A more accurate radiotherapy is implemented by using a vessel marker for radiotherapy having a deformation fixed shape for engaging with the inner wall of a vessel by deformation after being inserted into the vessel, and a position notification shape for notifying an outside of a radiation irradiation position. Also provided are a radiotherapy support method for supporting radiotherapy to be performed by using the vessel marker, a radiation irradiation control apparatus that irradiates, with radiation, a patient in which the vessel marker is indwelled, and a vessel marker indwelling support apparatus to be used when indwelling the vessel marker.