Abstract: The individual sensitivity of radiation is determined by specialized gene of people, so the patient with different radiotherapy dose has different results. Coinciding every patient with individual dose can improve the effect of radiotherapy, lower the incidence of hypothyroidism. Using modern molecular biology techniques, we have understood the relationships between several genes' products (Fas/FasL and Bcl-2 et al.) and apoptosis (or rays induced apoptosis), and all these methods and techniques make it possible for us to measure the products in vitro. Maybe in the future we can measure the index during the period of radiotherapy and use the suitable dose.