Radiobiology of metastasesRadiobiological parameters of liver and lung metastases derived from tumor control data of 3719 metastases

Background and purposeThe radiobiological parameters for liver and lung metastases treated with stereotactic body radiation therapy (SBRT) are poorly defined. This project aimed at estimating these parameters from published tumor control probability (TCP) data, and separately for metastases with colorectal cancer (CRC) and non-CRC histology.Materials and methodsA total of 62 studies with 89 different treatment prescriptions for a total of 3719 metastases were analyzed in a Bayesian framework using four different radiobiological models: The LQ, mLQ, LQ-L and the regrowth model which accounts for tumor regrowth after SBRT.ResultsDepending on the particular model, α/β ratios in the range 13-23 Gy for pulmonary metastases and 16-28 Gy for hepatic metastases were estimated. For CRC metastases the estimated α/β ratio was 43.1 ± 4.7 Gy compared to 21.6 ± 7.8 Gy for non-CRC metastases. Typical isocenter dose prescriptions of 3 × 12 Gy, 3 × 14.5 Gy and 3 × 17 Gy applied within 5 days were predicted sufficient to control 90% of lung, liver and CRC metastases after 1 yr, respectively.Conclusionsα/β ratios for liver and lung metastases are higher than the usually assumed 10 Gy. Differences between CRC and non-CRC histology were found. Future studies confirming these findings in individual patient data are needed.