Optimal Management of Brainstem Metastases

A Narrative Review

Joan Y. Lee; Danielle A. Cunningham; Erin S. Murphy; Samuel T. Chao; John H. Suh

Disclosures

Chin Clin Oncol. 2022;11(2):15 

In This Article

Dosage

SRS is often delivered in a single fraction, but may also be given in 2 to 5 fractions for larger targets or those near critical normal tissues such as the brainstem. No guidelines exist for tumor margin dose selection of SRS for brainstem metastases which is currently institution-dependent. Conflicting findings exist regarding the optimum margin dose, with some reports of correlation between higher marginal dose and longer survival,[16,42] although this may be at the expense of greater toxicity. Valery and colleagues reported a local control rate of 90% and median survival time of 10 months with a median marginal dose of only 13.4 Gy. Other series have recommended tumor margin doses as low as 12 Gy.[48] Factors influencing dose selection include tumor volume, tumor histology, and prior radiotherapy.[44,49] Additionally, the radiosurgical technology used (Gamma Knife versus linear accelerator-based radiosurgery) impacts the rate of dose fall-off which influences the margin dose.

Regarding doses for single fraction SRS for brainstem metastases, experts have recommended margin doses of 20 Gy for lesions <1 cc, 18 Gy for 1–2 cc lesions, and 15 Gy for lesions >2 cc. Other regimens in the literature for the tumors in or near the brainstem include 27 Gy in 3 fractions and 25–31 Gy in 5 fractions.[50] The brainstem maximum point set by Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC), which was based solely on single-fraction SRS data, indicates that 12.5 Gy in one fraction carries a <5% risk of brainstem injury, though other studies have indicated that a maximum brainstem dose of 15–20 Gy carries a low risk of injury.[35] The American Association of Physicists in Medicine (AAPM) Task Group 101 report recommends a maximum brainstem dose of <23.1 Gy in 3 fractions and ≤31 Gy in 5 fractions.[51] The AAPM Working Group on Biological Effects of Hypofractionated Radiotherapy/stereotactic body radiation therapy (SBRT) HyTEC study [2021] explicitly omitted studies that focused on brainstem toxicity and did not report specific recommendations or dose-volume metrics predictive of brainstem toxicity.[52]

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