Objective : Evaluate total blood radioactivity (BR) after SIR-Spheres yttrium-90 (90Y) radioembolization (TARE) and differences in BR based on delivery method and clinical variables.
Methods : 20 patients (10 men) with hepatic metastases undergoing first TARE were enrolled. Blood samples were drawn at baseline and 0, 10, 20, 30, 60, and 120 minutes after 90Y administration. BR was measured with a gamma counter and scaled by estimated blood volume. Time activity curves were fit to a biexponential model. Percent-instilled radioactivity in the bloodstream was calculated using area under the fitted curve; differences between delivery methods and clinical parameters were examined. Non-parametric statistical tests were utilized. Adverse events were recorded.
Results : In 10 patients, SIR-Spheres were instilled using 50% Isovue diluted in saline in the D line, and 10 were treated with D5W in the D line. Mean administered activity was 27.7 mCi and 36.2 mCi, respectively. Fraction of 90Y in the blood was significantly higher for those treated with dilute contrast compared to D5W (median 0.5% of the injected activity vs 0.2%, p = 0.001). Across both groups, maximum activity delivered to a patient was 55.9 mCi; a maximum of 1% of administered radioactivity was measured as free 90Y in the blood. Assuming these highest- case values and complete decay of all free 90Y in bone, we calculated a resulting dose to red marrow of 1.59 cGy using OLINDA/EXM. This represents only a small fraction of the procedure's cumulative radiation dose.
A non-significant decrease in fluoroscopy time was seen with contrast delivery medium (7.5 vs 8.3 minutes). No significant differences were seen in post-treatment leukocytes.
There were no immediate complications. Within the first month, 12 patients (60%) experienced adverse events: mild post-embolization syndrome (8), dehydration requiring IV fluids (1), liver failure (1), acute kidney injury (1), and death from sepsis related to UTI.
Conclusions : Blood sampling after radioembolization captured time activity curve and estimated BR. Delivery with dilute contrast resulted in a significant increase in BR compared to D5W, though the differences are not thought to be clinically meaningful.