Radiation-induced hepatic toxicity is common after liver irradiation. The Child-Pugh (CP) score is a combination of five clinical features used to assess the prognosis of chronic liver disease, and increases in CP score after irradiation can indicate reduced liver function and correlate with survival. We use the CP score changes and dosimetric data from liver cancer patients treated at MGH to fit a Lyman-Kutcher-Burman NTCP model to predict CP score increase from the normal liver DVH. Results show that the volume of healthy liver receiving low doses (5-10 Gy) is also strongly correlated with increases in CP score after irradiation, resulting in a volume effect not entirely consistent with mean liver dose.