BETHESDA, MdRadiofrequency ablation (RFA) is being used to
cook tumors where they lie and may be particularly useful
for destroying liver metastases. This quick, nontoxic, relatively
noninvasive approach will soon be tested in clinical trials, Bradford
Wood, MD, of Georgetown University Medical Center and the National
Institutes of Health, said in an interview.
Dr. Wood noted that his work is a relatively new application of
an old technologyhyperthermia. The main problem with RFA
tumor ablation in the past has been the small volume of tumor, about
1.5 cm in diameter, that could be destroyed with each treatment.
Now we are able to ablate volumes up to about 5 cm with a
single probe placement, and we can do multiple treatments. Each
clears a small sphere of tumor tissue, and we can add up these
spheres to create a larger sphere, Dr. Wood said.
To perform RFA, a needle electrode that has an insulated shaft and an
uninsulated tip is inserted into the lesion, using imaging
guidancemost often ultrasound, but also CT or magnetic
resonance imaging (MRI). Grounding pads on the patients thighs
or back muscles make the patient into an electrical circuit. The
energy released at the uninsulated tip causes ionic agitation and
frictional heat, which leads to cell death and coagulation necrosis.
RFA also cuts off the blood supply to the tumor, Dr. Wood
said. This partly explains the low complication rate (less than
2%). As the needle is removed, it cooks along the needle track, which
stops needle track seeding and bleeding. The technology is
similar to surgical electrocautery, used to stop bleeding during
surgery for more than 50 years, he added.
Over the months following RFA, fibrosis occurs in the ablated area,
and the cooked tumor typically shrinks. Stable or
shrinking lesion size is taken to indicate the absence of active disease.
However, technical problems in follow-up imaging remain to be solved.
RFA leaves a little rim of hyperemic tissue around the treated
site, Dr. Wood said. This is difficult to differentiate
from residual tumor at the margin using current methods. His
group is exploring the use of MRI and positron emission tomography
(PET) for follow-up after RFA tumor removal.
Patient Care After RFA
Most patients receiving radio-frequency ablation are discharged the
Patients may experience a low-grade fever for a few days following
Adequate hydration following the procedure is emphasized to limit the
Dr. Wood and his colleagues are working with two types of RFA. In the
coaxial expanding method, inner needles or hooks come out of the
hollow needle electrode like an umbrella after insertion into the
tumor (see Figure 1). Dr. Wood said
that this approach is preferable for lesions that move with breathing.
The water-cooled method (Figure 2)
uses a needle electrode that has a water-cooled tip to prevent
charring of tissue and three parallel needles to ablate
the lesions. Dr. Wood said that this approach can ablate a greater
volume of tissue without charring (overheating at the edges of the
needle with inadequate heating at the edges of the treatment sphere).
A number of different sources of thermal ablation have been
used in the past, including microwaves, lasers, and high-intensity-focused
ultrasound. RFA may be better than other ablative techniques
because it is fast, easy, predictable, safe, and relatively
cheap, Dr. Wood said.
Each ablation requires only 12 to 15 minutes and is usually done as
an outpatient procedure. Equipment costs include $12,000 to $30,000
for the generator and $500 to $1,000 for each needle used, Dr. Wood said.
The most promising potential use for RFA may be in treating liver
tumors. The definitive therapy for solitary liver tumors remains
surgical resection, but such surgery is not an option for some
patients. Dr. Wood said that only about 20% of patients with liver
metastases of colorectal cancer are candidates for resection and that
two thirds of those operated patients will have disease recurrence
within 5 years. The other 80% of patients are inoperable for medical
reasons or have unresectable lesions.
We are very limited in what we can do safely with surgical
resection, Dr. Wood said. We cannot use surgery to treat
huge tumors or large numbers of micrometastases. Patients with
two to five tumors are not generally considered candidates for
surgery, he said, but RFA can sometimes be used to remove or reduce
hepatic tumors in such patients.
Another use is in the patient who is inoperable due to diffuse
disease, such as lesions in both left and right lobes of the liver.
Many of these patients are considered inoperable by
conventional approaches, Dr. Wood said, but we can
sometimes convert such a patient to a candidate for surgery by using
RFA to ablate the lesion on one side, leaving the other side for resection.
He added that primary liver cancer (hepatocellular carcinoma or
hepatoma) may respond even better to RFA than colorectal metastases (Figure
3). This is because hepatocellular carcinoma usually occurs in
the setting of cirrhotic liver disease. In this situation, the tumor
is soft whereas the surrounding liver parenchyma is
hard. This produces an oven-like effect that promotes the
distribution of the frictional heat within the tumor, particularly
when the carcinoma is encapsulated.
Patients with liver metastases typically have normal (soft)
underlying hepatic parenchyma, whereas the metastasis is hard and
infiltrative and more difficult to pinpoint and treat with RFA.
RFA tumor removal has not been tested in prospective, controlled,
randomized clinical trials because such trials would be extremely
difficult to design, Dr. Wood said.
We are cautiously optimistic that RFA will provide a useful
approach for treating many tumors, but we do know that the most
important determinant of success appears to be the natural history of
the individual patients disease, and this is difficult to
predict, he commented.
Dr. Wood emphasized that the success of RFA tumor ablation is heavily
dependent on the skill and experience of the interventional
radiologist doing the procedure. This is an image-guided
procedure, and accurate placement of the needle determines both
safety and results, he said.
The procedure is currently limited to use at specialized centers,
including the Massachusetts General Hospital, George-town University
Medical Center, and the National Institutes of Health (NIH).
Radiofrequency ablation has been approved by the Food and Drug
Administration for ablation of soft tissue but not specifically for
tumor removal. Dr. Wood said that reimbursement for the procedure
should be covered by codes for hyperthermia involving placing the
needle into the tumor.
The NIH has an ongoing protocol/trial for RFA of liver tumors that
has been underway for several years, and Dr. Wood also performs the
procedure at Georgetown University Medical Center and at
Massachusetts General Hospital.
Kidney Tumor Trial
The NIH has a new research trial for radiofrequency ablation of
kidney tumors in patients with multiple or recurrent tumors,
contraindications to surgery, or solitary kidneys.
For example, Dr. Wood said, patients with Von Hippel Lindau disease
are predisposed to multiple recurrent renal tumors that eventually
require major surgery to be repeated at intervals until ultimately
there may not be enough kidney left to function. RFA might provide a
way to kill tumor and spare as much normal kidney as possible.
To date, Dr. Wood has performed more than 100 radiofrequency ablation
sessions, and more than 10 kidney tumor ablations.