The effect on tumour control probability of using AXB algorithm in replacement of AAA for SBRT of hepatocellular carcinoma located at lung-liver boundary region.

Objective: To retrospectively analyze the clinical impact on stereotactic body radiation therapy (SBRT) for hepatocellular carcinoma (HCC) located at lung-liver boundary due to the use of Acuros XB algorithm (AXB) in replacement of anisotropic analytical algorithm (AAA).

Methods: 23 SBRT volumetric modulated arc therapy (VMAT) plans for HCC located at lung-liver boundary were calculated using AAA and AXB respectively with the same treatment parameters. The dose-volume data of the planned target volumes (PTVs) were compared. A published tumour control probability (TCP) model was used to calculate the effect of dosimetric difference between AAA and AXB on tumour control probability.

Results: For dose calculated by AXB (Dose to medium), the D95% and D98% of the PTV were on average 2.4 and 3.1% less than that calculated by AAA. For dose calculated by AXB (dose to water), the D95% and D98% of the PTV were on average 1.8%, and 2.7% less than that calculated by AAA. Up to 5% difference in D95% and 8% difference in D98% were observed in the worst cases. The significant decrease in D95% calculated by AXB compared to AAA could result in a % decrease in 2 year TCP up to 8% in the worst case (from 46.8 to 42.9%).

Conclusion: The difference in dose calculated by AAA and AXB could lead to significant difference in TCP for HCC SBRT located at lung-liver boundary region.

Advances in knowledge: The difference in calculated dose and tumour control probability for HCC SBRT between AAA and AXB algorithm at lung-liver boundary region was compared.