Caren van Roekel

241 Use of an anti-reflux catheter in 166 Ho-radioembolization Treatment The ITT analyses were performed on 19/21 evaluable patients, including the two patients in whom catheter allocation was switched (i.e. the volume that was intended to be treated with the anti-reflux catheter was counted as volume treated with the anti-reflux catheter and vice versa). In one patient, 166 Ho-scout was not available due to a production failure and treatment simulation was performed using 99m Tc-MAA, but this patient was still evaluable for the primary endpoint. The patient with incomplete activity administration due to vial leakage (in one lobe, only 15% of calculated activity was administered) and the patient without a post-therapy 166 Ho-SPECT/CT were excluded from these analyses. The median T/N activity concentration ratio with the use of the anti-reflux catheter was 3.2 (range 0.9-8.7) versus 3.6 with a standard microcatheter (range 0.8-13.3) (difference in median -0.4, 95%CI -1.22 – 1.29, p=0.92) (Figure 4a). The median T/N activity concentration ratio with the anti-reflux catheter in the presence of spasm was 3.5 (range 2.4-4.7) versus 3.7 (range 0.9-8.7) without the occurrence of spasm (p=0.31, 95%CI -3.95 – 1.55). Both the median tumor-absorbed dose and the parenchymal-absorbed dose were (not-significantly) higher with the use of the anti-reflux catheter (difference in median tumor-absorbed dose +25 Gy, 95%CI -27 – 62, p=0.54 and difference in median parenchymal-absorbed dose +8 Gy, 95%CI -0.2 – 15.2, p=0.06) (Figure 4b,c). There was no difference in infusion efficiency between the use of the anti-reflux catheter (median residual activity 0.03%, range 0.001-0.37) and the standard microcatheter (median residual activity 0.04%, range 0.006-0.17) (difference in median -0.01%, 95%CI -0.05 – 0.03, p=0.93) (Figure 4d). 9