Résumé
The place of cerebral radiotherapy in the management of low-grade gliomas, immediate or delayed after incomplete resection surgery, is a controversial subject. Because of the slow evolution and complex morphology of these infiltrating tumors, the evaluation of the response to radiotherapy by MRI and the determination of the progression are also debated. This monocentric retrospective study aimed to describe the overall survival after radiotherapy in a cohort of 148 patients with low-grade gliomas who received maximally deferred radiotherapy (median time of 5.6 years), and to correlate the clinical, histo-molecular, radiological and therapeutic data with this survival. The median overall survival after radiotherapy was 34.9 months. In multivariate analysis, high Ki-67, non-co-deleted 1p19q status, ECOG – PS score ≥2, presence of contrast enhancement and absence of partial to total surgical resection before radiotherapy were factors of poor prognosis on overall survival after radiotherapy. The MRI morphological response after radiotherapy was also evaluated in 64 patients. On the preradiotherapy MRI, the average tumor volume was 63.7 cm³, i.e., a mean tumor diameter (MTD) of 47.2 mm. 68.8% of tumors were shrinking after radiotherapy. The average best response in volume was -22.9% or in MTD -9.6%. The average velocity of diametric expansion (VDE) before radiotherapy was 8.7 mm/year and after radiotherapy -1.0 mm/year in the first year. We also created a latent class mixed model (LCMM) separating MTD trajectories over time into 4 prognostic classes that were predictive of survival after radiotherapy.