Direct measurement method for 90Y activity in urine.

90Y radioembolization is an effective therapeutic method for unresectable hepatocellular carcinoma. A small amount of 90Y may detach from microspheres and be excreted in urine during treatment, and the accurate determination of 90Y activity in urine is crucial for radiation safety assessment. The β-particles emitted by 90Y have energy higher than the Cherenkov threshold, and its activity can be measured by liquid scintillation counting (LSC) and Cherenkov counting. This study explored the feasibility of direct determination of 90Y activity in urine by comparing LSC and Cherenkov counting methods. The focus was placed on investigating the effect of urine color (light transmittance), and the background count, counting efficiency, minimum detectable activity and method accuracy were analyzed. The results showed that the counting efficiency of both methods was positively correlated with light transmittance. Under the same light transmittance conditions, the counting efficiency of LSC was higher than that of Cherenkov counting. Cherenkov counting exhibited a lower background count and a smaller minimum detectable activity, with a superior performance especially under the conditions of high light transmittance. Verification with urine samples containing 90Y in the range of 0.195-6.696 kBq L-1 demonstrated that both methods had reliable accuracy, with the maximum relative deviation of 1.79% for LSC and 2.05% for Cherenkov counting. This study provides technical support for the reliable detection of 90Y in urine.