Biological dose-enhancement analysis with Monte Carlo simulation for Lipiodol for photon beams

Abstract

Background

Previously, the physical dose-enhancement factor (D_physEF) enhancement was introduced. However, the dose enhancement considering the biological effectiveness was not shown.

Purpose

The aim of the current study was to evaluate the biological dose-enhancement factor (D_bioEF) by the dose rate and to compare the D_physEF and the D_bioEF in Lipiodol for liver Stereotactic Body Radiation Therapy (SBRT).

Materials and methods

Flattening-filter-free (FFF) 6-MV (6MVX) and 10MVX beams were delivered by TrueBeam. A virtual inhomogeneity phantom and a liver SBRT patient-treatment plan were used. The D_physEF and lineal energy distribution ([[mml:math altimg="si8.gif"]][[mml:mi]]y[[/mml:mi]][[/mml:math]]) distribution was calculated from Monte Carlo simulations. Using a microdosimetric-kinetic (MK) model that is estimated based on the linear-quadratic formula for Lipiodol using human liver hepatocellular cells (HepG2), the biological dose and biological dose enhancement factor (D_bioEF) were calculated. The dose rate in the simulation was changed from 0.1 to 24Gy/min.

Results

The D_bioEF (DR:2Gy/min) and D_physEF with 10MVX FFF beam were 23.2% and 19.1% at maximum and 12.8% and 11.1% on average in the Lipiodol. In the comparison of the D_bioEF between 0.1–24Gy/min, the D_bioEF was 21.2% and 11.1% with 0.1Gy/min for 6MVX and 10 MVX, respectively. The D_bioEF was larger than DEF for the 6MVX and 10MVX FFF beams. In clinical cases with the 10MVX FFF beam, the D_bioEF and D_physEF in the Lipiodol region can increase the in-tumor dose by approximately 11% and 10%, respectively, without increasing the dose to normal tissue.

Conclusions

The lower-energy and higher-dose-rate beams were contributed to the biological dose. The Lipiodol caused the enhancement of the physical dose and biological effectiveness.

Advances in knowledge

The biological dose enhancement (D_bioEF) should be considered in the high-density material such as the Lipiodol.