Thoracic Imaging 2003 - Society of Thoracic Radiology

SUNDAY
60
Radiofrequency Ablation in Thoracic Intervention
Peter V. Kavanagh, M.D.
Introduction:
Percutaneous radiofrequency ablation (RFA) is a thermal
ablative technique used to produce local tissue destruction.
Methods of tumor ablation most commonly used in current
practice are divided into three broad categories: (1) thermal
ablation, which utilizes heat (such as RFA and laser therapy), or
cold (e.g. cryotherapy), (2) chemical ablation, where agents
such as ethanol and acetic acid are used, and (3) mechanical
methods using ultrasound energy, such as high-intensity focused
ultrasound (HIFU). RFA is currently the most frequently
employed tissue ablation technique in the thorax and is the most
effective ablative method for treating intra-thoracic malignancies.
Mechanism of action:
RFA delivers high amounts of thermal energy to produce
coagulation necrosis of targeted tissue. Thin, insulated metallic
electrode probes, similar to percutaneous biopsy needles, are
percutaneously inserted into the lesion under image guidance.
The probe is connected to a generator, producing RF waves
from the tip of probe, resulting in tissue heating by means of
ionic agitation. The resultant coagulative tissue necrosis is
induced in a controlled and reproducible manner.
RFA is an evolving technique for the treatment of cancers
throughout the body, including lung, liver, kidney, adrenal gland
and bone. In addition to treating malignant neoplastic processes,
percutaneous RFA is also used to treat osteoid osteomas.
Endovascular transcatheter RFA methods are employed in the
management of varicose veins, and to treat arrhythmogenic foci
that give rise to supraventricular tachycardias.
The technique is dependent on the maintenance of high local
temperatures in order to produce its effect. As air is an insulator,
normal lung parenchyma acts as a barrier to heat dissipation
so this is an advantage when treating patients with malignant
lung nodules and masses. The presence of flowing blood adjacent
to lesions impairs the technique as it acts as a ‘heat sink’
preventing the generation of very high local temperatures.
Hence, lesions close to the heart and adjacent to major pulmonary
vascular structures are less amenable to this form of
therapy.
Indications:
I. Primary lung cancer
A. In early stage primary bronchogenic cancer (Stage
1A/1B) RFA is a potentially curative technique.
Surgery is the conventional treatment in this group of
patients, however, in non-operative candidates RFA is
a valuable alternative. Lesions up to 3 cm in diameter
can reliably be treated by RFA.
B. For more advanced stages of bronchogenic cancer
(Stage 2 or greater) the objective in treating patients
with RFA is to achieve palliation. For example,
painful masses that involve the chest wall can be
effectively treated and excellent results for pain relief
can be obtained.
II. Metastatic disease:
RFA is primarily used as a palliative procedure in treating
pulmonary metastases secondary to primary renal cell carcinoma,
colorectal tumors, breast cancer, and carcinoid
tumors. While palliative in these cases, the quality and
quantity of the palliation can be superior to other treatments.
Technique:
A. Image guidance modalities: Computed tomography
(CT) is used for the majority of procedures.
Fluoroscopic guidance, preferably with C-arm or
biplanar capability, is also feasible. CT fluoroscopy,
if available, can be an advantage, especially for smaller
lesions.
B. Anesthesia
• General anesthesia is preferred by some operators.
The placement of a double lumen endotracheal
tube is a valuable adjunct since it allows
isolation of the treated lung should bleeding
develop. In this instance, ventilation can be
maintained via the contralateral lung.
• A combination of local anesthesia and conscious
sedation is used by many operators.
• MAC is a valuable alternative in select patients.
C. Contraindications:
• Coagulopathy, or patients on anti-coagulation
therapy with INR > 1.5. Aspirin should be withheld
for 5-7 days prior to the procedure.
• Contralateral pneumonectomy.
• Severe bullous emphysema.
• Severely diminished pulmonary reserve such that
a pneumothorax could not be tolerated.
D. Patient preparation:
In creating an RF circuit, grounding pads are placed
away from the operating area, usually on the thighs or
lower back. Care must be taken to ensure that these
are applied correctly as failure to do so can result in
burns. Some operators advocate the use of preprocedural
prophylactic antibiotics but there is no universal
consensus on the need for this. Informed consent is
obtained. Ensure that the platelet count is above
75,000.
E. Equipment:
For tumors < 3 cm, a single needle electrode is used.
Tumors > 3 cm are treated with a cluster of 3 electrodes,
or a single electrode with tangs at its distal
aspect which expand in an ‘umbrella’ type configuration.
RF applicators come in a variety of needle
lengths – a suitable length is selected on the basis of
the depth of the lesion from the percutaneous entry
site. There is also a choice in the length of the active
tip on some single electrode and triple electrode systems
– an appropriate choice is made based on lesion
size.
F. Procedural Aspects:
The general principles and approaches used in percutaneous
transthoracic needle biopsy of lung lesions
are followed. Usually the patient is positioned so that
the least distance of lung tissue is traversed en route
to the lesion. Traversing fissures is avoided, where
possible.
The electrode is placed close to the deepest part of
the tumor for the first treatment. Subsequent treatments
will then be applied at the more superficial
aspects of the lesion. At least one RF treatment is
performed with the maximum allowable current for
12 minutes. Intratumoral temperatures > 55° are
needed to achieve tissue necrosis. The electrode is