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Radiofrequency Ablation for Primary and Secondary Malignancy in the Lung
By William B. Ershler, MD
Patients with localized but non-resectable lung cancer generally are considered candidates for other types of therapy including external beam or stereotactic radiation therapy, chemotherapy, or percutaneous ablation. Similarly, patients who are considered to have resectable lesions but for whom surgical intervention would not be tolerated are also candidates for these alternative approaches. Of these, percutaneous radiofrequency ablation (RFA) has been increasingly reported in the recent literature as being both effective and safe in these settings1-6 and is the subject of this concise review.
PRINCIPLES OF RFA
RFA has been widely used for the treatment of malignancy, most notably for liver metastases from colorectal primary cancers. It is but one of a number of localized thermal ablative approaches that also include cryotherapy, laser, or microwave devices.7 For the procedure, a conductive probe (electrode) is inserted into the tumor and high-frequency alternating current is transmitted from the tip or tips into the tumor and immediately adjacent tissue. This results in heating to temperatures greater than 60° C and subsequent coagulative necrosis. The amount of destruction is correlated with the impedance of the tissue and distance from the electrode. For the treatment of liver metastases, the RFA probe has been directed toward the lesion(s) by both image guidance (in the radiology suite) or by direct palpation or visualization in the operating room by surgeons. If there are no technical restrictions, the percutaneous approach is the least invasive, has a well-established safety profile, is repeatable, and can be performed in an outpatient setting. The best results are achieved in patients with limited disease burden, for example, those with 4 or fewer tumors measuring less than 2.5 cm in maximum dimension each for a total of 10 cm or less.8
In applying RFA to the lung, evaluations aimed at selecting appropriate patients are of critical importance. This would include assessing the target tumor location relative to emphysematous blebs or major vessels to avoid complications including pneumothorax or bleeding. In general, the safety of the procedure is exemplified by the recent report of its successful employment in patients with a single lung.9 Yet, there is a distinct learning curve involved, as experience with the procedure has been shown to significantly reduce the risks of adverse outcomes including pneumothorax and need for chest tube placement.10
RFA FOR PRIMARY NSCLC
There is a subset of patients with potentially curable localized non-small cell lung cancer (NSCLC) that for one reason or another are not surgical candidates. The single institution (Rhode Island Hospital) 10-year experience of 79 evaluable patients who received primary RFA for NSCLC was reported recently.3 The mean patient age was 75 years (range 45-91 years) and the mean tumor size was 2.5 cm (range 1-5.5 cm), and of these 15 were central (entirely within the inner two-thirds of the lung) and 64 were peripheral. Of the 79 patients, 19 (24%) underwent adjuvant external beam radiation and 9 (11%) underwent concomitant brachytherapy. For 45 (57%) of the patients there was no evidence of recurrence at follow-up imaging (range, 1-72 months, mean 17 months). Recurrence was seen in 34 (43%) patients (range 2-48 months; mean 14 months). The recurrence was local (at the site of RFA) in 13 (38%), intrapulmonary in 6 (18%), nodal in 6 (18%), and distant in 7 (21%). The median disease-free survival was 23 months. Of the pretreatment characteristics, tumor size and stage were statistically associated with recurrence, but sex, tumor location, and radiation treatment were not.
RFA FOR METASTATIC LESIONS TO THE LUNG
The experience for treating metastatic lesions in the lung has been less well characterized and remains controversial although surgical approaches to metastatic renal carcinoma and sarcoma have met with some success.11 There have been a few series4,10,12 in which RFA has been applied to metastatic lesions in the lung. Certainly for patients for whom a local approach to metastatic disease is under consideration but who are not candidates for aggressive surgery, RFA may be considered. Candidates would include certain patients with slowly growing, accessible lesions.
RFA as an alternative to surgery or radiation is being actively investigated for malignancy within the lung and may become more widely used, particularly in patients who are not surgical candidates. However, much work needs to be done to refine the technique and to define who may best be served. It is clear that the technique can be challenging, but in the hands of experienced practitioners the associated morbidity is manageable. It also remains unclear which form of ablative thermal energy will be optimal, and it may turn out that using microwave energy will be more effective, and such technology is currently under development.13
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2. Jin GY, et al. Primary and secondary lung malignancies treated with percutaneous radiofrequency ablation: Evaluation with follow-up helical CT. AJR Am J Roentgenol 2004;183:1013-1020.
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4. Simon CJ, et al. Pulmonary radiofrequency ablation: Long-term safety and efficacy in 153 patients. Radiology 2007;243:268-275.
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7. Vogl TJ, et al. Radiofrequency, microwave and laser ablation of pulmonary neoplasms: Clinical studies and technical considerationsreview article. Eur J Radiol 2011;77:346-357.
8. Machi J, et al. Long-term outcome of radiofrequency ablation for unresectable liver metastases from colorectal cancer: Evaluation of prognostic factors and effectiveness in first- and second-line management. Cancer J 2006;12:318-326.
9. Hess A, et al. Pulmonary radiofrequency ablation in patients with a single lung: Feasibility, efficacy, and tolerance. Radiology 2011;258:635-642.
10. Yan TD, et al. Percutaneous radiofrequency ablation of pulmonary metastases from colorectal carcinoma: Prognostic determinants for survival. Ann Surg Oncol 2006;13:1529-1537.
11. Kondo H, et al. Surgical treatment for metastatic malignancies. Pulmonary metastasis: Indications and outcomes. Int J Clin Oncol 2005;10:81-85.
12. Steinke K, et al. Percutaneous imaging-guided radiofrequency ablation in patients with colorectal pulmonary metastases: 1-year follow-up. Ann Surg Oncol 2004;11:207-212.
13. Brace CL, et al. Pulmonary thermal ablation: Comparison of radiofrequency and microwave devices by using gross pathologic and CT findings in a swine model. Radiology 2009;251:705-711.