The Study About Dangerous Factors And Predictors Of Radiation Encephalic Necrosis After The Treatment Of Stereotactic Body Radiotherapy

Objective Nowadays, there are many therapies treating primary or metastatic brain tumors like surgery, radiotherapy, chemotherapy and target drug therapy. While no supporting guide us which one is the best. Stereotactic body radiotherapy(SBRT) is an accurate radiotherapy with high precision, large dose, accurate tracking and good effect widespread applied to the therapy of primary or metastatic brain tumors by oncologist. Radiation encephalic necrosis as the most common adverse reaction after Stereotactic body radiotherapy treating primary or metastatic brain tumors, its dangerous factors and predictors were seldom reported. The aim of the paper is to talk about the dangerous factors and predictors of radiation encephalic necrosis after Stereotactic body therapy.Methods and Materials Retrospectively analyzed patients treated by Stereotactic body radiotherapy who were diagnosed with primary or metastatic brain tumors at Cyber Knife center of Tianjin Medical University Cancer Institute and Hospital from September 2006 to October 2011. 94 patients(104 targets) were selected and median age is 51.5 months.Five people accepted whole brain radiotherapy. Stereotactic body radiotherapy used skull based tracking with a 60% to 87% isodose line between 1200 c Gy to 4500 c Gy doses and completed by 1 to 8 fractions. Radiation encephalic necrosis was diagnosed by imaging or pathological examination. Logistic regression was used to analysis the relevance between radiation encephalic necrosis and factors consisting of diabetes,cardio-cerebrovascular disease, target volume, isodose line, prescribed dosage,number of fractions, combination with whole brain radiation and biologically equivalent dose(BED). Predictability and critical dose threshold of all the risk factors for radiation encephalic necrosis were described by applying ROC curve.Results Twelve targets(11.54%) occurred radiation encephalic necrosis. Analysis the dangerous factors of radiation encephalic necrosis: Logistic regression showed that BED, combination with whole brain radiation and number of fractions were risk factors of radiation encephalic necrosis. The acreages under the ROC curves of 0.892±0.0335, 0.650±0.0717, 0.712±0.0637, respectively. Only BED can better forecast the radiation encephalic necrosis after Stereotactic body therapy and the dose of >7410 c Gy was identified as the threshold value.Conclusions BED, combination with whole brain radiation and number of fractions are risk factors inducing radiation encephalic necrosis. At the same time, BED is the best predictor of the radiation encephalic necrosis and the critical dose threshold of radiation encephalic necrosis is >7410 c Gy.