Prospective Trial Using Internal Pair-Production Positron Emission Tomography to Establish the Yttrium-90 Radioembolization Dose Required for Response of Hepatocellular Carcinoma.

Purpose: To prospectively assess the threshold dose for objective response of hepatocellular carcinoma (HCC), using Y internal pair-production positron emission tomography (PET) to quantify the radiation dose delivered to hepatic tumors after radioembolization.

Methods And Materials: A prospective study was performed under institutional review board approval from 2012 to 2014. Thirty-five patients with primary and secondary liver tumors undergoing Y treatment were recruited. Eight patients did not meet inclusion criteria, and 27 patients with HCC were included for analysis. Time-of-flight PET imaging was performed immediately after radioembolization and voxel values converted into Y activity. The radioembolization dose was calculated from PET images, and image segmentation was performed with volumetric analysis of dose deposition within tumors. Radiographic response was assessed on follow-up imaging.

Results: Treated HCC showed 84% objective response, 11% stable disease, and 5% progressive disease according to modified RECIST 1.1 response criteria. Responders had a higher median Y tumor dose than nonresponders (225 Gy vs 83 Gy, P < .01). Logistic regression models show tumor dose (P = .002) strongly predicted objective response. All nonresponders had tumor dose <200 Gy. No statistical difference for patient age, tumor volume, multifocal or extrahepatic disease, portal vein invasion, or injected Y activity was found between responders and nonresponders.

Conclusions: Hepatocellular carcinoma that resulted in objective response after radioembolization had a greater median tumor dose of 225 Gy, compared with 83 Gy in nonresponders. Delivered tumor dose can be assessed by PET and significantly impacts treatment response in HCC.