Although lung cancer has a high mortality rate, many pa-tients diagnosed with primary lung cancer will not be surgical candidates. Percutaneous image-guided radiofrequency ablation (RFA) has been used for other tumor types. The authors review the use of RFA for lung neoplasms. The article presents the mechanism, technique, and imaging features of pulmonary RFA.
is a Clinical Fellow, Abdominal Imaging Section, Department of
Radiology, Massachusetts General Hospital, Boston, MA.
is a Professor, Department of Diagnostic Imaging, Brown Medical
School and Director of Tumor Ablation, Rhode Island Hospital,
Dr. Dupuy has received grant support and honoraria from
Valleylab, a division of Tyco Healthcare Group LP, Boulder,
In 2005, an estimated 172,570 new cases of lung cancer were
diagnosed in the United States alone, and a staggering 1.2 million
new cases are diagnosed worldwide each year.
The lung cancer mortality rate far surpasses the mortality rates of
colon, breast, and prostate cancers combined--163,510 people are
expected to die of lung cancer this year in the United States.
The current overall 5-year survival rate for primary lung cancer is
Primary lung cancer can be divided into several histologic
types. Non-small-cell lung cancer (NSCLC) is the most common,
accounting for approximately 80% of diagnoses. Within the category
of NSCLC, the most common types are adenocarcinoma, squamous, and
large cell. Only 20% to 33% of patients with newly diagnosed lung
cancer will be eligible for surgical resection.
This may be because of an advanced state of disease (usually stage
IIIb or greater) at diagnosis or coexistent comorbid conditions.
Patients diagnosed with an earlier stage of disease may undergo
surgical resection and tend to have slightly higher-but still poor-
survival rates. Nonsurgical patients may be offered radiation
therapy with or without chemotherapy. However, the 5-year survival
in these patients is low (0% to 42%) even with medically inoperable
stage I or II NSCLC.
The addition of chemotherapy to primary treatment has been shown to
offer only moderate benefit to patients with NSCLC.
Given the suboptimal current treatment outcomes, alternative
therapies are being sought. Percutaneous image-guided
radiofrequency ablation (RFA) has been used in a variety of
applications to treat solid tumors in the liver, kidney, breast,
bone, and adrenal gland.
Lung RFA was first described in an animal model in 1995,
and multiple groups have reported their experience in humans since
Radiofrequency ablation has shown promise as a safe, minimally
invasive technique that may play a complimentary role or even
replace existing therapies in some patients with lung cancer. The
mechanism, technique, and imaging features of pulmonary RFA will be
Tissue heating is achieved in RFA through the conversion of an
electric current in the frequency of radio waves (460 to 480 KHz)
into heat by electron-molecular collision. The tissue heats by
resistive energy loss,which is also known as
The goal is to heat tissue to 50˚C to 100˚C, which is considered
lethal to target tissues.
An insulated RF electrode with an exposed conductive tip is placed
into the target tissue. The electrode is connected to an RF
generator. There is also a reference electrode (most commonly a
grounding pad) that is placed on the patient's skin in an area of
good electrical conductivity, generally on the thigh or the
opposite chest wall.
Patients referred to our institution for lung RFA are evaluated
clinically by a nurse practitioner and a radiologist with
experience in RFA. A thorough history and physical examination are
performed, and the imaging and laboratory studies are reviewed.
Treatment options are discussed with the patient, and a plan is
made in conjunction with the referring physician.
All patients are asked to fast overnight before the procedure.
Upon arrival on the day of the procedure, patients are evaluated by
the nursing staff, and a focused history and a physical examination
are performed. Intravenous access is obtained, and repeat
laboratory specimens are drawn if necessary. Patients are then
brought to the computed tomography (CT) suite. Most RFA procedures
are performed with the patients under conscious sedation following
administration of midazolam and fentanyl by the radiology
department nursing staff. The ground ing pad(s) are placed by
support staff, and an initial scout image is obtained. The
appropriate cranial-caudal level is chosen, and a computer grid is
applied to the image. The skin entry site is chosen and measured in
reference to the computer grid. This entry site is marked on the
patient using laser lights projected onto the patient from the
gantry. The area is then prepped and draped in sterile fashion, and
1% buffered lidocaine is used for local anesthesia. Superficial
anesthesia is administered with a 25-gauge needle, and a 22-gauge
spinal needle is used for deeper infiltration, including
administration of a generous amount of anesthesia instilled along
the superficial pleura. CT fluoroscopy is used to assess placement
of the spinal needle and to plan trajectory of the RF electrode.
Using CT fluoroscopic guidance, with the patient under controlled
respiration, the electrode is then placed through the chest wall
and pleura into the lesion.
At our institution, we use an internally cooled,
impedance-controlled and temperature-based RF electrode with a
200-W generator (Cosman Coagulator-1; Valleylab, Boulder, CO). The
choice of the electrode length and the active tip length depends on
the depth and size of the lesion. The electrode has an internal
thermocouple that measures intralesional temperature. The electrode
is also coupled to an infusion pump, which continuously infuses ice
water to internally cool the electrode tip. Because the system is
impedance-controlled, the wattage and current settings are
automatically chosen by the system. Treatment times are between 4
and 12 minutes at a given position. Upon completion of a treatment
cycle, the ice water infusion is stopped, and a maximal
intratumoral temperature is measured through the electrode's
thermocouple. A maximal intratumoral temperature should be >60˚C
to ensure that adequate coagulation necrosis has occurred.
The electrode typically used in lung RFA may be a single-tip or
cluster electrode (3 closely spaced electrodes), each a 17-gauge
diameter. Thermocoagulation diameters of up to 3 to 5 cm can be
obtained with the cluster electrode at full power. It has been
shown that the higher impedance level of the surrounding lung
tissue leads to more energy deposition in the tumor compared with
tumors in other solid tissues.
Since this elevated impedance limits the amount of energy that can
be delivered through a single electrode, we have found the cluster
electrode more effective at heating, especially in small
Upon completion of treatment, the electrode is removed and CT
fluoroscopy is used to assess for pneumothorax and hemothorax. If a
large pneumothorax or a symptomatic small pneumothorax is
identified, evacuation can be performed immediately with a
small-diameter drain-age catheter, and an immediate postprocedure
chest radiograph can be obtained. All patients are observed for a
minimum of 2 to 4 hours in our postprocedure recovery room. A
repeat chest radiograph is obtained prior to discharge to confirm
the absence of pneumothorax or the stability of a previously
identified small pneumothorax. If a chest tube has been placed, a
repeat chest radiograph is performed. If the pneumothorax has
decreased in size, patients are discharged with a one-way Heimlich
valve attached to the chest tube, and they are scheduled to return
to the department in 24 hours for a repeat chest radiograph and
clinical evaluation. Chest tubes can usually be removed at this
time. Occasionally, a persistent air leak occurs and requires
prolonged catheter placement. We have also occasionally admitted
patients for overnight observation for pain management or
significant apprehension related to the chest tube. All patients
are given 1-month follow-up appointments for chest CT without and
with intravenous contrast.
Changes in the CT appearance of the lesion are seen immediately
during treatment (Figure 1). Most commonly, there is surrounding
ground-glass parenchymal opacity.
Wrinkling of the edges, vaporization, and multiple surrounding
concentric rings ("cockade phenomenon") have been described by
Gadaleta and colleagues.
They also found that the tumor diameter did not change during
treatment. At 1-month follow-up, the lesion may appear as an area
of consolidation or nodularity. At this time, the mean lesion
diameter will generally be larger than the preablation size. The
increase in size should not be mistaken for tumor recurrence. There
may also be cavitation and the appearance of "bubbly lucencies."
Lung tumors that are successfully treated with RFA also show
decreased contrast enhancement (Figure 2). Suh and colleagues
found marked decreases in contrast enhancement at 1 and 2 months
postablation as compared with preablation enhancement levels using
nodule CT densitometry. Positron emission tomography (PET) has also
been shown to be useful in the follow-up evaluation of patients
treated with lung RFA. Complete resolution of increased
fluorode-oxyglucose (FDG) uptake on postablation PET has been shown
by Akeboshi and colleagues
and has also occurred at the authors' institution (Figure 3).
Residual or recurrent tumors will appear as an area of increased
FDG uptake, usually at the periphery of the treated lesion.
Ongoing research on RFA will likely further establish its place
in the treatment of pulmonary malignancy. The surrounding lung
parenchyma creates an ablation environment that is unique compared
with its application in other denser tissues. A recent study in a
canine tumor model demonstrated that characteristics of the tissue
surrounding the tumor, such as vascularity and conductivity, affect
Tailored protocols depending on the tumor site may be developed in
the future to improve outcomes. Liu and colleagues
have recently applied a computer model experimentally to RFA and
have found that optimal generator settings will be different for
different tissues to produce consistent volumes of coagulation. In
the future, clinicians may be able to predict the radiofrequency
parameter settings for optimal ablation of a given tumor. There may
also be changes in the way that we perform RFA, especially in the
lung. A study in the porcine lung showed significantly increased
thermally ablated lesion volume when ventilation to the treated
lung was blocked via bronchial balloon occlusion. Active
ventilation during RFA is suggested, as that is a significant cause
of in vivo heat loss.
Percutaneous lung RFA guided by magnetic resonance imaging may also
be feasible. A rabbit model demonstrated a high correlation between
the actual thermal ablation diameter seen on gross pathology and
that predicted by T1-weighted spoiled gradient-echo fast low-angle
Combination therapies are another treatment possibility in lung
RFA. Specifically, the addition of radiation therapy either
or externally may augment the treatment effects of RFA alone
(Figure 4). This powerful synergy has also been demonstrated in an
animal tumor model by Ahmed and colleagues.
Finally, studies recently concluded at the authors' institution
indicate that RFA can produce meaningful improvements in symptoms
and survival when used in palliation for chest wall invasion as
compared with alternatives.
Lung cancer continues to have a high mortality rate, and the
majority of patients diagnosed with primary lung cancer will not be
surgical candidates. Radio-frequency ablation has been shown to be
a safe and well-tolerated procedure. The unique conductive
properties of lung tissue allow a high level of heat deposition
into the tumor, and the RFA technique is, therefore, particularly
well suited to application in the thorax. With continued experience
and research, RFA can be expected to play a complementary role and
potentially a primary role in the treatment of lung cancer.