Brain metastasis accounted for 10-15% of all breast cancer patients and even higher in patients with triple negative and HER2 overexpressed subtype. Stereotactic radiation is the standard option for patients with 1-4 brain metastases. Among patients with 1-4 brain metastases, many studies suggest that stereotactic radiation results in fewer neurologic side effects than whole brain radiation. Also, several studies had demonstrated that 5-10 lesions had similar overall survival by using whole brain radiotherapy or stereotactic radiotherapy. Fractionated stereotactic radiotherapy(FSRT) is increasingly administered in the brain metastatic patients and retrospective studies had shown that FSRT had better local control and lower brain radiation necrosis than single fraction stereotactic radiation. Therefore, In this study, we explore to treat 1-10 brain metastasis lesion in breast cancer patients with FSRT.

Breast cancer patients with 1-10 brain metastasis will be treated with FSRT for brain metastasis. 3 to 5 fractions and 8Gy per fraction will be used for these patients based on the lesion number and volume.

Inclusion Criteria:

• Histologically confirmed HER2 positive advanced breast cancer
• Age>18 years.
• 1 to 10 brain metastases confirmed by enhanced brain MRI
• KPS≥70
• Life expectancy of more than 12 weeks
• Prior therapy of oral dexamethasone not exceeding 16mg/d
• Time interval from prior therapy was more than 2 weeks, and evaluation of adverse events is no more than grade 1.
• Maximum diameter of intracranial metastases is less than 3cm measured by enhanced brain MRI(2-3mm)
• Prior endocrine therapy were allowed
• Anti-Her2 targeted treatment were allowed
• Screening laboratory values must meet the following criteria( and should be obtained within 28 days prior to registration):

Absolute Neutrophil Count (ANC) ≥ 1.5 x 109/L, Platelets≥ 90 x 109/L, Hemoglobin ≥ 90 g/L Aspartate aminotransferase/alanine aminotransferase (AST/ALT) ≤2.5 x ULN without liver metastasis,≤ 5 x ULN with liver metastases Serum BUN and creatinine ≤ 1.5 x Upper Limit of Normal (ULN)

• Time interval from chemotherapy was more than 2 weeks, endocrine therapy and anti-Her2 targeted treatment are allowed to be used concurrently with FSRT
• Signed the informed consent form prior to patient entry

Exclusion Criteria:

• Leptomeningeal or hemorrhagic metastases
• Uncontrolled epilepsy
• Severe complication: cardiovascular disease, end-stage renal disease, severe hepatic disease, infection etc.
• Pregnancy or lactation period， women of child-bearing age who are unwilling to accept contraceptive measures.
• Inability to complete enhanced MRI
• Patients who are difficult or unable to be followed-up
• Not suitable for inclusion for specific reasons judged by sponsor
• Patients who are receiving cytotoxic drug concomitantly
• Have received prior radiotherapy for brain metastasis