Examining Array Layouts for Targeting a Single Lung with TTFields

Abstract

<h3>Purpose/Objective(s)</h3> Tumor Treating Fields (TTFields) are an anti-mitotic novel therapy, utilizing low-intensity alternating electric fields to arrest cell proliferation. TTFields are currently FDA-approved for treating Glioblastoma Multiforme (GBM) and Malignant Pleural Mesothelioma (MPM). The effect of TTFields is dose dependent: higher field intensities correlate with better survival rates for patients. TTFields are delivered using two pairs of arrays, placed on the patient's skin. The distribution of the fields is determined by the electric properties of the tissues and by the geometry of the patient and the system. Thus, the location of the arrays on the patient's body has a significant influence on the TTFields dose he or she may get. The array layout (TAL) is prescribed according to clinical guidelines for thoracic disease, taking into account the size of the patient. These guidelines are meant to target both lungs as a whole. However, in MPM patients, the disease is usually concentrated in one lung. In this study, we examined how placing one channel over a single lung and modifying the lateral channel will affect field distribution in the lungs. <h3>Materials/Methods</h3> To test new layouts, we placed cylinders imitating the arrays on the skin of a realistic human computerized model. We then used a simulation platform to simulate the TTFields distribution resulting from the different layouts. We tested the recommended layout by the guidelines, in which all four arrays are placed on the front and back of the thorax and are coupled in a cross formation (i.e., posterior left with anterior right and vice versa). We then compared this to layouts where one channel is focused around the right lung (front and back), paired with a layout in which one array is placed at the front or back of the left lung and the other under the right armpit. A current of 4A was set for channels consisting 20-disks arrays while a current of 2.6A was set for channels consisting at least one 13-disks array. For each layout, we calculated the average field intensity delivered to each lung. <h3>Results</h3> For patients receiving the recommended layout, average field intensity resulting from the recommended layout was 1.69 V/cm for each lung. The modified layouts provided 1.6-1.68 V/cm for the right lung, and 0.88-0.99 V/cm to the left lung. In terms of local minimum power density (LMiPD), the recommended layout provided 0.83 mW/cm³ for both lungs, while the modified layouts provided 0.62-0.81 mW/cm³ and 0.22-0.27 mW/cm³ to the right and left lungs, respectively. <h3>Conclusion</h3> Our results show that for patients eligible to be treated with the large cross layout, the modified single-lung layouts are not expected to provide a benefit in terms of TTFields dose. This is due the need for smaller arrays under the armpits, which reduces the expected output current from the device. However, further investigation is required for patients that are prescribed smaller arrays according to the guidelines.