Prospective Study of Systemic Yttrium-90 Elution during Radioembolization of Hepatic Metastases

To evaluate total blood radioactivity (BR) after SIR-Spheres yttrium-90 (⁹⁰Y) radioembolization and differences in BR based on delivery method.

Twenty participants with hepatic metastases undergoing first radioembolization were prospectively enrolled from December 2017 to June 2018. Blood samples were drawn at baseline and 0, 10, 20, 60, and 120 minutes after ⁹⁰Y administration. BR was measured with a γ-counter and scaled by estimated blood volume. Percentage of instilled radioactivity in the bloodstream was calculated as area under the fitted curve, and differences between delivery methods were examined with nonparametric statistical tests.

In 10 participants, resin microspheres were instilled with 50% Isovue 300 diluted in saline solution in the D line, and 10 others were treated with dextrose 5% in water (D5W) in the D line. Median administered activities were 944 MBq (range, 746-1,993 MBq) and 1,213 MBq (range, 519-2,066 MBq), respectively. Fraction of ⁹⁰Y in blood was significantly higher with dilute contrast agent than with D5W (median, 0.5% of injected activity vs 0.2%; P = .001). Among all participants, the maximum activity delivered was 2,066 MBq, and a maximum of 1% of administered radioactivity was measured as free ⁹⁰Y in blood. Assuming these highest-case values and complete decay of all free ⁹⁰Y in bone, a dose to red marrow of 132.3 mGy was calculated by Organ Level INternal Dose Assessment/EXponential Modeling.

Blood sampling after radioembolization allowed for estimation of the time-activity curve and BR. Delivery with 50% contrast agent in saline solution resulted in a significant increase in BR vs D5W, even though the total BR for both groups was nominal.