Internal radiotherapy for hepatic metastases II: The blood supply to hepatic metastases.

Given that metastatic hepatic malignancy remains as a significant cause of death, with a median survival after diagnosis of only 7 months despite treatment, there exists a need for some effective treatment modality. Internal radiotherapy in the form of yttrium-90 microspheres infused into the hepatic artery appears to be a promising method of therapy. One criterion required for the success of this treatment is that of a differentially greater arterial supply to tumor as opposed to liver tissue. This arterial hypervascularity of tumor has been demonstrated before. However, some conflict has been reported as to the maintenance of this state as tumor size increases. Using 15 micrometers Cobalt-57 microspheres for studying salivary adenocarcinoma implants in DA rat livers, these experiments have demonstrated a constant blood flow in the tumor periphery of 3.9 times that within the normal hepatic parenchyma, regardless of tumor size. Also demonstrated is a progressive decrease in central tumor arterial blood flow after a tumor diameter of 6 mm has been exceeded. Arterial hypervascularity of liver tissue adjacent to the tumor has been demonstrated while an intermediate zone of liver tissue appeared hypovascular, suggesting the presence of shunting. In three humans with metastatic liver disease, hepatic artery infusion of particulate radiotracer has demonstrated the peripheral tumor hypervascularity and relative central tumor hypovascularity with good correlation obtained with the images of the metastases on conventional colloidal hepatic scintigraphy. This method allows assessment of the patient's suitability for internal radiotherapy by enabling assessment of the tumor vascularity and the degree of potentially dangerous extrahepatic irradiation.