Radiation-induced malignant gliomas: a current review.

OBJECTIVE: Radiation-induced malignant gliomas (RIMGs) are known uncommon risks of brain irradiation. We describe 4 cases of RIMG that occurred at our institution and conduct the largest comprehensive review of the literature to characterize RIMGs better. METHODS: Patients were identified through the PubMed database. Pearson R linear correlation test was used to evaluate the correlation between radiotherapy (RT) dose and age and latency period. Student t test was used to evaluate differences between latency periods for original tumor lesions. A normalized biologic equivalent dose analysis was performed to indicate the minimum and maximum radiation threshold for neoplasia. A Kaplan-Meier analysis was used to illustrate the overall survival curves. RESULTS: The analysis included 172 cases from the PubMed database and 4 cases occurring at our institution. The median RT dose administered was 35.6 Gy, with the most common dosage ranges being 21-30 Gy (31%) and 41-50 Gy (21.5%). Median latency period was 9 years until diagnosis of RIMG, and RIMG occurred within 15 years in 82% of the patients. There was no correlation between the age of the patient at the time RT was administered (R(2) = 0.00081) or amount of RT (R(2) = 0.00005) and latency period for RIMG. The mean biologic equivalent dose for neoplasia of a RIMG was 63.3 Gy. The median survival of patients with RIMG improved over time (P = 0.004), with median survival of 9 months before 2007 and 11.5 months after 2007. CONCLUSIONS: The risk of RIMG appears to be the same for all age groups, histologies, and RT dosages. Although the risk is low, patients should be aware of RIMG as a possible complication of brain irradiation.