- RFA Radiofrequency Ablation
Why RadioFrequency Ablation (RFA)?
Recent developments in radiofrequency ablation technology make large volume tissue ablation more effective and safer for local control of neoplastic disease than ever before. Local tumor control is an attractive option for some patients who are not ideal surgical candidates, have failed conventional therapies, or have contraindications to surgery or recurrent tumors. Percutaneous radiofrequency ablation may also expand surgical options. For example, RFA may convert an inoperable patient into a surgical candidate by treating small liver lesions that are too difficult or too spread out to surgically resect. RFA may treat multiple liver tumors, if any one tumor is not too large. RFA may be repeated for tumor recurrence, regrowth, or incomplete treatments. RFA can also be added to any other treatment, like surgery, radiation therapy, chemotherapy, or hepatic arterial infusion therapy, alcohol ablation, or chemoembolization.
Needle-based tissue ablation techniques may provide alternatives to open surgical procedures in certain patients, and may augment conventional therapies. No long-term, prospective, randomized clinical trials using RFA have been reported, so the expected benefit is speculative, and not definite. The available world literature is sparse at best. However, early results are optimistic and suggest that RFA provides safe and effective local treatment of neoplastic disease, with very low complication rates. Reported preliminary survival curves for small, solitary colorectai carcinoma liver metastases (<3cm), and hepatocellular carcinomas (<4cm) are similar to those from surgery, but there is no long-term data yet.
How Does it Work?
The procedure may be performed on an outpatient basis under general anesthesia or conscious sedation. The patient can be awake, but drowsy, for the entire procedure, or alternatively may be put to sleep by an anesthesiologist. The patient receives pain medicine and sedation through an IV and skin-numbing medicine. Routine cardiovascular and respiratory monitoring ensures patient safety during the procedure. Most patients feel little or no pain during the procedure and go home the same day or the day after the procedures, usually with no pain or soreness.
The patient is made into an electrical circuit by placing grounding pads on the thighs. A very small needle-electrode with an insulated shaft, and an uninsulated distal tip is inserted through the skin and directly into the tumor. Ultrasound, CT scan, or MRI guide the needles to the correct spot and monitor treatment. Each treatment session has about 10 to 15 minutes of active ablation. The energy at the needle tip causes ionic agitation and frictional heat in the surrounding tissue, which, when hot enough, leads to cell death and coagulative necrosis. This results in a 3 cm to 5.5 cm sphere of dead tissue per treatment session. In large tumors, the physician may create more than one sphere next to each other to try to turn the tumor edges in three dimensions. A small margin of normal tissue next to tumors is also burned, to try to leave no single tumor cell behind.
The killed tumor cells are not removed, but are gradually replaced by fibrosis and scar tissue. Over the coming months, the treated tissue shrinks. If there is local recurrence, it occurs at the edge, and in some cases may be retreated. For this reason, a treatment margin free of tumor will be the goal of this local therapy.
What Equipment is Used?
There are two basic types of systems used for radiofrequency ablation. Both are available at NIH. The specific RFA system and guidance method are chosen to specifically meet the patient's needs according to tumor location and size, patient risk factors, and tumor histology. Each different system has strengths and weaknesses that will be taken into account to select the RFA method. The active tip of the needle-electrode may be different lengths or configurations. One method uses a "needle-within-a-needle" electrode system with an inner needle that expands like an umbrella once placed into the tumor. The other method uses one to three needles that have cold water flowing inside, which avoids overcooking (or charring) and increases energy dispersion. These two methods increase the volume of treated tissue, and make treatment of larger lesions feasible. The interventionalist uses three-dimensional thinking and knowledge of the underlying mechanism of killing tumors with heat to accurately predict treatment volume and shape, and to plan for disease-free treatment margins.
How is the Cooking Monitored?
The temperature and impedance are monitored so that the appropriate amount of wattage and current may be applied. The generator output is adjusted according to tissue temperature and impedance to limit charring and vaporization. Charring results in less energy deposited and less volume cooked, just as a hamburger that is grilled too quickly will be charred on the outside and raw in the middle. Vaporization near the needle tip insulates the needle and also decreases the amount of tissue that is cooked. The two different systems at NIH use slightly different methods to achieve adequate tissue cooking.
Is RFA New and Experimental?
RFA is not new, but the specific application to treat specific tumors is what we are studying. The RFA systems we use are FDA 510-K cleared for "soft tissue ablation," but not for specific tumor or organ ablation, although we think they may be useful in the treatment of liver, kidney, bone, and soft-tissue tumors. Heat has been used in medicine as long as history. Thousands of years ago, Hindu medics used heated metal bars to stop bleeding. Hippocrates said "what is not cured by the knife may be cured by fire." Electrocautery has been used for many decades in surgery to stop bleeding, coagulate blood vessels, and cut tissue. The RFA generator uses a slight modification of this old technology to deposit the energy over a larger tissue volume. RFA also cauterizes tissue as it heats it, thus limiting blood loss. The needle pathway may also be treated, further reducing the risk of bleeding.
This treatment has been used to successfully treat thousands of tumors around the world in the past few years with very few complications. It is a relatively new application of an old technology. Identical methods have been used for over ten years to treat benign bone tumors or to kill nerves to treat pain. Similar techniques are the treatment of choice for certain heart arrythmias. The preliminary medium and short-term results of RFA for tumors are optimistic. However, no randomized prospective clinical trials have been performed; therefore, the long-term benefits of RFA for specific tumors are unknown.
Is RFA Safe?
Although RFA is relatively safe and minimally invasive, the benefits do not come without slight risks. The reported complication rate is about 1 to 2%, with most of the complications characterized as minor and self-limiting. Many precautions are taken, including continuous monitoring of vital signs and oxygenation and pre-procedural blood tests. The heating treatment inherent to RFA actually stops bleeding, which may be why the rate of bleeding is so low.
Liver
There is no existing effective treatment for the vast majority of patients with hepatic metastases. Most liver tumors are unresectable at the time of presentation. Recurrence is common, even in candidates undergoing curative resection. This means that there is a large number of patients with colorectal carcinoma liver metastases who currently do not have effective treatment options. Local treatment preserves uninvolved liver parenchyma, has potentially fewer systemic complications and side-effects than systemic treatment options (like chemotherapy), and avoids the morbidity and mortality of major hepatic surgery.
Primary liver cancer (hepatocellular carcinoma or hepatoma) may even respond to RFA better than colorectal metastases. Preliminary reports suggest that RFA may be slightly more effective in the local control of these tumors than percutaneous alcohol injection, which has been the conventional treatment for many hepatomas. The largest clinical series reported to date showed a less than 2% initial recurrence rate with a median follow-up of 15 months in 169 lesions in 123 patients. However, 28% developed metastatic disease elsewhere. [Curley SA et al: ann Surg 1999; 230:1-8]. For more information see protocol #99-C-0025, "The Use of Radiofrequency Ablation to Treat Hepatic Neoplasms."
Kidney
Although surgery is certainly the treatment of choice for most primary kidney tumors (renal cell carcinoma), some patients could benefit from a minimally invasive, kidney-sparing treatment option. This includes patients who are high surgical risks, have multiple medical problems, have multiple recurrent tumors (as with Von Hippel Landau), have borderline kidney function, or only have one kidney. RFA may also be used pre-operatively to decrease intraoperative blood loss.
Preliminary results of RFA for small kidney tumors are promising. Two-thirds of all tumors treated and 4/5 of kidney tumors less than 3 cm showed no evidence of active tumor on post-RFA CT scan. However, results are preliminary as mean follow-up was only 5 months in these 21 tumors. [Wood BJ et al: Radiofrequency Ablation of Renal Tumors: Early Experience, SCVIR 25th Annual Meeting. J Vasc Interv Radiol 2000; 11s:225]. For more information see protocol #99-C-0170, "A Phase II Study to Evaluate Radiofrequency Ablation of Renal Cancer."
Bone
RFA has been used safely for over ten years to treat benign bone tumors called osteoide osteomas. There is hope that RFA of malignant bone metastases may provide an additional way to help treat refractory pain in this difficult situation. RFA can be used in addition to conventional treatments like radiation therapy.
Soft Tissue / Pain Palliation
Painful peripheral soft tissue tumors that are unresponsive to pain medication may respond to RFA. Patients who are not surgical candidates, or who have exhausted chemotherapy and radiation therapy, may still be candidates for percutaneous RFA. For large tumors, the goal may be palliation instead of cure.
Adrenocortical Carcinoma/Pheochromocytoma/Adrenal Metastases/Percutaneous RFA may be safely performed on adrenal tumorw, including unresectable adrenocortical carcinoma, adrenal metastases, and even pheochromocytoma (although only one pheochromocytoma has been treated as of August 2000 and this cannot be routinely recommended).
RFA may be effective for the short-term local control of adrenal tumors less than 6 cm. The survival rate for adrenocortical carcinoma is improved by radical excision; therefore local disease control could potentially influence survival as well. However, further study is required to document long-term efficacy, which remains purely speculative.
Summary
Percutaneous local treatment of neoplastic disease with hyperthermia is an attractive new tool for some cancer patients, especially for certain liver, kidney, bone, and soft tissue tumors. Radiofrequency ablation is fast, easy, predictable, safe, and relatively inexpensive. A multidisciplinary team approach is vital to the care of the oncology patient at the NIH. Inverventional radiology works closely with the oncology and surgical specialists to plan the best treatment plan for the cancer patient.