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Volume 24, Number 6, 2019

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

Daisuke Kawahara, Shuichi Ozawa, Hisashi Nakano, Katsumaro Kubo, Takehiro Shiinoki, Tomoki Kimura, Yasushi Nagata


Background Previously, the physical dose-enhancement factor (DphysEF) 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 (DbioEF) by the dose rate and to compare the DphysEF and the DbioEF 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 DphysEF and lineal energy distribution () 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 (DbioEF) were calculated. The dose rate in the simulation was changed from 0.1 to 24 Gy/min. Results The DbioEF (DR:2Gy/min) and DphysEF 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 DbioEF between 0.1–24 Gy/min, the DbioEF was 21.2% and 11.1% with 0.1 Gy/min for 6MVX and 10 MVX, respectively. The DbioEF was larger than DEF for the 6MVX and 10MVX FFF beams. In clinical cases with the 10MVX FFF beam, the DbioEF and DphysEF 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.

Signature: Rep Pract Oncol Radiother, 2019; 24(6) : 681-687

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Indexed in: EMBASE®, the Excerpta Medica database, the Elsevier BIOBASE (Current Awareness in Biological Sciences) and in the Index Copernicus.