Newton, MA--Imagine you go to your doctor and get the dread diagnosis: cancer. Your standard options: chemotherapy, conventional particle radiation, surgery, or a combination of all three.
Several companies in California believe that thermal ablation, or destruction through heat, of malignant tissue is a more effective way to attack cancer. It's being used today to treat liver cancer, which affects 114,000 people in the U.S. each year. More experimentally, thermal ablation is being tested for use in cancer of the prostate (see related story p. 53).
RadioTherapeutics Corp. (Mountain View, CA) launched a system that destroys liver tumors using radio frequency (RF) electrical waves at the joint meeting of the Society of Surgical Oncology and the World Federation of Surgical Oncology societies in late March. The RF Ablation System consists of a RF 2000(TM) radio frequency generator and surgical dispersive LeVeen(TM) needle electrodes, developed by Dr. Robert LeVeen of the University of Nebraska at Omaha.
The LeVeen needle electrode, which consists of 10 wires deployed through an insulated metal, 15-gauge needle cannula, is inserted into the tissue under direct vision or image guidance. The multi-wire electrode array is mechanically advanced out of the cannula, forming the umbrella-shaped design of the LeVeen needle electrode.
Radio frequency energy, a high-frequency ac, is passed through the electrode for up to 20 minutes of treatment, creating an electrical field within the tissue, which heats and desiccates it. The energy creates a thermal lesion with a spherical dimension up to 3.5 cm in diameter, according to Colin Nichols, vice president of development and regulation for RadioTherapeutics. "It's like microwaving lunch," he adds. "The therapy causes molecular agitation, which heats tissue."
Hot design. During the design process for the RF Ablation System, the company assumed a standard electrogenerator could be used to generate the energy. However, RadioTherapeutics found that it was "totally inappropriate" for this purpose, Nichols says. "The energy delivery rate is much too great," he adds. "It charred the tissue around the tumor and would not create the thermal lesion."
The RF 2000 constant-voltage generator has a 90W maximum output power. Delivery of that varies in response to changes in tissue impedance. As the ablation proceeds, the tissue becomes non-conductive, Nichols says. The generator visually signals the completion of tissue coagulation and automatically shuts off.
Nichols says the company, whose main project is the RF Ablation System, got involved with this technology because of the need for minimally invasive therapy for cancer treatment. Depending on the specific situation, the patient can use this treatment singly or with other treatments such as chemotherapy. "Physicians can use ablation when surgery is not an option," Nichols adds.
The therapy has 510K approval for the coagulation necrosis of soft tissue, and has been used in 100 clinical cases, Nichols says.
Getting hot. At the University of California, San Francisco, Mt. Zion Medical Center, a similar technology is going through trials. Called RF interstitial tumor ablation(TM) (RITA), the system employs a similar design to the RF Ablation System, but the difference is that the thermal ablation catheter's prongs used in the RITA system contain thermocouples at the tips of secondary electrodes that monitor temperature on a display which provides moment-by-moment temperature readings, Ryan says.
The RITA system consists of a Model 500 generator that operates from 0 to 50W in 0.2W increments at a 460 kHz frequency; and a 15-gauge, monopolar, disposable, electrosurgical electrode probe with a stainless-steel trocar and a plastic handle, called a thermal ablation catheter, which is about the size of pencil lead.
The treatment is for patients who have been told, "there's nothing else we can do for you," says Tamara Ryan, RN and clinical coordinator at the Mt. Zion Medical Center. However, most patients undergo simultaneous chemotherapy with the RITA therapy, according to Dr. Allen Siperstein, associate professor of surgery at the University of California, San Francisco.
For treatment, the patient is brought into the operating room, where surgeons locate the tumor through laproscopy and the aid of intraoperative ultrasound. The specialized needle probe is inserted into the center of the tumor, and the prongs open up. Energy is applied, which heats the tumor up and "cooks" it, along with 1 to 2 mm of liver tissue surrounding the tumor, Ryan says. Some tumor tissue is left, which is reabsorbed by the body, and shrinks down over time, she adds.
This therapy is particularly suitable for use in the liver, because cancers there are not generally responsive to chemotherapy, Ryan says. The ideal patient has primary tumors in the liver or metastatic ones, or else has failed standard chemotherapy. Indeed, liver metastatic tumors, or ones spread from other sources such as colorectal or breast cancer, are the most frequent cause of death of cancer patients in Western countries, according to a published paper in Radiology clinical journal.
"We have patients who have been told, basically, write your will, you don't have that much longer to live, and two years later they're doing just fine," Ryan says.
The probe with built-in thermocouples and the Model 500 generator are made by RITA Medical Systems Inc. (Mountain View, CA). "The thermocouples are actually built into the machine, so you can monitor the temperature of the tissue as you're ablating it," Siperstein says. The endpoint for creating a lesion is temperature, he adds, because what destroys the tumor is getting the tissue temperature up to 60 to 70C. Using temperature at the periphery of the tumor as a guide, the clinician can tell how much tissue has been ablated. The system also monitors impedance.
As the Model 500 generator monitors temperature in real time, the machine ramps the power up or down. This automatic feedback control prevents the lesion from heating too quickly, which can cause the tissues around the probe to char. When this happens, electrical impedance will go up, and the system can no longer create a lesion, Siperstein says.
RITA Medical Systems Inc. worked with Siperstein to develop the RITA techniques to perform laparoscopically, which allows treatment of lesions on the periphery of the liver, he says. The company was formed to design, develop, and manufacture devices for the treatment of cancerous tumors with RF energy, according to Edward Gough, vice president of operations and engineering for RITA.
Initially, engineers considered a bipolar RF system requiring multiple penetrations and deployable electrodes to surround the targeted tissue area. However, during initial animal studies it became apparent that these devices were complex and difficult to position, Gough says.
Rather than surround the tissue or tumor, system designers focused on developing a device that would penetrate the tumor just once and deploy the multiple electrodes from the inside out rather than the outside in, he adds.
The first case using the RITA system was done at the University of California in January 1996, and since then 115 lesions have been treated using this system. Researchers followed the patients for approximately nine months, and in that time, only three lesions in two patients have recurred, Siperstein says. The devices used in the RITA medical system have 510K approval by the FDA.
"The technique is not in widespread use yet," he adds. "But within the next year or so, it will become more widely available."