Radioembolization, also known as selective internal radiation therapy, involves threading tiny radioactive microspheres through the arteries that feed liver tumors, delivering high doses of radiation directly to cancerous tissue while sparing healthy liver. The field has steadily moved toward increasingly selective strategies, with radiation segmentectomy now often favored over whole-liver or lobar approaches because it can treat early hepatocellular carcinoma in an ablative manner. But greater selectivity comes at a price: when a patient has multiple tumors in different liver segments, physicians frequently need to access several separate injection positions within the arterial network, and each repositioning step creates a practical dilemma that has long frustrated operators.

The problem is fundamentally one of contamination. Conventional microcatheters have a single lumen that serves both as the guidewire track and the injection channel. Once radioactive microspheres have passed through that channel, any subsequent manipulation of a guidewire through the same space risks smearing radioactive material onto the wire and, by extension, the sterile field. Current clinical practice therefore mandates discarding the microcatheter after each injection position and inserting a fresh one for the next target vessel. That approach generates additional radioactive waste, extends procedure time, and adds cost, particularly in complex cases where selective catheterization is technically demanding.

The Utrecht team hypothesized that a catheter with two physically separate lumens could eliminate this risk entirely. They employed a 3.2-Fr dual-lumen microcatheter, the Sasuke device from Asahi Intecc in Japan, which was originally designed for cardiac interventions. The device features a rapid-exchange lumen extending from the catheter tip to an exit port located 20 centimeters proximally, which accommodates a 0.016-inch guidewire, and an over-the-wire lumen that runs from the proximal catheter end to an exit port just 6.5 millimeters from the tip, which serves as the microsphere injection pathway. Because the guidewire and the microspheres travel through entirely separate channels, they never come into contact, theoretically eliminating guidewire contamination regardless of how many times the catheter is repositioned.

The technique itself unfolds in a deliberate sequence. After standard femoral arterial access with a 6-Fr sheath, a 6-Fr guiding catheter was advanced into the celiac trunk, since the 3.2-Fr microcatheter is too large to pass through standard 4 to 5 Fr diagnostic catheters. The dual-lumen microcatheter was then navigated to the first target vessel over the guidewire. Once the position was confirmed, the guidewire was retracted so that its tip resided safely within the rapid-exchange lumen, well away from any microspheres. Two microsphere administration systems were connected to the injection lumen through a three-way stopcock, the first dose was delivered, and the lumen was thoroughly flushed with saline. To move to the second site, the guidewire was simply advanced again through its dedicated lumen to steer the catheter to the next target, retracted once more, and the second dose was injected through the same channel.

The first patient was an 80-year-old man with two hepatocellular carcinoma lesions, one in liver segment 4 and one in segment 8, undergoing radioembolization work-up. The dual-lumen microcatheter successfully delivered scout doses of holmium-166 microspheres to both positions, first through the left hepatic artery and then, after repositioning, through the segment 8 artery. Cone-beam computed tomography from both positions demonstrated the expected vascular territories, and subsequent single-photon emission computed tomography confirmed adequate microsphere distribution to both tumors. The total procedure, from vascular access to closure, took 95 minutes, with cumulative fluoroscopy time of 18 minutes and 50 seconds and a total dose-area product of 330 Gy·cm².

The second case put the technique to a therapeutic test. A 79-year-old patient with neuroendocrine tumor liver metastases required treatment doses at two positions, the right hepatic artery and the segment 4 artery. Using a single dual-lumen microcatheter, the team delivered a first therapeutic dose of 4100 MBq of holmium-166 microspheres into the right hepatic artery and then repositioned to deliver a second dose of 3000 MBq into the segment 4 artery. One technical wrinkle emerged: at both injections, pressure inside the administration system rose rapidly to its maximum, indicated by the fluid level in the V-vial climbing to the rubber septum, so the team injected at a substantially reduced rate with roughly 20 seconds of additional time between flushing and microsphere administration to allow pressure normalization. A calibrated dose calibrator confirmed no significant residual activity afterward, and post-procedural imaging verified adequate microsphere distribution. This procedure took just 65 minutes, with 14 minutes and 29 seconds of fluoroscopy and a dose-area product of 86.3 Gy·cm².

Critically, radiation safety monitoring validated the central premise of the approach. As part of standard institutional protocol, all disposable materials, including the guidewire, were surveyed with a contamination monitor after each procedure. In both cases, count rates fell below the institutional threshold of 200 counts per second, the level below which materials can be discarded as regular non-radioactive waste. Catheter repositioning in both procedures was accomplished smoothly without technical difficulties, suggesting that maintaining the guidewire within its own lumen throughout the procedure neither impedes navigation nor compromises delivery precision.

The researchers are candid about the technique’s limitations. The 3.2-Fr outer diameter exceeds the typical 2.7-Fr profile of standard microcatheters, requiring guiding catheters rather than conventional diagnostic ones, a setup change that some centers may need to make. The injection port sits 6.5 millimeters proximal to the catheter tip, meaning the tip must be advanced slightly beyond the intended injection point, which could prove difficult in small vessels, and the protruding tip could theoretically pick up surface contamination. More significantly, the narrow 0.016-inch inner diameter of each lumen generates higher injection pressures than standard microcatheters, and not all microsphere delivery systems tolerate this. The instructions for use of widely used yttrium-90 glass and resin microsphere systems recommend minimum inner diameters of 0.020 and 0.021 inches respectively, making pressure compatibility an important barrier to broader adoption.

Two complementary developments could ease that constraint. Pressure-resistant delivery systems, such as the recently introduced SIROS system for yttrium-90 resin microspheres, may better accommodate narrow-lumen catheters; in a retrospective study of 48 SIROS administrations through a microcatheter with a 0.021-inch inner diameter, mean residual activity was just 4.9 percent, and 94 percent of administrations retained less than 10 percent residual activity with a double-flush protocol. Alternatively, manufacturers could design dual-lumen catheters specifically for microsphere delivery, with a larger dedicated injection lumen and a smaller guidewire channel. The authors also note that delivering predetermined doses at multiple positions currently requires multiple administration systems connected via stopcocks, and point to dose-titration systems such as the Eye90 microsphere platform as potential solutions. Guidewireless steerable microcatheters offer another route around contamination, having achieved guidewire-free catheterization in 93 percent of applications in a 50-patient multicenter trial, but they carry elevated risks of vessel injury and catheter kinking, particularly in tortuous or very wide vessels. The dual-lumen approach retains guidewire support throughout, trading a slightly larger catheter profile for potentially safer navigation.

For now, the findings rest on just two cases performed by a single experienced operator at one institution, without a control group for comparison, so the authors caution that the results do not yet support routine clinical use. Still, the proof of principle is compelling: a single catheter served two injection positions in each patient, no guidewire contamination was detected, and the technique could plausibly cut radioactive waste and procedure time in multi-position treatments. The team, whose work is supported by the European Union-funded IMAGIO consortium under the Innovative Health Initiative, calls for larger studies evaluating the technique with different microspheres and delivery systems, assessing its applicability to more complex multi-position procedures, and directly comparing repositioning time, total procedure duration, and residual activity against conventional single-lumen catheter exchange. If those studies bear out the promise, a device borrowed from the cardiology catheterization lab may become a quiet workhorse of precision liver cancer therapy.

Subject of Research: Dual-lumen microcatheter technique for multi-position radioembolization of liver tumors

Article Title: Dual-lumen microcatheter facilitating multiple injection positions in radioembolization: proof of principle

Article References: Smits, M. L. J., Wijnen, N., Lam, M. G. E. H., de Bruijne, J., & Vonken, E.-J. P. A. (2026). Dual-lumen microcatheter facilitating multiple injection positions in radioembolization: proof of principle. CVIR Oncology, 2(1), Article 28. https://doi.org/10.1007/s44343-026-00055-1

Image Credits: AI Generated

DOI: 10.1007/s44343-026-00055-1

Keywords: dual-lumen microcatheter, radioembolization, guidewire contamination, holmium-166 microspheres, radiation segmentectomy, liver tumors, interventional radiology, hepatocellular carcinoma, microsphere delivery, catheter repositioning, Dual-lumen, microcatheter

The research, published in CVIR Oncology, examined whether balloon-occlusion microcatheters could improve tumor targeting during holmium-166 radioembolization. These devices carry a small inflatable balloon near their tip. When inflated inside a hepatic artery branch, the balloon temporarily halts blood flow beyond it, creating a zone of static flow arrest that proponents believe should push injected microspheres deeper into the tumor bed while preventing reflux back toward healthy liver. The idea has gained traction in transarterial chemoembolization, where several studies have reported better tumor control when the balloon is deployed. But rigorous, head-to-head evidence in radioembolization, where the physics of microsphere delivery matters just as much, has remained scarce.

What makes the Leuven study unusual, and scientifically valuable, is its within-patient design. Seven patients with unresectable primary liver tumors, six with hepatocellular carcinoma and one with hepatic angiosarcoma, each received two separate scout injections of holmium-166 microspheres at exactly the same arterial sites. The first scout dose, delivered during the standard work-up roughly two weeks before treatment, used a conventional end-hole catheter. The second, performed on the day of treatment, used an inflated balloon-occlusion catheter positioned at the identical location, with matching injection pressures, microsphere numbers, and imaging protocols. Because holmium-166 scouts and therapeutic doses use identical poly-L-lactic acid microspheres, the researchers could isolate the effect of the catheter itself with unusual precision, avoiding the confounding that arises when technetium-99m macroaggregated albumin, a particle with different size and shape characteristics, is used as a proxy.

After each scout injection, the team acquired single-photon emission computed tomography combined with CT to map exactly where the radioactive microspheres had settled. Their primary endpoint was the tumor-to-normal liver uptake ratio, a key measure of targeting quality that predicts whether a tumor receives a tumoricidal dose. The result ran counter to expectations. In six of the seven patients, the balloon catheter produced a lower tumor-to-normal liver uptake ratio than the conventional catheter. The median ratio fell from 3.1 with the conventional device to 1.7 with the balloon, a geometric mean ratio of 0.41. While this comparison did not reach conventional statistical significance with only seven pairs, the pattern was remarkably consistent, and a binomial test of the six-to-one split did reach significance.

Cone-beam CT scans told an equally sobering story. In six patients, the balloon catheter shrank the measured liver perfusion territory by between 7 and 60 percent compared with the conventional catheter. On its face, a tighter perfusion territory might sound like an improvement, suggesting more selective delivery. But in all six of those patients, the contracted territory no longer encompassed the entire tumor, leaving parts of the malignancy outside the treated zone. In one striking case, the balloon catheter actually raised the tumor-to-normal liver ratio while coverage of the tumor dropped to just 63 percent, a combination that could concentrate radiation in a fraction of the lesion while leaving the rest untreated. Because the balloon consistently produced lower targeting ratios or incomplete coverage, the treating physicians selected the conventional catheter for every therapeutic delivery.

Why would a device designed to improve targeting do the opposite? The researchers point to the distinctive hemodynamics of balloon occlusion. Unlike pressure-enabled drug delivery systems, which preserve forward flow through a one-way valve while blocking reflux, a balloon catheter creates abrupt static flow arrest and a pronounced pressure drop downstream of the balloon. The liver’s arterial anatomy is richly interconnected, with communicating arcades linking segments and even lobes. When the balloon cuts off flow at one branch, blood finds its way back into the occluded territory through these collaterals, and the redirected inflow can carry microspheres away from the intended target. Tumors situated at the boundary between adjacent vascular territories, so-called watershed tumors, are particularly vulnerable, because their arterial supply may come from more than one feeder artery and flow modulation at a single injection site leaves portions of the lesion poorly perfused.

The injection protocol may also have played a role. Holmium-166 scout doses at Leuven are delivered through a standardized low-pressure administration box designed to prevent overpressurization of the vial, a safety necessity for the radioactive microsphere system. That low-pressure regimen contrasts with balloon-assisted chemoembolization, where operators can push high injection pressures through a syringe mounted directly on the catheter, potentially overcoming watershed effects. Bench testing confirmed the balloon catheter’s pressure profile closely matched that of the conventional catheter, so the team attributes the lower targeting ratios not to injection mechanics but to genuine alterations in intrahepatic flow dynamics caused by the occluding balloon itself.

The study’s authors are careful about how far these conclusions travel. The trial was terminated early after seven patients when the QuiremScout and QuiremSpheres platform was discontinued, and all scout injections followed the same fixed order, meaning an order effect from the first microsphere injection, though unlikely given published concordance between scout and therapeutic distributions, cannot be fully excluded. The patient mix also included several watershed tumors that were never ideal balloon candidates, and one patient had an angiosarcoma, complicating flow analysis. The findings characterize holmium-166 scout distribution under a low-pressure protocol and may not extend to yttrium-90 platforms, alternative delivery systems permitting higher pressures, or dynamic antireflux devices, which preclinical work suggests could behave quite differently.

There is also a broader lesson about measurement. A tumor-to-normal liver uptake ratio on its own, the authors argue, is an incomplete yardstick, because a high ratio achieved at the cost of partial tumor coverage can be actively harmful. They propose judging targeting quality as a composite of the ratio, the completeness of tumor coverage, and the exposure of non-tumoral parenchyma, an approach made practical by dual-phase cone-beam CT, which can map arterial perfusion territories far more accurately than conventional anatomical segmentation. For now, the message for clinicians is one of caution rather than condemnation: the benefit of balloon-occlusion microcatheters in radioembolization cannot be assumed, and appears to depend heavily on each patient’s vascular anatomy. Larger, randomized studies with sequence inversion, ideally comparing across microsphere platforms, delivery systems, and injection pressures, will be needed to determine whether flow modulation earns a place in the radioembolization toolkit, or whether the humble end-hole catheter, in most patients, still delivers the best dose to the tumor.

Holmium-166 itself deserves attention when weighing these results. The isotope emits both beta particles for therapeutic effect and gamma photons at 81 keV, which is what allows the same scout injection used for planning to be imaged quantitatively on SPECT rather than merely serving as a rough surrogate. Yttrium-90, by contrast, produces almost no useful gamma signal, so planning scans with technetium-99m macroaggregated albumin must stand in for the therapeutic agent, introducing known discrepancies in particle size, density, and flow behavior. The Leuven team’s paired design exploits this holmium advantage: because scout and therapy microspheres are chemically and physically identical, the observed differences in distribution can be attributed to the catheter and the altered hemodynamics rather than to a mismatch between tracer and treatment.

The clinical stakes of targeting quality are considerable. Absorbed tumor dose is one of the strongest predictors of response in radioembolization, while inadvertent delivery of activity to non-tumoral liver parenchyma drives the risk of radioembolization-induced liver disease, a potentially serious decline in hepatic function that is especially concerning in patients with compromised liver reserve. A tumor-to-normal liver uptake ratio that drops from above three to below two, as observed in most patients here, implies a substantial shift of activity away from the malignancy, which could translate into lower tumoricidal doses and reduced treatment efficacy if such a distribution were used for therapy.

The study also illustrates a practical constraint of radioembolization logistics that is easy to overlook. Holmium-166 decays with a half-life of about 26 hours, and therapeutic activity must be manufactured and calibrated for a pre-specified treatment time. Because the balloon-occlusion scout was performed on the treatment day itself, the prescribed activity could not be recalculated from the alternative dosimetry, meaning the final delivery necessarily followed the conventional catheter plan. This timing structure, while a limitation for flexibility, is precisely what allowed the two work-ups to be compared within the same patient under otherwise matched conditions.

Finally, the findings add to a growing recognition that flow-modulating devices are not interchangeable. Static occlusion and dynamic antireflux systems alter intrahepatic pressure and flow in fundamentally different ways, and their effects may diverge across tumor types, vascular architectures, and injection protocols. Careful per-patient evaluation, rather than blanket adoption of any single device, remains the soundest approach.

Subject of Research: The effect of balloon-occlusion microcatheters on tumor targeting in holmium-166 transarterial radioembolization.

Article Title: Effect of balloon-occlusion microcatheters on tumor targeting in holmium-166 radioembolization: a within-patient comparative study

Article References: Bonne, L., Deroose, C. M., Deckers, W., Laenen, A., Terwinghe, C., Baete, K., Verslype, C., & Maleux, G. (2026). Effect of balloon-occlusion microcatheters on tumor targeting in holmium-166 radioembolization: a within-patient comparative study. CVIR Oncology, 2(1), Article 23. https://doi.org/10.1007/s44343-026-00056-0

Image Credits: AI Generated

DOI: 10.1007/s44343-026-00056-0

Keywords: radioembolization, holmium-166, balloon-occlusion catheter, tumor targeting, interventional radiology, liver cancer, hepatocellular carcinoma, SPECT/CT, cone-beam CT, transarterial radioembolization, microspheres, hemodynamics