(Radiographics. 2002;22:S259-S269.)
© RSNA, 2002
Clinical Applications of Radio-Frequency Tumor Ablation in the Thorax1
Damian E. Dupuy, MD,
William W. Mayo-Smith, MD,
Gerald F. Abbott, MD and
Thomas DiPetrillo, MD
1 From the Departments of Diagnostic Imaging (D.E.D., W.W.M.S., G.F.A.) and Radiation Oncology (T.D.), Brown Medical School, Rhode Island Hospital, 593 Eddy St, Providence, RI 02903. Presented as an education exhibit at the 2001 RSNA scientific assembly. Received January 28, 2002; revision requested March 18 and received April 12; accepted April 26. Address correspondence to D.E.D. (e-mail: ddupuy@lifespan.org).
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Abstract
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Minimally invasive alternatives to surgery for the treatment of malignancy are becoming more attractive owing to improvements in technology, reduced morbidity and mortality, and the ability to provide treatment in an outpatient setting. Radio-frequency (RF) ablation has become the imaging-guided ablative method of choice because of its relatively low cost, its capability of creating large regions of coagulative necrosis in a controlled fashion, and its relatively low toxicity. RF ablation in the thorax involves the use of computed tomography (CT) to localize the tumor and determine the optimal approach. The size of the tumor determines whether a cluster of electrodes or a single electrode of a particular length will be used to perform the ablation. CT fluoroscopy aids in guiding placement of the electrode. In patients with non–small cell lung malignancy who are not candidates for surgery owing to poor cardiorespiratory reserve, RF ablation alone or followed by conventional radiation therapy with or without chemotherapy may prove to be a treatment option. In patients with metastatic disease, RF ablation may be suitable for treatment of a small tumor burden or for palliation of larger tumors that cause symptoms such as cough, hemoptysis, or pain. Patients with chest wall or osseous metastatic tumors in whom other therapies have failed may benefit from RF ablation as an alternative to radiation therapy.
© RSNA, 2002
Index Terms: Lung neoplasms, therapeutic radiology, 60.1249, 60.30, 60.33 • Radiofrequency (RF) ablation, 60.1249 • Thorax, interventional procedures, 60.1249
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Introduction
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During the past two decades, many ablative therapies have been studied as minimally invasive alternatives to surgery. Possible advantages of ablative therapies over surgical resection are their anticipated reduced morbidity and mortality, low cost, suitability for real-time imaging guidance, and capability of being performed on an outpatient basis. Ethanol ablation of small hepatocellular carcinomas and cryosurgery for hepatic tumors have been used with some success. However, treatment of larger or multiple tumors and precise control of tumor destruction can be problematic, particularly with chemical ablation.
The capability of heat to kill cancerous cells has been known for several decades. Tumor cells are more sensitive to heat than is normal tissue, and temperatures as low as 41°C can cause cancer cell death (1). Heating of tumors had been achieved with the perfusion of heated blood (2), the heating of anesthetic gases (3), and the application of external electromagnetic devices (4,5). Heat-based ablative methods such as radio-frequency (RF) ablation, microwave ablation, and laser ablation have recently received attention as minimally invasive strategies for treating liver tumors. RF ablation works through the deposition of energy into tissue via a percutaneously placed electrode. The energy from the electrical current in the frequency of radio waves emitted by the electrode creates heat in the local tissue, and thus, necrosis, in a controlled fashion. RF ablation is at present the most robust technique for the treatment of solid malignancies, and in the United States its use is dominating percutaneous, imaging-guided therapy (6).
RF-induced tissue coagulation has been used in early clinical trials for the treatment of primary and secondary liver tumors (7,8). Despite promising early results in hepatic RF ablation, extrahepatic applications for malignancy have only recently been investigated (9–12). Early attempts to treat lung tumors with external RF devices were limited by the inability to deliver accurately targeted heat (4,5). Temperatures achieved were typically between 43°C and 50°C. Normal tissue, such as that in skin, fat, muscle, and lung, was susceptible to injury. Small RF needle electrodes that could deliver more focal heat have been available for decades, but the size of the heat lesion they created was small and percutaneous imaging-guided placement was limited to fluoroscopic guidance. Advances in computed tomography (CT) and ultrasound technology during the 1980s allowed accurate localization of an electrode. However, further refinement of the electrode was necessary to deliver a well-defined area of thermal energy to larger volumes of tumor tissue. Increased availability of this technology has led to resurgence in the application of RF ablation for solid tumor therapy. Intraparenchymal lung tumors seem well suited to RF ablation because the surrounding air in adjacent normal lung parenchyma provides an insulative effect that may concentrate the RF energy (13). Chest wall and osseous masses of the thoracic cage are common clinical challenges, and focal palliative therapy with RF energy has great potential.
In this article, we discuss and illustrate RF tumor ablation in terms of technique, applications in primary lung cancer, metastatic disease, and pain palliation, and possible complications.
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Technique
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RF ablation is usually performed with the patient under conscious sedation (achieved with intravenous administration of midazolam and fentanyl, for example), although in certain situations in which procedural pain is problematic, a general anesthetic may be required. Patients undergo monitoring with continuous pulse oximetry and electrocardiography, with checking of blood pressure every 5 minutes. CT is used to localize the tumor and determine the optimal approach. Standard surgical preparation and draping are performed. Local anesthesia is achieved with injection of a 1% lidocaine hydrochloride solution both intradermally and into deeper tissues. At our institution, the preferred RF system is an internally cooled RF electrode with a 200-watt RF generator (Cosman Coagulator-1; Radionics, Burlington, Mass) (Figs 1, 2). The electrode is available in varied lengths and has an insulated shaft and an uninsulated active tip that emits the RF current. Tumors larger than 4 cm are treated with a cluster RF electrode that consists of three 17-gauge RF electrodes spaced 5 mm apart. Tumors smaller than 4 cm are treated with a single RF electrode. Tumors smaller than 2 cm are treated with a 1-cm-long active tip, those between 2 and 3 cm are treated with a 2-cm-long active tip, and those between 3 and 4 cm are treated with a 3-cm-long active tip. When possible, the RF electrode is positioned with the electrode shaft parallel to the longitudinal axis of the tumor. The tip of the RF electrode is positioned against the deepest margin of the tumor for the first treatment. Axial and craniocaudal placement of the RF electrode is confirmed with CT fluoroscopy (5-mm collimation, 10 mA). The RF electrode contains an internal thermocouple for temperature measurement. The electrode is coupled to the RF generator and perfusion pump. The electric current is grounded by means of four grounding pads in a horizontal configuration (1,800 cm3 surface area each) that are applied to the opposite chest wall or thighs. Proper application of the electrode gel to the patient’s skin may require shaving of body hair in the region where the pad is applied. Internal cooling of the electrode (tip temperature, 10°C–20°C) is performed by means of continuous infusion of ice water at 80 mL/min with the perfusion pump. At the end of each treatment, perfusion is stopped and the maximal temperature is recorded. The quantity of RF energy cannot be standardized because the heat capacity of tumors varies depending on tumor histologic composition, local blood flow, and previous treatments. At least one RF treatment is performed with the maximum allowable current, given the impedance of the system (typical current range, 1,100–1,600 mA), usually for no longer than 12 minutes. The maximal intratumoral temperature is recorded. An intratumoral temperature greater than 60°C must be achieved to ensure adequate thermocoagulation. If the temperature exceeds 60°C, the RF electrode is withdrawn in increments of 1 cm up to the length of the active tip (eg, three 1-cm increments for a 3-cm active-tip single electrode or 3 cm for a 2.5-cm active-tip cluster electrode) while the intratumoral temperature is measured. This technique allows the operator to measure the temperature within the tumor at different points along the treatment axis. If the temperature falls below 60°C and the RF electrode is still within the tumor as confirmed with repeated CT, another treatment is performed at the new position. If, after the first treatment, the maximal intratumoral temperature does not exceed 60°C, an additional treatment is performed at the same position. This treatment is repeated for a maximum of 12 minutes at any given electrode position. After the entire longitudinal dimension of the tumor is treated with a series of overlapping temperature-based treatments, the RF electrode is repositioned in a new portion of the tumor with the electrode shaft 1.5–2 cm away from the longitudinal axis of the previous treatment. This process is repeated until multiple cylinder-shaped treatment regions encompass the volume of the tumor mass. This temperature-dependent treatment protocol standardizes the RF therapy despite differences in tumor size, local blood flow, and histologic composition. A single 12-minute heat treatment with a cluster electrode can create a volume of thermocoagulation of approximately 3.5 cm3 in liver tissue, depending on regional tissue perfusion. The aeration of normal lung tissue limits the penetration of RF energy. No accurate data about ablation size in human lung tumors are available, but in our experience, a comparable ablation size can be achieved in less time (usual range, 2–8 minutes at each electrode position) than in the liver.
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Applications
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Primary Lung Cancer
Primary lung cancer often occurs in patients who are not candidates for surgery owing to poor cardiorespiratory reserve. Treatment options for such patients are external radiation therapy with or without chemotherapy, or no treatment. In patients with non–small cell lung malignancy who are not candidates for surgery owing to poor cardiorespiratory reserve, RF ablation alone or followed by conventional radiation therapy with or without chemotherapy may prove to be a treatment option. Our institutional protocol allows treatment of patients with T1-T3, N0, M0 cancer with RF ablation followed by conventional radiation therapy with or without chemotherapy. The preliminary results of this two-phase trial indicate that RF ablation can be safely performed (Fig 3).We are evaluating local tumor control and survival rates in patients who are currently undergoing treatment versus those in earlier studies. Treatment may consist of external-beam radiation therapy alone, or brachytherapy may be performed at the time of RF ablation (Fig 4). We are also using RF ablation alone to treat patients whose lung function prevents external-beam radiation therapy or who refuse to undergo radiation therapy. In such patients, many treated tumors have shown no growth at follow-up. On the other hand, these tumors do not necessarily shrink. Many liver and kidney lesions treated with RF ablation persist indefinitely. Histopathologic studies show infiltration of the treated tissue with fibroblasts and collagen. In these patients, lack of tumor growth, CT attenuation characteristics, or positron emission tomographic findings may be better indicators of disease activity. In our early experience, lesions in the lung appear to behave similarly (Fig 5).
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Figure 3a. Results of RF ablation in a 78-year-old woman with emphysema and a right suprahilar mass. Results of biopsy showed squamous cell carcinoma. The patient was a poor surgical candidate due to comorbid conditions (heart disease, emphysema). (a) CT scan obtained prior to external-beam radiation therapy shows an electrode inserted into the mass for percutaneous RF ablation. (b) CT scan obtained 3 months after RF ablation (6 weeks after radiation therapy) shows the mass with adjacent parenchymal stranding but no retraction. (c) CT scan obtained 27 months after RF ablation demonstrates shrinkage of the tumor with parenchymal fibrosis and contraction medially. This dramatic response in such a large tumor would be unusual in a patient treated with irradiation alone. Tissues treated with RF ablation become cicatricial, and the lesions may still be apparent at imaging.
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Figure 3b. Results of RF ablation in a 78-year-old woman with emphysema and a right suprahilar mass. Results of biopsy showed squamous cell carcinoma. The patient was a poor surgical candidate due to comorbid conditions (heart disease, emphysema). (a) CT scan obtained prior to external-beam radiation therapy shows an electrode inserted into the mass for percutaneous RF ablation. (b) CT scan obtained 3 months after RF ablation (6 weeks after radiation therapy) shows the mass with adjacent parenchymal stranding but no retraction. (c) CT scan obtained 27 months after RF ablation demonstrates shrinkage of the tumor with parenchymal fibrosis and contraction medially. This dramatic response in such a large tumor would be unusual in a patient treated with irradiation alone. Tissues treated with RF ablation become cicatricial, and the lesions may still be apparent at imaging.
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Figure 3c. Results of RF ablation in a 78-year-old woman with emphysema and a right suprahilar mass. Results of biopsy showed squamous cell carcinoma. The patient was a poor surgical candidate due to comorbid conditions (heart disease, emphysema). (a) CT scan obtained prior to external-beam radiation therapy shows an electrode inserted into the mass for percutaneous RF ablation. (b) CT scan obtained 3 months after RF ablation (6 weeks after radiation therapy) shows the mass with adjacent parenchymal stranding but no retraction. (c) CT scan obtained 27 months after RF ablation demonstrates shrinkage of the tumor with parenchymal fibrosis and contraction medially. This dramatic response in such a large tumor would be unusual in a patient treated with irradiation alone. Tissues treated with RF ablation become cicatricial, and the lesions may still be apparent at imaging.
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Figure 4a. Biopsy-proved metachronous primary tumor of the left lung in a 75-year-old man who had undergone right pneumonectomy for bronchogenic carcinoma several years earlier. Owing to the size of the lesion, RF ablation and brachytherapy implantation were performed during one session. (a) CT scan obtained with the patient prone shows the RF electrode inserted into the lesion. Four overlapping ablations were performed. (b) CT scan obtained after RF ablation shows a brachytherapy catheter being used to place radioactive iodine seeds around the periphery of the mass. (c) Chest radiograph obtained 2 hours after RF ablation shows the lesion with the brachytherapy seeds in place. (d) Follow-up CT scan obtained 11 months later shows retraction of the soft tissue in the area of treatment with brachytherapy and RF ablation.
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Figure 4b. Biopsy-proved metachronous primary tumor of the left lung in a 75-year-old man who had undergone right pneumonectomy for bronchogenic carcinoma several years earlier. Owing to the size of the lesion, RF ablation and brachytherapy implantation were performed during one session. (a) CT scan obtained with the patient prone shows the RF electrode inserted into the lesion. Four overlapping ablations were performed. (b) CT scan obtained after RF ablation shows a brachytherapy catheter being used to place radioactive iodine seeds around the periphery of the mass. (c) Chest radiograph obtained 2 hours after RF ablation shows the lesion with the brachytherapy seeds in place. (d) Follow-up CT scan obtained 11 months later shows retraction of the soft tissue in the area of treatment with brachytherapy and RF ablation.
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Figure 4c. Biopsy-proved metachronous primary tumor of the left lung in a 75-year-old man who had undergone right pneumonectomy for bronchogenic carcinoma several years earlier. Owing to the size of the lesion, RF ablation and brachytherapy implantation were performed during one session. (a) CT scan obtained with the patient prone shows the RF electrode inserted into the lesion. Four overlapping ablations were performed. (b) CT scan obtained after RF ablation shows a brachytherapy catheter being used to place radioactive iodine seeds around the periphery of the mass. (c) Chest radiograph obtained 2 hours after RF ablation shows the lesion with the brachytherapy seeds in place. (d) Follow-up CT scan obtained 11 months later shows retraction of the soft tissue in the area of treatment with brachytherapy and RF ablation.
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Figure 4d. Biopsy-proved metachronous primary tumor of the left lung in a 75-year-old man who had undergone right pneumonectomy for bronchogenic carcinoma several years earlier. Owing to the size of the lesion, RF ablation and brachytherapy implantation were performed during one session. (a) CT scan obtained with the patient prone shows the RF electrode inserted into the lesion. Four overlapping ablations were performed. (b) CT scan obtained after RF ablation shows a brachytherapy catheter being used to place radioactive iodine seeds around the periphery of the mass. (c) Chest radiograph obtained 2 hours after RF ablation shows the lesion with the brachytherapy seeds in place. (d) Follow-up CT scan obtained 11 months later shows retraction of the soft tissue in the area of treatment with brachytherapy and RF ablation.
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Figure 5a. Two-centimeter-long, poorly differentiated squamous cell carcinoma (stage 1) of the right lower lobe in a 69-year-old woman with emphysema, which precluded surgery or external-beam radiation therapy. (a) CT scan shows an electrode inserted for percutaneous RF ablation, which seemed to be a reasonable treatment option in this case. (b) CT scan obtained 14 months after RF ablation shows no interval growth of the tumor and peritumoral pleural and parenchymal stranding. The treated tumor continued to show lack of growth 2 years after RF ablation.
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Figure 5b. Two-centimeter-long, poorly differentiated squamous cell carcinoma (stage 1) of the right lower lobe in a 69-year-old woman with emphysema, which precluded surgery or external-beam radiation therapy. (a) CT scan shows an electrode inserted for percutaneous RF ablation, which seemed to be a reasonable treatment option in this case. (b) CT scan obtained 14 months after RF ablation shows no interval growth of the tumor and peritumoral pleural and parenchymal stranding. The treated tumor continued to show lack of growth 2 years after RF ablation.
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Metastatic Disease
Although local therapies for metastatic disease can be successful, limitations include extended recovery time from surgical procedures, injury to or removal of functional lung tissue, and the risk of local recurrence, among others. RF ablation may be suitable for treatment of a small tumor burden (Fig 6) or for palliation of larger tumorsthat cause symptoms such as cough, hemoptysis, or pain (Figs 7–9). Because ablation of each tumor may require more than one placement of the RF electrode, this type of therapy is probably best suited for patients with only a small number of slow-growing metastases. A similar approach has been applied to colorectal hepatic metastaseswhereby treatment is limited to four or fewer metastases with the percutaneous approach (6).
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Figure 6a. Single small pulmonary metastasis in the right lower lobe in a 54-year-old woman who had undergone right mastectomy for breast carcinoma. (a) Axial CT scan shows metastasis in the right lower lobe. (b) CT scan shows an RF electrode within the metastasis. (c) Follow-up CT scan obtained 6 months later shows the mass abutting the pleural surface with surrounding retraction of adjacent parenchyma, but with no significant increase in size.
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Figure 6b. Single small pulmonary metastasis in the right lower lobe in a 54-year-old woman who had undergone right mastectomy for breast carcinoma. (a) Axial CT scan shows metastasis in the right lower lobe. (b) CT scan shows an RF electrode within the metastasis. (c) Follow-up CT scan obtained 6 months later shows the mass abutting the pleural surface with surrounding retraction of adjacent parenchyma, but with no significant increase in size.
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Figure 6c. Single small pulmonary metastasis in the right lower lobe in a 54-year-old woman who had undergone right mastectomy for breast carcinoma. (a) Axial CT scan shows metastasis in the right lower lobe. (b) CT scan shows an RF electrode within the metastasis. (c) Follow-up CT scan obtained 6 months later shows the mass abutting the pleural surface with surrounding retraction of adjacent parenchyma, but with no significant increase in size.
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Figure 7a. Metastatic colon carcinoma and a painful pleura-based mass in a 59-year-old woman. (a) CT scan obtained with the patient prone shows a large, pleura-based lesion in the right lung. A cluster RF electrode was inserted into the mass, and thermocoagulation was performed in five overlapping areas. (b) Follow-up gadolinium-enhanced magnetic resonance (MR) image obtained 18 months later shows a thick, enhanced soft-tissue rind around the lesion, a finding that is consistent with residual tumor tissue. A central area of low signal intensity indicating necrosis is also seen.
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Figure 7b. Metastatic colon carcinoma and a painful pleura-based mass in a 59-year-old woman. (a) CT scan obtained with the patient prone shows a large, pleura-based lesion in the right lung. A cluster RF electrode was inserted into the mass, and thermocoagulation was performed in five overlapping areas. (b) Follow-up gadolinium-enhanced magnetic resonance (MR) image obtained 18 months later shows a thick, enhanced soft-tissue rind around the lesion, a finding that is consistent with residual tumor tissue. A central area of low signal intensity indicating necrosis is also seen.
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Figure 8a. Nasopharyngeal carcinoma metastatic to the mediastinum in a 52-year-old man. The patient refused additional radiation therapy and chemotherapy. RF ablation was performed to retard tumor growth and prevent involvement of the left hilum. CT scan obtained prior to RF ablation showed a safe window for ablation adjacent to the manubrium of the sternum. (a) CT fluoroscopic image shows a mass into which a cluster RF electrode has been inserted. The untreated tumor grew, and a second RF ablation procedure was performed 7 months later. (b, c) Follow-up CT scans show a large tumor cavity that communicates with the left upper lobe bronchus. Note also the peripheral contrast-enhanced tumor tissue.
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Figure 8b. Nasopharyngeal carcinoma metastatic to the mediastinum in a 52-year-old man. The patient refused additional radiation therapy and chemotherapy. RF ablation was performed to retard tumor growth and prevent involvement of the left hilum. CT scan obtained prior to RF ablation showed a safe window for ablation adjacent to the manubrium of the sternum. (a) CT fluoroscopic image shows a mass into which a cluster RF electrode has been inserted. The untreated tumor grew, and a second RF ablation procedure was performed 7 months later. (b, c) Follow-up CT scans show a large tumor cavity that communicates with the left upper lobe bronchus. Note also the peripheral contrast-enhanced tumor tissue.
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Figure 8c. Nasopharyngeal carcinoma metastatic to the mediastinum in a 52-year-old man. The patient refused additional radiation therapy and chemotherapy. RF ablation was performed to retard tumor growth and prevent involvement of the left hilum. CT scan obtained prior to RF ablation showed a safe window for ablation adjacent to the manubrium of the sternum. (a) CT fluoroscopic image shows a mass into which a cluster RF electrode has been inserted. The untreated tumor grew, and a second RF ablation procedure was performed 7 months later. (b, c) Follow-up CT scans show a large tumor cavity that communicates with the left upper lobe bronchus. Note also the peripheral contrast-enhanced tumor tissue.
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Figure 9a. Recurrent synovial sarcoma of the pleura in a 47-year-old woman. A 9-cm mass developed in the right pulmonary apex after surgery and radiation therapy. RF ablation was performed with a cool-tip cluster RF ablation probe. (a, b) CT scans show that multiple placements of the probe were required to thermocoagulate the mass. (c) Sagittal gadolinium-enhanced MR image obtained after RF ablation shows extensive central thermocoagulation of the tumor, which demonstrates a thin rim of enhancement. Residual tumor tissue extends between the ribs.
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Figure 9b. Recurrent synovial sarcoma of the pleura in a 47-year-old woman. A 9-cm mass developed in the right pulmonary apex after surgery and radiation therapy. RF ablation was performed with a cool-tip cluster RF ablation probe. (a, b) CT scans show that multiple placements of the probe were required to thermocoagulate the mass. (c) Sagittal gadolinium-enhanced MR image obtained after RF ablation shows extensive central thermocoagulation of the tumor, which demonstrates a thin rim of enhancement. Residual tumor tissue extends between the ribs.
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Figure 9c. Recurrent synovial sarcoma of the pleura in a 47-year-old woman. A 9-cm mass developed in the right pulmonary apex after surgery and radiation therapy. RF ablation was performed with a cool-tip cluster RF ablation probe. (a, b) CT scans show that multiple placements of the probe were required to thermocoagulate the mass. (c) Sagittal gadolinium-enhanced MR image obtained after RF ablation shows extensive central thermocoagulation of the tumor, which demonstrates a thin rim of enhancement. Residual tumor tissue extends between the ribs.
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Pain Palliation
Osseous metastatic disease is by far the most common cause of cancer pain. Conventional treatment of osseous metastatic disease has consisted primarily of external-beam radiation therapy and chemotherapy. Current treatment is often ineffective in this complex group of patients, and many die with inadequate analgesia. Patients with chest wall or osseous metastatic tumors in whom other therapies have failed may benefit from RF ablation as an alternative to radiation therapy. In patients with localized disease that can be safely treated with RF ablation, tumor control can be achieved (Fig 10). A combination of RF ablation and radiation therapy can be used in larger tumors (Fig 11). In the future, as more data are produced, RF ablation may be considered a less invasive and less costly alternative for small, well-confined tumor burdens or for cytoreduction prior to conventional external-beam radiation therapy.
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Figure 10a. Lung cancer metastatic to the sternum in a 49-year-old man. The patient had undergone external-beam radiation therapy but had persistent pain. (a) Axial CT scan shows a destructive mass within the midsternum. (b) CT fluoroscopic image shows placement of a single RF electrode into the mass. Two overlapping treatments were performed. The patient experienced relief of symptoms after undergoing ablation.
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Figure 10b. Lung cancer metastatic to the sternum in a 49-year-old man. The patient had undergone external-beam radiation therapy but had persistent pain. (a) Axial CT scan shows a destructive mass within the midsternum. (b) CT fluoroscopic image shows placement of a single RF electrode into the mass. Two overlapping treatments were performed. The patient experienced relief of symptoms after undergoing ablation.
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Figure 11a. Large, expansile mass at the left first rib in a 65-year-old man who had undergone nephrectomy for renal cell carcinoma 12 years earlier. (a) Follow-up CT scan shows that the mass had continued to grow despite external-beam radiation therapy. (b) CT fluoroscopic image used to guide RF ablation shows the RF electrode inserted into the mass. Because of the size of the mass, nine overlapping treatments were performed. (c) Follow-up coronal gadolinium-enhanced MR image obtained 5 months after RF ablation shows the mass with lack of enhancement centrally, a finding that is consistent with adequate thermocoagulation. The surrounding peripheral enhancement represents granulation tissue or residual tumor tissue. The tumor near the spine was not treated for fear of neural toxicity.
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Figure 11b. Large, expansile mass at the left first rib in a 65-year-old man who had undergone nephrectomy for renal cell carcinoma 12 years earlier. (a) Follow-up CT scan shows that the mass had continued to grow despite external-beam radiation therapy. (b) CT fluoroscopic image used to guide RF ablation shows the RF electrode inserted into the mass. Because of the size of the mass, nine overlapping treatments were performed. (c) Follow-up coronal gadolinium-enhanced MR image obtained 5 months after RF ablation shows the mass with lack of enhancement centrally, a finding that is consistent with adequate thermocoagulation. The surrounding peripheral enhancement represents granulation tissue or residual tumor tissue. The tumor near the spine was not treated for fear of neural toxicity.
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Figure 11c. Large, expansile mass at the left first rib in a 65-year-old man who had undergone nephrectomy for renal cell carcinoma 12 years earlier. (a) Follow-up CT scan shows that the mass had continued to grow despite external-beam radiation therapy. (b) CT fluoroscopic image used to guide RF ablation shows the RF electrode inserted into the mass. Because of the size of the mass, nine overlapping treatments were performed. (c) Follow-up coronal gadolinium-enhanced MR image obtained 5 months after RF ablation shows the mass with lack of enhancement centrally, a finding that is consistent with adequate thermocoagulation. The surrounding peripheral enhancement represents granulation tissue or residual tumor tissue. The tumor near the spine was not treated for fear of neural toxicity.
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Complications
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In our experience, postprocedural pleurisy and small pleural effusions have occurred in patients with pleura-based and peripheral lesions, but in no instance have symptoms been severe enough to require thoracentesis. Productive cough with brown sputum that lasts 1–2 weeks after ablation has occurred in a minority of patients. Pneumothoraces have occurred in approximately 20% of patients after RF ablation, approximately 66% of whom have required chest tube drainage (Fig 12). Acute pulmonary hemorrhage has not been a complication in our experience. However, one patient did have a lethal hemorrhage 2 days after undergoing RF ablation that was related to platelet dysfunction. Patients undergo screening for bleeding diatheses, and the use of any anticoagulants or antiplatelet drugs is discontinued for the appropriate period before ablation. In patients who have undergone treatment of larger tumors near large bronchi, tumor cavitation and fistula formation have been seen (Fig 8).
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Figure 12a. Small squamous cell lung cancer of the right upper lobe in a 78-year-old man. The patient was undergoing home oxygen therapy and was a poor candidate for surgery or irradiation. (a) CT scan obtained with the patient prone shows a mass into which a single RF electrode has been inserted. (b) Conventional radiograph shows a chest tube that was required because of development of a pneumothorax. The patient underwent 1 week of chest tube treatment. Extensive subcutaneous emphysema is also noted.
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Figure 12b. Small squamous cell lung cancer of the right upper lobe in a 78-year-old man. The patient was undergoing home oxygen therapy and was a poor candidate for surgery or irradiation. (a) CT scan obtained with the patient prone shows a mass into which a single RF electrode has been inserted. (b) Conventional radiograph shows a chest tube that was required because of development of a pneumothorax. The patient underwent 1 week of chest tube treatment. Extensive subcutaneous emphysema is also noted.
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Discussion
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Percutaneous RF tumor ablation can be safely applied in the treatment of thoracic malignancies. Several animal studies have demonstrated the thermal effects of RF energy in lung tissue and its capability of being used in the treatment of small pulmonary masses (13–15). Reports of limited numbers of treatments in human beings have also shown promise (9,16). The goal of such a minimally invasive local therapy is to provide a consistent zone of tumor necrosis without the additional complications that are inherent with a surgical procedure that requires general anesthesia, chest tube drainage, and hospitalization. RF tumor ablation cannot realistically be expected to achieve the same degree of tumor eradication as complete lobar resection. However, as has been shown with limited pulmonary resections, patients may live longer than if they had not undergone the therapy at all (17). With the same rationale applied to the synergy of postoperative radiation therapy or brachytherapy (18) and limited pulmonary resections, RF ablation may prove complementary to chemotherapy and radiation therapy in the treatment of thoracic neoplasms. Hypoxic cells with limited blood flow such as those found in the center of necrotic tumors can be resistant to chemotherapy and external-beam radiation therapy. These central hypoxic cells may be more sensitive to RF ablation because of increased cell sensitivity to heat in the hypoxic state and decreased heat dissipation due to poor tumor perfusion.
Our initial experience shows that lung RF ablation is well tolerated even in patients with severe emphysema. In the subset of patients enrolled in our phase II study of T1, N0, M0 non–small cell lung cancer, RF ablation was well tolerated, even after they underwent postablation external-beam radiation therapy. As noted earlier, approximately 66% of patients in whom pneumothoraces were seen required chest tube drainage. We believe this higher chest tube placement rate (compared with the needle biopsy rate) may be related to the larger electrode size compared with needle biopsy, as well as the large number of patients with severe underlying pulmonary disease (eg, emphysema) who have undergone treatment. Despite the higher rate of chest tube placement, most of the chest tubes were removed within 24 hours and the patients could undergo treatment in an outpatient setting with a Heimlich valve. Follow-up examinations have shown shrinkage of small tumors after ablation, but larger tumors have shown interval growth consistent with residual tumor tissue. Cavitation has been seen in larger treated tumors, and development of communication with the left primary bronchus in one patient led to intermittent infection. Localized pulmonary hemorrhage similar to that encountered with lung biopsies has been seen at CT during and after RF ablation, but in no patient has hemoptysis developed. In one patient, delayed pulmonary hemorrhage occurred in the pleural space 43 hours after treatment, an event that may have been due to platelet dysfunction secondary to anti-inflammatory medication.
Chest wall involvement by either primary lung cancer or metastatic deposits is common. Large chest wall tumors are difficult to treat with radiation therapy alone, and many patients with intractable pain have already received the maximal dose of radiation. Palliation with narcotics is difficult in patients with large, painful tumors that continue to grow; affected patients often spend the last months of their lives with inadequate analgesia. Therefore, the use of a minimally invasive alternative such as RF ablation to reduce tumor volume or provide local palliation may be beneficial in these patients.
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Conclusion
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RF ablation is a local percutaneous tumor treatment that has many potential applications in the thorax. A number of studies are under way to quantify its efficacy in both primary and metastatic neoplasms of the thorax.
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Footnotes
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Abbreviation: RF = radio-frequency
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References
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Abstract
Introduction
