Objectives:

Brainstem necrosis is a potential catastrophic complication of radiotherapy. Stereotactic radiosurgery uses ablative doses of radiotherapy which may increase risk of radiation necrosis. We retrospectively evaluated the disease control and incidence of radiation necrosis following LINAC-based stereotactic radiosurgery (SRS) for brainstem metastases.

Methods:

From July 2017 to November 2021, 23 patients underwent treatment to 26 brainstem metastases (located in the midbrain, pons, or medulla) with single-fraction SRS (n=23) or fractionated stereotactic radiosurgery (FSRS) in 5 fractions (n=3). Median prescription dose was 1600cGy (range: 1400-2025cGy) for SRS and 2625cGy (range: 2500-2750cGy) for FSRS. Patients underwent surveillance MRI 2-3 months post-treatment and every 3 months in the first year, every 4 months in the second year, and every 6 months thereafter.

Results:

Median follow-up was 10.3 months. Median patient age was 63 years (range: 35-89), and 12 (52.2%) patients were female. Lung was the most common primary site of disease (n=11), followed by breast (n=9), kidney (n=3), rectal (n=1), melanoma (n=1), and thyroid (n=1). Median planning treatment volume (PTV) was larger in patients treated with FSRS (3.921cc (range: 4.226-1.981)) compared to those treated with SRS (0.131cc (range: 0.012cc – 3.591cc)) (p=0.02). Eight (34.8%) patients additionally received whole brain radiotherapy (WBRT) with prescription dose of either 2000cGy in 5 fractions (n=3) or 3000cGy in 10 fractions (n=6). Four patients received WBRT prior to SRS, and 4 patients received WBRT after SRS. Overall survival at 1-year was 51.5%. There were zero radiographic local failures in the cohort. There were also zero instances of radiation necrosis. In total, 14 (60.9%) patients passed away since the time of treatment. Nine patients passed due to progression of extracranial disease. The remaining 5 patients exhibited neurologic symptoms prior to death concerning for progression of intracranial disease. Of these 5 patients, 2 had radiographic evidence of progression of distant intracranial disease.

Conclusion(s):

LINAC-based stereotactic radiosurgery was well-tolerated for brainstem metastases with no instances of radiation necrosis observed in the post-treatment setting. Although overall survival rates were low, all treated lesions were controlled at last radiographic follow-up, and the majority of deaths observed were due to progression of extracranial disease. SRS appears to be a safe and effective treatment for brainstem metastases.