Caren van Roekel

231 Use of an anti-reflux catheter in 166 Ho-radioembolization INTRODUCTION Radioembolization is an established treatment option for colorectal cancer patients with liver-dominant, chemorefractory, unresectable metastases (mCRC) (1, 2). Unfortunately, mCRC patients generally have relatively hypovascular, disseminated liver metastases, often leading to a suboptimal activity distribution (3, 4). It has been hypothesized that the use of an anti-reflux catheter may improve treatment outcomes in two ways. First, (partial) obstruction of the vascular lumen induces a decreased downstream pressure, possibly leading to a better tumor targeting (5-10). Also, the anti-reflux catheter causes a turbulent flow allowing particles to cross the laminar blood flow, leading to a more homogenous distribution (5). In a small pilot study of nine patients with various tumor types, the use of an anti- reflux catheter led to a significant decrease in hepatic non-target embolization and a significant increase in activity deposition in the tumors (11). Holmium-166 ( 166 Ho)-microspheres (QuiremSpheres ® , Quirem Medical, The Netherlands) were developed as an alternative to yttrium-90 ( 90 Y)-microspheres. Instead of using 99m Tc-MAA as a predictor of activity distribution, 166 Ho-scout (QuiremScout ® , QuiremMedical, The Netherlands), a small batch of identical 166 Ho- microspheres, can be used. This 166 Ho-scout has proven to be a more accurate predictor of the distribution of the treatment dose (12). 166 Ho can be visualized in- vivo by SPECT and MRI to assess activity distribution (13). Precise quantification of 166 Ho is possible using Monte Carlo simulation that simultaneously compensates for scatter, attenuation and collimator-detector response (14). The aim of this study was to investigate whether the use of an anti-reflux catheter increases tumor targeting in comparison with a standard microcatheter in mCRC patients treated with 166 Ho-radioembolization (15). MATERIALS AND METHODS Patients The SIM study (‘Surefire Infusion system® versus standard Microcatheter use during holmium-166 radioembolization’) was a single-center, within- 9