A Study to Assess the Ability of Stereotactic Radiotherapy to Restore the Efficacy of Immunotherapy in Patients With Metastatic Cancer.

"Patients will perform stereotactic radiotherapy with 3 sessions (8 Gy) during 20 minutes each and with 72 hours in-between.~Patients enrolled in the study would not have received this stereotactic radiotherapy outside the study, that is why this procedure is additional (compared to Standard of care) and considered as burdensome (as this is radiation). Before performing the stereotactic radiotherapy, patients will do a radiotherapy CT scanner (no injected) in order to prepare precisely the radiotherapy (treatment plan)."