Tumor Treating Fields (TTFields) Treatment Planning for a Patient With Astrocytoma in the Spinal Cord.

Abstract

PURPOSE/OBJECTIVE(S)\nThe use of TTFields following resection and chemoradiation has increased survival in patients with Glioblastoma (Stupp, et al. JAMA. 2015;314:2535-2543). Randomized data provide a strong rationale for the treatment of high-grade gliomas using TTFields with individualized array placement that maximizes the dose at the tumor in a patient-specific manner: providing higher TTFields intensity (≥1.0 V/cm) and power density (≥1.1 mW/cm3) which are associated with improved overall survival (Ballo, et al. Int J Radiat Oncol Biol Phys. 2019;104:1106-11). Here for the first time, we present a case demonstrating the use of numerical simulations for patient-specific TTFields treatment planning for a spinal tumor.\n\n\nMATERIALS/METHODS\nTreatment planning was performed for a 48-year-old patient following T10-L1 laminectomy, gross total resection, and postoperative chemoradiation for an anaplastic astrocytoma of the spinal cord. An MRI at 3 weeks following chemoradiation showed tumor recurrence. Based on the post-chemoradiation MRI, a patient-specific model was created. The model was created by modifying a realistic computational phantom of a healthy female. To mimic the laminectomy, the lamina in T10-L1 was removed and the region was assigned an electric conductivity similar to that of muscle. A virtual mass was introduced into the spinal cord. Virtual transducer arrays were placed on the model at multiple positions, and delivery of TTFields simulated. The dose delivered by different transducer array layouts was calculated, and the layouts that yielded maximal dose to the tumor and spine identified.\n\n\nRESULTS\nCombinations of the best layouts targeting the tumor (all above 2.5 mW/cm3) and the best layouts targeting the spinal cord were investigated. Transducer array layouts where the arrays were placed on the back of the patient with one above the tumor and one below yielded the highest doses at the tumor site. Such layouts yielded TTFields doses of over 2.5mW/cm3, which is well above the threshold dose of 1.1 mW/cm3. Three such layouts were presented as possibilities for a recommended treatment plan. As patient usage, or time on treatment, is correlated with improved patient outcomes, an interactive process was followed to adjust the treatment so that it incorporates both increased therapeutic dose to the tumor and increased overall patient usage and comfort.\n\n\nCONCLUSION\nThese data represent the first ever study on utilizing numerical simulations to plan treatment for a spinal tumor in a patient-specific manner. This is an important milestone in the development of a framework for TTFields dosimetry and treatment planning. This framework will have the potential to increase dose delivery to the tumor bed while optimizing placement that may enhance comfort and encourage device usage.