Table 1: Catalogue of criteria for the quality gates of a minimal invasive image-guided surgery at lateral skull base. The customer is the responsible surgeon as he/she is responsible for the outcome of the surgery.


QG1 Criteria

(1.1)Presence of all documents of diagnosis:
(i) anamnesis, clinical examinations,
(ii) indication/necessity of surgery is stated in the patient chart,
(iii) hearing test,
(iv) CT data set
Patient chart

(1.2)In principle the target area is accessible by minimally invasive surgerySurgeons

(1.3)Available CT data suggests based on the patient’s anatomy that it is possible to position drill trajectories. Sensitive structures are not unusually closeSurgeon/radiologist

(1.4)Patient has been informed of advantages and disadvantages of a minimally invasive surgery. The information is available in the patient chartPatient chart

QG2 Criteria

(2.1)Reference structures have been fixed firmly to the patient’s skullSurgeon and residence

(2.2)High-resolution CT images have been taken and are availableRadiology

(2.3)High-resolution images have been processed.
Risk structures (including cochlea, semicircular canals, facial nerve, chorda tympani, ossicles, internal carotid artery, and internal and external auditory canal) are segmented and drill trajectories are planned; anatomical structures and reference structures are clearly visible.
The therapeutic risk index (TRI) is larger than or equal to 1. The uncertainties of the navigation process and the medical imaging have been taken into account for its calculation

(2.4)The mechanical positioning device to adjust the drill has been attached to the skull. The axes’ position (linear and rotary axis) has been checked based on their scale and the calculated positions from the softwareSurgeon and resident

QG3 Criteria

(3.1)The continuous process control (using a C-arm) during insertion of the drill has not shown any abnormalitiesSurgeon

(3.2)The target area has been reached. The surgeon can insert an endoscope and has visual contact to the target area. The target area can furthermore be reached by a surgical instrumentSurgeon and resident

(3.3)No vital structures have been affected (C-arm scan shows no damage of defined sensitive structures and heart rate has been normal)Surgeon, anesthetist