The subjects will undergo laser interstitial thermotherapy after the screening process is completed. There will be no restrictions on other treatment methods.

The LITT procedure was performed using the LS1 laser ablation system and SR1 stereotactic robotic system (Sinovation, Beijing, China). The ablation system was equipped with a 980-nm laser with a maximum of 15 W of power, a core silica fiber optic with a 1.8-mm diameter cooling catheter, and a cooling pump to make saline flow into and out through the catheter. The optic and catheter approaches were planned with the preoperative simulation software (Sinovation, Beijing, China) using the preoperative T1-weighted MRI scan, and passing through important cerebral vascular and functional zones was avoided。. The catheter was implanted by neurosurgeons under stereotactic guidance, and a laser probe was inserted through the catheter. After LITT, a T1-weighted intraoperative MRI scan was performed to confirm the effect of ablation. The ablation rate was calculated by another neurosurgeon who did not participate in the study.

The ablation results were evaluated by an independent third-party imaging review panel. Two junior physicians from the third-party review panel drew the boundaries of the brain metastases and the actual ablation areas separately, and when ≥ 90% of the tumor tissue was ablated, it was considered a complete surgical resection or near-complete resection, and the ablation was deemed effective.

The RANO-BM standard was used for evaluation. Taking the MRI images of the lesion as the baseline, MRI images were re-scanned at 30 ± 7 days, 90 ± 7 days, and 180 ± 14 days after the operation. The total long diameter of the brain metastases before ablation and the total long diameter of the remaining lesions at each follow-up point after the operation were measured respectively. If the long diameter of the lesion could not be measured due to reasons such as lesion size, it was recorded as "unable to measure", and the assessment would be conducted again at the next follow-up. Taking the total long diameter of the brain metastases before ablation as the baseline, the total long diameter changes of the affected lesions were calculated, and finally, it was evaluated whether the affected lesions had progressed.