Optimization of dual electron multileaf collimator materials by use of EGSnrc.

A dual electron multileaf collimator (eMLC) has recently been proposed and ascertained to be effective in the collimation of therapy electron beams. The EGSnrc Monte Carlo code has been used in the optimization of the dual eMLC by simulation of the Varian 2100C medical linear accelerator with the applicator completely replaced by the dual eMLC, and calculation of the dose distributions in a water phantom. The planar fluence results showed that the material combination of 2-cm-thick brass and 2-cm-thick tungsten (eMLCT1) as upper and lower eMLCs, respectively, offers minimal radiation leakage outside the treatment field. Dose calculation results used in estimation of the maximum dose, depth of the maximum dose, surface dose, bremsstrahlung background, and penumbra indicate that eMLCT1 offers better beam qualities than do the other dual eMLCs that were considered. Maximum optimization was obtained with the dual eMLC designed such that the material of the lower eMLC had a higher density than that of the upper eMLC.