces such as the patient’s skin and dependably calculates the relative position and orientation of the patient’s current 3D image compared to the reference 3D image,” Sprangers explains. “We don’t need to spend time creating and repeatedly correcting the ROI over a patient’s successive treatment fractions.”

Vermylen adds that Catalyst HD can identify particular areas of the patient that are out of position and are relevant to the tumor’s location.

“While the clear advantage of Catalyst HD system is the lack of a radiation dose, the deformable registration algorithm is useful to highlight patient posture differences on the patient surface,” she observes. “For example, if a patient’s shoulder is slouched, the algorithm calculates that the tumor isn’t in the correct treatment position. The SGRT system will identify the local area that is out of position and use color projections to guide the RTT to correct the patient’s posture. The color projection is a clever way of maximizing patient setup time and accuracy. I love to search within the visual and numerical data on how to position the patient perfectly.

“This also enables the user to verify not only the surface of the patients but also the calculated isocenter from this surface,” Vermylen continues. “Therefore, you can monitor your patients with multiple parameters. This can be somewhat confusing and overwhelming in the beginning, but it makes Catalyst HD so versatile.”

She also notes that the algorithm’s variable speed is helpful.

“It provides a fast calculation for relative gross positioning and a more accurate representation of the patient’s surface once the patient is in a stable treatment position,” she says.

Catalyst HD tracks the patient’s movement constantly during treatment, improving safety, Van Dyck adds.

“Even if the RTT is momentarily busy and the patient has moved without the RTT seeing it, Catalyst HD patient monitoring never stops. The system will automatically shut off the treatment beam,” she says. “You’re able to solve it within two or three minutes – you don’t have to take the patient from the table. So, it’s a very nice benefit that helps the physician and physicist decide whether or not the patient needs to be imaged again.”

While Catalyst HD was designed to make the RTT’s life easier as they strive for more accurate positioning, she notes that even patients have commented about the advantages.

“Having a completely markerless and tattoo-less environment wasn’t our main goal, but patients who had external markings before love the fact that these are now a thing of the past,” Vermylen says. “Patients are also impressed by the precision and accuracy of Catalyst HD. It’s a reassuring feeling for patients that the treatment machine automatically stops the beam, if they cough, for example. Our attention is more on patient weight loss because this alters the patient’s body contour. So, by using the system, it increases the focus on the patient.”

An Optimized Workflow 

Now, about one year into their new positioning workflow, Sprangers, Vermylen and their Iridium colleagues are Catalyst HD veterans and true believers in SGRT.

SGRT enables us to position our patients in a standardized way. The system opens automatically and is very intuitive in clinical mode,” Vermylen remarks. “I have the feeling that we not only position our patients more accurately, but also faster. We now have a tolerance threshold on which our patients need to be positioned. This also results in higher reproducibility of the patient posture and position.

SGRT is a powerful tool that can positively impact patient safety, treatment quality, motion management, and risk surveillance and management,” she adds. “It also potentially provides a decision-support tool in radiotherapy, so Catalyst HD is much more than a positioning solution.”

About the Iridium Network

Since its foundation in 2006, the Iridium Network has grown into the largest radiotherapy network in Belgium. It is the unique provider of radiotherapy for all three hospital networks in the Antwerp-Waasland region: GZA/ZNA, HELIX and MIRA. Together they are further developing the Iridium Network into a leading expertise center with an international reputation. The head office, including the general secretariat, is located in the GZA Hospitals campus Sint-Augustinus in Wilrijk. The operating area of the Iridium Network covers more than 1.5 million inhabitants, and in 2021 it delivered over 6,000 treatments.


  1. Meyer, J, Smith, W, Geneser, S. (2020) Characterizing a deformable registration algorithm for surface-guided breast radiotherapy. Med. Phys. 47 (2): 352-362.
  2. Stanley, DN, McConnell, KA, Kirby, N et al (2017) Rad Onc Phys. Comparison of initial patient setup accuracy between surface imaging and three-point localization: A retrospective analysis.

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