Evaluation of the diagnostic and prognostic role of PET with Amino Acid Radiotracers associated with simultaneous acquisition of MRI with administration of paramagnetic contrast medium based on Gadobutrol in assessing diagnostic accuracy and therapeutic response in adult individuals affected by primary and secondary brain tumors. This is a purely observational study that does not introduce any procedures beyond those already scheduled as part of routine clinical practice. All imaging procedures and clinical assessments will be performed exclusively within the standard care pathway. This study will analyze two cohorts of patients:
1\. Cohort A: Adult patients with primary or secondary brain tumors undergoing neuro-oncological therapy, presenting with lesions suspected to be either disease progression or post-treatment changes.
2\. Cohort B: Adult patients with a first diagnosis of primary or secondary brain tumor.