Clinical application of optical and electromagnetic navigation system in CT-guided radiofrequency ablation of lung metastases

Abstract

Purpose

To evaluate the clinical value of CT-guided radiofrequency ablation (RFA) in the diagnosis and treatment of pulmonary metastases under optical and electromagnetic navigation.

Methods

Data on CT-guided radiofrequency ablation treatment of 93 metastatic lung lesions in 70 patients were retrospectively analyzed. There were 46 males and 24 females with a median age of 60.0 years (16–85 years). All lesions were ≤3cm in diameter. 57 patients were treated with 17 G radiofrequency ablation needle puncture directly ablated the lesion without biopsy, and 13 patients were treated with 16 G coaxial needle biopsy followed by radiofrequency ablation. There were 25 cases in the optical navigation group, 25 in the electromagnetic navigation group, and 20 in the non-navigation group. The navigation group was performed by primary interventionalists with less than 5 years of experience, and the non-navigation group was performed by interventionalists with more than 5 years of experience.

Result

All operations were successfully performed. There was no statistically significant difference in the overall distribution of follow-up results among the optical, electromagnetic, and no navigation groups. Complete ablation was achieved in 84 lesions (90.3%). 7 lesions showed incomplete ablation and were completely inactivated after repeat ablation. 2 lesions progressed locally, and one of them still had an increasing trend after repeat ablation. No serious complications occurred after the operation.

Conclusions

Treatment with optical and electromagnetic navigation systems by less experienced operators has similar outcomes to traditional treatments without navigational systems performed by more experienced operators.

Keywords:

• Optical navigation
• electromagnetic navigation
• lung metastases
• computed tomography
• radiofrequency ablation

Introduction

The lung is the main organ for metastasis and dissemination of various tumor lesions. Hypoxia and inflammatory conditions in the lung microenvironment can promote the occurrence of lung metastases [1]. Previous studies have confirmed that effective local control of lung metastases is beneficial to prolong patient survival [2]. The clinical treatment methods mainly include surgical resection, radiotherapy, local treatment, and systemic treatment [3]. As a local treatment method for tumors, image-guided tumor ablation is more and more widely used in the treatment of pulmonary metastases with the development of image-guided equipment and ablation instruments, as well as the advantages of good efficacy, high safety, few complications, and low cost of ablation technology, including radiofrequency ablation, cryoablation, microwave ablation, chemical ablation, nanoknife ablation and so on [4].

Ct-guided ablation does not allow real-time imaging, and the patient and the physician are exposed to radiation [5]. Both the preoperative planning and the intraoperative procedure of ablation depend on the experience of the interventionist [6,7]. The needle placement is an important factor affecting the quality of surgery. When the operation is difficult, and the interventional doctor is inexperienced, the puncture results will be affected [8,9]. The optical and electromagnetic navigation systems can be used to effectively improve the accuracy of puncture operation to reduce the difficulty of puncture, the influence of inexperience and operation error on the operation [10,11]. It also reduces the radiation dose to both patients and physicians and enhances the confidence of new interventionalists [12,13].

The application of ablation to pulmonary metastases has been common [14–16], but the application of navigation systems to pulmonary metastases has been rarely studied. In this study, we retrospectively analyzed 70 patients who underwent optical-guided, electromagnetic-guided, and navigation-free CT-guided radiofrequency ablation of metastatic lung lesions at our hospital (Chinese PLA General Hospital, Beijing, China) to investigate the efficacy and safety of the navigation system in ablation of lung metastases.

Materials and methods

Study population

70 patients (46 males and 24 females, aged from 16.0 to 85) with pulmonary metastatic lesions who underwent RFA with optical navigation, electromagnetic navigation, and non-navigation CT-guided in our hospital from January 2021 to December 2022 were selected. The median age was 60.0 years. All patients had primary lesion pathological diagnosis or lung lesion puncture pathological diagnosis, and some patients underwent needle biopsy simultaneously to confirm the molecular pathology of lung lesions. Primary tumor distribution: 28 cases of colorectal cancer, 14 cases of hepatocellular carcinoma, 8 cases of lung cancer with intrapulmonary metastasis, 7 cases of salivary gland tumor, 5 cases of renal cell carcinoma, 2 cases of endometrial cancer, 2 cases of thyroid cancer, 1 case of breast cancer, 1 case of thymoma, 1 case of osteosarcoma, and 1 case of brain perivascular cell tumor. (See Table 1 for details of lesion location.) All 93 lesions were ≤3cm in diameter. Patient inclusion and exclusion criteria before operation are shown in Table 2. A flow chart of the patient selection process is shown in Figure 1. Before treatment, written informed consent for ablation therapy was obtained from the patient and/or relatives, as appropriate. Ethical permission for the study was obtained from the Ethics Committee of the PLA General Hospital (No: S2023-694-01).

Figure 1. Flow chart of the patient selection process.

Table 1. Statistics of lesion location.

location	Quantity
Upper lobe of right lung	28
Middle lobe of right lung	5
Lower lobe of right lung	20
Upper lobe of left lung	22
Lower lobe of left lung	18
Total	93

Table 2. Surgical inclusion and exclusion criteria.

Inclusion Criteria	Exclusion Criteria
Primary lesion was stable or controlled	Tumor spread widely and the KPS < 60
Good cardiopulmonary function and could tolerate minimally invasive surgery	Cardiopulmonary function was poor, and the maximum ventilatory capacity <40%
Number of lesions ≤ 5	Number of lesions > 5
Preoperative evaluation had a safe puncture path and ablation range	No safe access or ablation area

KPS: Karnofsky Performance Status.

Equipment

Philips Brilliance large-aperture 16-slice spiral CT (scanning parameters: tube voltage 120 kV, tube current 250mAs, slice thickness 5 mm, slice spacing 5 mm); Electromagnetic positioning and navigation system (Veran, USA); Optical navigation system (XinAo MDT, China); The Cool-tip radiofrequency ablation system was from the United States, and the Celon-Surgical radiofrequency ablation system was from Germany. From daily use, it was found that the two devices were not very different.

Methods

All patients were examined for blood routine, coagulation function, blood biochemistry, serum virus surface antibody (hepatitis B, hepatitis C, syphilis, HIV), electrocardiogram, lung function, and routine enhanced CT before surgery (Figure 2). The patients fasted 6 h before surgery, analgesic and antitussive drugs were used 1 h before surgery, intravenous access was established, and ECG, blood pressure, and oxygen saturation were routinely monitored. The patient’s position was reasonably selected according to the location of the lesion, and the puncture point and puncture route were determined by CT scan (The navigation group needed additional external devices for navigation positioning and preoperative path planning because the navigation system requires the interventionist to indicate the path to be guided (Figure 3). Local injection of 1% lidocaine hydrochloride 10 ml was performed after sterilizing and laying out the sterile sheet. RFA needles were implanted according to the preoperative protocol using a step-by-step puncture method or after biopsy with a 16 G sheath. In the navigation group, electrodes were placed into the lesion under the guidance of the corresponding navigation system. A Chiba needle was placed close to the ablation of the pleural lesion for continuous infusion of lidocaine for analgesia. The position of the probe was determined by CT scan until the probe was in place, and the navigation system assisted the doctor’s puncture operation by virtual three-dimensional images in real-time (Figure 3). The ablation power was adjusted according to the impedance of the machine monitoring to maintain the ablation power between 40 and 80 W, and the ablation time was 12 to 25 min. Intravenous analgesia and hemostatic drugs were given during the procedure, and intermittent scanning was performed to observe the ablation (Figure 4). If the monitoring image showed incomplete ablation, the ablation could be performed after adjusting the needle path. The position of the needle was adjusted to ensure that the thermal field could cover the non-ablated lesion. After satisfactory ablation, a CT scan was performed routinely to observe whether there were complications such as hemorrhage, pneumothorax, and air embolism. Electrocardiogram (ECG), blood pressure (BP), and oxygen saturation (SPO2) were monitored for 6 h during and after operation. Antibiotics were routinely used for 3 days to prevent infection. The operation time (from the beginning of the operation to the end of the operation, and the navigation group also included the preparation time of navigation equipment), hospitalization time and ablation time were recorded.

Figure 2. Female patient 66 with bilateral lung metastases after rectal cancer surgery (arrow).

Figure 3. ( A) Position layout of the optical navigation system in the CT room. (B,C) With the assistance of optical and electromagnetic navigation, the interventional doctor performed the puncture operation. The virtual real-time 3D monitoring display screen of the (D) navigation system can simulate the specific position of the probe.

Figure 4. Radiofrequency electrode needles were implanted under CT monitoring (thin arrow) according to different positions of the lesions. A thousand leaf needle was placed near the pleura to continuously infusion 5% lidocaine to maintain anesthesia (thick arrow). After ablation, a halo sign was observed around the lesions.

Intraoperative and postoperative complications were observed. Plain and enhanced CT scans were performed at 1, 3, and 6 months after surgery, and follow-up was performed every 6 months thereafter to observe the ablation area and the presence or absence of new lesions (Figure 5).

Figure 5. Female patient 66, postoperative rectal cancer, CT review 1 month after ablation, the ablation area showed triangular and cord-like consolidation without significant enhancement (arrow).

Postoperative local efficacy evaluation criteria (the efficacy was judged based on the lesion at 1–1.5 months after surgery, and the evaluation was completed by three interventionalists with more than 5 years of experience):

1. complete ablation (any one of the following features): ① disappearance of lesions; ② complete cavity formation; ③ Fibrosis of the lesion, which may be scar; ④ the solid nodules shrank or remained unchanged or increased, but there was no enhancement sign on enhanced CT scan and/or no metabolic activity on PET/CT; ⑤ atelectasis, the lesion in atelectasis has no contrast enhancement on CT scan and/or the tumor has no metabolic activity on PET/CT;

2. incomplete ablation (any one of the following features): ① incomplete cavitation, partial solidity, enhancement on enhanced CT scan and/or metabolic activity on PET/CT; ② Partial fibrosis, contrast enhancement on CT scan around fibrosis or edge and/or metabolic activity on PET/CT; (3) solid nodules with no change or increase in size, accompanied by contrast enhancement on CT scan and/or metabolic activity on PET/CT; (4) tumor cells detected by biopsy;

3. local progression (any of the following types): ① the lesion was enlarged by 10 mm, with an increased irregular or internal enhancement area on CT and a significant increase in FDG uptake on PET/CT; ② new local lesions with new enhancement signs on CT and/or new significant FDG uptake on PET/CT; ③ Tumor cells found on biopsy.

Statistical analysis

The cases of complete ablation, incomplete ablation, and local progression in the optical navigation, electromagnetic, and non-navigation groups were statistically analyzed. Using SPSS 25 statistical software, a one-way analysis of variance was used to compare the differences in procedure time, hospital stay, and ablation time among the three groups. The chi-square test or Fisher’s exact test was used to compare the differences in complications among the three groups. The Kruskal-Wallis rank sum test was used to compare the overall data distribution differences of the case results among the three groups. p < 0.05 is considered statistically different for differences in the distribution of results.

Results

A total of 93 lesions in 70 patients were successfully operated. The operational time, hospitalization time, and ablation time of the three groups are shown in Table 3. Because the operational time, hospitalization time, and ablation time were not normally distributed in each group, the Kruskal-Wallis rank sum test was performed. The results showed that there was no significant difference in procedure time, hospitalization time, and ablation time among the three groups. Ten patients had a small amount of hemoptysis during the operation, which was stopped after local injection or intravenous drip of hemostatic drugs. Twenty-four patients had mild to moderate pain during ablation, which was relieved after local pleural injection and intravenous infusion of analgesic drugs. There were 8 cases with a small amount of pneumothorax after operation, and 4 cases with moderate or large amounts of pneumothorax underwent closed thoracic drainage. Eight patients had postoperative fever (37.5–38.5 °C), which improved after symptomatic treatment. No serious complications such as massive bleeding and bronchopleural fistula occurred. Complications in each group are shown in Table 4. According to the characteristics of the data, the chi-square test showed that there was no significant difference between the mild and moderate pain groups (p = 0.954). Fisher’s exact test showed that there was no significant difference between the groups in mild hemoptysis (p = 1), mild pneumothorax (p = 1), closed thoracic drainage (p = 0.673), and postoperative fever (p = 0.727).

Table 3. Results of procedure time, procedure time, and ablation time for each group.

Time(mins)	$\overline{x}$±SD			p
	Optical navigation group	Electromagnetic navigation group	No navigation group
Operational time	43.0 ± 10.5	42.8 ± 9.8	47 ± 12.7	0.497
Hospitalization time	7 ± 0.9	6.6 ± 0.9	6.7 ± 1.1	0.200
Ablation time	16.0 ± 4.5	16.4 ± 4.7	17.4 ± 4.9	0.480

Table 4. Complications in each group.

	Optical navigation group	Electromagnetic navigation group	No navigation group	p
Mild to moderate pain	9	8	7	0.954
Mild hemoptysis	3	4	3	1
Mild pneumothorax	3	3	2	1
Closed thoracic drainage	1	1	2	0.673
Postoperative fever	4	2	2	0.727

CT scan immediately after ablation showed that the ablation area was enlarged, the edge of the lesion was blurred, and the halo change of the edge was blurred in the adjacent lung tissue. Thirty-two lesions showed low-density cavitation after ablation, and 57 lesions showed low-density needle track after needle extraction. At 1, 3, and 6 months after operation, 84 of 93 lesions were completely ablated. CT images showed that the consolidation area of the lesions was not enhanced, the edge was clear, and the volume was gradually reduced to varying degrees, showing fibrous cord, nodule, cavity, and nodule disappearance. Seven lesions showed nodular enhancement at the edge of the reexamination, and the lesions were completely inactivated after two times RFA. Two lesions were enlarged with a large enhancement range. RFA was performed twice, and 1 case still showed an increasing trend after operation. The results of postoperative follow-up are summarized in Table 5.

Table 5. Results of postoperative follow-up in each group.

Results of follow-up	Case
	Optical navigation group	Electromagnetic navigation group	No navigation group
Complete ablation	29	28	27
Incomplete ablation	2	2	3
Local progression	0	1	1

The results of the Kruskal-Wallis rank sum test in SPSS25 showed χ²=1.08, p = 0.582. There was no significant difference in the follow-up results among the three groups with different surgical methods.

Discussion

Lung is rich in blood supply, making it an important metastatic organ for all human malignant tumors [17]. As a minimally invasive treatment method, radiofrequency ablation is an effective treatment for metastatic lung cancer [18], especially for patients who cannot tolerate lobectomy. Computer-assisted navigation is a method defined as assisting doctors in surgery, including optical navigation and electromagnetic navigation [19]. The optical navigation system recognizes the positioning marks on the body and equipment through the camera and then locates the target through image registration and spatial positioning technology to provide real-time monitoring and navigation for doctors [20]. The electromagnetic navigation system uses the known magnetic field geometry to determine the magnetic flux and the attitude of the sensor to realize the attitude monitoring and dynamic tracking of the target [21]. For interventional surgery, the navigation system aims to solve the problem that puncture interventional surgery cannot monitor the Angle and depth of the needle in real-time and relies heavily on the personal experience of the doctor.

Through the analysis of the intraoperative treatment and follow-up of the postoperative efficacy, it can be concluded that the operation time and complications of radiofrequency ablation by inexperienced interventional doctors under the guidance of navigation are similar to those of the interventional doctors with more than 5 years of experience. Relying on the navigation system can give more confidence to the primary interventionalist and may shorten the learning curve for the interventionalist who is just learning the ablation procedure. At the same time, it can also promote the popularization of ablation technology. The mechanical system has relatively better stability, so the navigation system is helpful in reducing the impact of operation errors and operation difficulty on the operation effect and improving safety. Our junior interventionalists reported that they were indeed more confident with navigation assistance, and our senior interventionalists reported that learning to use the navigation system was easy.

In the actual operation, different from the intermittent CT scanning in the group without navigation to confirm the position of the probe, the real-time guidance of the navigation system can omit multiple intermittent CT scans during the operation. This would also significantly reduce the radiation dose from the CT scan. The navigation system also has a respiratory monitoring module. For the set error range, the red and green signs tell the operator whether the error during the current puncture is within the set acceptable error range. Navigation systems all require time for device placement, navigation image reconstruction, and registration, which are necessary for a skilled engineer to accomplish in less than 5 min. However, this time had little effect on the overall procedure time (the results showed no statistically significant difference in procedure time), especially for patients with multiple lesions. There were 3 cases of navigation failure in the process of case screening, all of which were electromagnetic navigation. The reason may be that electromagnetic navigation is very sensitive to electromagnetic interference and magnetic field distortion, and when the distance between the transmitter and the receiver is too far, the stability and accuracy of the system will be reduced, resulting in a large deviation of puncture results and navigation failure.

The navigation system also has some limitations. There is a certain degree of deformation during the puncture process, so the navigation system only guides the operation according to the preoperative CT image, which will produce a certain error. The area between the infrared camera of the optical navigation system and the tracker on the patient’s body is easy to be occluded by objects, and the navigation process will be interrupted [22], affecting the puncture accuracy. Therefore, it is necessary to ensure that the area is not obscured, which again limits the freedom of the operator. Electromagnetic navigation is highly sensitive to electromagnetic interference and magnetic field distortion [20]. When there are magnetic objects in the electromagnetic field, the propagation of electromagnetic waves will be affected by various disturbances, and the positioning of sensors will be affected [23]. As the distance between the transmitter and receiver increases during electromagnetic navigation, its stability and accuracy decrease. Since the electromagnetic navigation system is positioned by a magnetic field, non-magnetic instruments are required, which is bound to increase the cost of surgery [24].

Generally, the electromagnetic transmitter can be placed as close to the operating table as possible, and the appropriate needle entry point can be selected to reduce the distance between the receiver and the transmitter during the operation, which can reduce the influence of the increased distance between the transmitter and the receiver to a certain extent. To improve the reliability and robustness of electromagnetic navigation systems, several manufacturers have proposed that developing custom systems for different environments and applications may improve the robustness of electromagnetic navigation systems. Today, several commercial tracking device models are on the market, covering a variety of technical specifications [20]. The mutual integration of optical navigation and magnetic navigation may be a future development direction to overcome the inherent shortcomings of each technology. We need to overcome the registration problem of different spatial coordinate systems and the synchronization problem of collected data. Vaccarella et al. [25] proposed a sensor fusion algorithm based on the extension of the standard Kalman filter to realize the possibility of fusion. The operator can choose and switch between tracking techniques to better fit the needs of the clinical procedure. For the accuracy errors caused by intraoperative deformation and slight movements of patients, we can consider adding a dynamic calibration module and adding a CT scan during the operation to realize the correction of dynamic errors.

In conclusion, our results indicate that optical navigation and electromagnetic navigation are safe and effective in CT-guided radiofrequency ablation of lung metastases, which can reduce the difficulty of puncture operation and achieve the surgical effect of senior interventional doctors.

Ethical approval

The study was approved by the ethics committee of the Chinese PLA General Hospital (No: S2023-694-01) and was conducted in accordance with the Declaration of Helsinki and its later amendments or similar ethical standards.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data used to support the findings of this study are available from the corresponding author upon request. The authors will provide the original data without reservation.

Additional information

Funding

This work was supported by the Military Equipment Comprehensive Research project of China under Grant [No. LB2022B010100].