Novel Ga68-PSMA PET/CT-tracer to Differentiate Between Radiation Necrosis and Tumor Progression in Brain Metastases

Inclusion Criteria:

For all groups:

* Written informed consent
* Age ≥ 18 years old
* WHO PS 0-3
* Measurable lesion ≥10mm according to RANO BM

For brain metastases groups:

\- newly diagnosed brain metastases from either NSCLC (group 1) or melanoma (group 2) or breast cancer (group 7).

For radiation necrosis groups:

\- Brain lesion at the location of a formerly brain metastases that has been treated with SRT (\> 9 months ago), with the definite diagnosis of radiation necrosis at the location of formerly SRT-treated brain metastases of NSCLC (group 3), melanoma (group 4) and/ or breast cancer (group 8).

For diagnostic dilemma groups:

\- Brain lesion at the location of a formerly brain metastases with a diagnostic dilemma of radiation necrosis and recurrent brain metastases of NSCLC (group 5), melanoma (group 6) and/ or breast cancer (group 9).

Exclusion Criteria:

For all groups:

* Known allergy to Ga68-PSMA
* Epileptic seizure less than 7 days before Ga68-PSMA PET/CT scan
* Life expectancy less than 3 months
* Patients with known prostate carcinoma
* Pregnancy