TUMOR-TO-NORMAL UPTAKE RATIO OF Y-90 MICROSPHERES IN HEPATIC CANCER ASSESSED WITH TC-99(M) MACROAGGREGATED ALBUMIN

The selective delivery of a high dose of radiation to malignant hepati c tumours by infusion of non-biodegradable yttrium-90 (Y-90) microsphe res via the hepatic artery while sparing the nontumorous liver parench yma depends on the tumour-to-normal uptake ratio (T/N) of the therapeu tic radiopharmaceutical. Using intrahepatic arterial technetium-99m ma croaggregated albumin (Tc-99(m)-MAA), the effect of tumour type, tumou r vascularity assessed by hepatic angiography (HAG), tumour size and t he degree of extrahepatic shunting on the T/N was investigated in 377 patients with hepatocellular carcinoma (HCC) and 25 patients with colo rectal liver metastases. HCC was shown to have a wider range of T/N (0 .2-26.5) compared with liver metastases (2.3-7.2). HCC with vascularit y grade 1 on HAG had significantly lower T/N but there was no signific ant difference in HCC with higher vascularity grades. This confirmed t hat vascularity on HAG does not predict T/N. Overall there was no corr elation between T/N and tumour size. Large rumours (>20 cm) had a sign ificantly lower T/N, probably due to necrosis in the tumour centres. A decrease in mean T/N with increasing percentages of lung shunting was observed in HCC. Determination of T/N by simulation with Tc-99(m)-MAA is recommended before internal radiation therapy with Y-90 microspher es.