[Radiotherapy of glioblastoma]

Glioblastoma cells appear to be inherently radioresistant and to present a significant fraction of hypoxic cells. The most significant prognostic factors to compare results achieved in several series of patients are the age, performance status and quality of surgical resection. Several randomized trials have provided evidence supporting the efficacy of radiation therapy in the treatment of glioblastoma. Prescription of a 60-Gy dose delivered according to a conventional dose-fractionation scheme (single daily fractions of 1.7 to 2 Gy five times per week) in a target volume with a 2-3 cm margin of tissue surrounding the perimeter of the contrast enhancing lesion on computerized tomography and magnetic resonance imaging is derived from observations made in several retrospective and prospective studies. Evidence of improvement in survival was observed neither in patients receiving hyperfractioned and accelerated radiotherapy, nor in patients for whom radiation sensitizers such as nitroimidazole compounds or halogenated pyrimidine analogs were associated to radiation therapy. The addition of nitrosourea to radiotherapy increases the 2-year survival rate by about 10%. Combination of full-dose external beam radiotherapy and brachytherapy or radiosurgery boost in selected patients with glioblastoma leads to an increase in the median survival, while external beam radiation alone in patients with similar prognosis does not.