This is a prospective, interventional, monocentric, clinical study of Stereotactic Body Radiation Therapy (SBRT) for primary or secondary renal tumors, delivering from 25-26 Gy/1 fraction to 42-48 Gy/3-4 fractions or 40-50 Gy/5 fractions (standard prescriptions for the internationl guidelines, according to tumor size), using a robotic accelerator -CyberKnife® (Accuray, Sunnyvale, CA)-, with fiducial-tracking, to observe the acute and late toxicity reduction (as primary objectives), due to the maximum precision of the treatment. Secondary objectives are Local Relpase-Free Survival (LRFS), Regional Relapse-Free Survival (RRFS), Distant Metastasis-Free Survival (DMFS), Disease-Free Survival (DFS), Cancer Specific Survival (CSS), Overall Survival (OS) and Quality-of-Life (QoL). A total of 60 participants are expected to be enrolled over four years, and the follow-up of enrolled patients will be three years.