Overview

The study aims to enroll the small cell lung cancer(SCLC) who meet the indications for prophylactic cranial irradiation (PCI): patients with limited-stage SCLC who have achieved complete or partial remission after first-line treatment, or patients with extensive-stage SCLC whose tumors are effectively controlled after systemic therapy with no definitive evidence of brain metastases. Additional inclusion criteria are expected survival≥6 months, completion of at least 12 months of follow-up, and signed informed consent obtained before enrollment after explaining the study objectives and methods.The observation group consists of patients with extensive-stage SCLC receiving first-line chemotherapy combined with concurrent immunotherapy. After two cycles, patients with a confirmed response (CR, PR, or SD) undergo PCI. The control group consists of patients with limited-stage SCLC receiving standard concurrent chemoradiotherapy (systemic therapy plus thoracic radiotherapy). After two cycles of systemic therapy, those with a confirmed response undergo PCI.Starting from the completion of PCI, contrast-enhanced MRI of the brain (plain scan, contrast-enhanced scan, and DWI) and contrast-enhanced CT of the chest and whole abdomen are performed every three months. Treatment-related toxicity is evaluated using CTCAE v5.0. Cognitive function is assessed every three months using the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA). Venous blood samples are collected one day before radiotherapy and every three months thereafter to measure white blood cells, neutrophils, lymphocytes, platelets, hemoglobin, liver function, renal function, electrolytes, and coagulation function; stool and urine tests are also performed. The data are analyzed to determine whether whole-brain radiotherapy combined with immunotherapy exacerbates neurological impairment.

Eligibility

Inclusion Criteria:

1. Histologically or cytologically confirmed limited-stage or extensive-stage small cell lung cancer, and meeting the indications for prophylactic cranial irradiation (PCI): patients with limited-stage disease achieving complete response (CR) or partial response (PR) after first-line treatment; patients with extensive-stage disease achieving effective tumor control after systemic therapy, with no clear evidence of brain metastasis.
2. Age 18-75 years, Karnofsky Performance Status (KPS) score ≥ 70.
3. Estimated survival ≥ 6 months, with completion of at least 12 months of follow-up.
4. No contraindications to radiotherapy, chemotherapy, or immunotherapy.
5. Good compliance with the treatment protocol and follow-up, and provision of informed consent.

Exclusion Criteria:

1. Patients with brain metastases, cerebral infarction, cerebral hemorrhage, sequelae of traumatic brain injury, or other primary brain diseases (e.g., Alzheimer's disease, multiple sclerosis) confirmed by MRI before enrollment.
2. Patients who have previously received brain radiotherapy, brain surgery, or immunotherapy.
3. Patients with psychiatric disorders or cognitive impairment (MMSE score \< 26) unable to cooperate with follow-up assessments.
4. Patients with a history of other malignancies prior to or concurrent with the current treatment.
5. Severe cardiac, pulmonary, or renal disease, active autoimmune disease, or uncontrolled active infectious disease.
6. Pregnant or lactating women.