original_query: What is the purpose of prophylactic cranial irradiation (PCI) in patients with complete responders (ED)?
query: What is the purpose of prophylactic cranial irradiation (PCI) in complete responders with extensive disease (ED) small cell lung cancer?
answer: In complete responders with extensive disease (ED) small cell lung cancer, prophylactic cranial irradiation (PCI) aims to eliminate any micrometastases to the brain.