Abstract and Introduction
Abstract
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 microspheres based on size and necrosis criteria using CT and comparing the results to PET and to describe imaging features related to Y therapy.
Materials and Methods: We reviewed the imaging studies of 42 patients with unresectable liver metastases treated with lobar radioembolization with Y. 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 treatment in patients with liver metastases and detect response earlier than standard size criteria.
Introduction
Traditionally, the role of radiation for the treatment of liver malignancies has been limited by the inability to deliver high radiation doses to the tumors. Yttrium-90 microsphere (TheraSphere, MDS Nordion) therapy delivers high radiation doses to the tumors while the normal liver tissue is relatively preserved. In this treatment technique, Y microspheres administered transarterially are preferentially retained in the tumor bed.
Imaging studies have an essential role in the assessment of response to Y treatment. PET depicts the metabolic activity of the tumors, whereas CT shows anatomic features, including lesion size and enhancement. Guidelines from the World Health Organization (WHO) and the Response Evaluation Criteria in Solid Tumors (RECIST) have traditionally been used to assess the therapeutic response of malignant tumors. These criteria are based on changes in lesion size. The utility of other imaging criteria, such as lesion necrosis relative to and in addition to size criteria (WHO and RECIST), for assessment of response of liver metastases to Y treatment has not been evaluated. In addition, the role of anatomic and functional imaging techniques for assessment of response to Y in the setting of metastatic liver disease has not been satisfactorily investigated.
The purpose of our study was to evaluate response of liver metastases to Y microspheres and to assess specific imaging findings and treatment complications. We compared the WHO and RECIST criteria with necrosis criteria and combined criteria of size (RECIST) and necrosis for assessment of response on cross-sectional imaging. In addition, treatment response on CT was correlated with response on PET.