Abstract 692: Treating spinal cord metastases with tumor treating fields

Abstract

Abstract Introduction: Tumor Treating Fields (TTFields) is an anti-mitotic technology utilizing low-intensity (1-3 V/cm) electric fields within the medium frequency range (100-300 kHz) to treat solid tumors. TTFields are currently approved for the treatment of Glioblastoma (GBM). Some cancer types, such as breast cancer, lung cancer, and melanoma, frequently result in metastases to the spinal cord. Transducer array positioning used to treat abdominopelvic diseases (e.g. pancreatic cancer), in which one pair of arrays are placed on the anterior and posterior of the patient, and another pair of arrays placed on the lateral aspects of the patient have been shown to be inefficient for treating the spinal cord because the clinical threshold for field intensity of 1V/cm is not reached in the spine when these layouts. The structure of the spine, in which a relatively resistive bone structure encapsulates a highly conductive layer of fluid (cerebrospinal fluid), shunts the current delivered across the body by the arrays away from the spine, reducing the field within the spine to below the therapeutic threshold. To overcome this limitation, a new approach of array placement on the body is needed. Here we present a simulation-based study designed to identify array layouts that effectively deliver TTFields to the spine. Methods: To simulate delivery of TTFields to the spine, we used a human male 34 years old realistic computerized model (DUKE v3.1 by ITI’S, Zurich). In order to generate TTFields, an alternating current with current density of 200mA/disk with a frequency of 150 kHz was imposed on the outer surfaces of the disks of each pair of arrays. The simulations were performed using ZMT's Sim4Life v4.0 electro-quasi-static solver. Results: One of the array layouts tested was placement of a pair of arrays on the back of the patient. One array is placed above the target region in the spine to which treatment would be delivered, and the other array is placed below the region. With this configuration, a high electric field is induced within the spinal cord and surrounding CSF. Mean field intensity within the spine and nerves in between vertebrae T8-T9 at the top, and L3-L4 at the bottom were calculated at a value of 1.77 V/cm. It is important to note that the electric field is oriented along the spine in this instance (a vertical field). In general, the whole spine could be treated by placing one array on the neck, and one at the bottom of the spine. Conclusions: Placing two transducer arrays on the patient’s back allows single-direction treatment of the spinal cord and nerves. Further work should be conducted to find an effective treatment in the perpendicular direction. Citation Format: Ofir Yesharim, Ariel Naveh, Ze'ev Bomzon. Treating spinal cord metastases with tumor treating fields [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 692.