Clearance of parenchymal tumors following radiotherapy: analysis of hepatocellular carcinomas treated by proton beams

Clearance of a parenchymal tumor following radiotherapy was determined by using follow-up CT scans of 18 hepatocellular carcinoma tumors treated with focused proton beams. Regression analysis of the daily decrement ( DD) and the diameter ( D) of a tumor mass in each CT observation interval, DD = a ∗D b , showed that the exponent b was 3.0 or larger in early periods and 2.0 or smaller in late periods. This suggests that the clearance depends initially on the tumor volume, subsequently on the tumor surface area, and then it becomes much more moderate, possibly due to radiation damage to the parenchymal tissues.