Internal radiotherapy for hepatic metastases I: The homogeneity of hepatic arterial blood flow.

Internal radiotherapy, in the form of arterially infused yttrium-90-labeled microspheres, theoretically appears encouraging as a method of treatment for hepatic metastases. Previous investigators have assumed a homogeneous distribution of these microspheres and given dosages of isotope based solely on an estimated liver mass. The purpose of this study has been to establish the homogeneity of isotope distribution in liver substance when 15 micrometers microspheres are arterially injected. This has been done in three mammalian species, with the results expressed as a mean percentage coefficient of variation of 28 +/- 5%. Also demonstrated is the fact that 15 micrometers particles, while not penetrating to the venous circulation, achieve a more homogeneous spread throughout the liver than larger particles. It has been demonstrated that to achieve this maximum homogeneity distribution, 4000 beads/g of liver tissue are required. This equates in the therapeutic situation to a maximum activity of 4 Ci/g of infused microspheres. These results are considered significant in that they indicate criteria necessary to achieve the maximum homogeneity of therapeutic agent within liver substance when it is administered by this method, and will allow confidence limits to be attached to direct in vivo measurement of hepatic irradiation.