[Experimental validation of a Monte Carlo-based treatment-planning system for electron beams]

Commercial, Monte Carlo-based 3-D treatment-planning systems will become more important for electron beams, e. g., for combined electron-photon fields or for intensity-modulated electron beams.

Using the commercial Monte Carlo algorithm (Oncentra MasterPlan 1.42), simulations were compared with measured data for electron energies from 4 MeV to 18 MeV of an Elekta linear accelerator. For the standard applicator size 14 x 14 cm(2) different square and rectangular apertures down to 2 x 2 cm(2) and arranged symmetrically as well as asymmetrically were fabricated. After optimizing the simulation parameters, depth dose curves, profiles and output factors were compared.

The results for standard electron applicators are satisfying in most cases. However, a major problem of this actual release is the resolution of the calculation matrix fixed by phantom size. From there, larger deviations up to 11% occur with decreasing aperture size for low and high electron energies, especially in the output factors. At medium electron energies and not too small apertures the simulations can be used clinically.

The Monte Carlo algorithm of the Oncentra MasterPlan treatment-planning system 1.42 can be used clinically in a wide range. However, a critical checkup of the results is necessary because nonacceptable deviations at low and high electron energies can occur in small electron fields.