The system comprises at least three anchors (2, 2', 2") intended to be attached to the patient and equipped with markers (5, 5', 5"), an insertion guide device (6) with an insertion guide (7) intended to be attached to said anchors (2, 2', 2"), an external calibration device (8) with at least three calibration markers (10,10', 10") corresponding to said markers (5, 5', 5") and a planning and imaging software. The planning and imaging software is used to determine the position of a target point in the patient with respect to the markers (5, 5', 5"), the calibration device is used to calibrate and orient the insertion guide (7) of the insertion guide device (6) mounted on said calibration markers (10,10', 10") using the determination of the software before the insertion guide device is mounted on said markers (5,5',5") attached to the patient.