SU‐F‐T‐630: Energy Spectral Study On Lipiodol After Trans‐Arterial Chemoembolization Using the Flattened and Unflattened Photon Beams

Abstract

Purpose:SBRT combining transarterial chemoembolization with Lipiodol is expected to improve local control. Our showed that the dose enhancement effect in the Lipiodol with 10X flattening filter free (FFF) was inserted. This study was to investigate the energy fluence variations of electron in the Lipiodol using flattened (FF) and FFF beams.Methods:FF and FFF for 6X and 10X beams by TrueBeam were used in this study. The Lipiodol (3 X 3 X 3 cm3) was located at the depth of 5 cm in water, the dose enhancement factor (DEF) and energy fluence were calculated by Monte Carlo (MC) calculations (PHITS).Results:DEFs with FF and FFF of 6X were 17.1% and 24.3% at rebuild‐up region in the Lipiodol (5.3cm depth), 7.0% and 17.0% at the center of Lipiodol (6.5cm depth), and −13.2% and −8.2% at behind Lipiodol (8.3cm depth). DEFs with FF and FFF of 10X were 21.7% and 15.3% at rebuild‐up region, 8.2% and 10.5% at the center of Lipiodol, and −14.0% and −8.6% at behind Lipiodol. Spectral results showed that the FFF beam contained more low‐energy (0–0.3MeV) component of electrons than FF beam, and FF beam contained more high‐energy (over 0.3MeV) electrons than FFF beam in Lipiodol. Behind the Lipiodol, build‐down effect with FF beam was larger than FFF beam because FF beam contained more high energy electrons. The difference of DEFs between FFF and FF beams for 6X were larger than for 10X. This is because 10X beam contained more high‐energy electrons. Conclusion: It was found that the 6XFFF beam gives the largest change of energy fluence and the largest DEF in this study. These phenomena are mainly caused by component of low‐energy electrons, and this energy is almost correspond to the boundary of photo electronic dominant and Compton scattering dominant region for photon beams.