Brief Summary: This phase II single-arm pilot study will evaluate the safety and preliminary efficacy of Optune-Tumor Treating Fields (TTFields) therapy as a prophylactic approach to reducing small cell lung cancer (SCLC) that has spread to the brain (brain metastases). Optune is a portable battery powered device that produces alternating electrical fields, termed tumor treatment fields ("TTFields") within the human body. These TTFields are applied to the patient by electrically insulated surface transducer arrays, which function to disrupt the rapid cell division of cancer cells.

Detailed Description: PRIMARY OBJECTIVE: I. Observed rate of brain metastases following TTFields therapy at 6 months. SECONDARY OBJECTIVES: I. Observed rate of brain metastases following TTFields therapy at 12 months. II. Survival of participants with SCLC after using TTFields therapy. III. Usage and overall safety characteristics of TTFields therapy. IV. Quality of life among participants using TTFields therapy. V. Observed rate of SCLC brain metastases at 6 months from the beginning of the 4th cycle of chemotherapy to development of brain metastases. OUTLINE: Participants will receive TTFields therapy on a continuous basis (i.e., 18-24 hours a day, 7 days a week) for a period of 12 months or until the development of brain metastases, whichever comes first. Participants will be able to carry the device in an over-the-shoulder bag or backpack so that they can receive continuous at-home treatment. The investigator or other designated healthcare provider will provide detailed instructions regarding the placement/replacement and positioning of the transducer arrays on the participants head. TTFields are applied to the shaved scalp via two pairs of orthogonally positioned transducer arrays. Each pair of transducer arrays will be centered on the participants shaved head such that one pair is placed on the left and right side of the head, and the second pair placed anteriorly and posteriorly. Transducer arrays should be replaced every 2 to 3 days, with a slight relocation of the new arrays \~2 cm from the prior location. After completion of study treatment, patients are followed up periodically.