Bipolar radiofrequency ablation of liver metastases during laparotomy. First clinical experiences with a new multipolar ablation concept.

Abstract

Radiofrequency ablation (RFA) is a promising method for local treatment of liver malignancies. Currently available systems for radiofrequency ablation use monopolar current, which carries the risk of uncontrolled electrical current paths, collateral damages and limited effectiveness. To overcome this problem, we used a newly developed internally cooled bipolar application system in patients with irresectable liver metastases undergoing laparotomy. The aim of this study was to clinically evaluate the safety, feasibility and effectiveness of this new system with a novel multipolar application concept.
Patients with a maximum of five liver metastases having a maximum diameter of 5 cm underwent laparotomy and abdominal exploration to control resectability. In cases of irresectability, RFA with the newly developed bipolar application system was performed. Treatment was carried out under ultrasound guidance. Depending on tumour size, shape and location, up to three applicators were simultaneously inserted in or closely around the tumour, never exceeding a maximum probe distance of 3 cm. In the multipolar ablation concept, the current runs alternating between all possible pairs of consecutively activated electrodes with up to 15 possible electrode combinations. Post-operative follow-up was evaluated by CT or MRI controls 24-48 h after RFA and every 3 months.
In a total of six patients (four male, two female; 61-68 years), ten metastases (1.0-5.5 cm) were treated with a total of 14 RF applications. In four metastases three probes were used, and in another four and two metastases, two and one probes were used, respectively. During a mean ablation time of 18.8 min (10-31), a mean energy of 48.8 kJ (12-116) for each metastases was applied. No procedure-related complications occurred. The patients were released from the hospital between 7 and 12 days post-intervention (median 9 days). The post-interventional control showed complete tumour ablation in all cases.
Bipolar radiofrequency using the novel multipolar ablation concept permits a safe and effective therapy for the induction of large volumes of coagulation in the local treatment of liver metastases.

Full text

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Int J Colorectal Dis (2006) 21: 25–32
DOI 10.1007/s00384-005-0781-y
ORIGINAL ARTICLE
Joerg-Peter Ritz
Kai S. Lehmann
Christoph Reissfelder
Thomas Albrecht
Bernd Frericks
Urte Zurbuchen
Heinz J. Buhr
Accepted: 21 April 2005
Published online: 5 May 2005
# Springer-Verlag 2005
Bipolar radiofrequency ablation of liver
metastases during laparotomy. First
clinical experiences with a new
multipolar ablation concept
Abstract Background and
objective: Radiofrequency ablation
(RFA) is a promising method for local
treatment of liver malignancies. Cur-
rently available systems for radio-
frequency ablation use monopolar
current, which carries the risk of
uncontrolled electrical current paths,
collateral damages and limited effec-
tiveness. To overcome this problem,
we used a newly developed internally
cooled bipolar application system in
patients with irresectable liver metas-
tases undergoing laparotomy. The aim
of this study was to clinically evaluate
the safety, feasibility and effective-
ness of this new system with a novel
multipolar application concept.
Patients and methods: Patients with
a maximum of five liver metastases
having a maximum diameter of 5 cm
underwent laparotomy and abdominal
exploration to control resectability. In
cases of irresectability, RFA with the
newly developed bipolar application
system was performed. Treatment was
carried out under ultrasound guid-
ance. Depending on tumour size,
shape and location, up to three
applicators were simultaneously
inserted in or closely around the
tumour, never exceeding a maximum
probe distance of 3 cm. In the mul-
tipolar ablation concept, the current
runs alternating between all possible
pairs of consecutively activated elec-
trodes with up to 15 possible elec-
trode combinations. Post-operative
follow-up was evaluated by CT or
MRI controls 24–48 h after RFA and
every 3 months. Results: In a total of
six patients (four male, two female;
61–68 years), ten metastases (1.0–5.5
cm) were treated with a total of 14 RF
applications. In four metastases three
probes were used, and in another four
and two metastases, two and one
probes were used, respectively. Dur-
ing a mean ablation time of 18.8 min
(10–31), a mean energy of 48.8 kJ
(12–116) for each metastases was
applied. No procedure-related com-
plications occurred. The patients were
released from the hospital between 7
and 12 days post-intervention (medi-
an 9 days). The post-interventional
control showed complete tumour
ablation in all cases. Conclusions:
Bipolar radiofrequency using the
novel multipolar ablation concept
permits a safe and effective therapy
for the induction of large volumes of
coagulation in the local treatment of
liver metastases.
Keywords In situ ablation.
Radiofrequency ablation.Liver
metastases.Liver surgery.
Radiofrequency.Bipolar.Multipolar
J.-P. Ritz (*).K. S. Lehmann.
C. Reissfelder.U. Zurbuchen.
H. J. Buhr
Department of General,
Vascular and Thoracic Surgery,
Charité, University Medicine Berlin,
Campus Benjamin Franklin,
Berlin, Germany
e-mail: joerg-peter.ritz@charite.de
Tel.: +49-30-84452543
Fax: +49-30-84452740
T. Albrecht.B. Frericks
Department of Radiology, Charité,
University Medicine Berlin,
Campus Benjamin Franklin,
Berlin, Germany

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Introduction
In recent years, a number of so-called in situ ablation
techniques like radiofrequency ablation, laser-induced ther-
motherapy or cryotherapy have been developed for the
minimal invasive treatment of liver malignancies [1]. Ra-
diofrequency thermal ablation (RFA), in particular, has ex-
panded the treatment options for these patients and is
broadly introduced in clinical use. In RFA, a small needle
electrode with an insulated shaft and an uninsulated tip is
inserted directly into the tumour percutaneously, via lapa-
roscopy or laparotomy [2–6]. An alternating current is
applied to the tissue and by conductive heating, tempera-
tures exceeding 50°C are achieved in the tumour volume,
leading to an immediate death of affected cells and for-
mation of thermal coagulation necrosis [5, 7]. However, a
more effective and safer application of this therapy is still
restricted due to limited ablation volumes and the use of
monopolar devices.
Currently available systems for radiofrequency ablation
use monopolar current, which requires neutral electrodes in
order to close the electrical circuit. The current flows be-
tween the active electrode and the neutral electrode through
the body of the patient. This technique carries several dis-
advantages: possible skin burns at the grounding pad loca-
tion due to high power densities guided through the patient
[5, 8]; collateral damages by uncontrolled electrical current
paths [9]; and limited effectiveness [10, 11]. The latter must
be seen as the crucial point with regard to treatment out-
come and local recurrence rate. The complete destruction
of a tumour requires ablation with a certain safety margin.
Consequently, the effectiveness of an RFA system, i.e. the
maximum thermally destroyed volume, limited the tumours
to be involved in RFA treatment protocols. Therefore, com-
mercially available systems were improved in effectiveness
by using internally cooled or openly perfused electrodes
[12–14] and by the introduction of umbrella-shaped, multi-
prong electrodes [8, 15]. However, with monopolar de-
vices, the currently available maximum coagulation mass
in vivo is limited to about 4 cm in diameter [5, 8].
Bipolar radiofrequency systems in which both electrodes
are located on one application instrument separated by an
insulator have been recently developed to overcome these
problems of monopolar RFA, and have already demon-
strated their safety and effectiveness in experimental stud-
ies [16]. One further innovation is the multipolar RFA
concept which allows up to three bipolar radiofrequency
probestobeplacedsimultaneouslywithinorcloselyaround
the tumour. No grounding pad is required and the electrical
current runs between up to six electrodes with up to 15 pos-
sible electrode combinations. As the energy is focused on
the target zone, more homogenous energy deposition and
larger ablation lesions should be possible. The aim of the
present study was to demonstrate the first clinical experi-
ence with this new multipolar ablation concept in patients
undergoing laparotomy for treatment of liver metastases.
Patients and methods
Patient population
Patients with hepatic metastases of colorectal carcinoma
were included in the study. The basis for the treatment
planning was a recent (not older than 4 weeks) contrast-
enhanced, high-field MRI or spiral CT of the liver. The
sizes of the metastases, as well as the radiofrequency-
induced necroses, were determined in plain and contrast-
enhanced images. Volumes of the tissue structures were
calculated using the ellipsoid approximation. In all cases
the diagnosis was proofed histologically. The decision to
apply RFA was made by a multidisciplinary meeting con-
sisting of surgeons, radiologists and oncologists. Criteria
for performing bipolar RFA were (1) no more than five
hepatic lesions; (2) lesion diameter of less than 5 cm; (3) no
evidence of extra-hepatic metastases; (4) complete ablation
of all metastases seemed possible; (e) functional, technical
or oncological irresectability. Also, patients unsuited for
general anaesthesia were not treated. The subjects gave
their written informed consent 1 day prior to therapy. De-
finitive decision against resection of metastatic tissue was
made intra-operatively. All tumours present in a patient
were treated in one session. The abdominal cavity was
completely explored including palpation and intra-opera-
tive ultrasound (US) of the liver and biopsies of suspicious
areas or lymph nodes. Admission to hospital was at least
24 h prior to therapy.
Radiofrequency equipment
We used a newly developed bipolar radiofrequency abla-
tion system (Celon AG Medical Instruments, Teltow, Ger-
many). The basic concept features two improvements
compared to monopolar devices. It is designed as a bipolar
unit that does not require the use of grounding pads. Both
electrodes required to close the electrical circuit are located
on one application instrument (Fig. 1). Secondly, the unit
was designed for the simultaneous operation of up to three
bipolar electrodes within a single tumour. Previous inves-
tigations have shown that the simultaneous operation of
multiple energy sources for tissue coagulation has a sig-
nificantly increased effectiveness compared to the same
number of subsequently applied applicators with the same
amount of energy [17].
For RFA, at least one rigid bipolar coagulation electrode
(CelonProSurge; Celon AG) with a diameter of 1.8 mm
(15 F) and a shaft length of 15 cm was introduced into the
tumour. The conducting part of the applicators was 40 mm,
including both electrodes, the insulator and the tip. In bi-
polar mode, the high-frequency current flowed between the
two electrodes at the tip of the bipolar coagulation elec-
trode and heated up the tissue surrounding the electrodes.
An internal liquid circulation of the applicator enabled the
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efficiency of coagulation to be increased. The delivery rate
was set to 30 ml/min using saline solution at room tem-
perature. The liquid flow was provided by a triple peristal-
tic pump, which is part of the system. The electrodes were
operated by a power control unit working at 470 kHz and
providing a maximum output power of 250 W (CelonLab
Power; Celon AG). The unit controlled up to three bipolar
electrodes where the actual number could be individually
adapted to the clinical situation between one and three.
With one connected bipolar electrode, the unit was in bi-
polar operating mode, in which the device provided an
acoustic output of the coagulation status. If the resistance
increased beyond a specific limit value power (700 Ω),
delivery was stopped automatically.
Multipolar ablation concept
For small lesions (smaller than 1.5 cm), a single probe
centrally placed within the tumour is usually adequate.
However, small and hard metastases may be difficult to
puncture centrally as they have a tendency to veer away
from the needle. Therefore, an alternative approach with
two or three probes placed closely around the lesion is
possible with the multipolar system. In bigger lesions, two
or three probes are placed in the outer third of the lesion,
potentially with a second ablation after partial retraction or
repositioning of the probes in order to achieve an adequate
safety margin.
If more than one bipolar electrode were connected, the
unit was in multipolar mode, i.e. all possible electrode pairs
were automatically activated alternating for up to 2 s de-
pending on the actual local tissue resistance. Here, a pair of
electrodes was not only defined as the two electrodes lo-
cated on a specific bipolar applicator shaft, but included
also all other possible electrode combination between the
different applicators. Consequently, the current also passed
between one electrode of a specific applicator shaft and an
electrode of another applicator shaft, crossing the tumour.
When three bipolar applicators were placed in a tumour, up
to 15 possible combinations (pairs of electrodes) between
the current may have passed (Fig. 2). If the resistance of
an electrode pair increased beyond a specific limit value
(700 Ω) by three folds or the power output was inade-
Fig. 1 Bipolar radiofrequency
ablation system with two elec-
trodes on one application system
separated by an insulator
B
A
B
B
A
A
B
B
A
A
B
B
A
A
B
B
A
A
B
B
A
A
B
B
A
A
B
B
A
A
B
B
A
A
B
B
A
Fig. 2 Diagram of the multipolar ablation concept. The current
passes between all electrodes (15 possible combinations)
27

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quate (less than one third of the preset power output), this
electrode pair was excluded from further ablation cycles.
Power output was stopped automatically if the resistance
of all possible electrode pairs exceeded the limit by three
folds, indicating that dehydration has extended along the
electrodes completely and that the coagulation process has
ended. Under microprocessor control, the RF output was
divided between the individual electrodes according to the
momentary tissue resistance, providing a three-dimension-
al impedance feedback control.
RFA Procedure
An epigastric transverse laparotomy was performed for
optimal liver exposure. The abdominal cavity was explored
in order to exclude extra-hepatic tumour manifestations.
After palpation and ultrasound (7.5 MHz) of the liver, de-
cision for RFA was made in case of irresectable metasta-
ses. We then mobilized the liver and identified structures
of the hepatoduodenal ligament. In the Pringle group, the
hepatoduodenal ligament was looped and occluded directly
before RF application. Hepatic blood flow was released
immediately after completing RF application. Depending
on the size of the lesion, up to three applicators were in-
serted to the tumour and a Pringle manoeuvre was applied
to occlude hepatic inflow according to the dosimetry pro-
tocol. The intra-hepatic position of the applicators was
monitored with the ultrasound system (Fig. 3). A single
applicatorwasplacedintothecentreofthetumour,whereas
multiple applicators were placed at the tumour margin with
a defined distance of minimal 2.0 cm or maximum 3.0 cm
between them (Fig. 4a and b). Insertion depth of the ap-
plicator tip was at least 50 mm. RF application was per-
formed at a power setting of 20–90 Wand the ablation was
performedaslongastheincreaseintissueresistancedidnot
lead to an automatic interruption of power output. To pre-
vent bleeding from the puncture track and possible seeding
of tumour cells, the electrodes were withdrawn from the
tissue during power output in bipolar mode with a power
setting of 25 W (track ablation). The first follow-up exami-
nation was performed 24–48 h after RFAwith unenhanced
T1- and T2-weighted and dynamic Gd-BOPTA (Multi-
hance, Bracco, Milan, Italy) enhanced T1-weighted 3D
gradient echo MR imaging (Somatom Vision, Siemens).
Tumour ablation was classified as complete or incomplete
based on signal characteristics on T1- and T2-weighted im-
ages pre- and post-contrast enhancement, especially at the
Fig. 3 Intra-operative ultrasound image showing the bipolar appli-
cation system (arrows) in the hepatic tumor
Fig. 4 a Intra-operative view during multipolar radiofrequency in a
patient with liver cirrhosis. A rubber band is placed around the
hepatoduodenal ligament for Pringle maneouver. b Close intra-oper-
ative view showing the distance holder between the three applicators
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periphery of ablative lesion and upon comparison with pre-
interventional imaging (Fig. 5).
Results
Six patients (four male, two female) suffering from a total
of ten metastases (1–3) of colorectal cancer were included
in the present study, which commenced in June 2003. Their
mean age was 65.6 years (61–68) at the time of RFA. All
patients had a complete (R0) resection of the primary
tumour. Patients had been treated previously with chemo-
therapy (n=3), laser interstitial thermotherapy (LITT) (n=3)
or immunotherapy (n=1). The tumours had a mean diam-
eter of 27±13 mm (range 10– 55 mm) and were located
subcapsularly (n=4), centrally within the liver parenchyma
(n=3), adjacent to a large hepatic or portal vein (n=2), or
close to the diaphragm (n=1). Two metastases exhibited a
diameter of less than 1.5 cm, four metastases exhibited a
diameter between 1.6 and 3 cm, two metastases demon-
strated a diameter between 3.1 and 4 and another two were
larger than 4 cm. Reasons for irresectability were impaired
liver function due to cirrhosis (n=2), bilobar involvement
(n=2) clinical status unsuited for extensive liver surgery
(n=1) or central location of the tumour (n=1). All patients
underwent a single laparotomy to perform the abdominal
explorationandtreatmentofthemetastaticdisease(Table1).
A Pringle manoeuvre was performed during six RF
applications in four of the lesions in patients with a tumour
diameter of more than 30 mm in order to reduce perfusion-
mediated cooling and thus to increase the volume of ab-
lated tissue.
In eight of 14 ablations three probes were used, and in
another four and two ablations two and one probes were
used, respectively. In order to achieve an adequate ablation
margin, the probes were repositioned during four ablations
(using three probes each) after the tissue impedance in-
creased and energy flow was interrupted. Under ultrasound
guidance, all applicators were then placed in the area of the
tumour which was not reached during the initial applica-
tion. If more than one probe was used, the mean distance
between the probes was 22 mm (range 10– 30 mm). The
positioning of the RF system, with the help of palpation
and ultrasound guidance, was possible without problems.
The tip of the bipolar applicator could be well visualized as
a hyperechoic spot at real-time US (Fig. 3), so that the
Fig. 5 CT scans 3 (left), 6
(middle) and 12 months (right)
after multipolar radiofrequency
ablation
Table 1 Results of bipolar RFA in relation to the diameter of the metastases
Diameter of metastases
≤1.5 cm [Range]1.6–3.0 cm [Range]3.1–4.0 cm [Range]>4.0 cm [Range]
Number of Metastases
RF-Applications
RF+ Pringle-Maneuver
Mean Tumor Diameter (cm)
Mean RF-Lesion Diameter (cm)
Applicators
Application Time (min)
Applied Energy/Metastases (kJ)
2
2
0
1.1×1.2×1.2 [1.0–1.5]
2.5×3.1×2.4 [1.8–3.3]
1
13.5 [10–16]
17.1 [12–22]
4
4
0
2.3×2.5×2.5 [1.8–2.9]
4.0×4.5×4.1 [3.4–4.6]
2
25.2 [12–29]
43.5 [32–68]
2
4
2
3.5×3.4×3.5 [3.3–3.8]
4.5×5.0×4.3 [4.3–5.0]
3
21.4 [11–31]
77.8 [38–116]
2
4
4
4.8×5.1×4.9 [4.5–5.5]
6.5×8.2×6.5 [6.1–8.5]
3
18.9 [12–24]
70.4 [37–108]
29