Room: Karl Dean Ballroom A1
Purpose: Previously, we demonstrated Lipiodol-related dose enhancement using 10X flattening filter free (FFF) beams for liver stereotactic body radiotherapy (SBRT). This study aims to reveal the biological effectiveness and biological dose enhancement by Lipiodol using Monte Carlo calculation.
Methods: TrueBeam was used to deliver 6X and 10X FFF beams. A virtual inhomogeneity phantom and a liver SBRT patient treatment plan were used. The dose enhancement factor (DEF) and the lineal energy distribution ( D) value were calculated from Monte Carlo simulations (PHITS). Using an MK model that is estimated based on the Î² value in the LQ formula for Lipiodol using human liver hepatocellular cells (HepG2), the biological dose and biological dose enhancement factor (BDEF) were calculated.
Results: The difference in the mean D values with and without Lipiodol were 4.8% for 6 MVX and 3.6% for 10 MVX FFF beams. The BDEF and DEF with 6X FFF beam were at a maximum of 40.3% and 34.8%, respectively, and at an average of 22.9% and 19.3%, respectively, in Lipiodol. The BDEF and DEF with 10X FFF beam were at a maximum of 21.0% and 19.3%, respectively, and at an average of 12.7% and 11.6%, respectively in Lipiodol. The BDEF was larger than the DEF for the 6X and 10X FFF beams. In clinical cases with 10X FFF beam, the BDEF and DEF in the Lipiodol region can increase by approximately 11% and 10%, respectively, in tumor dose without the increase in normal tissue dose.
Conclusion: The 6X FFF beam was found to provide more biological effectiveness. Notably, the presence of Lipiodol appeared to locally increase the absorbed dose, as well as cause enhanced biological effectiveness in the tumor area; this may lead to clinical benefits.