Effect of stereotactic body radiotherapy on regional metabolic liver function investigated in patients by dynamic [18F]FDGal PET/CT

Purpose: Stereotactic body radiotherapy (SBRT) is increasingly used for treatment of liver tumors but the effect on metabolic liver function in surrounding tissue is largely unknown. Using 2-deoxy-2-[¹⁸F]fluoro-D-galactose ([¹⁸F]FDGal) positron emission tomography (PET)/computed tomography (CT), we aimed to determine a dose-response relationship between radiation dose and metabolic liver function as well as recovery.

Procedures: One male subject with intrahepatic cholangiocarcinoma and five subjects (1 female, 4 male) with liver metastases from colorectal cancer (mCRC) underwent [¹⁸F]FDGal PET/CT before SBRT and after 1 and 3 months. The dose response was calculated using the data after 1 month and the relative recovery was evaluated after 3 months. All patients had normal liver function at time of inclusion.

Results: A linear dose-response relationship for the individual liver voxel dose was seen until approximately 30 Gy. By fitting a polynomial curve to data, a mean TD₅₀ of 18 Gy was determined with a 95% CI from 12 to 26 Gy. After 3 months, a substantial recovery was observed except in tissue receiving more than 25 Gy.

Conclusions: [¹⁸F]FDGal PET/CT makes it possible to determine a dose-response relationship between radiation dose and metabolic liver function, here with a TD₅₀ of 18 Gy (95% CI 12-26 Gy). Moreover, the method makes it possible to estimate metabolic recovery in liver tissue.