Response of Liver Metastases After Treatment with Yttrium-90 Microspheres: Role of Size, Necrosis, and PET

Abstract

Yttrium-90 radioembolization is an emerging treatment for liver malignancies. The purpose of this study was to evaluate the imaging response of liver metastases to 90Y microspheres based on size and necrosis criteria using CT and comparing the results to PET and to describe imaging features related to 90Y therapy. We reviewed the imaging studies of 42 patients with unresectable liver metastases treated with lobar radioembolization with 90Y. CT response was determined using traditional size criteria (World Health Organization [WHO] and Response Evaluation Criteria in Solid Tumors [RECIST]), necrosis criteria, and combined criteria (RECIST and necrosis). We compared the response on CT with the response on PET. Complications of treatment were assessed. The response rate was 19% (8/42) by WHO criteria, 24% (10/42) by RECIST, 45% (19/42) by necrosis criteria, and 50% (21/42) by combined criteria. Stabilization of lesion size occurred in 50% of patients. Necrosis and combined criteria identified responders earlier than RECIST and WHO criteria. Seven responders by combined criteria had an increase in lesion size on initial follow-up and would have been considered nonresponders. PET scans were obtained in 23 patients (33 treated lobes). PET detected significantly more responses to treatment (21/33, 63%) than CT using RECIST (2/33, 6%) or combined criteria (8/33, 24%) (p < 0.05, McNemar test). Complications of treatment included radiation cholecystitis (10 patients, 23%) and liver edema (18 patients, 42%). The use of necrosis and size criteria on CT and correlation with PET may improve the accuracy of assessment of response to 90Y treatment in patients with liver metastases and detect response earlier than standard size criteria.