Influence of tumor grade on time to progression after irradiation for localized ependymoma in children - Merchant, Thomas E.; Jenkins, Jesse J.; Burger, Peter C.; Sanford, Robert A.; Sherwood, Scot H.; Jones-Wallace, Dana; Heideman, Richard L.; Thompson, Stephen J.; Helton, Kathleen J.; Kun, Larry E. (International Journal of Radiation Oncology, Biology, Physics, 2002)