Abstract:

Objective To investigate the efficacy and safety of fractionated stereotactic radiotherapy （FSRT） based on linear accelerator for small volume brain metastases. Methods A total of 21 patients with small volume brain metastases who received FSRT from August 2020 to June 2022 were enrolled as subjects， including 45 lesions. Small-volume brain metastases were defined as ≤3 cm in diameter and ≤6 cm³ in volume， and the dose/fractionation scheme was 27-30 Gy/3 F or 30-40 Gy/5 F. Three months after radiotherpy，the efficacy of FSRT in small brain metastases and the incidence of radiation brain injury were evaluated， and the incidence of radiation brain injury in subgroup analysis was performed according to the diameter， volume， dose/fractionation scheme， biological effective dose （BED）₁₀， and location of lesions. Results Twenty-four lesions （53.33%， 24/45） were evaluated as complete response， another 13 lesions （28.89%， 13/45） were evaluated as partial response， and in the remaining 8 lesions （17.78%， 8/45） were evaluated as stable disease. The local control rate was 100% （45/45）， the objective remission rate was 82.22% （37/45）， and the intracranial distant progression rate was 23.81% （5/21）. During the treatment and follow-up， there were 7 lesions （15.56%， 7/45） of radiation-induced brain injury， and the incidence of symptomatic radiation-induced brain injury was 11.11% （5/45）. Subgroup analysis showed that the incidence of radiation brain injury in the group with a lesion diameter of 2-3 cm was higher than that with a lesion diameter of <2 cm group， with a statistically significant difference [80.00% （4/5） vs. 7.50% （3/40）， χ²=12.69， P<0.001]； the incidence rate of radiation brain injury in the group with lesion volume of 4-6 cm³ was higher than that with lesion volume of <4 cm³ group， with a statistically significant difference [57.14% （4/7） vs. 7.89% （3/38）， χ²=7.49， P=0.006]. There was no significant difference in the incidence of radiation brain injury between the dose/fractionation scheme of lesions 27-30 Gy/3 F and 30-40 Gy/5 F [9.52% （2/21） vs. 20.83% （5/24）， χ²=0.40， P=0.527]. There was no significant difference in the incidence of radiation brain injury between the BED₁₀<60 Gy and ≥60 Gy [28.57% （2/7） vs. 13.16% （5/38）， χ²=0.22， P=0.641]. There was no significant difference in the incidence of radiation brain injury between the lesions in the same lobe and the single or multiple lesions in different lobes [28.57% （4/14） vs. 9.68% （3/31）， χ²=1.38， P=0.240）. Conclusion FSRT based on linear accelerator is effective for small volume brain metastases. Brain metastases with the diameter <2 cm or volume <4 cm³ are associated with a lower incidence of radiation brain injury than that of lesions with the diameter of 2-3 cm or volume of 4-6 cm³.

Key words: Chemoradiotherapy, Radiosurgery, Brain metastases, Fractionated stereotactic radiotherapy