832 administration. Venous blood samples (1 mL) were taken before, just after, 5 days after and 10 days after administration of HoAcAcMS. Blood was centrifuged at 3,000 rpm for 10 min at 4°C and the serum was collected and stored at −20°C for further analysis. The serum levels of alkaline phosphatase (ALP) as an indicator of biliary toxicity, alanine aminotransferase (ALAT), aspartate amino transferase (ASAT) and gamma glutamyltransferase (γ-GT) as indicators of hepatocellular toxicity and albumin as indicator for liver function were analysed on a UniCel DxC 800 Clinical System (Beckman Coulter B.V., Woerden, The Netherlands). In addition, the serum holmium levels were measured using inductively coupled plasma−optical emission spectroscopy (ICP OES), as described in section 2.9. Histology Rabbits were euthanized 4 weeks after administration of HoAcAcMS. After termination, the lungs, heart, stomach, liver, kidneys, and a femur were excised and fixed in a 4% formalin solution. The tumor bearing liver was dissected and embedded in paraffin. After haematoxylin-eosin staining the liver and tumor tissue Bult et al. was histologically evaluated, to verify the presence of microspheres in the tumor and liver. Determination of Holmium Concentration The holmium concentration in buffer, serum, urine, faeces and bone samples was determined using ICP OES. Buffer samples were prepared by diluting 100 μL of supernatant to 5 mL nitric acid (5% w/v). Approximately 1 g of urine or faeces sample was destructed overnight using 5 mL nitric acid (30%). After overnight destruction the samples were centrifuged at 4,000 g and 1 mL of supernatant was diluted to 5 ml with nitric acid (5% w/v). The bone was separated from the marrow of the femur samples. Approximately 500 mg bone sample was weighed accurately, and was destructed in 4 mL aqua regia (one volume of nitric acid (65% w/w) mixed with three volumes hydrochloric acid (36% w/w)) under heating to 100°C. After evaporation to dryness, the residue was dissolved in 5 mL nitric acid (5% w/v). All samples were measured at three different wavelengths (339.898 nm, 345.600 nm and 347.426 nm respectively) by ICP-OES, using an Optima 4300 (PerkinElmer, Norwalk, USA). Analytical calibration curves from the holmium ICP standard solution were used to assess the precision and accuracy of the measurements. Fig. 4 (a) Schematic outline of rabbit anatomy on X-ray CT image (L=liver, T=tumor, S=stomach, I=intestine). (b) X-ray CT image of rabbit before intratumoral administration of 166HoAcAcMS showing the tumor, (c) X-ray CT image of rabbit after intratumoral administration of 166HoAcAcMS showing the selective deposition in the tumor as white artifacts, (d) X-ray CT image 4 weeks after administration, before termination, the white area in the tumor is still present as a cluster, although the shape has changed.