The Use of Normal Tissue Complication Probability to Predict Radiation Hepatitis

Purpos e :Although It has been known that the tolerance of the liver to external beam irradiation depends on the irradiated volume and dose, few data exist which quantify this dependence. However, recently, with the development of three dimensional (3- D) treatment planning, have the tools to quantify the relationships between dose, volume, and normal tissue complications become available. The objective of this study is to investigate the relationships between normal tissue complication probability (NTCP) and the risk of radiation hepatitis for patients who received variant dose partial liver irradiation. Mate ria ls and Me thod : From March 1992 to December 1994, 10 patients with hepatoma and 10 patients with bile duct cancer were included in this study. Eighteen patients had normal hepatic function, but 2 patients (prothrombin time 73%, 68%) had mild liver cirrhosis before irradiation. Radiation therapy was delivered with 10MV linear accelerator, 180∼200 cGy fraction per day. The total dose ranged from 3,960 cGy to 6,000 cGy (median dose 5,040 cGy). The normal tissue complication probability was calculated by using Lyman's model. Radiation hepatitis was defined as the development of anicteric elevation of alkaline phosphatase of at least two fold and non-malignant ascites in the absence of documented progressive. Results :The calculated NTCP ranged from 0.001 to 0.840 (median 0.05). Three of the 20 patients developed radiation hepatitis. The NTCP of the patients with radiation hepatitis were 0.390, 0.528, 0.844 (median : 0.58±0.23), but that of the patients without radiation hepatitis ranged from 0.001 to 0.308 (median : 0.09±0.09). When the NTCP was calculated by using the volume factor of 0.32, a radiation hepatitis was observed only in patients with the NTCP value more than 0.39. By contrast, clinical results of evolving radiation hepatitis were not well correlated with NTCP value calculated when the volume factor of 0.69 was applied. On the basis of these observations, the volume factor of 0.32 was more correlated to predict a radiation hepatitis. Conclusion :The risk of radiation hepatitis was increased above the cut- off value. Therefore the NTCP seems to be used for predicting the radiation hepatitis.ope