Inclusion Criteria:
1. Age between 18 and 80 years (inclusive), regardless of gender.
2. Eastern Cooperative Oncology Group (ECOG) performance status ≤ 2.
3. Diagnosis of brain metastasis confirmed by histopathological examination and/or imaging, and deemed suitable for stereotactic radiotherapy according to the investigator's judgment.
4. Tumor diameter of brain metastasis ≤ 4 cm, with ≤ 10 metastatic lesions.
5. At least one measurable tumor lesion as defined by the RECIST 1.1 criteria for assessment of treatment efficacy.
6. Ability to understand the study objectives, voluntarily consent to participate, and sign a written informed consent; willingness to undergo all necessary examinations and follow-up assessments.
Exclusion Criteria:
1. Expected survival time \< 6 months.
2. Patients requiring surgical treatment or other local therapies for the target lesions during radiotherapy.
3. Patients who have received other local treatments (including radiofrequency ablation, cryoablation, particle therapy, etc.) within 30 days prior to screening, or those who have received systemic therapy (chemotherapy, endocrine therapy, immunotherapy) within 14 days or less than five half-lives of a drug prior to screening (whichever is longer).
4. Patients who have previously received radiotherapy at the same site or for the same lesion.
5. Patients with extensive metastasis, severe cachexia, or clear signs of malignant cachexia.
6. Patients deemed by the investigator to be unable to tolerate radiotherapy.
7. Patients with psychiatric disorders or who are unable to accurately describe their condition or cooperate with required examinations.
8. Patients with systemic active infections or infections of the pericardium or lungs.
9. Patients with severe liver or renal dysfunction, or those with significant concurrent diseases in other systems.
10. Patients with septic hemorrhagic shock.
11. Patients with esophageal cancer at risk for deep ulceration or perforation, or those with large pleural effusion in lung cancer or significant ascites in abdominal tumors.
12. Pregnant or breastfeeding women, or women planning to become pregnant during the study period or unwilling to take appropriate contraceptive measures (acceptable methods include hormonal therapies (oral, implant, etc.), intrauterine devices, barrier methods (spermicide + condom), spermicide + diaphragm/cervical cap, abstinence, etc.).
13. Low blood counts (leukocyte count \< 2.0 × 10⁹/L, platelet count \< 50 × 10⁹/L, or hemoglobin \< 80 g/L), or abnormal laboratory values exceeding the normal range with clinical significance.
14. Participation in any drug or medical device clinical trial within 30 days prior to screening or currently enrolled in another clinical study.
15. Any other condition deemed by the investigator to be inappropriate for participation in this study.
