Caren van Roekel

121 One-day treatment in 166 Ho-radioembolization INTRODUCTION Radioembolization is a minimally invasive treatment option for patients with primary or metastatic liver disease. Holmium-166 ( 166 Ho)-microspheres were developed as an alternative for yttrium-90 ( 90 Y)-microspheres because the same microspheres can be delivered both as a simulation dose ( 166 Ho-scout; 250 MBq) and as a treatment dose. This 166 Ho-scout has proven to be a more accurate predictor of lung shunt and intrahepatic distribution than the widely used technetium-99m macro aggregated albumin ( 99m Tc-MAA), and its safety has been established (1-3). Recently, interest in performing radioembolization as a one-day treatment procedure is growing, with several studies describing the feasibility and logistics of one-day treatment in 90 Y-radioembolization (4-6). A one-day procedure may be of clinical benefit for patients with rapidly progressive disease or symptomatic disease (e.g. in patients with neuro-endocrine tumors (NETs)), and it may be convenient for patients who need to travel long distances. Traditionally, treatment simulation is done 1-2 weeks before treatment, which provides the opportunity of personalized dosimetry. The aim of the current study was to assess the safety, feasibility, and practicality of one-day treatment with 166 Ho-radioembolization. MATERIALS AND METHODS Patients This was a secondary analysis of the patients from all the prospective studies on 166 Ho-radioembolization (i.e. the HEPAR I, HEPAR II, HEPAR PLuS and SIM studies), included between March 2012 and April 2019 (7-10). All patients in these studies were scheduled to undergo one-day 166 Ho-radioembolization. In total, 105 patients were treated. Three patients underwent whole-liver treatment in two stages and were included twice. Patient characteristics are summarized in Table 1. Before study inclusion, all patients provided written informed consent. The institution’s Medical Ethics Committee approved all studies. 4