Radiation tolerance of cirrhotic livers in relation to the preserved functional capacity: Analysis of patients with hepatocellular carcinoma treated by focused proton beam radiotherapy

Purpose : To determine the preserved functional capacity of the liver as a probable determinant of radiation tolerance in patients with cirrhosis and hepatocellular carcinoma, who underwent proton beam radiotherapy. Materials and Methods : We reviewed computed tomographic (CT) scans of 26 patients with cirrhosis and hepatocellular carcinoma during a period of 12–27 months after proton beam radiotherapy. Tumors were treated with focused proton beams with target doses of 140–186 TDF (time, dose, and fractionation). We measured the degree of hypertrophy of the untreated liver volume by measuring the total liver volume and the treated liver volume which was radiologically identified on contrast-enhanced CT scans. The risk of radiation-induced liver failure was estimated using the prediction score (PS) originally used for estimating posthepatectomy liver failure, substituting the planned treated liver volume for the resection liver volume. Results : The degree of hypertrophy ranged from —19% to 51%, and was significantly positively correlated with the ratio of the planned treated liver volume to the functional liver volume. The PS agreed well with observed radiation tolerance in 21 patients, but underestimated the tolerance in 5. This underestimation was diminished when the PS was recalculated using the identified untreated liver volume in lieu of the planned untreated liver volume. Conclusion : As in surgical treatment, radiation tolerance of the cirrhotic liver after focused treatement is closely related to the preserved functional capacity of the identified untreated liver volume, which shows compensatory hypertrophy following radiotherapy.