Contribution of the CEST Sequence in the Characterization of Radionecrosis of Brain Metastases of Pulmonary Origin

This imaging study is testing whether a specialised MRI technique called CEST (Chemical Exchange Saturation Transfer) can help doctors distinguish between true regrowth of brain metastases from lung cancer and tissue damage caused by radiation treatment (radionecrosis), which can look similar on standard scans. **You may be eligible if...** - You are over 18 years old - You have been diagnosed with primary lung cancer - You have brain metastases (cancer that has spread to the brain) that were treated with radiotherapy - Your brain imaging shows a lesion that appears to have grown on a recent MRI (suggesting either recurrence or radiation damage) - You are covered by French social security **You may NOT be eligible if...** - You have a contraindication to MRI (e.g., pacemaker, certain implants) - You have severe cognitive impairment that prevents informed consent - You are under guardianship or in custody Talk to your doctor to see if this trial is right for you.