Treating Spinal-Cord Tumors with TTFields — A Simulation Study

Abstract

<h3>Purpose/Objective(s)</h3> Tumor Treating Fields (TTFields) are an anti-mitotic non-invasive therapy approved for the treatment of certain solid tumors such as glioblastoma (GBM) and malignant pleural mesothelioma (MPM). TTFields are low intensity electrical fields in the medium frequency range (100-500 kHz). TTFields are applied to the patient using two pairs of transducer arrays (TAs) placed on the patient skin. The therapeutic threshold for treatment is considered to be 1 V/cm. The distribution of the electric field within the body is determined by the geometry of the arrays, the anatomical area being treated, and the electric parameters of the different tissues, specifically their electrical conductivity. Treatment planning is necessary to maximize the efficacy of the treatment. However, some regions of the body are more challenging to treat with TTFields due to their geometrical characteristics. One such example is the spinal cord. The spinal cord is an elongated structure with high electric conductivity encompassed within relatively electrically insulating bone structure of the spine. This results in a cable-like structure. The unique structure of the spine makes delivering TTFields to spinal tumors a non-trivial task. While the electric fields can propagate well along the spinal cord, they cannot easily penetrate the vertebrae to reach the spinal cord. In this study, we used simulations to establish ground rules for treating the spinal cord. Specifically, we tested the feasibility of using TTFields for treating leptomeningeal metastases of breast cancer. <h3>Materials/Methods</h3> A realistic computational full body model of a healthy female was used in the study. Virtual transducer arrays were placed on the model's back at different heights, to the left and right of the spine. Arrays were also placed on the head and hips of the model. To simulate the delivery of TTFields to the spinal cord and CSF, we used Sim4Life v6.0 (ZMT Zürich) Ohmic-quasi-static solver. We applied 1A current at 150 kHz to the virtual arrays. In each simulation, we paired one array on the left to one array on the right, with different heights. The resulting field distribution along the spinal cord, CSF and nerves was then extracted. <h3>Results</h3> The field distribution has been analyzed along the axial plane of the patient. The mean field value for every slice was calculated, and the resulting axial-distribution was compared to the location of the two arrays along the models back. The results show that the maximal slice-averaged field intensity in the spinal cord is obtained between the arrays and in most cases is above the required 1 V/cm. <h3>Conclusion</h3> This work demonstrates that by orthogonally positioning the two pairs of arrays on the patient back to surround the tumor area, it may be possible to provide sufficient field intensity to tumors within the CSF or of the spinal cord.