A micro-radiation therapy apparatus includes an isotope-based micro-radiotherapy brachytherapy small animal irradiator useful for radiating a biological system, the irradiator having an external radiation source proximate the biological system comprising a collimated radiation beam. A method of effectively irradiating at least one cell in a biological system includes applying micro-radiation from an isotope-based micro-radiation small animal irradiator, the irradiator having an external radiation source proximate the biological system including a collimated radiation beam to a target cell of the biological system.