Caren van Roekel

131 One-day treatment in 166 Ho-radioembolization Limitations of this study included the heterogeneous disease cohort. Furthermore, this study suffers from a selection bias due to the portion of patients treated in the HEPAR I and II studies who received an additional simulation angiography with administration of 99m Tc-MAA. To overcome this issue findings on 99m Tc-MAA were also taken into consideration. Another limitation and confounding factor was the learning curve. Over time, practical skills and knowledge increased, and certain practices that were used in patients in the HEPAR I study are now no longer common practice (e.g. routine coiling of the gastroduodenal artery and proper hepatic artery injections). The large percentage (12%) of patients who were excluded from treatment is expected to be much lower in current clinical practice. This learning curve also applies to the interpretation of the scintigraphic images after administration of 99m Tc-MAA. Given the findings of the current study, the same-day treatment method will no longer be standard for treating patients with 166 Ho-radioembolization at our center. Calculation and ordering of the prescribed activity limits the feasibility of same-day treatment. However, in those cases where exclusion or adjustment of treatment are unlikely (e.g. radiation segmentectomy) and prescribed activity can be pre-calculated, without the information from 166 Ho-scout, same-day treatment may still be an option. In conclusion, 166 Ho-radioembolization as a one-day treatment procedure is feasible in the majority of selected patients, although treatment was adjusted in 12% of patients and cancelled in 12% of patients. This approach may be beneficial for a select patient population, however, personalized treatment planning based on 166 Ho-scout distribution does not allow for same-day procedures. ACKNOWLEDGEMENTS We thank Remmert de Roos and Gerard Krijger for preparing the microspheres. We thank Christiaan van Kesteren for his assistance in designing the figures. 4