Response of liver metastases after treatment with yttrium-90 microspheres: Role of size, necrosis, and PET

OBJECTIVE. 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 Y-90 microspheres based on size and necrosis criteria using CT and comparing the results to PET and to describe imaging features related to Y-90 therapy. MATERIALS AND METHODS. We reviewed the imaging studies of 42 patients with unresectable liver metastases treated with lobar radioembolization with Y-90. 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. RESULTS. 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%). CONCLUSION. The use of necrosis and size criteria on CT and correlation with PET may improve the accuracy of assessment of response to Y-90 treatment in patients with liver metastases and detect response earlier than standard size criteria.