Caren van Roekel

245 Use of an anti-reflux catheter in 166 Ho-radioembolization the liver, and are hypovascular compared to other tumor types (3, 4). As a consequence, tumor targeting is often poor and response rates after radioembolization in mCRC patients are modest (22, 23). The hypothesis was tested that the use of an anti-reflux catheter improves tumor targeting during radioembolization. However, in this within-patient RCT, the use of the anti-reflux catheter did not lead to significant differences in T/N activity concentration ratio, tumor- and parenchymal-absorbed dose or infusion efficiency. To our knowledge, this is the first prospective study in humans investigating the supposed improved tumor targeting when using the Surefire® anti- reflux catheter for radioembolization. In the first study investigating this anti- reflux catheter, renal artery embolization with tantalum beads in a porcine model was performed with a standard microcatheter (n=3) versus an anti- reflux catheter (n=3). Embolization efficiency was 99.9%±1 with the anti-reflux catheter, versus 72%±13 with a standard microcatheter (9). Early studies found that infusion efficiency with the anti-reflux catheter was significantly improved due to a decrease in blood pressure in the downstream vascular territory (7, 8). Mean blood pressure with the tip closed was 79 mm Hg versus 58 mm Hg with the tip expanded (7). Besides a higher infusion efficiency, the use of anti-reflux catheters was found to lead to a higher tumor-absorbed dose in a mixed tumor-type cohort of nine patients who received pre-treatment infusion with 99m Tc-MAA twice, using both the anti-reflux catheter and a standard microcatheter. Relative increase in tumor deposition ranged from 33%-90% (11). Most studies were performed with the first version of the Surefire® anti- reflux catheter. A new version, the Surefire Precision Infusion System®, was introduced in January 2018 and is expected to have similar effects, although it has a different deployment mechanism: the anti-reflux umbrella is no longer situated at the tip of the catheter but is positioned slightly more proximal. Also, the catheter-shaft of the later version is less rigid. In contrast to the studies described before, we did not find significant differences between the anti-reflux catheter and the standard microcatheter. Possible reasons for this are the differences in patient population (only mCRC versus mixed tumor-type cohorts / even porcine models), embolic device ( 166 Ho versus 90 Y, 99m Tc-MAA, tantalum beads or chemoembolization particles) and treatment approach (lobar versus segmental). In addition, the manufacturer of the anti-reflux was in no way involved in this investigator-initiated study. 9