Does multidetector CT attenuation change in colon cancer liver metastases treated with⁹⁰Y help predict metabolic activity at FDG PET?

Purpose: To evaluate the correlation between change in attenuation and tumor metabolic activity assessed by using fluorodeoxyglucose (FDG) positron emission tomography (PET) in colon cancer liver metastases treated with yttrium 90 (⁹⁰Y) radioembolization. Materials and Methods: This Health Insurance Portability and Accountability Act-compliant retrospective study was approved by the institutional review board; patient informed consent was waived. Unresectable chemorefractory colon cancer liver metastases treated with ⁹⁰Y radioembolization in 28 patients were evaluated at pre- and posttreatment multidetector computed tomographic (CT) and FDG PET scans. Maximum cross-sectional diameter, volume, and overall attenuation of target lesions were calculated. The percentage change (%Δ) in these parameters after treatment was calculated and correlated with the standardized uptake value (SUV) analysis at FDG PET. The accuracy of the radiologic parameters in helping predict response to treatment at FDG PET was assessed. Data were analyzed by using the Student t, Wilcoxon matched pair, Mann-Whitney, Spearman rank correlation, and xχ² tests. The signifi cance level was set at .05. Results: Seventy-four metastatic lesions in 10 women and 18 men (mean age, 61.5 years ± 14.3 [standard deviation ]) were evaluated. Mean follow-up interval for multidetector CT after treatment was 30 days. A signifi cant reduction in maximum cross-sectional diameter, volume, and attenuation was observed from pre- to posttreatment multidetector CT (P < .05). The %Δ in attenuation had higher correlation with %Δ in SUV (r = 0.61) than diameter ( r = 0.39) or volume ( r = 0.49) and also predicted the metabolic activity at FDG PET with higher sensitivity (P < .001). By using a threshold level of a reduction in attenuation of 15% or greater, attenuation showed 84.2% sensitivity and 83.3% specificity in predicting response at FDG PET evaluation. Conclusion: Changes in attenuation of colon cancer liver metastases treated with ⁹⁰Y radioembolization correlate highly with metabolic activity at FDG PET and may be useful as an early surrogate marker for assessing treatment response.