Small cell lung cancer (SCLC) is an aggressive malignancy with a high incidence of brain metastases. Prophylactic cranial irradiation (PCI) was developed to reduce central nervous system (CNS) relapses and has been shown to improve survival, particularly in limited-stage disease. The pivotal Auperin meta-analysis and subsequent studies confirmed its role in patients achieving a complete response to initial therapy. In extensive-stage SCLC, earlier trials demonstrated reduced brain metastases and modest survival gains, but more recent studies incorporating routine magnetic resonance imaging (MRI) surveillance failed to show overall survival benefits, supporting MRI monitoring with salvage therapy as an alternative. Neurocognitive toxicity remains the major limitation of PCI, especially in older adults. Common effects include memory impairment, cognitive changes, and a reduced quality of life. Advances such as hippocampal avoidance PCI and neuroprotective strategies like memantine have shown the ability to mitigate long-term decline. Modern radiotherapy techniques, including intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), enable the precise sparing of critical structures while maintaining intracranial control. The integration of immunotherapy has shifted treatment paradigms in SCLC. While checkpoint inhibitors have improved systemic outcomes, their impact on brain relapses and interactions with PCI remain uncertain. This review provides an overview of the evolution of PCI in SCLC, while emphasizing current challenges and future directions.