4:03 PM Abstract No. 128 Real-time feedback on Y-90 microsphere delivery efficiency

Abstract

In Y-90 microsphere therapy, the prescribed tissue dose is achieved by effectively transferring all of the microspheres from the treatment delivery device (TDD) into the target tissue. Microsphere delivery efficiency is determined AFTER treatment via measurement of the residual microspheres in the TDD. A real-time dosimetry system was investigated in order to provide intraprocedural feedback on the presence of residual microspheres DURING treatment. For 22 clinical Y-90 glass microsphere administrations (BTG Biocompatibles Ltd, Farnham, UK), a wireless RaySafe i2 dosimeter (Unfors RaySafe AB, Billdal, Sweden) was placed inside the TDD beneath the outlet tubing. During administration, the dosimetry system displayed the instantaneous radiation dose rate associated with microspheres transiting or remaining residual in the tubing. Dosimetric data was compared with standardized quantification of residual microspheres (%) post-therapy, in order to establish the dosimeter’s utility in predicting residual. During the 1 year study period, there were 22 administrations. Only 2 cases exhibited elevated residual, which is consistent with our institutional experience of elevated residual in ∼10% of cases. In the 20 cases with minimal post-therapy residual (mean residual: 0.3% ± 0.1%), the instantaneous dose rate peaked and then rapidly decreased below 2% of peak within 9.5 ± 0.6 seconds. In the 2 administrations with elevated post-therapy residuals (5% and 2%), the real-time dose rate peaked but then slowly decreased and remained at approximately 20% of the peak thereafter, indicative of residual microspheres in the TDD. The persistent, elevated, real-time dose rate resulted in treatment delivery modification in 1 of these 2 cases. With treatment delivery modification, the post-therapy residual was 2%. Without delivery modification, the post-therapy residual was 5%. The RaySafe i2 dosimetry system can reliably provide valuable, real-time feedback regarding residual Y-90 microspheres in the outlet tubing during patient treatment. Administering physicians can then make intraprocedural modifications to improve microsphere delivery efficiency for more complete treatment delivery.