When performing liver-directed therapy, precise targeting of tumours is crucial to protect healthy liver tissue. Supporting a tailored and flexible approach to radioembolization, SIR-Spheres (Sirtex Medical) Y90 resin microspheres—used in selective internal radiation therapy (SIRT)—have fast become favoured among clinicians.
In a cross-departmental discussion, Interventional News hears how interventional radiologist Geert Maleux and nuclear medicine physician Christophe Deroose (both University Hospitals Leuven, Leuven, Belgium) use the technology, outlining the specific benefits that have reinforced its place in their treatment algorithm.
Deroose begins, stating that central to the appeal of the technology is the ability to separate the ordering and planning process from the final dose administration.
“For us, the main advantage of using SIR-Spheres is that we can plan our workflow and then actually decouple the order for the microspheres from the intended amount that we want to inject to the specific site,” explains Deroose. “In addition, SIR-Spheres allow us to inject subdivided doses in different catheter tip positions to treat several tumours separately and selectively, while also improving lesion coverage in case of multiple feeding vessels,” he adds.
Precise workflow planning
This flexibility enables his team to thoroughly plan each procedure. Deroose describes how his team begins with a workup using technetium-99m-labelled macroaggregated albumin (99mTc-MAA), followed by nuclear medicine imaging. “If we see that there’s no problem with extrahepatic uptake, no major lung shunt fraction, no extrahepatic intra-abdominal sites of accumulation, no problems with catheterisation, and the intrahepatic uptake is favourable, then we will activate the order of SIR-Spheres.”
“The FLEXdose Delivery Programme [Sirtex] allows us to select the right activity per microspheres and optimal number of microspheres. For example, we favour high activity per spheres with low density of particles for small volumes, and higher number of microspheres with lower activity per spheres for lobar treatments.”
From there, Deroose details that they proceed with a dosimetry-based prescription “using all the information that we need, which includes FDG PET [fluorodeoxyglucose Positron Emission Tomography] scans, angiographic data including cone-beam computed tomography (CBCT) imaging and lab values.” He continues: “We pull all this together. We get inputs from our colleagues in interventional radiology [IR], defining the liver perfusion territories or so-called ‘angiosomes’. All that is processed in our SurePlan LiverY-90 [MIM Software] workflow, where we then draw the territories, draw the tumours and finally plan the microsphere dosage we want to give based on normal liver and tumour dose.”
Deroose highlights that this level of detailed planning is supported by the flexibility of the SIR-Spheres technology. The SIR-Spheres arrive at the hospital preloaded with Y90, allowing for real-time adaptation of the Y90 activity without adding logistical burden. In contrast, he notes, other technology requires full dosimetry workup before ordering, “so that puts time pressure at a point that is not convenient for us.”
The capacity to adapt the number of microspheres and the activity to be injected until the final moment before administration is seen as a major advantage. “Until the arrival of the vial on the day of the treatment, you can still adapt your treatment strategy,” Deroose adds. “You can even potentially do a re-simulation with a different catheter and inject 99mTc-MAA—that’s something we can do daily if we want. So, this flexibility is very welcome for us.”
Personalised dosimetry
Reflecting on his centre’s evolving approach, Deroose describes how current practices have transitioned from older methods. “When I started as a staff member, around 2008 or 2009, the prescription was based on the BSA [body surface area] formula. Back then, the percentage of tumour involvement was provided by our radiology team based on CT segmentation, which I believe we’ve always used.”
However, the use of BSA as a surrogate for liver volume was seen as inconsistent. “We’ve always had the exact volumetric data from the liver, so that has always been a paradox when we were using this BSA formula,” he says.
The team adopted personalised dosimetry strategies early on. “We’ve not used [the BSA method] for a very long time. We very rapidly switched to medical internal radiation dose [MIRD]-based or partition model-based strategies for activity prescription. Because of course, these make much more sense from a scientific perspective.”
Real-time control
Speaking from an IR perspective, Maleux highlights how SIR-Spheres also deliver procedural advantages at the point of treatment. His team has adopted the SIROSTM (Sirtex) delivery system, which enhances control and usability. “It is very handy and straightforward to use,” Maleux states. “In addition, you do not have to position or reposition needles anymore. So that’s a big advantage compared to the previous system.”
While workup workflows remain largely consistent between devices, Maleux emphasises that SIR-Spheres offer more real-time control during treatment. “With SIR-Spheres compared to competitors, you have the advantage that during the injection of the spheres, you can also inject contrast medium,” he explains. “Then you can have a kind of control—if there are any signs of reduced flow or, worst-case scenario, if you see some reflux, you can anticipate this by, for instance, stopping the procedure or slowing it down and waiting a few minutes until there is once again antegrade flow.”
This added layer of intra-procedural assessment supports safer, more controlled delivery. “Non-target embolization is associated with some potentially major complications,” both Maleux and Deroose agree.
Shifting indications
Both clinicians outline hepatocellular carcinoma (HCC) as a key indication for SIR-Spheres in their practice, particularly in unifocal disease. By contrast, they note the shifting profile of colorectal liver metastases (CRLM) cases in recent years: “Today we only treat a few CRLM cases a year, whereas 10–15 years ago this was the majority of our patient population for radioembolization,” Maleux notes. CRLM treatment is now largely reserved for select scenarios, such as patients with “low tumour burden and limited surgical options,” Deroose adds. Due to this shift toward more focal and personalised treatment, risks such as non-target embolization have been significantly reduced. “We rarely perform lobar or bilobar treatments. During these procedures you have the highest risk of non-target embolization,” Maleux comments.
Asked to summarise the key advantages of SIR-Spheres, Deroose states: “Flexibility and control—from simulation to the very last moment of treatment—are the major benefits. We can treat the patient how we see fit and how we planned it. Plus, with the FLEXDose Delivery Programme, we can go for higher doses if needed.”
Maleux, echoing this, concludes that the ability to perform angiography and contrast-enhanced delivery in parallel avoids “injecting blindly,” increasing confidence in treatment accuracy and safety.
