No abstract

Electron applicators and cut-outs have been used for some time in the delivery of electron beam therapy. A dual electron multileaf collimator (eMLC) consisting of upper and lower eMLCs was designed, and dose distributions of electron beams delivered by it were evaluated by Monte Carlo simulations by use of the EGSnrc Monte Carlo code. The percentage depth dose (PDD), dose profiles, dose gradient falloff (G), depth of maximum dose (R(100)), surface dose, bremsstrahlung background, beam flatness, and penumbra of the dual eMLC were evaluated and compared with those simulated and measured with the standard applicators inserted into the treatment head of the medical linear accelerator (linac). The results showed good agreement in most cases. Specifically, the flatness and penumbra obtained with the dual eMLC were better than those obtained with standard applicators. It is therefore possible to use the proposed dual eMLC in the delivery of electron beam therapy without the need for applicators and cut-outs. This will minimize the inconvenience of placing cut-outs on the patients; also, changes in the required field can be effected without the therapist going into the accelerator room when the dual eMLC is finally automated. The absence of a helium bag between the upper and lower eMLCs did not offer significant changes in the dosimetry parameters compared to the eMLC fitted with the helium bag.

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.

No abstract

The use of a dual electron multileaf collimator (eMLC) to collimate therapeutic electron beam without the use of cutouts has been previously shown to be feasible. Further Monte Carlo simulations were performed in this study to verify the nature and appearance of the isodose distribution in water phantom of irregular electron beams delivered by the eMLC. Electron fields used in this study were selected to reflect those used in electron beam therapy. Results of this study show that the isodose distribution in a water phantom obtained from the simulation of irregular electron beams through the eMLC conforms to the pattern of the eMLC used in the delivery of the beam. It is therefore concluded that the dual eMLC could deliver isodose distributions reflecting the pattern of the eMLC field that was used in the delivery of the beam.