The clinical significance of three-dimensional conformal radiotherapy for lung cancer brain metastases was investigated by observing and analyzing the results of conformal radiotherapy cases. Methods A total of 35 patients with brain metastases from lung cancer, including 12 cases with combined extra-cranial metastases and 23 cases with non-extracranial metastases. All patients were treated with whole brain radiotherapy 1.8-2GY/time, 5 times/week, total DT30-40GY. Then, conformal radiotherapy was administered, 90% of the isodose curve included the target area; the split dose was divided into DT2-6GY/time, 5 times/week according to the size of the target area, and the total conformal radiotherapy dose was 20-40GY. . Tumor shrinkage was better in patients with pre-treatment brain tumor diameter less than 3 cm than in those with diameter greater than 3 cm. Survival time: median survival was 10.3 months. Conclusion Three-dimensional conformal radiotherapy can increase the dose of metastases, which is significantly effective in improving the local control rate of lesions and can reduce the proportion of deaths due to recurrence of brain lesions. Three-dimensional conformal radiotherapy is very important in treating brain metastases along with extracranial metastases and primary foci. MATERIALS AND METHODS 1. Study subjects The primary lung foci were pathologically confirmed, including 11 cases of squamous carcinoma, 13 cases of small cell carcinoma, and 11 cases of adenocarcinoma. The ages ranged from 38 to 70 years, with a median age of 52 years, 27 cases in men and 8 cases in women. All metastatic lesions in the brain were diagnosed by CT or MRI, among which 26 cases were single lesions and 9 cases had two lesions. There were 28 cases with neurological symptoms and 7 cases without neurological symptoms. The neurological symptoms included headache, motor disturbance, and confusion, respectively. There were 12 cases with concurrent extracranial metastases, 8 cases with bone metastases, 4 cases with intrapulmonary metastases, and 2 cases with adrenal metastases, respectively. Brain lesion size: the maximum diameter was 1.0~5cm by MRI, among which 17 cases were larger than 3cm in diameter and 18 cases were smaller than 3cm. Tumor volume: the volume ranged from 0.6 cm3 to 65 cm3, with a median volume of 24.6 cm3. Treatment of extracranial lesions: 31 cases had been treated, including 10 cases with surgery, all of which were completely resected; 8 cases were treated with combined radiotherapy, 7 cases with radiotherapy alone, and 6 cases with chemotherapy alone. Among the 21 patients who received radiotherapy or/and chemotherapy, 11 cases were in partial remission, 10 cases were stable, and there were no progressive cases; 4 cases did not undergo antitumor therapy, and their extracranial lesions did not progress. All patients were placed in the supine position before treatment, and the head was fixed with a face mask and foam pillow, and lateral films were taken under the analog positioning machine for positioning. Then the multi-lobe raster was developed according to the irradiation field outlined on the X-ray and radiotherapy was given with 6MV high-energy X-ray. Radiotherapy method: patients were treated with whole brain pair penetration radiotherapy 1.8~2GY/time, 5 times/week, total DT30~40GY. mannitol, dexamethasone or high sugar dehydration symptomatic treatment was given during radiotherapy. 3.Stereotactic radiotherapy for brain metastases After the whole brain radiotherapy, the patient continues to wear the original mask under the CT localization enhancement scan (the mask is marked with localization guide wire), the scan layer thickness is about 2.5~3mm, the scan range is from the cranial vault to 5cm below the skull base line, and then the localization CT results are transmitted to the TPS system in the form of network or film scan for processing. The RENDERPLAN 3D TPS system from ELEKTA is used in our hospital. The physician outlines the clinical target volume (CTV) on the TPS system, and then the physicist uses the TPS system to reconstruct the CT information for processing. With the highest dose point reference, the 90% isodose curve fully includes the PTV. and keeps the dose to the brainstem, eye and other endangered organs within safe limits. The physiatrist makes the radiotherapy plan according to the size and location of the tumor, and uses pull-arc, 4- to 6-wild coplanar or non-coplanar field radiotherapy. After the radiotherapy plan is made, the radiotherapy is again taken under the simulated positioning machine for verification, and radiotherapy is started after the verification is passed. The tumor segmentation dose was divided into DT2~6GY/time, 5 times/week according to the size of the target area, and the cumulative conformal radiotherapy dose was 20~40GY. symptomatic treatment was continued along with the conformal radiotherapy. The recent efficacy: the neurological symptoms were relieved to different degrees, and the patients’ quality of life was improved to different degrees. 31.4% (11/35) for CR, 54.2% (19/35) for PR, and 85% (30/35) for efficiency (CR+PR). Based on the criterion of review MRI, the number of patients with tumor diameter greater than 3 cm in the brain before treatment was 2 (2/17 cases) for CR and 9 (9/18 cases) for those with diameter less than 3 cm. There was a significant difference between the two (P=0.01). 2. Survival: The follow-up after treatment ranged from 3 to 25 months, with a median follow-up of 11 months, and two cases were lost after three months and were counted as deaths. The median survival time of patients after treatment was 10.3 months. The six-month survival rate was 83.3% (30/35) and the one-year survival rate was 48.5% (17/35 cases). The one-year survival rate of patients without extracranial metastases before treatment was 65.2% (15/23 cases), and the one-year survival rate of patients with extracranial metastases was 16.7% (2/12 cases). The one-year survival rate with and without extracranial metastases was significantly different (P=0.003), as shown in Figure 1. The one-year survival rates for patients with single and two metastases were 50% (13/26) and 40% (4/9), respectively. Up to now, there were 26 deaths, and the causes of death were analyzed: 6 cases died from recurrence of brain lesions (uncontrolled), 10 cases died from extracranial metastases (including 7 cases with extracranial metastases before treatment), 4 cases died from primary lung lesions, and 6 cases died from other non-tumor causes. 3. Recent toxic side effects: According to the RTOG criteria, the main side effects were alopecia, bone marrow suppression, cerebral edema, etc. Most of them were grade 1~2, which were relatively mild and tolerated after supportive symptomatic treatment. All patients did not have significant radiation brain injury after treatment.