During gamma scalpel treatment of brain tumors and metastases, a follow-up magnetic resonance imaging (MRI) scan is performed. The radiologist who reviews the MRI assesses whether there is an increase in signal at the tumor site. This increase potentially indicates that the treatment was not effective. However, in 25% of cases (one in four people), this signal enhancement is not due to ineffective treatment, but to inflammation (swelling/damage) and tissue death around the tumor. This is why when an increase in signal is detected, additional follow-up is essential. The standard additional follow-up has an accuracy of about 83%.

This is an observational study on patients with brain metastatis comparing MRI alone or combined to PET-FET to improve accuracy of diagnosis of metastasis recurrence.

Inclusion Criteria:

• Male or female over 18 years of age;
• Having undergone gamma knife radiosurgery for brain metastasis;
• Presenting for a first MRI follow-up (Cohort C1);
• Presence of one or more brain metastases with increased enhancement on follow-up MRI (Cohort C2.1 and C2.2); A participant recruited for Cohort C1 could be recruited for follow-up in Cohort C2.1 or C2.2 if the MRI result is ambiguous.

Exclusion Criteria:

• Pregnancy or breastfeeding;
• Other condition that may influence the imaging result;
• Renal impairment (<30 mL/min/1.73 m2). This threshold is consistent with recent RAC recommendations; Note: For participants with intermediate renal clearance (30-60 mL/min/1.73 m2), the total gadobutrol dose injected is set at the manufacturer's recommended clinical dose. For patients with renal clearance greater than 60 mL/min/1.73 m2, a dose of 1.5x the normal dose is used. These dose values have been approved by Dr. Chénard and are consistent with the RAC recommendations.
• Inability to maintain supine position for the required duration (variable, depending on the sequence);
• Patients who have previously received full brain irradiation;
• Patients who are claustrophobic and cannot tolerate insertion into the MRI scanner;

Adults with brain metastases undergoing MRI