Radiation to the brain and adjuvant chemotherapy may produce late delayed changes from several months to years after treatment of intracranial malignancies with a reported prevalence of 5-24%. The pattern of treatment-related injury may vary from diffuse periventricular white matter lesions to focal or multifocal lesions. Differentiation of treatment-related injury from tumor progression/recurrence may be difficult with conventional MR imaging (MRI). With both disease processes, the characteristic but nonspecific imaging features are vasogenic edema, contrast enhancement, and mass effect. This pictorial essay presents MRI spectra of late therapy-induced injuries in the brain with a particular emphasis on radiation necrosis, the most common and severe form. Novel MRI techniques, such as diffusion-weighted imaging (DWI), proton MR spectroscopy (MRS), and perfusion MRI, improve the possibilities of better characterization of treatment-related changes. Advanced MRI techniques allow for the assessment of metabolism and physiology and may increase specificity for therapy-induced changes.

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Presented is the analysis of patients who underwent external beam radiotherapy (EBRT) to the brain in the period from 2003 to 2006 at the department of Radiation Oncology of the St. Elisabeth Cancer Institute.The aim of our analysis was to identify risk factors of late delayed therapy induced injuries (LDTI) in the brain. The patients were regularly examined with magnetic resonance (MRI), including conventional and advanced techniques: perfusion imaging (pMRI), diffusion weighted imaging (DWI), MRI spectroscopy (MRS). The results from MRI were correlated with 18 fluoro-deoxyglucose positron emission tomography ( 18 FDG/PET) scans, as none of the listed method is sufficiently sensitive and specific by itself. Also clinical data records and treatment plans of these patients were analyzed.In our cohort we found 6 patients with abnormal post-therapeutical changes, 4 of them with MR and 18 FDG/PET scans characteristics for LDTI -radiation necrosis. In one patient biopsy was performed and radiation necrosis (RN) was confirmed.