The present invention pertains to a system for electronic brachytherapy wherein a layer of target material can produce reflection and transmission X-rays when struck by electrons from a cathode. An alternative system can have a fixed-size containment structure around a miniature X-ray source, with X-ray attenuating coolant fluid between the source and containment structure. A balloon can be around the fixed-size containment structure and can be inflated with an X-ray inert gas.