| RFA for lung cancers |
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| Tuesday, 22 December 2009 21:44 | |
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What is RFA? RFA stands for Radio Frequency Ablation. RFA is successfully used to treat certain tumors of lung, liver, kidney, and bone. Radiofrequency energy oscillation agitates cells thereby increasing the frictional heating with in tissues resulting in cell death. The feasibility of lung RFA has been demonstrated in animals (1-3), and the feasibility, safety and long term efficacy of lung RFA to treat tumors have been reported in humans, both in the United States and internationally (4-13). During the RFA procedure, rapidly alternating current is applied with a frequency in the range of 460-500 kHz through the RFA electrode (14). The alternating current causes movement of ions in the tissue resulting in tissue heating. Applying a temperature greater than 50 degrees centigrade for five minutes results in tumor cell death. Too high a temperature is not desirable as it will cause charring and gas formation immediately adjacent to the electrode and prevent the homogeneous heating of the entire tumor. During RFA, reaching a temperature of 60-100 degrees centigrade within the tumor is generally desired, as charring and gas formation occur at approximately 105-115 degrees centigrade (14, 15). Ideally, the goal is to achieve complete cell death within the tumor, as well as in a 1 cm margin of the adjacent normal lung (14, 16). Who is suitable for RFA? Patients with tumors that are 3 cm or smaller are best suited for RFA treatment. A typical patient undergoing RFA is an adult who cannot undergo lung cancer surgery despite having a tumor that is at an early stage. Examples of patients who may not be able to undergo surgery include those with poor lung function, other coexisting other diseases, poor general performance status which might deteriorate further following lung surgery, and patients with lung tumors that either do not respond to maximum conventional therapy, including radiation therapy, or recur after treatment. In other words, these patients have tumors that can be potentially removed by surgery, but the presence of other additional diseases in these patients prevent them from undergoing surgery. Also in this group are patients who cannot afford to lose any more lung tissue. Although few studies report that RFA can be safely performed in tumors close to vital organs such as the heart, generally tumors that are close to the lung hilum (where the airtubes and blood vessels enter the lung) are not amenable to RFA (17, 18). How is RFA performed? This technique has many similarities to CT-guided lung biopsy procedures. Throughout the world, lung RFA is commonly performed in a CT scanner suite. Patients undergo this procedure either under moderate sedation with pain relief or under general anesthesia. General anesthesia has the advantage of complete control over patient's breathing pattern and motion that helps to accurately place the RFA electrode within the tumor. One study comparing conscious sedation to general anesthesia did not show any major difference in tumor control or procedure related complication rates, however the number of patients in both groups was small (19). A survey of centers performing RFA for lung tumors indicated that conscious sedation is used more commonly than general anesthesia (12). During the procedure, tumor cells are destroyed by placing a needle (RFA electrode) within the center of the tumor. The RFA electrodes come in various shapes, length and thickness, depending on the manufacturer (Figure 1). The RFA electrodes are carefully placed into the center of the tumor undergoing ablation using the guidance of images in the CT suite. Multiple CT images are taken to confirm the safe placement of RFA electrodes, and to avoid adjacent vital organs. Following placement, RFA electrodes are connected to an external RF generator (Figure 2). High-frequency alternating energy is then applied through the RF electrodes. This causes ionic agitation in tumor cells which raises tissue temperature. As the temperature increases above 45-50 degrees centigrade within the tumor, cellular proteins denature and cell structure disintegrates. This results in thermal coagulation in tumor cells, ultimately leading to tumor destruction. The entire RFA procedure session usually takes 3-4 hours or less. Following completion of therapy, RFA probes are withdrawn from the patient. Subsequently, patients are closely observed for any post procedural complications such as lung collapse. Following an uncomplicated RFA procedure, patients are discharged home mostly after overnight observation or rarely the same day. Lung tissue characteristics may play a role in the effectiveness of RFA. The normal lung tissue surrounding the tumor is relatively resistant to heating due to its high electrical impedance (20, 21). Therefore, the heat energy created by RFA is preferentially deposited in the tumor facilitating higher temperatures. Also, large blood vessels (> 3 mm) near a tumor constantly cool the tissue due to the flowing blood that takes heat away from the area being treated, commonly known as the heat sink effect (14, 20). As a result, tumors in continuity with large blood vessels may be suboptimally treated with RFA. Some electrodes are believed to produce necrosis measuring up to 4-5 cm in diameter. This allows for the treatment of a 3 cm lesion and a 1 cm margin of normal lung (14). Tumors larger than 3 cm may require multiple electrodes to create overlapping tissue RFA zones. Add this page to your favorite Social Bookmarking websites         
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