Radiation necrosis and brain edema association with CyberKnife treatment.

The CyberKnife (CK) is a frameless and image guided robotic controlled instrument for stereotactic irradiation. The authors studied CK treatment of glioma and glioblastoma, and analyzed frequency and risk factors of radiation necrosis. Of 61 patients with glioma and glioblastoma treated with CyberKnife, four patients showed symptomatic radiation necrosis. All of these patients were treated with stereotactic radiotherapy, varying from 3 to 6 fractions without previous radiation therapy. Two patients required necrotomy through craniotomy. Two patients were treated conservatively. Our four patients with radiation necrosis were not specific in terms of tumor volume and dose delivery. Glioma cells invade the normal brain tissue and over-radiation to this intermingling area is one of the risk factors for injury to normal endothelial cells. The homogeneity of the maximum dose area is an important factor to reduce over radiation to the normal brain parenchyma. The dose volume effect has been discussed in terms of risk factor; however, the number of fractions and dose per fraction should be considered to avoid radiation necrosis. We consider that conformal treatment with inverse algorism, fractionated stereotactic radiotherapy and precise anatomic targeting reduce the risk of radiation necrosis.