Caren van Roekel

237 Use of an anti-reflux catheter in 166 Ho-radioembolization FIGURE 2. Stepwise process of absorbed-dose estimation after treatment. First, left- and right perfusion territories were manually delineated on the low-dose CT from the baseline [ 18 F]-FDGPET/CT, based on the cone-beamCTs (if available) or the baseline contrast-enhanced CTs. Afterwards, tumors were automatically defined on the baseline [ 18 F]-FDGPET/CT using a threshold-based approach. Then, the low-dose CTs of the baseline [ 18 F]-FDG PET/CT and the post-treatment 166 Ho-SPECT/CT were coregistered. Using a rigid transformation, the volumes of interest of the tumors and the healthy liver tissue (the left and right perfusion territories) were transferred to the 166 Ho-SPECT/CT and absorbed doses were obtained. RESULTS This study was discontinued prematurely because of slow recruitment and a high drop-out rate. In total, 28 patients were included in this study between June 2014 and April 2019. Two patients were diagnosed with rapid progressive disease and no longer meeting the inclusion criteria and excluded before administration of 166 Ho-scout and/or 166 Ho-radioembolization. In five patients (18%) an anti-reflux catheter could not be used because of unsuitable vascularity, meaning that because of vessel size, tortuosity or the occurrence of vasospasm, an adequate injection position with the anti-reflux catheter could not be obtained. Twenty-one patients received 166 Ho-radioembolization using the anti-reflux catheter(Table 1, Figure 3). Median time from pre-treatment imaging using [ 18 F]-FDG PET/CT to treatment was 14 days (range 6-42 days) and median time from pre-treatment imaging to post-treatment 166 Ho-SPECT/CT was 17 days (range 9-46 days). Administration characteristics are listed in Table 2. In two of these patients, catheter allocation was switched during treatment because of vessel size and tortuosity. In one patient, due to a vial deficiency, only a small part (15% in one lobe) of the activity was injected in the liver. Furthermore, follow-up imaging was not (fully) available in two patients and a post-therapy 166 Ho-SPECT/CT was not acquired in one patient (Figure 1). Sixteen patients were treated with the first version of the Surefire® anti-reflux catheter and five patients were treated with the updated second version: the Surefire Precision infusion system®. In six of 21 treated patients (29%), vasospasm occurred during the use of the anti- reflux catheter, both with the initial version (5/16 patients) and with the newer Surefire Precision system® (1/5 patients). Nitroglycerin was administered in 18/21 Surefire® injections during vasospasm or as prophylaxis to prevent vasospasm. Adverse device effects are listed in Table 3. 9