Various treatment options are available for brain metastases, depending on factors such as lesion site or number lesions. Radiotherapy is a commonly used treatment. Following stereotactic radiotherapy for brain metastases, a potential complication, namely brain radionecrosis, can occur subsequently. It is essential to differentiate between this radionecrosis and lesion recurrence in order to determine the appropriate treatment approach. Contrast-enhanced magnetic resonance imaging (MRI) is the most widely used technique for monitoring brain metastases. Therefore, patients undergo routine MRI at 3 months and during subsequent follow-ups, but if the lesion evolve and if distinguishing between recurrence and radionecrosis is challenging, an [18F]-FDG PET scan is then prescribed by oncologists or radiotherapists during follow-up consultations. As part of the standard patient management protocol, a 10-minute image acquisition begins after a 45-60 minutes wait following the radiotracer injection. A second image acquisition is then conducted 3-4 hours later. For both acquisitions, a low-dose X-ray scanner is synchronously coupled to allow attenuation correction of the PET images.

Patient for whom a [18F]-FDG PET cerebral examination has been prescribed as part of the usual management of brain metastases will be eligible to the protocol. If the patient agrees to participate, an early imaging session is initiated immediately upon radiotracer injection, lasting 15 minutes in addition to the standard acquisition protocol.

Inclusion Criteria:

• Patient referred for cerebral [18F]-FDG PET examination prescribed as part of his usual medical care for brain metastasis.
• Age ≥ 18 years old
• Affiliation to a social security program
• Ability of the subject to understand and express his consent

Exclusion Criteria:

• Age under 18 years old
• Person under guardianship or curatorship
• Pregnant or breastfeeding woman
• Primary brain tumors
• Brain metastases from renal, thyroid or other cancers known to have low avidity for [18F]-FDG

Patient for whom a [18F]-FDG PET cerebral examination has been prescribed as part of the usual management of brain metastases will be eligible to the protocol