Ziel/Aim In selective internal radiotherapy (SIRT), to achieve the planned target dose, complete implantation of the prescribed amount of microspheres is necessary. Recently, polylactic acid microspheres loaded with holmium-166 became available. This study was undertaken to evaluate the outflow dynamics during planning and treatment procedures with these microspheres, and to assess the distribution of residual activity in the delivery set.
Methodik/Methods 15 planning and 12 therapeutic radioembolization procedures were performed with poly-L-lactic acid microspheres loaded with Ho-166. The amount and distribution of residual activity was assessed by dose calibrator measurements and SPECT imaging. The activity flow profile from the microcatheter was assessed dynamically. For planning procedures, different injection methods were evaluated in order to attempt to decrease the residual activity.
Ergebnisse/Results The median residual activities for planning and treatment procedures using standard injection methods were 31.2% (range 17.3-44.1%) and 4.3% (range 3.5-6.9%), respectively. Planning residual activities could be decreased significantly with two injection methods similar to treatment procedures, to 17.5% and 10.9%, respectively (p = 0.002). Main predilection sites of residual microspheres were the 3-way stopcock and the outflow needle connector. During treatment procedures, more than 80% of the injected activity is transferred during the first three injection cycles.
Schlussfolgerungen/Conclusions After treatment procedures with holmium-loaded microspheres, mean residual activity in the delivery set is reproducibly low and between reported values for glass and resin microspheres. The majority of microspheres is transferred to the patient during the second and third injection cycle. An estimated residual waste of 3-4 % may be included in the treatment activity calculation. For planning procedures, a modified injection technique should be used to avoid high residual activities.
