## 4 Discussion
In this way, every movement of the patient between the scan previously acquired and needle placement can lead to a path error. This leads to a greater number of controls and therefore an increase in the radiation dose and procedure time. This is particularly true for small lung lesions, but also lesions localized in the lower lobes, more sensitive to respiratory motions. Studies have shown that this kind of drawback can possibly be overcome by the use of fusion systems with ultrasound images [14; 1; 26]. However, this kind of system is not applicable in the specific field of lung biopsies. Despite these respiratory motions, the use of CT-Navigation(tm) system was reliable enough to demonstrate a very high diagnostic success rate. Note that the number of CT acquisitions was significantly lower in the NAV-group during step \(\Delta 2\) for \"easy\" lesions, meaning that the radiologist's confidence in this system is probably higher for this kind of lesion. Our study found significant lower radiation exposure using the navigation system than using the conventional method. However, these results must be balanced by the fact that the CT acquisition parameters for lung biopsies were modified during the study. When the CT-Navigation(tm) system was implemented in our department, the CT acquisition parameters for lung biopsies were optimized. The difference in acquisition parameters may thus partly explain the difference in radiation dose between the two groups. However, the radiation doses in each group were comparable to those presented in the literature [19]. For \"easy\" lesions, less CT acquisitions were required during step \(\Delta 2\) in the NAV-group. A dose reduction is thus expected when using CT-Navigation(tm) system, at least for this kind of lesion. CT-Navigation(tm) provides a reliable tool to assist PLB procedures even for small lesions. Lesions included in the NAV-group were significantly smaller. In addition, more complex trajectories were performed in the NAV-group, with significantly greater angulations than in the CT-group. Significantly more lesions were classified \"difficult\" in the NAV-group. These data may suggest that the physician feels more confident with the CT-Navigation(tm) system when faced with smaller lesions or lesions that are more difficult to access with an out-of-plane trajectory. The use of CT-Navigation(tm) systems might thus contribute to the achievement of more complex PLB procedures. A previous phantom study evaluating the CT-Navigation(tm) system showed that operators, including novice ones, performed faster and more accurately punctures with out-of-plane trajectories with the help of the navigation system [16]. In accordance with more out-of-plane trajectories when using the navigation system, the acquisition length was longer in the CT-NAV group than in the CT-group during step \(\Delta\)2. All the identified complications were related to the usual adverse events of the PLB procedure. None of these adverse events could be directly related to the use of the navigation system. No difference was found between the two groups. The rates of pneumothorax (31.6% in the CT-group; 25% in the NAV-group; \(p=0.418\)) were similar to those found in the literature [27; 28]. The CT-Navigation(tm) system had already been studied for various procedures with a high rate of technical success [13; 14; 18; 29], but the present study is the first study evaluating this system in the specific field of lung biopsies. An experiment similar to ours has been described by [PERSON] et al. comparing lung biopsies with CT-fluoroscopy guidance or with CT-fluoroscopy using an electromagnetic navigation system in 60 patients [12]. No significant difference was found in terms of procedure time, radiation dose, number of control acquisitions and complication rate. However, eight cases required the abandonment of the navigation system due to technical issue. In the present study, the navigation system has proven to be reliable. No dysfunction has been reported.