gms | German Medical Science

Objective: Tumor Treating Fields (TTFields) are low intensity, alternating electric fields that disrupt cell division through physical interactions with key molecules during mitosis. TTFields are delivered clinically via insulated ceramic transducer arrays applied to the scalp for the treatment of glioblastoma.Currently these transducer arrays are removed from the scalp for the irradiation process. Preclinical data suggest that synergistic effects of simultaneous treatment with radiation and TTFields may improve clinical outcome. The purpose of this project is to examine the interaction of radiation and TTFields by simulating dose depositions with electric fields inside the irradiated structures. This should give information about whether TTFields have a significant impact on charged secondary particles produced by photon irradiation and thereby influence the final dose deposition.

Methods: Electric field distributions during radiotherapy are modeled and simulated with the C++ Monte-Carlo toolkit Geant4. Hence a Geant4 simulation of a medical linear accelerator and the processes occurring during irradiation with 6 MV photons has been extended by the possibility to switch on electric fields inside the used phantom. The alternating electric fields with intensities between 1 V/cm and 3 V/cm emitted by the electrode arrays are approximated by constant electric fields for the first investigations. The simulated dose distribution with an electric field switched on and off will be used to compare the dose distributions inside the phantom after irradiation with and without electric field.

Results: The implementation of the electric field into the accelerator simulation has been successfully tested. In a first approach an electric field with a field intensity of 2 kV/cm pointing in irradiation direction was simulated and no significant differences in the depth dose curves with and without electric field occurred. Neither the depth of the maximum dose was shifted nor was a significant change in the amount of deposited energy observed.

Conclusion: The result of this first investigation indicates that lower field intensities of TTFields should also show no significant differences in the depth dose depositions. The impact on the inplane and crossplane dose profilesis currently analyzed. The information provided by three dimensional simulation in this study contributes to the understanding of simultaneous tumor therapy with TTFields and radiotherapy that may improve the outcome of cancer patients.