The present invention relates to a method for obtaining an optimized irradiation time point of radiation by finding out the time point at which radiation is least irradiated to general tissue during the respiration of a patient. Specifically, the present invention relates to a method for obtaining the time point at which radiation is least irradiated to general tissue during the respiratory period of a patient by defining a three-dimensional geometric relationship between peripheral tissue and a target volume using biological characteristics of general tissue, such as esophagus or spine, where tumors are not formed, for radiation and an overlap volume histogram. In a method for irradiating radiation to a tumor of a patient according to an aspect of the present invention, the method comprises: a first step for determining an irradiation timing of the radiation using the radiation sensitivity of at least one first organ within a predetermined distance from the tumor among a plurality of organs and the geometric overlapping degree between the first organ and the tumor； and a second step for irradiating the radiation to the tumor at the irradiation timing, wherein the radiation sensitivity and the geometric overlapping degree may vary according to the respiration of the patient.La présente invention concerne un procédé permettant d'obtenir un point temporel de rayonnement optimisé en trouvant le moment auquel le rayonnement est au moins irradié au tissu général pendant la respiration d'un patient. En particulier, la présente invention concerne un procédé permettant d'obtenir le moment auquel le rayonnement est au moins irradié au tissu général pendant la période respiratoire d'un patient en définissant une relation géométrique tridimensionnelle entre le tissu périphérique et un volume cible en utilisant les caractéristiques biologiques du tissu général, tels que l'oesophage ou la colonne vertébrale, où les tumeurs ne sont pas formées, pour un rayonnement et un histogram
