SU‐E‐T‐450: Can Low Frequency Electric Fields Be Generally Used as a Sensitizer for Radiation Therapy and Chemo‐Therapy?

Abstract

Purpose: A low frequency electric field applied to a tumor is called a Tumor Treatment Field (TTF) and works by arresting cells during mitosis (M‐ phase). I have numerically simulated E‐field distributions to determine if a TTF can be applied to arbitrary tumor masses. This modality is currently under clinical trail with chemotherapy as a sensitizer. Because cells in M‐phase are also sensitive to radiation this method may also work as a radiotherapy sensitizer. Methods: Previous published results showed a TTF applied in to an intracranial glioma in a rat brain and subsequent tumor shrinkage. The TTF was numerically modeled. I have also modeled several therapies. The E‐field is calculated in inhomogeneous tissue using the Finite Element Method with normal and tangential boundary conditions applied to the exterior of the patient. These boundary conditions correspond to electrodes that may be manipulated to design treatment plans. Results: An AC electric field of amplitude 1V/cm–2V/cm in the 100kHz–200kHz range was previously found to be the most effective for arresting mitotic cells. In this range, however, the dielectric constant is very large and varies considerably between tissue layers. These large variations cause large impedances in layers of, e.g., fat and bone, i.e., these layers effectively “shield” deeper tissue layers against E‐fields applied in the normal direction. This requires large external voltages on surface electrodes to penetrate and achieve the required 1V/cm–2V/cm at deeper tissue layers, especially in human treatments. These large impedances are avoided with an E‐field applied in the tangential direction. The tangential fields are also patient size independent, greatly simplifying treatment planning. Results from several simulations comparing methods are presented. Conclusions: This work shows that an external applied device can produce an effective TTF at reasonably safe voltages if the applied field is not applied normally to the tissue layers.