Secondary Logo

Journal Logo

Innovative Technique of Transbronchial Radiofrequency Ablation for Intrapulmonary Tumors: A Preliminary Study in a Rabbit Model

Suzuki, Hidemi MD, PhD*,†; Sekine, Yasuo MD, PhD*,†; Saito, Kazuyuki MD, PhD; Nakajima, Takahiro MD, PhD*; Sakairi, Yuichi MD*; Yoshida, Shigetoshi MD, PhD*; Yoshino, Ichiro MD, PhD*

Journal of Bronchology & Interventional Pulmonology: July 2011 - Volume 18 - Issue 3 - p 211–217
doi: 10.1097/LBR.0b013e318229671b
Original Investigations
Free

Background: Radiofrequency ablation (RFA) has emerged as a potential alternative for surgery in clinical oncology. This animal experiment was conducted to evaluate the feasibility, safety, and effectiveness of transbronchial RFA in the treatment of lung tumor.

Methods: VX2 lung cancer model was established in Japanese white rabbits by transbronchial injection of tissue clot suspension. After waiting for tumor growth to approximately 10 to 20 mm in diameter, transbronchial RFA was performed on VX2 tumors using the Celon-ProCurve microprobe with a 12 mm active tip, a diameter of 1.3 mm, without cooled-tip electrode under the guidance of biplane x-ray scanning. At first, the power of delivery of RFA was increased in a stepwise manner beginning at 1 W/min up to a maximum of 4 W/min, to seek appropriate power deposition. Next, the extent of ablation under determined power deposition was examined for various time periods. The therapeutic efficacy was evaluated by grossly and pathologically 1 week after transbronchial RFA.

Results: All rabbits tolerated the experimental procedures well. Transbronchial RFA at 2 W/min for 20 minute was the most effective setting in this study. Application of more than 2 W/min was not technically feasible using this equipment, leading to destruction of the probe due to high resistance. In transbronchial RFA at 2 W/min condition, the extent of ablation depended on the duration of ablation.

Conclusions: This study demonstrates the potential of transbronchial RFA therapy for treatment of lung tumors. Probe improvement and additional study will be required for further progress.

*Department of Thoracic Surgery, Graduate School of Medicine

Department of Thoracic Surgery, Tokyo Women's Medical University, Yachiyo Medical Center

Research Center for Frontier Medical Engineering, Chiba University, Chiba, Japan

Supported in part by Grant-in-Aid for Young Scientists Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (No. 19790964).

The authors have no commercial associations that might pose a conflict of interest in connection with the work reported herein.

H. Suzuki and Y. Sekine contributed equally and are considered first coauthors.

Reprints: Yasuo Sekine, MD, PhD, Department of Thoracic Surgery, Tokyo Women's Medical University, Yachiyo Medical Center 477-96 Owada-Shinden Yachiyo, Chiba, 276-8524 Japan (e-mail: ysekine@tymc.twmu.ac.jp).

Received 00 00, 000

Accepted 00 00, 000

Radiofrequency ablation (RFA) has been widely accepted for the treatment of hepatocellular carcinoma1 and hepatic2 and cerebral3 metastases. RFA is also used in patients with primary lung cancer or metastatic lung disease, because these patients are often not candidates for surgery due to poor cardiopulmonary reserve, comorbidities, or advanced age.4,5 In these cases, RFA alone, or RFA followed by conventional radiation therapy with or without chemotherapy may become a treatment option.6 Cooled-tip electrode-mediated RFA is suggested to be an effective, minimally invasive alternative to partial pneumonectomy for the treatment of lung cancer.7 RFA is at present a robust technique for the treatment of solid malignancies, and its use dominates other types of percutaneous, computed tomography (CT)-guided ablative therapy.8 However, therapy for lung tumor using CT-guided RFA has possible dangerous complications, such as pneumothorax, hemorrhage, cavity formation, and lung abscess. Therefore, RFA is generally not considered an acceptable therapy for tumors that are centrally located within the lung. No experimental studies have been conducted using a transbronchial approach to deliver RFA for the treatment of pulmonary tumors. The purpose of this investigation was to assess the technical feasibility, safety, and effectiveness of transbronchial RFA in a rabbit model.

Back to Top | Article Outline

MATERIALS AND METHODS

All animals received humane care as specified in the “Guide for the Care and Use of Laboratory Animals” published by the National Research Council of the National Academies. This study was also conducted with previous approval of the Animal Care Committee of the Chiba University Graduate School of Medicine. The study was conducted on Japanese white rabbits weighing 2.0 to 3.0 kg. Rabbits were purchased from Takasugi Experimental Animal Supply Co., Ltd. (Saitama, Japan). All surgical procedures were conducted while the animals were under general anesthesia, as induced by an intramuscular injection of ketamine hydrochloride (50 mg/kg) and xylazine hydrochloride (4 mg/kg) and maintained with isoflurane at an inspired concentration of 1.5% by an intubation tube.

Back to Top | Article Outline

Isolation of VX2 Lung Tumors

VX2 lung tumor cells were initially implanted and maintained in the thigh muscles of rabbits. After the tumors had grown to approximately 10 mm in diameter, they were surgically removed under general anesthesia, minced to 1 mm pieces using a scissors, filtered through a metal mesh to obtain a suspension of single tumor cells, and centrifuged at 1000 rpm for 5 minutes. Roswell Park Memorial Institute 1640 medium (Immuno-Biological Laboratories, Gumma, Japan) with 10% fetal calf serum (Mitsubishi Kagaku, Tokyo, Japan) was added to make a suspension of approximately 1.5×108 cells/mL. Incubation was performed in a humidified incubator at 37°C under 5% CO2.

Back to Top | Article Outline

Preparation of VX2 Model

The Japanese white rabbits were intubated using a 3.5-French, noncuffed, pediatric endotracheal tube as previously reported9 (Fig. 1A). The rabbits were positioned supine under general anesthesia and ventilated with a pressure-controlled ventilator. Under x-ray guidance, the guide sheath was transbronchially inserted into the lung and its tip was positioned in the right lower lobe (Figs. 1B, C). Through a 20-gauge aspiration needle, we slowly injected 0.4 mL of the VX2 cell suspension (1.5×108 cells/mL) mixed with 1.5 mL of collagen cell matrix (Fig. 1D). Tumor growth was monitored using x-ray examination. VX2 nodules larger than 2 cm in diameter were considered appropriate for transbronchial RFA (Fig. 2A). The period required for tumors to reach the size of 2 cm ranged from 14 to 21 days.

FIGURE 1

FIGURE 1

FIGURE 2

FIGURE 2

Back to Top | Article Outline

RFA procedure

A total of 8 rabbits with VX2 tumors underwent transbronchial RFA. The self-adhesive neutral electrode was applied to the shaved abdomen. Under general anesthesia, a flexible applicator (Celon Pro Curve micro probe 800-c12, Celon, Teltow, Germany) with a 12 mm active tip and an outer diameter of 1.3 mm, (without cooled-tip electrode) was transbronchially inserted into the basal segment of the right lower lobe under the guidance of biplane x-ray scanning (Figs. 2B, C). The probe was pushed forward through the working channel of the applicator to the target area. After confirming that the probe was located within the tumor, a 470 KHz RF generator (celonLab POWER), which was capable of producing 250 W of power, was started at 1 W/min. Power was increased in a stepwise manner to 4 W/min to determine the appropriate power setting. After the appropriate power setting was determined, exposure time was varied from 10 minutes to up to 20 minutes to examine the time-dependent effect.

Back to Top | Article Outline

Therapeutic Evaluation

All rabbits that underwent transbronchial RFA were euthanized using an overdose of ketamine and xylazine 1 week after RFA. The therapeutic efficacy was evaluated by gross and histopathologic examination. The tissue specimens were suspended in 10% formalin solution for fixation, sliced, embedded in paraffin, sectioned with a microtome, and stained with hematoxylin and eosin for histopathologic examination.

Back to Top | Article Outline

RESULTS

All rabbits tolerated the experimental procedures well. No anesthesia-related or procedure-related deaths occurred.

Back to Top | Article Outline

Effects of Tissue Ablation

Power output was initially set at 1 W/min and increased up to a maximum 4 W/min in a stepwise manner, with duration of each exposure fixed at 20 minutes. Macroscopic examination of the ablated nodules revealed that the ablated area was generally limited within the nodules and that the surrounding lung tissue was intact. However, even when an entire nodule seemed to be well ablated, the border of the tumor sometimes remained unablated. Histologic examination revealed peribronchial necrosis and complete destruction of the parenchyma with formation of a small cavity. The tumor margins had 2 zones of eosinophilic coagulative necrosis and a peripheral hemorrhagic rim (Fig. 3). There were no viable tumor cells in the necrotic area. The mean maximum diameters of ablation with 20 minutes of exposure were 0 mm at 1 W/min, 5.0 mm at 2 W/min, 2.0 mm at 3 W/min, and 1.5 mm at 4 W/min (Fig. 4). Therefore, 2 W/min for 20 minutes obtained the most effective ablation. From these results, a power output of 2 W/min was considered an appropriate setting.

FIGURE 3

FIGURE 3

FIGURE 4

FIGURE 4

The diameters of ablation using 2 W/min of power over different exposure times were 3.0 mm at 10 minutes, 5.0 mm at 15 minutes, and 8.0 mm at 20 minutes (Figs. 5, 6).

FIGURE 5

FIGURE 5

FIGURE 6

FIGURE 6

In the 8 rabbits that underwent transbronchial RFA, there was 1 incidence of hemothorax and no incidence of pneumothorax or thermal injury to the chest wall.

Back to Top | Article Outline

DISCUSSION

Lung cancer is the most frequent cancer-related cause of death in the world.10 Furthermore, the lungs are one of the most common sites of metastasis, involving 30% to 40% of all patients with various types of tumors.11 Surgical resection is still considered the treatment of choice for early stage non-small cell lung cancer and for carefully selected patients with metastatic lesions.12 However, lung cancers often are diagnosed at advanced stages and in patients with compromised cardiopulmonary status or coexistent medical problems that contraindicate a surgical approach.13 For such patients, radiation, chemotherapy, or both may be used for treatment of lung cancer. Although these treatment methods provide modest improvements in survival, the gain often comes with substantial toxicity, especially for patients who are already suffering from other comorbidities.14 This necessitates the development and use of alternative treatments, especially for patients who are not candidates for surgery. Various thermal ablative techniques, such as RFA, laser photoresection, cryoablation, and microwave ablation, have been introduced as adjuvants to or as substitutes for surgical therapy for liver tumors. Encouraging results from use of RFA in the liver have prompted some researchers to suggest that the procedure could also be used for the treatment of lung tumors.5,7,15

Percutaneous, image-guided RFA has been successfully applied to local control in various locations, including bone, liver, kidney, and lung. However, large pneumothorax or persistent hemoptysis are potential complications when this procedure is used to treat lung cancer. In a study of 30 patients who underwent CT-guided RFA to treat lung cancer, pneumothorax was the most common complication and occurred more frequently in patients whose tumors were located in the central portion (inner two thirds) of the lung compared with those whose tumors were located in the peripheral portion (outer one third) of the lung.16 At present, the greatest clinical use of CT-guided RFA is for the treatment of small peripheral lung tumors in patients who are poor candidates for surgery. However, if the incidence of pneumothorax could be reduced, more patients may benefit from RFA therapy. The transbronchial approach for RFA may potentially develop into a minimally invasive therapy with a low frequency of pneumothorax that can be used to treat patients with inoperable lung tumors located within either the central or peripheral areas of the lung.

To our knowledge, this is the first report of the transbronchial approach for RFA treatment of lung tumors. The transbronchial approach has several advantages over the percutaneous approach. First, because the transbronchial approach does not puncture the chest wall, the risk of pneumothorax and hemothorax due to injury of the intercostal or chest wall vessels is reduced. Second, the transbronchial approach can more readily be used to treat tumors that are located in the central portion of the lung, where use of the percutaneous approach may result in an unacceptably high rate of pneumothorax. Third, because the transbronchial approach is minimally invasive, it can more readily be used repeatedly, in contrast to percutaneous RFA. A disadvantage of the transbronchial approach is that it can be difficult to reach and treat small, peripherally located tumors. In these cases, a navigation system17 or endobronchial ultrasound system18 may be helpful.

There were some limitations in this study. First, the number of rabbits was too small to definitively analyze the effectiveness or potential complications of the procedure. Second, the probe was not sufficiently powerful to ablate effectively using the transbronchial approach because of the still small area of ablation, and probe improvement will be needed to optimize the settings. Currently, the upper limit of homogeneous tissue ablation for most RFA systems operating in living tissue is between 4 and 5 cm in diameter. Our results showed 8 mm in diameter of ablation with 20 minutes of exposure at 2 W/min. When a tumor larger than 8 mm is treated at the time of improvement of the probe, the risk of hemorrhage or hemothorax might be higher. Crocetti et al19 compared feasibility and safety of microwave and RFA of the lung tissue in a rabbit model. In this study, the small vessel occlusion including thrombosis by RFA was much less than microwave ablation. Third, the tumor location was limited to the right lower lobe in this study, because a flexible bronchoscope that could reach other locations, particularly an upper lobe, could not be used in small animals. Lastly, this study could not examine the survival rate after RFA therapy. However, it is generally difficult to evaluate the survival rate using an animal model of VX2 tumors, because this tumor line is extremely malignant.20 This experimental study demonstrates that transbronchial RFA therapy could be a feasible, safe, and effective therapy for treating lung VX2 tumors in a rabbit model, although improvement of the probe will be required for further investigation. Additional experiments are needed to optimize a technique that can be used for clinical therapy.

Back to Top | Article Outline

REFERENCES

1. Livraghi T, Goldberg SN, Lazzaroni S, et al. Hepatocellular carcinoma: radio-frequency ablation of medium and large lesions. Radiology. 2000;214:761–768
2. Solbiati L, Goldberg SN, Ierace T, et al. Hepatic metastases: percutaneous radio-frequency ablation with cooled-tip electrodes. Radiology. 1997;205:367–373
3. Anzai Y, Lufkin R, DeSalles A, et al. Preliminary experience with MR-guided thermal ablation of brain tumors. AJNR Am J Neuroradiol. 1995;16:39–48 discussion 49–52.
4. Wagner KJ. Surgical management of non-small cell lung cancer. Semin Oncol Nurs. 2008;24:41–48
5. Dupuy DE, Zagoria RJ, Akerley W, et al. Percutaneous radiofrequency ablation of malignancies in the lung. AJR Am J Roentgenol. 2000;174:57–59
6. Chhajed PN, Tamm M. Radiofrequency heat ablation for lung tumors: potential applications. Med Sci Monit. 2003;9:ED5–ED7
7. Miao Y, Ni Y, Bosmans H, et al. Radiofrequency ablation for eradication of pulmonary tumor in rabbits. J Surg Res. 2001;99:265–271
8. Dupuy DE, Mayo-Smith WW, Abbott GF, et al. Clinical applications of radio-frequency tumor ablation in the thorax. Radiographics. 2002;22(Spec No):S259–S269
9. Yoshida S, Sekine Y, Saitoh Y, et al. Surgical technique of experimental lung transplantation in rabbits. Ann Thorac Cardiovasc Surg. 2005;11:7–11
10. Parkin DM, Bray F, Ferlay J, et al. Global cancer statistics, 2002. CA Cancer J Clin. 2005;55:74–108
11. Erhunmwunsee L, D'Amico TA. Surgical management of pulmonary metastases. Ann Thorac Surg. 2009;88:2052–2060
12. Pastorino U, Buyse M, Friedel G, et al. Long-term results of lung metastasectomy: prognostic analyses based on 5206 cases. The International Registry of Lung Metastases. J Thorac Cardiovasc Surg1997;113:37–49
13. Janssen-Heijnen ML, Schipper RM, Razenberg PP, et al. Prevalence of co-morbidity in lung cancer patients and its relationship with treatment: a population-based study. Lung Cancer. 1998;21:105–113
14. Marino P, Preatoni A, Cantoni A. Randomized trials of radiotherapy alone versus combined chemotherapy and radiotherapy in stages IIIa and IIIb non-small cell lung cancer: a meta-analysis. Cancer. 1995;76:593–601
15. Goldberg SN, Bazelle GS, Compton CC, et al. Radiofrequency tissue ablation in the rabbit lung: efficacy and complications. Acad Radiol. 1995;2:776–784
16. Lee JM, Jin GY, Goldberg SN, et al. Percutaneous radiofrequency ablation for inoperable non-small cell lung cancer and metastases: preliminary report. Radiology. 2004;230:125–134
17. Eberhardt R, Anantham D, Herth F, et al. Electromagnetic navigation diagnostic bronchoscopy in peripheral lung lesions. Chest. 2007;131:1800–1805
18. Turner JF. Endobronchial ultrasound and peripheral pulmonary lesions: localization and histopathologic correlates using a miniature probe and the flexible bronchoscope. Chest. 2002;122:1874–1875
19. Crocetti L, Bozzi E, Faviana P, et al. Thermal ablation of lung tissue: in vivo experimental comparison of microwave and radiofrequency. Cardiovasc Intervent Radiol. 2010;33:818–827
20. Yamada K, Jinbo T, Miyahara K, et al. Contrast-enhanced MRI with gadodiamide injection in rabbit carcinoma models. J Vet Med Sci. 1996;58:389–396
Keywords:

Transbronchial radiofrequency ablation; lung tumor; rabbit model

© 2011 Lippincott Williams & Wilkins, Inc.