This presentation describes low dose radiation treatments for more than 120 years. Describes mechanism for beneficial effects. Ionizing radiation effects on DNA and H2O. Radiotherapy for sinus infections, pneumonia, wound healing, bronchial asthma, inflammatory disease. Discussion of Threshold model versus Linear No-Threshold model for estimating radiation induced cancer. Radiobiological basis of low-dose irradiation in prevention and therapy of cancer. Radon therapy for cancer. Rheumatoid arthritis. Diabetes. Phemphigus auto immune disease. Neurodegenerative diseases. Parkinsons disease. Alzheimer's disease. Important conclusions.