This study is a multicenter, open label, randomized controlled, adaptive phase II/III seamless design clinical trial aimed at comparing the efficacy and safety of methylprednisolone (MP) and dexamethasone (DEX) in the treatment of peritumoral edema in patients with brain metastases during radiotherapy. The research plan includes brain metastasis patients aged 18-75 years, with KPS scores of 40-80, who plan to undergo whole brain radiotherapy or stereotactic radiotherapy. They will be randomly divided into MP group (40-60 mg/day) or DEX group (8-12 mg/day) in a 1:1 ratio, and medication will be continued until the end of radiotherapy, followed by gradual reduction and cessation within one week. The study is divided into two stages: the first stage (stage II exploration) includes 120 cases to preliminarily evaluate the efficacy and safety, and provide a basis for re estimating the sample size in the second stage; The second stage (Phase III confirmation) will expand the sample size based on the results after analysis during the transition period, with a total sample size of no more than 400 cases. The primary endpoint was the change in KPS score and the incidence of grade ≥ 2 hormone related adverse reactions within one week after radiotherapy. Secondary endpoints include cerebral edema index, cognitive function, quality of life, radiotherapy interruption rate, neurotoxicity, survival, and serum biomarkers (IL-6, S100B). The study is supervised by an independent data security monitoring committee and uses statistical methods such as stratified block randomization and mixed effects models to ensure the scientific and ethical compliance of the data. This study is expected to provide high-level evidence-based basis for hormone selection during the perioperative radiotherapy period for patients with brain metastases, and optimize clinical practice.

Inclusion Criteria:

• 1. 18 ≤ age ≤ 75 years old, gender not limited, generally acceptable, 40 ≤ KPS ≤ 80 points, the main reason for the patient's limited functional status is related neurological symptoms caused by edema of brain metastases; 2. Confirmed by cranial MRI or CT imaging, there is at least one brain metastasis with cerebral edema or neurological symptoms. All patients are scheduled to undergo WBRT (30 Gy/10f or 20 Gy/5f) or SBRT (20-40 Gy/1-6f, with ≤ 5 brain metastases and a maximum diameter of ≤ 5cm per lesion); 3. Expected survival of ≥ 3 months; 4. Having sufficient cognitive and understanding abilities, able to cooperate with scale assessments, and able to sign a written informed consent form (ICF); 5. Baseline neurological symptoms are stable (no need for emergency surgical decompression), and if surgery/radiotherapy has been performed, the following conditions must be met: postoperative/radiotherapy interval ≥ 4 weeks; 6. Baseline blood glucose/metabolism is controllable (e.g., HbA1c ≤ 8.0% in diabetes patients;If HbA1c is high, endocrinology evaluation is required and written permission for enrollment is granted.

Exclusion Criteria:

• 1. Immediate surgical decompression is required, or there may be progressive cerebral herniation, intracranial pressure crisis, or life-threatening intracranial space occupying lesions present; 2. Has received systemic corticosteroid treatment within 7 days prior to the start of the study medication (such as due to the treatment of systemic lupus erythematosus, bronchial asthma, etc.); 3. Recent cranial surgery or radiation therapy (<4 weeks); 4. Individuals with contraindications to glucocorticoids or severe immunosuppression; 5. Suffering from serious basic diseases such as uncontrolled hypertension and diabetes (HbA1c>8%), untreated mental illness, active gastric ulcer, heart failure (NYHA III-IV grade), etc; 6. Pregnant/lactating women; 7. Unable to complete the primary assessment scale (severe cognitive/behavioral impairment) or unable to sustain Follow up period (e.g. no fixed address, difficult to ensure follow-up); 8. Participated in other intervention therapy trials within the past 4 weeks (which may affect the evaluation results), or is currently receiving drugs that may have serious drug interactions with the investigational drug; 9. Other serious systemic diseases or unsuitability.