Chemotherapy plus thoracic radiation followed by prophylactic cranial irradiation (PCI) is the standard of care in management of limited stage small cell lung cancer patients. However, whole brain radiation therapy (WBRT) is also associated with many side effects including consolidation of new memory, poor attention span/concentration, visual spatial difficulties, difficulty with executive planning, and poor fine motor control. There exists significant preclinical and clinical evidence that radiation induced injury to the hippocampus correlates with neurocognitive decline of patients who received WBRT. Reducing radiation dose to the hippocampus during WBRT has been postulated as an approach to mitigate neurocognitive impairment. The present study hypothesize that hippocampal sparing PCI will allow improved performance on tests of short term memory and executive function compared to a historical control receiving the same dose of conventional PCI. The primary objective of this study is to evaluate performance on the Hopkins Verbal Learning Test-Revised for delayed recall at 6 months following hippocampal-sparing PCI relative to the historical control. Secondary objectives are to estimate: composite cognitive function following hippocampal-sparing PCI relative to the historical control and the rate of metastases in the hippocampus at 2 years following hippocampal-sparing PCI.