Urinary excretion of Yttrium-90 following intra-arterial microsphere treatment for liver tumours

Objectives To measure the urinary excretion of Yttrium-90 (90Y) following intra-arterial (IA) treatment with 90Y-microspheres for liver tumours.

Methods Urine was collected over 12h. 3 samples of 2 ml were analysed in a gamma counter (Cobra 5003, Packard, Meriden). The energy window was set at 15-300 keV. Following correction for decay, background and total volume of urine, measurements were normalized to the administered activity of 90Y. From a 90Y solution a calibration curve was constructed to assess the correlation between activity and counts per minute. Results are compared between patients treated with TheraSphere (Nordion, Canada)-mainly suffering HCC- and patients treated with SIR-Spheres (SIRTEX, Australia) for colorectal liver metastasis.

Results 15 patients were treated with TheraSphere, with an activity ranging from 977-6537 MBq (mean 2541). In 13 of 15 treatments it concerned primary liver cancer. 6 patients treated with SIR-Spheres were included. The mean activity was 1785 MBq (range: 1145-3212). The 12h urine collection contained on average a total activity of 52 kBq (range: 8-113) for TheraSphere and 1128 kBq (range: 438-2118) for SIR-Spheres. Approximately 0,0025% of the total activity was excreted in the urine during the first 12h following treatment with TheraSphere versus 0,0641% in case of SIR-Spheres. Microscopy did not reveal presence of microspheres in the urine.

Conclusions Activity measurements in urine yielded consistent results, with a significant difference between SIR-Spheres and TheraSphere (26 times lower). However, the overall excreted activities for both products remain low. In case of urinary incontinence a short hospital stay is not strictly essential but can be considered in individual cases when treated with SIR-Spheres. No specific guidelines seem necessary in case of TheraSphere