Modulation of Tumor-Treating Fields by Cerebral Edema from Brain Tumors

Cerebral edema is an important component of brain metastasis, and its presence may alter the distribution of tumor-treating fields (TTFields). We therefore performed a computational study to model the extent of this alteration according to various edema conditions associated with the metastasis.

Postacquisition magnetic resonance imaging data sets were obtained from 2 patients with solitary brain metastases from non-small cell lung cancer. After delineation of various anatomies, a 3-dimensional finite element mesh model was generated and then solved for the distribution of applied electric fields, rate of energy deposition, and current density at the gross tumor volume (GTV), edema, and other cranial structures. Electric field-volume histograms, specific absorption rate-volume histograms, and current density-volume histograms were generated, by which plan quality metrics were derived from and used to evaluate relative differences in field coverage between models under various conditions.

Changes in the conductivity of cerebral edema altered the electric fields, rate of energy deposition, and current density at the GTV region. At the cerebral edema region, increasing electric conductivity of the edema only decreased the electric fields and rate of energy deposition while the current density increased. The ratio of edema-to-tumor is also important because the plan quality metrics increased linearly when the edema-to-GTV ratio decreased, and increased vice versa. Furthermore, a conductive necrotic core additionally altered the distribution of TTFields according to the plan quality metrics.

Our modeling study demonstrated that cerebral edema alters the distribution of applied TTFields in patients. Personalized treatment planning will need to take into account the modulating effects of cerebral edema on TTFields as well as additional effects from a necrotic core inside the GTV.