This study is testing if using only brain scans (called MRI, or Magnetic Resonance Imaging) can help patients with small cell lung cancer (SCLC) live as long as using brain scans plus a type of radiation called Prophylactic Cranial Irradiation (PCI). MRI uses magnets and computers to take pictures of the brain to see if cancer has spread. PCI is a way to prevent cancer from spreading to the brain by using radiation. The study checks if patients who just have MRI scans might have fewer side effects and live longer without needing PCI.

• The study involves regular MRI scans at specific months: 3, 6, 9, 12, 18, and 24 months.
• Participants must have no history of brain cancer spread and must agree to have cognitive testing if they speak English or French.
• Patients will be chosen randomly to either receive MRI alone or MRI with PCI.