Biomed Imaging Interv J 2006; 2(3):e39
© 2006 Biomedical Imaging and
�How I Do It� Article
Radiofrequency ablation of lung tumours
PYT Goh, MBBS, FRCR
Department of Radiology, Mount Elizabeth Hospital, Singapore
Radiofrequency ablation is a well-established local therapy
for hepatic malignancies. It is rapidly emerging as an effective treatment
modality for small lesions elsewhere in the body, in particular, the kidney and
the lung. It is a relatively safe and minimally invasive treatment for small
lung malignancies, both primary and secondary. In particular, it is the
preferred form of treatment for non-surgical candidates.
This paper describes the technique employed for
radiofrequency ablation of lung tumours, as well as the protocol established,
at the Mount Elizabeth Hospital, Singapore. � 2006 Biomedical Imaging and
Intervention Journal. All rights reserved.
Keywords: Radiofrequency ablation, lung tumours
Mode of imaging
All cases are performed under CT fluoroscopic guidance.
RF system used
The Valley Lab Cool-tip RF system (Valley Lab, Boulder, CO),
with the 17-gauge single prong electrode, connected to a 200 W radiofrequency
generator was used in all cases. The length of the exposed tip of the electrode
chosen is 1 to 3 cm depending on the size of the lesion. In general, the length
of the exposed tip should be greater than the diameter of the lesion. For
lesions larger than 3 cm in diameter, multiple cycles of ablation are performed
with re-positioning of the electrode between each cycle, to achieve overlapping
areas of ablation larger than the lesion itself. The Cool-tip cluster electrode
system was not used in any of these cases. Each cycle of ablation is 12
minutes, as per the standard protocol determined by the Valley Lab system for
RF ablation under impedance control. Track ablation is performed at the end of
the ablation cycle by switching off the cooling system after 11 minutes of
ablation. The electrode is withdrawn when the temperature increases beyond
The other RF system available in our department is the LeVeen
needle (Boston Scientific, Watertown, MA). This system was not used in any of
our lung lesions. It was felt that the larger gauge needle and as well as its
co-access or co-axial system subjected the patients to a higher risk of pneumothorax.
Track ablation is not as easily achieved as in the Valley Lab system. The track
is sequentially ablated at a power of 10 W and withdrawn following roll-off.
Furthermore, from a purely subjective point of view, this author
finds the Cool-tip electrode a much easier electrode to place into a lesion
accurately. It is a slimmer and a more flexible electrode. The technique of
placing the electrode is to skewer the lesion so that the tip of the electrode
is just distal to the far margin of the lesion. The stiffer and larger gauge
co-access needle of the LeVeen system is more difficult to target lesions with,
especially lesions with locations that require angling the needle superior or
inferior to the skin entry point. The system also requires that the tip of the
needle is a short distance away from the far margin of the lesion so that the
tines of the LeVeen needle, when extended, achieve optimal coverage of the
lesion. This takes some practice and experience and it may involve greater
CT-fluoroscopy time. Furthermore, it is this author�s opinion that co-access or
co-axial systems in the lung run a higher risk of pneumothorax.
The CT images are reviewed prior to ablation (Figures 1 and 2). The CT images
should be recent; no more than four weeks prior to the procedure.
The number, size, and location of the lesions are evaluated.
Lesions close to vital structures need to be studied carefully
as these may potentially be damaged by the heat generated during
RFA. These include the heart, the main pulmonary vessels, the
trachea, and the main bronchi. In general, the major vessels
as well as the heart are protected from the heat as a result
of the blood flow resulting in a heat sink effect .
Nevertheless, care is always taken to ensure that the electrode
does not cross or abut a major vessel or the heart directly.
Arbitrarily, the electrode is placed at a minimum of approximately
1 cm from these structures. Although the heat sink effect protects
these structures from heat damage, it also implies that the
portion of the lesion abutting these structures may also be
protected form heat damage, resulting in sub-total ablation.
In such cases, alcohol ablation of the portion of the tumour
abutting the major vessels may be considered if RFA alone does
not achieve complete ablation.
Figure 1 PET/CT image
of single lung metastasis for RFA. This is a typical lesion
and ideal for RFA.
Figure 2 CT image of single
lung metastasis pre-RFA.
The clinical history of the patient is also reviewed. Care
is taken to evaluate co-morbid conditions, especially other lung diseases, such
as, chronic obstructive airway disease, bronchiectasis, and asthma. These cases
have a higher risk as they will not tolerate complications of RFA of the lung,
such as, pneumothorax and pulmonary haemorrhage. The theoretical risks of
performing RFA on patients with pacemakers seem to be unfounded , and the
procedure has been performed in these patients without significant
complications. Nevertheless, a cardiologist, in particular, an
electro-physiologist if available, should evaluate all patients with
pacemakers. If the patient does not require the pacemaker constantly, it may be
temporarily deactivated at the time of ablation, with external pacing on
standby. If the patient is entirely dependent on the pacemaker and any
disruption of its function cannot be tolerated, it may be prudent to explore
other means of local ablative therapy, if available. These include laser
ablation or microwave ablation, which do not employ RF energy.
The coagulation profile of the patient should always be
assessed prior to the procedure.
Contraindications to RFA of lung lesions:
Extensive lung involvement with life expectancy of less than six months
Invasion of pericardium and mediastinum
The procedure is performed in the CT fluoroscopy room. A
pre-RF, unenhanced CT of the thorax is performed. The site of the lesion and
the entry point are chosen. The patient may be turned and re-positioned
accordingly, e.g., in the prone or oblique position. The shortest possible path
to the lesion, avoiding major structures and fissures, is usually selected.
A pleural drainage set is placed in the procedure room for
use in the case of significant pneumothorax requiring immediate chest tube
insertion. Usually, a simple 6Fr multi-purpose pigtail drainage catheter is all
that is necessary.
As in all cases of radiofrequency ablation in our
department, lung ablations are performed under heavy conscious sedation with
the aid of an anaesthetist. Midazolam, fentanyl, and propofol are titrated
during the procedure. The patient is placed on intra-nasal oxygen, and the
vital signs are monitored. No intubation or general anaesthetic is required
The 17-gauge RF electrode is inserted into the lesion under
CT fluoroscopic guidance, under strict aseptic conditions.
After the tip of the electrode is successfully placed within
the lesion (Figure 3), the portion of the electrode outside the patient�s body is
supported by hand throughout the ablation cycle. This is necessary because the
lung parenchyma is not as firm as the liver parenchyma. The weight of the
electrode may cause it to change position, if left unsupported. Furthermore,
respiratory movement, progressive atelectasis, and change in consistency of the
lung parenchyma adjacent to the lesion during the ablation may result in a
change in position of the electrode relative to the lesion. Therefore,
intermittent CT fluoroscopy is performed during the ablation cycle, and the
electrode position is readjusted appropriately. Arbitrarily, the lesion is
imaged every three minutes during ablation.
Figure 3 RF electrode
inserted into lesion under CT fluoroscopic guidance. Note
that the tip of the electrode has gone beyond the far margin
of the tumour nodule to ensure that a good rim of normal lung
tissue is also ablated.
The water-cooling system is switched off towards the end of
the cycle, usually after 11 minutes of ablation, and the electrode is allowed
to heat up. The electrode is withdrawn, after the temperature exceeds about 70�C,
to coagulate the track. The rationale behind track coagulation is to reduce the
risk of tumour track seeding  and to reduce the risk of pneumothorax.
If the lesion is larger than 3 cm in diameter, the
water-cooling system is left on for the full 12 minutes. The electrode is
partially withdrawn at the end of the cycle and re-positioned for further
ablation. The track is not coagulated at this point in time. Re-positioning and
repeat ablation is performed up to three to four times, depending on the size
of the lesion. If the lesion requires more than three to four cycles of
ablation, the procedure will be re-scheduled for further ablation one month
later. Track ablation is only performed during the final complete withdrawal of
At present, there is no means of evaluating the adequacy of
ablation of a lesion during the procedure. The end-point of ablation for small
lesions (2 to 3 cm) is taken as the arbitrary 12-minute cut-off point in the
Valley Lab Cool-tip system. The Cool-tip system set on impedance control will
alternate between �on� (active) and �off� (inactive) modes depending on the
impedance of the lesion being ablated. Long periods of inactivity (30 to 40 s)
by the machine followed by short periods of activity (5 to 7 s) with impedance levels of greater than 100 ohms, indicate that the target volume of tumour
has been ablated .
At our centre, the only other RFA system available is the LeVeen
needle by the Boston Scientific Corporation. The end-point of ablation using
this system is the roll-off when impedance increases rapidly following tumour
cell death. Till date, however, we have not used the LeVeen system for RFA of
It has been suggested that an indication of complete tumour
ablation is the presence of a good surrounding rim of ground glass opacification
around the tumour (Figure 4). This is a useful sign to look out for when ablating lesions
larger than 3 cm, which require multiple ablations and re-positioning of the
electrode to achieve overlapping zones of ablation .
Figure 4 RFA in progress.
Surrounding area of ground glass opacification is typical
during ablation. There is also surrounding focal parenchymal
haemorrhage, which is sometimes seen during RFA.
If a pneumothorax is sustained during the insertion of the
electrode, prior to the actual placement of the electrode within the lesion,
aspiration may be required. This is because the presence of a pneumothorax
sometimes makes accurate placement of the electrode within the lesion
difficult. A 6 Fr multiple side-hole drainage catheter is usually used. After
complete aspiration of the pneumothorax, the catheter is left in-situ and
closed off. If the pneumothorax, however, does not interfere with the placement
of the electrode and if the patient is not clinically compromised, no
aspiration is necessary.
An arbitrary maximum of 3 to 4 cycles of ablation are
performed during a single session of RF ablation. This is irrespective of the
number of lesions. If more cycles of ablation are required or if there are
multiple lesions, further RFA is performed at a later date, usually at
RFA for bilateral lung lesions during a single session is a
relative contraindication. In such patients, it is better to perform RF for one
side first and to schedule the lesions on the contra lateral side to be
ablated, a month later. Depending on the clinical status of the patient and in
the absence of complications during the ablation on one side, however, ablation
of the contra lateral lesions may be performed during the same session.
Follow-up serial chest radiographs are performed after the
procedure, as per standard post-lung biopsy protocol, to check for a pneumothorax
or to track an existing one. Not all cases with pneumothorax require chest tube
insertion. This is only inserted if the patient is symptomatic or if the pneumothorax
The use of prophylactic antibiotics is debatable. At our
centre, a single dose of peri-procedural broad-spectrum antibiotics is usually
Post-procedural analgesia is prescribed only if the patients
require this. For subpleural lesions, there may be pain following the ablation
and analgesia may be mandatory. Some patients with sub pleural lesions may
develop a pleural effusion. This is drained percutaneuosly only if the patient
Follow-up CT of the thorax (Figure 5) with intravenous contrast
enhancement is performed at one month, three months, and six months
post-procedure. After that, follow-up is at six-month intervals for two years
and, then, yearly. If the ablation scar shows any evidence of increase in size
or enhancement, repeat ablation may be performed. A review article by Rose et
al  on radiofrequency ablation of lung cancer suggests that if there is an
increase of at least 10HU between the non-contrast scan and the
contrast-enhanced scan, this is suggestive of residual viable tumour. Repeat
ablation is then advised.
Figure 5 CT scan performed
one-month post-RFA. This is a typical appearance of an oval
area of coagulation necrosis scarring following RFA. Note
that the area of scarring is larger than the original lesion,
indicating a positive outcome.
PET/CT scans are far more sensitive than contrast enhanced
CT scans in detecting recurrent or residual viable tumour. Not all patients,
however, can afford to be followed up with PET/CT. Where possible, a PET/CT is
recommended at one month post-RFA and at one year, with contrast enhanced CT
scans in between, at the intervals suggested above.
Tumour markers should be monitored if these were elevated,
prior to RFA.
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| Received 15 June 2006; received in revised form 24 July 2006; accepted 30 July 2006
Correspondence: Department of Radiology, Mount
Elizabeth Hospital, 3 Mount Elizabeth, Singapore 228510,
Republic of Singapore. Tel.: 65-67312107; Fax: 65-67323368;
Please cite as: Goh PYT,
Radiofrequency ablation of lung tumours, Biomed Imaging Interv J 2006; 2(3):e39
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