Patients with lung cancer and brain metastases undergo HA-WBRT-SIB using image-guided radiotherapy, receiving a total dose of 30-36 Gy delivered in 18-20 fractions to the whole brain (CTV), while the dose to the GTV is boosted to 44 Gy-52 Gy in 18-20 fractions, five times a week. The optimal mean dose (Dmean) to the bilateral hippocampus should optimally be ≤ 8 Gy, with a mandatory maximum dose (Dmax) to the hippocampus not exceeding 10 Gy; the preferred Dmean to the hippocampus PRV should optimally be ≤ 9 Gy, while the mandatory Dmax to the hippocampus PRV should be ≤ 12 Gy. The HVLT-R immediate recall scores are obtained at baseline and 1, 3, and 6 months after treatment.

Inclusion Criteria:

1. pathologically diagnosed primary lung cancer with brain metastasis confirmed via magnetic resonance imaging (MRI);
2. 18-75 years old;
3. BM outside a 10 mm margin around either hippocampus;
4. at least one BM existed if prior resection of BM was done;
5. BM measuring less than 5.0 cm in maximal extent;
6. Eastern Cooperative Oncology Group (ECOG) performance status scores of 0-2

Exclusion Criteria:

1. previous brain radiotherapy or brain metastasis resection;
2. history of malignancies other than lung cancer;
3. radiographic evidence of hydrocephalus or other architectural distortion of the ventricular system, leptomeningeal metastases
4. presence of other serious illnesses such as acute myocardial infarction, severe arrhythmia, or psychiatric disorders within the past 6 months.