Evaluation of variable relative biological effectiveness and the creation of homogenous biological dose in the tumor region in helium ion radiation to the V79 cell line

In radiation therapy, ions heavier than proton have more biological advantages than a proton beam. Recently, ion helium has been considered due to high linear energy transfer (LET) to the medium and a higher relative biological effect (RBE). To design the spread-out Bragg peak (SOBP) of biological dose for radiation with any type of ion, we need exact values of RBE, which is dependent to dose, LET, and tissue specific parameter, and has spatial variations relative to depth in the tissue. Here, we calculate the exact value of RBE in helium ion irradiating V79 cell line by applying a parametric expression for RBE variations relative to LET, as well as using the Monte Carlo simulation code Geant4 to calculate the LET and the dose profile. The profiles of the Bragg Peak and LETs are calculated for each slice in the tumor region. To generate an appropriate biological SOBP, we compute a set of weighting factors using matrix computations, and by modulating helium ion beams, creation of optimal homogeneity at SOBP for biological doses was done.