Direct Quantification and Comparison of Intratumoral Hypoxia following Transcatheter Arterial Embolization of VX2 Liver Tumors with Different Diameter Microspheres

Purpose: To evaluate the effect of embolic diameter on achievement of hypoxia after embolization in an animal model of liver tumors. Materials and Methods: Inoculation of VX2 tumors in the left liver lobe was performed successfully in 12 New Zealand white rabbits weighing 3.7 kg +/- 0.5 (mean +/- SD). Tumors were deemed eligible for oxygen measurements when the maximum transverse diameter measured 15 mm or more by ultrasound examination. Direct monitoring of oxygenation of implanted rabbit hepatic VX2 tumors was performed with a fiberoptic electrode during and after transarterial embolization of the proper hepatic artery to angiographic flow stasis with microspheres measuring 70-150 mu m, 100-300 mu m, or 300-500 mu m in diameter. Results: Failure to achieve tumor hypoxia as defined despite angiographic flow stasis was observed in 10 of 11 animals. Embolization microsphere size effect failed to demonstrate a significant trend on hypoxia outcome among the diameters tested, and pair-wise comparisons of different embolic diameter treatment groups showed no difference in hypoxia outcome. All microsphere diameters tested resulted in similar absolute reduction (24.3 mm Hg +/- 18.3, 29.1 mm Hg +/- 1.8, and 19.9 mm Hg +/- 9.3, P =.66) and percentage decrease in oxygen (56.0 mm Hg +/- 23.9, 56.0 mm Hg +/- 6.4, and 35.8 mm Hg +/- 20.6, P =.65). Pair-wise comparisons for percent tumor area occupied by embolic agents showed a significantly reduced fraction for 300-500 pm diameters compared with 70-150 pm diameters (P <.05). Conclusions: In the rabbit VX2 liver tumor model, three tested microsphere diameters failed to cause tumor hypoxia as measured by a fiberoptic probe sensor according to the adopted hypoxia defmitions.