285 - Fractionated Stereotactic Radiotherapy for Limited Small Volume Brain Metastases: A Single-Center, Single Arm, Phase II Trial

03:05pm - 03:15pm ET

Room 162

Presenter(s)

Jia-Xuan Yang, MS - National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy, Beijing, Beijing

Y. Ma¹, X. Chen¹, J. YI¹, Y. Zhang¹, and J. X. Yang²; ¹Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, ²Department of Radiation Oncology, National Cancer Center / National Clinical Research Center For Cancer / Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China

Purpose/Objective(s):

For limited small-volume brain metastases (BMs), stereotactic radiosurgery (SRS) achieves 1-year local control rates (LCR) of approximately 85-95%. However, the incidence of treatment-related symptomatic radiation necrosis (SRN) may reach 10%. With the increasing application of targeted and immunotherapy agents, the incidence of SRN has also increased.

A single-center, single-arm, phase II trial was conducted to investigate the intracranial efficacy and the occurrence of SRN of fractionated stereotactic radiotherapy (FSRT) for 1- 4 BMs no larger than 2 cm.

Materials/Methods:

Patients (pts) with un-radiated 1-4 BMs, with a maximum diameter of no larger than 2 cm, were enrolled. The sample size was calculated based on the hypothetical 1-year LCR free from SRN of 90%, ?=0.1, a=0.05 and a drop-out rate of 10%. Finally, 33 pts was needed. The primary endpoint was the 1-year LCR free from SRN after FSRT. The secondary endpoints included the disease control rate (DCR), 1-year intracranial progression-free survival (iPFS), overall survival (OS), FSRT-related toxicities, and the asymptomatic radiation necrosis (ARN) rate.

Results:

From August 2022 to October 2025, 33 pts (male: female = 8:25) were enrolled, with a median age of 55 (range: 32-77) years. Eighteen pts (54.5%) were diagnosed with non-small cell lung cancer (NSCLC), and the other 15 pts (45.5%) were breast cancer (BC). All of the NSCLC pts received either targeted therapy (66.7%) and/or immunotherapy (38.9%), while 73.3% of the BC pts received targeted agents (60.0%) and/or antibody-drug conjugate (53.3%). Twenty-six pts (78.8%) had BMs at the initial diagnosis of cancer. The extra-cranial disease status of 22 pts (66.7%) were stable. The median graded prognostic assessment (GPA) and Karnofsky Performance Status (KPS) before FSRT were 2.5 (1- 3.5) and 80 (70-90), respectively. The median number of BMs was 1 (1-4), and the median largest diameter and volume of BMs were 1.2 cm (0.5-1.8 cm) and 1.0 cc (0.3-4.4 cc), respectively.

The DCR after FSRT was 100% (complete response [CR] 6.1%, partial response [PR] 45.5%, stable disease [SD] 48.5%). The median time to best response of the radiated lesions was 2.6 months (0.1- 28.9 months). The median follow-up time after FSRT was 27.0 months (3.6 - 41.8 months). None of the pts experienced acute radiation toxicities or SRN. The 1- year and 2 - year LCR free from SRN were both 96.7%, and the median LC time was 27.0 months (95% CI 23.7 - 30.4 months). The 1-year iPFS and OS rates were 64.3% and 96.8% respectively. Eight pts developed ARN, with the median time being 10.9 months after FSRT (4.7 - 22.2 months).

Conclusion:

This prospective trial demonstrated that FSRT offers favorable LC with a low SRN rate in limited, small-volume BMs, in the era of targeted therapy and immunotherapy. Further studies with a larger sample size are warranted.