Reducing the probability of radiation-induced hepatic toxicity by changing the treatment modality from helical tomotherapy to fixed-beam intensity-modulated radiotherapy

Purpose: To estimate and compare the risk of radiation-induced hepatic toxicity (RIHT) in helical tomotherapy and fixed-beam intensity-modulated radiotherapy (IMRT) for the treatment of hepatocellular carcinoma (HCC). Materials and Methods: Twenty patients with unresectable HCC treated with tomotherapy were selected. We performed tomotherapy re-planning to reduce the non-target normal liver volume receiving a dose of more than 15 Gy (NTNL-V_15Gy), and we created a fixed-beam IMRT plan (FB-P). We compared the dosimetric results as well as the estimated probability of RIHT among the tomotherapy initial plan (T-IP), the tomotherapy re-plan (T-RP), and the FB-P. Results: Comparing the T-RP and FB-P, the homogeneity index was 0.11 better with the T-RP. However, the mean NTNL-V_15Gy was 6.3% lower with the FB-P. These differences result in a decline in the probability of RIHT from 0.216 in the T-RP to 0.115 in the FB-P. In patients whose NTNL-V_15Gy was higher than 43.2% with the T-RP, the probability of RIHT markedly reduced from 0.533 to 0.274. Conclusions: By changing the treatment modality from tomotherapy to fixedbeam IMRT, we could reduce the liver dose and the probability of RIHT without scarifying the target coverage, especially in patients whose liver dose is high.