Investigation of the efficacy and safety of CyberKnife hypofractionated stereotactic radiotherapy for brainstem metastases using a new evaluation criterion: ‘symptomatic control’

The treatment of brainstem metastases remains a challenge as the brainstem itself is considered a neurological organ at risk. We aimed to investigate the efficacy and safety of CyberKnife hypofractionated stereotactic radiotherapy (HFSRT) for brainstem metastases, and to examine the balance between efficacy and safety for the management of neurological symptoms. A total of 26 lesions [pons (n = 18), medulla (n = 4) and midbrain (n = 4)] in 20 patients treated with CyberKnife hypofractionated stereotactic radiotherapy were retrospectively analyzed. The total radiation doses (18-30 Gy) were delivered in 3 or 5 equal fractions. The median follow-up was 6.5 (range, 0.5-38.0) months. The 6- and 12-month local control rates were 100% and 90%, respectively. Symptomatic failures, defined as the worsening and appearance of neurological symptoms due to the brainstem lesion after CyberKnife HFSRT, were observed in 6 patients [local failure (n = 1) and adverse events (n = 5). The symptomatic control and overall survival rates were 90% and 72% (after 6 months), respectively, and 76% and 53% (after 12 months), respectively. Longer symptomatic control was associated with site of lesion origin, and longer overall survival was associated with a graded prognostic assessment score of >2. To our knowledge, this is the second study to investigate the efficacy and safety of CyberKnife HFSRT for brainstem metastases. The local control rate was comparable with that of prior stereotactic radiosurgery studies. We propose a new evaluation criterion-'symptomatic control'-to evaluate the efficacy and safety of brainstem radiotherapy.