Stem to stern.
Top Line: Brainstem metastases are scary.
The Study: Resection obviously isn’t a popular option, so radiation is the mainstay palliative treatment for this population. Nonetheless, they’re typically excluded from trials leaving data and crystallized recommendations on approach lacking. Making the most of what we have, here is a pooled analysis of 32 retrospective studies including 1590 brainstem metastases treated with radiosurgery. The vast majority were treated with Gamma Knife in a single fraction of 16 Gy prescribed to 50% isodose line (median max dose in tumor was 31.4 Gy in a single fraction). Where reported, local control at one year (n=1410) was 86%, symptom control (n=323) was 55%, and grade 3+ toxicity (n=1421) was only 2.4%. Granted the median volume was only 0.4 cc (range: 0.0024-24.88)--if these were perfect spheres, the median diameter would be 0.9 cm (range: 0.2-3.6). Indeed, correlates with toxicity included the usual contenders: size, melanoma histology (think hemorrhage risk), and previous whole brain radiation. So while this still doesn’t provide specific fractionation guidelines, a single fraction without a constrained hotspot is likely very safe when done to a small target in the brainstem.
TBL: Safety and efficacy of radiosurgery for brainstem metastases appears comparable to that for other brain mets. | Chen, JAMA Oncol 2021