Saline-enhanced radiofrequency thermal ablation of the lung: a feasibility study in rabbits

Enhancing precision in lung tumor ablation through innovations in CT-guided technique and angle control

BACKGROUND

This retrospective study aimed to evaluate the precision and safety outcomes of image-guided lung percutaneous thermal ablation (LPTA) methods, focusing on radiofrequency ablation (RFA) and microwave ablation (MWA). The study utilized an innovative angle reference guide to facilitate these techniques in the treatment of lung tumors.

METHODS

This study included individuals undergoing LPTA with the assistance of laser angle guide assembly (LAGA) at our hospital between April 2011 and March 2021. We analyzed patient demographics, tumor characteristics, procedure details, and complications. Logistic regressions were employed to assess risk factors associated with complications.

RESULTS

A total of 202 patients underwent ablation for 375 lung tumors across 275 sessions involving 495 ablations. Most procedures used RFA, especially in the right upper lobe, and the majority of ablations were performed in the prone position (49.7%). Target lesions were at a median depth of 39.3 mm from the pleura surface, and remarkably, 91.9% required only a single puncture. Complications occurred in 31.0% of ablations, with pneumothorax being the most prevalent (18.3%), followed by pain (12.5%), sweating (6.5%), fever (5.0%), cough (4.8%), hemothorax (1.6%), hemoptysis (1.2%), pleural effusion (2.0%), skin burn (0.6%), and air emboli (0.2%). The median procedure time was 21 min. Notably, smoking/chronic obstructive pulmonary disease emerged as a significant risk factor for complications.

CONCLUSION

The LAGA-assisted LPTA enhanced safety by improving accuracy and reducing risks. Overall, this investigation contributes to the ongoing efforts to refine and improve the clinical application of these thermal ablation techniques in the treatment of lung tumors.

Long-term Survival Results following Endobronchial RF Ablation in a Healthy-Porcine Model

This paper presents results from long-term survival study where healthy swine were ablated with a novel technology designed for treating early-stage non-small cell lung cancer using an endobronchial flexible catheter.Methods - The radiofrequency ablation (RFA) system has been presented previously and consisted of an ablation catheter, radiofrequency generator, irrigation pump for infusion of hypertonic saline (HS) and a laptop. The catheter carried an occlusion balloon, a 5 mm long RF electrode, with irrigation holes, and a 1 mm long electrode for bipolar impedance measurements. The outer diameter (OD) was 1.4 mm for compatibility with current bronchoscopes, navigation systems and radial EBUS. Nine swine were treated in this study with survival times of 1, 4 and 12 weeks (N=3 at each time point). In all animals, the treatment sites consisted of one location in the upper right lung (RUL) and another one in the lower right lung (RLL). CTs were taken pre-op, immediately post-op and at every 2 weeks post treatment. Ablation times ranged from 6 to 8 min and average applied power was 68 W (range 63 - 72 W).Results - At 1-week survival, large zones of necrotic tissue were observed in all respective 6 ablations. Ablation volumes had an average diameter of 3.2 cm at RUL locations and 3.8 cm in RLLs (likely due to longer RLL ablation durations). As time progressed, the necrotic tissue was gradually replaced with fibrotic tissue. At 4-week survival, the replacement was almost complete in all respective 3 animals. As a result, ablation volumes decreased to an average diameter of 1.3 cm at RUL locations and 2.3 cm in RLLs (likely due to longer RLL ablation durations). At 12-week survival, as the replacement process continued, histopathology revealed zones of residual necrotic tissue that were further reduced in size. Ablation zones had been resorbed and contracted by fibrous scar tissue. The average volume of the treatment effect decreased to 1.1 cm (RUL) and to 1.6 cm (RLL) in equivalent diameter. There were no complications in any of the nine animals.Conclusion - In healthy swine lungs, RFA with a 1.4-mm OD, radial-EBUS-sheath-compatible, endobronchial catheter was effective and safe. This system and therapeutic approach may be considered for further evaluation in minimally invasive treatment of tumorous lung nodules.

Early Preclinical Experience with a Novel Endobronchial Radiofrequency Ablation System for Lung Cancer Treatment

This paper introduces a novel technology for treating early-stage non-small cell lung cancer using an endobronchial approach via a flexible radiofrequency ablation (RFA) catheter. Methods - The RFA system consisted of an ablation catheter, radiofrequency generator, irrigation pump for infusion of hypertonic saline (HS) and a laptop. The catheter carried an occlusion balloon, a 5 mm long RF electrode, with irrigation holes, and a 1 mm long electrode for bipolar impedance measurements. The outer diameter was 1.4 mm for compatibility with current bronchoscopes, navigation systems and radial EBUS. The RFA system was extensively bench tested on fresh heart, liver and lung animal tissues using power levels of 30 - 60 W, RF energy delivery durations of 3 - 15 min and HS concentrations of 5% and 23.4%. Two swine were then treated at 60 W for 15 min per bronchus. Several bronchi were involved. For both animals and for all treatment sites, 20% HS was used. Animals were survived for six weeks. Results - Bench studies showed that 60 W, 7 - 15 min ablations can produce large ablation volumes, in excess of 3 - 4 cm diameter. In the chronic animal study, no clinically adverse events occurred. There was no evidence of hemorrhage. Animals vital signs, breathing patterns and their behavior were normal throughout the six-week period. Their appetite was normal and they gained weight according to expectations. The RF ablation created discrete volumes of thermal coagulative necrosis which were subsequently encapsulated ("walled off") by zones of organized fibrosis. The dimensions of coagulative necrotic sequestra met expectations, as at six weeks they exceeded volumes corresponding to 2 cm nodules, the size of tumors normally addressed in the peripheral lung by localized therapy. Conclusion - This therapy showed promise. Appropriate energy settings combined with suitable treatment locations safely produced large ablation volumes of uniform thermal coagulative necrosis. Further studies and optimization of treatment parameters can develop it into a mainstream therapy for treating early-stage lung tumors in humans.

Percutaneous radiofrequency lung ablation combined with transbronchial saline injection: an experimental study in swine

To evaluate the efficacy of radiofrequency lung ablation with transbronchial saline injection. The bilateral lungs of eight living swine were used. A 13-gauge bone biopsy needle was inserted percutaneously into the lung, and 1 ml of muscle paste was injected to create a tumor mimic. In total, 21 nodules were ablated. In the saline injection group (group A), radiofrequency ablation (RFA) was performed for 11 nodules after transbronchial saline injection under balloon occlusion with a 2-cm active single internally cooled electrode. In the control group (group B), conventional RFA was performed for 10 nodules as a control. The infused saline liquid showed a wedge-shaped and homogeneous distribution surrounding a tumor mimic. All 21 RFAs were successfully completed. The total ablation time was significantly longer (13.4 +/- 2.8 min vs. 8.9 +/- 3.5 min; P = 0.0061) and the tissue impedance was significantly lower in group A compared with group B (73.1 +/- 8.8 Omega vs. 100.6 +/- 16.6 Omega; P = 0.0002). The temperature of the ablated area was not significantly different (69.4 +/- 9.1 degrees C vs. 66.0 +/- 7.9 degrees C; P = 0.4038). There was no significant difference of tumor mimic volume (769 +/- 343 mm(3) vs. 625 +/- 191 mm(3); P = 0.2783). The volume of the coagulated area was significantly larger in group A than in group B (3886 +/- 1247 mm(3) vs. 2375 +/- 1395 mm(3); P = 0.0221). Percutaneous radiofrequency lung ablation combined with transbronchial saline injection can create an extended area of ablation.

Radiofrequency ablation using a monopolar wet electrode for the treatment of inoperable non-small cell lung cancer: a preliminary report

Objective

To assess the technical feasibility and complications of radiofrequency ablation (RFA) using a monopolar wet electrode for the treatment of inoperable non-small cell lung malignancies.

Materials and Methods

Sixteen patients with a non-small cell lung malignancy underwent RFA under CT guidance. All the patients were non-surgical candidates, with mean maximum tumor diameters ranging from 3 to 6 cm (mean: 4.6 ± 1.1 cm). A single 16-gauge open-perfused electrode with a 2 cm exposed tip was used for the procedure. A 0.9% NaCl saline solution was used as the perfusion liquid with the flow adjusted to 30 mL/h. The radiofrequency energy was applied for 10-40 minutes. The response to RFA was evaluated by performing contrast-enhanced CT immediately after RFA, one month after treatment and then every three months thereafter.

Results

Technical failure was observed in six (37.5%) of 16 patients: intractable pain (n = 2) and non-stop coughing (n = 4). The mean follow-up interval was 15 ± 8 months (range: 9-31 months). The mean maximum ablated diameter in the technically successful group of patients ranged from 3.5 to 7.5 cm (mean 5.1 ± 1.3 cm). Complete necrosis was attained for eight (80%) of 10 lesions, and partial necrosis was achieved for two lesions. There were two major complications (2/10, 20%) encountered: a hemothorax (n = 1) and a bronchopleural fistula (n = 1).

Conclusion

Although RFA using a monopolar wet electrode can create a large ablation zone, it is associated with a high rate of technical failure when used to treat inoperable non-small cell lung malignancies.

Radiofrequency ablation for the treatment of lung neoplasm

Lung cancer is the most common cause of cancer-related mortality in the USA. Surgical resection is the standard treatment for resectable disease; however, a significant percentage of patients with otherwise resectable lung cancer may have other comorbidities, precluding surgical resection. In patients with Stage I non-small-cell lung cancer, conventional external-beam radiotherapy is typically offered as treatment in medically inoperable, high-risk patients with reported 5-year survival rates of 10-30%. An emerging technology in the treatment of lung tumors is radiofrequency ablation, which is a thermal ablative technique and may be applicable in high-risk patients with lung cancer. In this article we will review the principles of radiofrequency ablation, the common devices in use, the experimental background, the results of 'ablate and resect' studies and the clinical experience with radiofrequency ablation in the treatment of lung neoplasm.

[Interventional oncology for lung tumors]

Lung tumors and pulmonary metastases together are the most common cause of cancer-related death in men and the second most frequent in women. Up to now, surgical resection has remained the gold standard in the treatment of pulmonary tumors, being the only treatment option that was potentially curative and offered the possibility of a significant increase in life expectancy after successful therapy. Over the past decade, percutaneous radiofrequency ablation (RFA) has gained worldwide acceptance in the treatment of primary and secondary tumors of the liver with curative intent, so that indications for RFA have been extended to embrace tumors in other organs, e.g. the lung. Since the first case results were described, the number of publications dealing with the treatment of lung tumors using thermal ablative therapies has increased significantly. The aims of the present article are to give a short overview of emerging therapies such as cyberknife surgery and also, especially, to describe the indications for and technique of RFA, to discuss the ideal method of follow-up, and to highlight possible complications of the therapy and the current results of RFA of primary and secondary lung tumors. In addition, the value of combining RFA with other therapy modes (especially chemotherapy and radiation therapy)is briefly treated.

Effects of blood flow and/or ventilation restriction on radiofrequency coagulation size in the lung: an experimental study in swine

The purpose of this study was to investigate how the restriction of blood flow and/or ventilation affects the radiofrequency (RF) ablation coagulation size in lung parenchyma. Thirty-one RF ablations were done in 16 normal lungs of 8 living swine with 2-cm LeVeen needles. Eight RF ablations were performed as a control (group G1), eight with balloon occlusion of the ipsilateral mainstem bronchus (G2), eight with occlusion of the ipsilateral pulmonary artery (G3), and seven with occlusion of both the ipsilateral bronchus and pulmonary artery (G4). Coagulation diameters and volumes of each ablation zone were compared on computed tomography (CT) and gross specimen examinations. Twenty-six coagulation zones were suitable for evaluation: eight in G1, five in G2, seven in G3, and six in G4 groups. In G1, the mean coagulation diameter was 21.5 +/- 3.5 mm on CT and 19.5 +/- 1.78 mm on gross specimen examination. In G2, the mean diameters were 26.5 +/- 5.1 mm and 23.0 +/- 2.7 mm on CT and gross specimen examination, respectively. In G3, the mean diameters were 29.4 +/- 2.2 mm and 27.4 +/- 2.9 mm on CT and gross specimen examination, respectively, and in G4, they were 32.6 +/- 3.33 mm and 28.8 +/- 2.6 mm, respectively. The mean coagulation volumes were 3.39 +/- l.52 cm(3) on CT and 3.01 +/- 0.94 cm(3) on gross examinations in G1, 6.56 +/- 2.47 cm(3) and 5.22 +/- 0.85 cm(3) in G2, 10.93 +/- 2.17 cm(3) and 9.97 +/- 2.91 cm(3) in G3, and 13.81 +/- 3.03 cm(3) and 11.06 +/- 3.27 cm(3) in G4, respectively. The mean coagulation diameters on gross examination and mean coagulation volumes on CT and gross examination with G3 and G4 were significantly larger than those in G1 (p < 0.0001, p < 0.0001, p < 0.0001, respectively) or in G2 (p < 0.05, p < 0.005, p < 0.005, respectively). Pulmonary collapse occurred in one lung in G2 and pulmonary artery thrombus in two lungs of G3 and two lungs of G4. The coagulation size of RF ablation of the lung parenchyma is increased by ventilation and particularly by pulmonary artery blood flow restriction. The value of these restrictions for potential clinical use needs to be explored in experimentally induced lung tumors.

Radio frequency ablation in the rabbit lung using wet electrodes: comparison of monopolar and dual bipolar electrode mode

Objective

To compare the effect of radio frequency ablation (RFA) on the dimensions of radio frequency coagulation necrosis in a rabbit lung using a wet electrode in monopolar mode with that in dual electrode bipolar mode at different infusion rates (15 mm/hr versus 30 ml/hr) and saline concentrations (0.9% normal versus 5.8% hypertonic saline).

Materials and Methods

Fifty ablation zones (one ablation zone in each rabbit) were produced in 50 rabbits using one or two 16-guage wet electrodes with a 1-cm active tip. The RFA system used in the monopolar and dual electrode wet bipolar RFA consisted of a 375-kHz generator (Elektrotom HiTT 106, Berchtold, Medizinelektronik, Germany). The power used was 30 watts and the exposure time was 5 minutes. The rabbits were assigned to one of five groups. Group A (n = 10) was infused with 0.9% NaCl used at a rate of 30 ml/hr in a monopolar mode. Groups B (n = 10) and C (n = 10) were infused with 0.9% NaCl at a rate of 15 and 30 ml/hr, respectively in dual electrode bipolar mode; groups D (n = 10) and E (n = 10) were infused with 5.8% NaCl at a rate of 15 and 30 ml/hr, respectively in a dual electrode bipolar mode. The dimensions of the ablation zones in the gross specimens from the groups were compared using one-way analysis of variance by means of the Scheffe test (post-hoc testing).

Results

The mean largest diameter of the ablation zones was larger in dual electrode bipolar mode (30.9±4.4 mm) than in monopolar mode (22.5±3.5 mm). The mean smallest diameter of the ablation zones was larger in dual electrode bipolar mode (22.3±2.5 mm) than in monopolar mode (19.5±3.5 mm). There were significant differences in the largest and smallest dimension between the monopolar (group A) and dual electrode wet bipolar mode (groups B-E). In dual electrode bipolar mode, the mean largest diameter of the ablation zones was larger at an infusion rate of 15 ml/hr (34.2±4.0 mm) than at 30 ml/hr (27.6±0.1 mm), and the mean smallest diameter of the ablation zones was larger at an infusion rate of 15 ml/hr (27.2±7.5 mm) than at an infusion rate of 30 ml/hr (24±2.9 mm).

Conclusion

Using a wet electrode, dual electrode bipolar RFA can create a larger ablation zone more efficiently than monopolar RFA.

Radiofrequency ablation in pig lungs: in vivo comparison of internally cooled, perfusion and multitined expandable electrodes

The purpose of this study was to compare the amounts of in vivo coagulation obtained by radiofrequency (RF) ablation in porcine lung, using three types of electrodes. 15 in vivo ablation procedures were performed in the lungs of five pigs using three kinds of currently available RF devices under CT guidance. After placing an electrode in the lung, three ablation zones were created at each of three different regimens: Group A: RF ablation with an internally cooled electrode; Group B: RF ablation with a perfusion electrode, with instillation of 0.9% NaCl solution at a rate of 1.5 ml min(-1); Group C: RF ablation with a multitined expandable electrode. According to the manufacturer's recommendations, RF application times were 12 min in group A and 20 min in group B. In group C, RF energy was delivered for 7 min after a mean temperature of 110 degrees C was reached at 5 cm deployment. 36 min after the procedures, contrast-enhanced CT scans were obtained to evaluate the volume of zone of coagulation, and lungs were harvested for gross measurements. After macroscopic and histopathological analyses of 5 mm-thick lung sections, diameters, volumes and variation coefficients of regions of central coagulation were assessed. During RF ablation, the perfusion electrode allowed a larger energy delivery than the internally cooled or the multitined expandable electrodes, i.e. 33.6+/-4.7 kJ in group A, 40.0+/-8.2 kJ in group B and 23.5+/-6.1 kJ in group C (p<0.05). On gross observation, the cut surface of the gross specimen containing RF-induced coagulation showed that the ablated tissue appeared to be a central, firm, dark-brown area surrounded by an irregular outer margin (approximately 3-10 mm thick) of bright red tissue. In vivo studies showed that RF ablation using the perfusion electrode achieved larger coagulation volume than RF ablation using the other electrodes (p<0.05): 7.2+/-4.1 cm3 in group A; 16.9+/-5.5 cm3 in group B; 7.5+/-3.3 cm3 in group C. The corresponding variation coefficients were 0.55, 0.31, and 0.45, respectively. Our study shows that RF ablation using a perfusion electrode achieves a larger coagulation volume with an irregular margin than RF ablation using internally cooled or multitined expandable electrodes in the porcine lung.

Excessive hyperthermic necrosis of a pulmonary lobe after hypertonic saline-enhanced monopolar radiofrequency ablation

Although there has been a feasibility study of saline-enhanced radiofrequency ablation of the lung in rabbits, there has been no report on hypertonic saline-enhanced radiofrequency ablation of human pulmonary tumors or its complication. We report a case in which a large necrotic cavity was produced in the lung after hypertonic saline-enhanced radiofrequency ablation of recurrent metastatic tumor from hepatocellular carcinoma. Although hypertonic saline-enhanced radiofrequency ablation is powerful and efficient in local ablation, it is difficult to predict the exact extent of ablation, especially in the lungs. This can be dangerous, as there is a high chance of producing an ablation area much larger than expected and, hence, major complications. Special attention is required not to overablate while using this technique.

Effect of vessel diameter on the creation of ovine lung radiofrequency lesions in vivo: Preliminary results

OBJECTIVE

We sought to evaluate the effect of radiofrequency ablation (RFA) on pulmonary vessels with respect to potential of injury of these structures, to assess perfusion-mediated "heat sink" effect, and to consider acute and chronic complications.

MATERIAL AND METHODS

RFAs targeted to perihilar, middle third, and peripheral lung regions were created in vivo in the lung of 10 crossbred sheep. The RITA generator and the Starburst XLi electrode with deployable hooks were used. The approach was open, performed under general anesthesia. Lesions 4 cm in diameter at a target temperature of 80 degrees C were created. Acute (immediate postinterventional euthanasia), subacute (96 h), and chronic (28 days) lesions were evaluated macroscopically, and histologic analysis of the vessels was performed. Patency of the vessels, both arteries and veins, was macroscopically assessed by presence or absence of thrombus and the degree of vascular injury and the viability of perivascular pneumocytes as well as endobronchial injury were histologically assessed.

RESULTS

In the acute, subacute, and chronic setting, heat sink effect, indicated by invagination of the tissue between vessel and ablated region, was only observed in vessels greater than 3 mm in diameter. Thrombus was seen in 20% of the vessels smaller than 3 mm. On histopathology, vessels smaller than 3 mm showed at least partial vessel wall injury, characterized by endothelial cell necrosis and luminal thrombus. In the vessels greater than 3 mm the extent of vessel wall injury decreased with increasing vessel diameter. No acute complications were noted. For the chronic complications a bronchopleural fistula and a lung abscess were found.

CONCLUSION

There seems to be a narrow transition zone for pulmonary vessels around 3 mm, beyond which the heat sink effect was seen consistently and substantial vascular injury was rare.

Radiofrequency Ablation of Thoracic Lesions: Part 2, Initial Clinical Experience—Technical and Multidisciplinary Considerations in 30 Patients

OBJECTIVE

The purpose of our study was to report our initial experience with patients who underwent percutaneous imaging-guided radiofrequency ablation of thoracic lesions, and to emphasize technical and multidisciplinary issues and adjunctive procedures specific to thoracic tumor ablation.

MATERIALS AND METHODS

Our cohort consisted of 30 patients with a spectrum of primary (n=18) and secondary (n=11) lung tumors, mesothelioma (n=1), and five secondarily eroded, painful ribs who underwent ablation of 36 total lesions (one patient had two ablations). Patients either were nonsurgical candidates because of medical comorbidities or extent of disease, or had exhausted chemotherapy and radiation therapy options, or had refused surgery or undergone unsuccessful surgery. Patients were treated with radiofrequency ablation after agreement among oncologists, thoracic surgeons, and interventional radiologists. An array-style electrode under impedance control was used to treat 29 thoracic tumors and the adjacent rib metastases (n=5). A cool-tip radiofrequency probe was used for two patients. CT guidance and general anesthetic were used for all but one patient. Sonographic guidance and IV conscious sedation were used in one patient. Pain (n=11) and tumor cure or control (n=19) were the primary indications for the procedures. Adjunctive procedures to the radiofrequency ablations included the creation of saline or water windows (n=3); establishment of transosseous and transchondral routes (n=4); use of intercostal and paravertebral nerve blocks (n=15); and use of an intraprocedural catheter (n=1), needle (n=1), or sheath (n=3) for treatment of pneumothoraces. Follow-up was from 2 to 26 months.

RESULTS

All ablations were technically successful. No periprocedural mortality occurred. Necrosis of tumor was greater than 90% in 26 of 30 lesions based on short-term follow-up imaging (CT, PET, MRI). In the 11 patients who underwent ablation for pain, relief was complete in four and partial in the other seven. One patient developed a local skin burn, four patients had self-limited hemoptysis up to 4 days after ablation, one had transient atrial fibrillation, one developed hoarseness, and two patients were transiently reintubated after extubation. Eight pneumothoraces developed; one patient underwent placement of a chest tube. Four patients died within 1 year of ablation from extrathoracic spread of tumor.

CONCLUSION

Radiofrequency ablation for a variety of thoracic tumors can be performed safely and with a high degree of efficacy for pain control and tumor killing. The effect of ablation can be assessed with CT, MRI, or PET. Various technical issues differentiate thoracic tumor ablation from standard abdominal ablations. Numerous other thoracic interventional radiology procedures are beneficial to assist the radiofrequency ablation. A multidisciplinary approach offers valuable expertise for patient care.

Saline infusion markedly reduces impedance and improves efficacy of pulmonary radiofrequency ablation

Radiofrequency ablation (RFA) is a relatively new technique that has been investigated for the treatment of lung tumors. We evaluated for the first time the in vivo use of saline infusion during radiofrequency ablation of sheep lung. We performed RFA on 5 sheep using open and closed chest RFA and the RITA starburst XL and Xli probes using saline infusion with the Xli probe. The impedance and volume of ablation were compared. A total of 16 ablations were produced, 5 percutaneously and 11 open. The impedance during percutaneous and open RFA without saline infusion was 110 +/- 16.2 and 183.3 +/- 105.8 ohms, respectively. With the saline infusion the impedance was 71.3 +/- 22 ohms and 103.6 +/- 37.5 ohms. The effect of this was significantly larger volume of ablation using the saline infusion during percutaneous RFA (90.6 +/- 23 cm3 vs 10.47 +/- 2.9 cm3, p = 0.01) and open RFA (107.8 +/- 25.8 cm3 vs 24.9 +/- 19.3 cm3, p = 0.0002). Saline infusion during RFA is associated with lower impedance, higher power delivery and larger lesion size.