Metabolic response after intraarterial ⁹⁰Y-glass microsphere treatment for colorectal liver metastases: Comparison of quantitative and visual analyses by ¹⁸F-FDG PET

Our aim was to assess the feasibility of using PET for quantifying metabolic response after intraarterial ⁹⁰Y-glass microspheres for metastatic colorectal cancer to the liver by comparing visual estimates with hepatic standardized uptake values (SUVs). Methods: Twenty-seven patients (15 men, 12 women; age, 68 ± 12 y [±SD]) with metastatic colorectal cancer to the liver, and tumor progression despite polychemotherapy, were included. All patients had baseline CT or MRI, ¹⁸F-FDG PET, hepatic angiography, and intraarterial ^99mTc-labeled macroaggregated albumin scanning. Patients were treated with ⁹⁰Y-glass microspheres and were monitored for 3 mo using PET and serum carcinoembryonic antigen. The average absorbed dose was 139 ± 22 Gy. All treatments were performed on a lobar basis. For each case analyzed, regions of interest were drawn along the liver edge to measure SUVs on maximum-intensity-projection (MIP) and resliced axial images. Concomitantly, the visual estimate was graded as -1, 0, -1, -2, or -3 for progression, no change, and mild, moderate, and dramatic improvement at posttreatment PET. Results: Visual estimates placed 20 patients in the response category (-3 to -1) and 7 patients in the nonresponse category (0 to +1). There was a significant drop in the median SUV on the resliced axial images from 10,455 at baseline to 9,075 after treatment (P = 0.011) for the entire group. The percentage of metabolic response was significantly greater in the response group compared with that of the nonresponse group (-26% ± 25% vs. +6% ± 15%, P = 0.004). This correlated significantly with the respective visual estimates (r = 0.75, P < 0.0001). Furthermore, the direction of change agreed in 85% of patients using both methods. There was no significant correlation when the SUV from the simplified MIP images were used in the coronal or sagittal manner. Conclusion: It is feasible to quantify reduction of hepatic tumor metabolism objectively after ⁹⁰Y treatment for unresectable metastatic disease to the liver. SUVs of the entire axial slices of liver agree well with subjective visual evaluations. Quantitative PET is a useful technique in the treatment response evaluation of patients after ⁹⁰Y-glass microspheres.