[Physical considerations on the method for improving the outcome of radiation therapy]

The outcome of radiation therapy is closely related to the dose that has been delivered to the target volume and the organs at risk. In this report, sources of errors in dose delivery and their magnitudes at each step of radiation therapy from data acquisition of patient to execution of irradiation, and the methods for reducing the errors are discussed. The influences of systematic or random errors in the target dose level and of dose inhomogeneities throughout the target volume on the dose-effect curve are also described. To improve the outcome of radiation therapy, a constant effort from radiotherapists, physicists and technicians is required for reducing the systematic and random errors at each step of radiation therapy.