1. A method for computer-assisted medical navigation, said method comprising: during a medical treatment procedure, detecting a position of a patient or a part of the patient's body with the patient being in position for treatment, and without removing the patient from the position for treatment, acquiring patient-characteristic, two dimensional detection data; detecting a position(s) of at least one medical treatment device or treatment-assisting device; creating patient-specific body structure data, wherein creating the patient-specific body structure data includes: projecting a three-dimensional generic model onto the acquired patient-characteristic, two-dimensional detection data, adapting the projection(s) of the three-dimensional generic model to the the patient-characteristic, two-dimensional detection data, and adapting the three-dimensional generic model to conform to the adapted projection(s) of the three-dimensional generic model; and assigning the detected position(s) of the patient and/or the at least one medical treatment device or treatment-assisting device to the created patient-specific body structure data.