[Radiotherapy of brain tumors]

When radiotherapy is employed for central nervous system tumours, several clinical considerations relating to the special normal tissue environment in which they are located deserve recognition. First of all the radiosensitivity of normal brain is nearly equivalent to that of the majority of the primary tumours requiring irradiation. Secondly destroyed normal neural tissue never regenates, but partial recovery is possible following limited injury. Thirdly definition of the target volume is determined mostly by indirect means from a synthesis of neuroradiological findings (C.T. scans, M.R.I.). Finally the rigidity of the intact cranium confers greater clinical significance on mass effects including postradiotherapeutic edema. Most brain tumours respond to external irradiation which may be applied either postoperatively or definitively, e.g. gliomas, lymphomas, medulloblastomas, and metastases. New stereotactic techniques, including radiosurgery, interstitial brachytherapy, and proton beam radiotherapy allow the delivery of larger dose in a limited volume.