Five-fraction CyberKnife radiotherapy for large brain metastases in critical areas: Impact on the surrounding brain volumes circumscribed with a single dose equivalent of 14 Gy (V14) to avoid radiation necrosis

The efficacy and toxicity of five-fraction cyberknife radiotherapy were evaluated in patients with large brain metastases in critical areas. a total of 85 metastases in 78 patients,including tumors >30 cm3 (4 cm in diameter) were treated with five-fraction cyberknife radiotherapy with a median marginal dose of 31 gy at a median prescribed isodose of 58%. changes in the neurological manifestations,local tumor control,and adverse effects were investigated after treatment. the surrounding brain volumes circumscribed with 28.8 gy (single dose equivalent to 14 gy: v14) were measured to evaluate the risk of radiation necrosis. neurological manifestations,such as motor weakness,visual disturbances and aphasia improved in 28 of 55 patients (50.9%). local tumor control was obtained in 79 of 85 metastases (92.9%) during a median follow-up of eight months. symptomatic edema occurred in 10 patients,and two of them (2.6%) required surgical resection because of radiation necrosis. the v14 of these patients was 3.0-19.7 cm3. there were 16 lesions with a v14 of ≥7.0 cm3,and two of these lesions developed extensive brain edema due to radiation necrosis. none of the patients with a v14 of <7.0 cm3 exhibited edema requiring surgical intervention. we therefore conclude that a high rate of local tumor control and low rates of complications can be obtained after five-fraction cyberknife radiotherapy for large metastases in critical areas. the v14 of the surrounding brain is therefore a useful indicator for the risk of radiation necrosis in patients with large metastases. © 2013 the author 2013. published by oxford university press on behalf of the japan radiation research society and japanese society for therapeutic radiology and oncology.