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European Radiology
ISSN 0938-7994
Volume 25
Number 1
Eur Radiol (2015) 25:246-257
DOI 10.1007/s00330-014-3391-7
Robotic-assisted thermal ablation of liver
tumours
Basri Johan Jeet Abdullah, Chai Hong
Yeong, Khean Lee Goh, Boon Koon
Yoong, Gwo Fuang Ho, Carolyn Chue
Wai Yim & Anjali Kulkarni
1 23
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INTERVENTIONAL
Robotic-assisted thermal ablation of liver tumours
Basri Johan Jeet Abdullah &Chai Hong Yeong &
Khean Lee Goh &Boon Koon Yoong &Gwo Fuang Ho &
Carolyn Chue Wai Yim &Anjali Kulkarni
Received: 9 April 2014 /Revised: 20 June 2014 /Accepted: 7 August 2014 /Published online: 5 September 2014
#European Society of Radiology 2014
Abstract
Objective This study aimed to assess the technical success,
radiation dose, safety and performance level of liver thermal
ablation using a computed tomography (CT)-guided robotic
positioning system.
Methods Radiofrequency and microwave ablation of liver
tumours were performed on 20 patients (40 lesions) with the
assistance of a CT-guided robotic positioning system. The
accuracy of probe placement, number of readjustments and
total radiation dose to each patient were recorded. The perfor-
mance level was evaluated on a five-point scale (5–1: excel-
lent–poor). The radiation doses were compared against 30
patients with 48 lesions (control) treated without robotic
assistance.
Results Thermal ablation was successfully completed in 20
patients with 40 lesions and confirmed on multiphasic
contrast-enhanced CT. No procedure related complications
were noted in this study. The average number of needle
readjustment was 0.8± 0.8. The total CT dose (DLP) for the
entire robotic assisted thermal ablation was 1382 ±
536 mGy.cm, while the CT fluoroscopic dose (DLP)
per lesion was 352±228 mGy.cm. There was no statis-
tically significant (p>0.05) dose reduction found be-
tween the robotic-assisted versus the conventional
method.
Conclusion This study revealed that robotic-assisted planning
and needle placement appears to be safe, with high accuracy
and a comparable radiation dose to patients.
Key Points
•Clinical experience on liver thermal ablation using CT-
guided robotic system is reported.
•The technical success, radiation dose, safety and perfor-
mance level were assessed.
•Thermal ablations were successfully performed, with an
average performance score of 4.4/5.0.
•Robotic-assisted ablation can potentially increase capabili-
ties of less skilled interventional radiologists.
•Cost-effectiveness needs to be proven in further studies.
Keywords Robot .Radiofrequency ablation .Microwave
ablation .Liver tumour .CT-guided
Introduction
Image-guided thermal ablations such as radiofrequency abla-
tion (RFA) and microwave ablation have emerged as attractive
minimally invasive interventional treatments of liver malig-
nancies, as first-line therapy and in patients ineligible for
surgery. Probes are percutaneously inserted into the tumour
B. J. J. Abdullah :C. H. Yeong
Department of Biomedical Imaging and University of Malaya
Research Imaging Centre, Faculty of Medicine,
University of Malaya, 50603 Kuala Lumpur, Malaysia
B. J. J. Abdullah (*):C. H. Yeong :K. L. Goh
Department of Internal Medicine, Faculty of Medicine,
University of Malaya, 50603 Kuala Lumpur, Malaysia
e-mail: basrij@ummc.edu.my
B. K. Yoong
Department of Surgery, Faculty of Medicine, University of Malaya,
50603 Kuala Lumpur, Malaysia
G. F. Ho
Department of Oncology, Faculty of Medicine,
University of Malaya, 50603 Kuala Lumpur, Malaysia
C. C. W. Yim
Department of Anesthesia, Faculty of Medicine,
University of Malaya, 50603 Kuala Lumpur, Malaysia
A. Kulkarni
Perfint Healthcare Corporation, Florence, OR 97439, USA
Eur Radiol (2015) 25:246–257
DOI 10.1007/s00330-014-3391-7
Author's personal copy
and a volume of tissue is devitalized either by heat (using
radiofrequency or microwave) or freezing (cryoablation). Ac-
curate placement of the probe is critical to achieving not only
technical success (for lesions high in the dome or large lesions
requiring multiple overlapping ablations), but also vital in
ensuring adequate ablation margins to prevent local tumour
recurrence [1]. Additionally, patient safety is compromised
with imprecise electrode placement, which may lead to major
complications such as pleural and gastrointestinal perfora-
tions, laceration of vessels with bleeding, or thermal collateral
damage with bile duct stenosis, biloma, gastrointestinal in-
flammation and subsequent perforation [2].
To improve trajectory planning and targeting, surgical nav-
igation systems have recently been adapted to the needs of
interventional radiology [3,4]. The navigation systems (com-
monly known as “robots”) assist in either planning and plac-
ing of the needles/probes, or allow tracking the position of a
surgical tool that is projected in real-time in the patient’s
corresponding computed tomography (CT) or magnetic reso-
nance (MR) images [5]. The aim of these CT or MR compat-
ible robots is to increase the accuracy of needle or probe
placement through three-dimensional (3D) imaging and com-
puterized trajectory planning in arbitrary orientated tracks, to
improve the outcomes of interventional therapies. Further-
more, in highly inaccessible lesions that require multiple plane
angulations, robotically assisted needle placement may im-
prove access to the target by allowing off-axial paths of needle
placement. Previous studies have confirmed high targeting
accuracy of a commercially available robot in phantom and
animal experiments [4], as well as in clinical settings [3,5].
Reduction of exposure to radiation during CT fluoroscopy to
clinical staff and patient is another potential benefit [3]. Al-
though ultrasound-guidance provides a radiation-free environ-
ment and allows off-axial needle paths, it has several limita-
tions. These include ultrasound-occult lesions, difficulty in
visualizing deep lesions, shadowing artefacts caused by air,
bone or bowel, and increased operator variability.
The goal of our study was to evaluate the technical success,
radiation dose, ease of use and safety of a new commercially
available CT-guided robotic system, Maxio (Perfint
Healthcare, Florence, Oregon, USA), in assisting treatment
planning and tumour targeting for liver tumours ablative
therapy.
Materials and methods
This study has been granted with medical ethics approval
(MEC No. 949.9) from the Medical Ethics Committee,
University of Malaya Medical Centre, Kuala Lumpur,
Malaysia. Informed consent was obtained from all the
patients.
Patients
A total of 20 patients (40 lesions) with primary or secondary
liver tumours were treated with thermal ablative therapy
(August 2013 to February 2014) with the guidance of
the robotic needle positioning system, Maxio (Perfint
Healthcare, Florence, Oregon, USA), attached to a CT fluo-
roscopy system (SOMATON Definition AS 128, Siemens
Healthcare, Munich, Germany).
Ten patients had new and recurrent hepatocellular carcino-
ma (HCC), while the other ten patients had liver metastases.
Twelve patients were treated with the RITA StarBurst radio-
frequency system (Angiodynamics, Latham, New York,
USA), three patients were treated with the Cool-tip RFA
system (Valleylab, Boulder, Colorado, USA), and the remain-
ing five patients were treated with the Avecure microwave
system (Medwaves, San Diego, California, USA). All the
lesionswerelessthan50mminmaximumdiameter
(the average dimension of the tumour was 19× 23 mm).
Maxio robotic needle positioning system
Maxio is an image-guided, physician controlled stereotactic
accessory to a CTsystem, intended as an instrument guide for
the stereotactic spatial positioning to assist in manual advance-
ment of one or more needle-based devices for CT-guided
percutaneous procedures such as biopsy and RFA. The system
(Fig. 1) consists of a treatment planning workstation that is
compatible with 3D DICOM images and a robotic positioning
device docked on a registration plate (InstaReg
TM
, Perfint
Healthcare, Florence, Oregon, USA), as shown in Fig. 2,
adjacent to the CT table during the interventional procedure.
The robotic arm has five degrees of freedom to the point of
interest and is able to provide orbital, cranio-caudal angula-
tions or a combination of both for thoracic, abdominal and
pelvic interventional procedures.
Figure 3demonstrates the operational flow of the Maxio
robotic system for interventional procedures.
Treatment planning and simulation
All the thermal ablation procedures were performed under
general anaesthesia. After intubation, the patients were
wrapped in reusable immobilisers to minimise patient move-
ment during the procedure. Following baseline CT with
suspended expiration, the lesions were identified. All the
patients had non-contrasted baseline CTs, except six patients
whose lesions were difficult to localize. The CT images were
then reconstructed to 1 mm thickness and transferred to the
Maxio workstation for simulation and treatment planning. The
application software allows 2D and 3D visualization of the
Eur Radiol (2015) 25:246–257 247
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volumetric data. Once the volume of interest (VOI) was
identified, the tumour was segmented automatically by the
software to allow verification of the target volume (Fig. 4a).
This is displayed in axial coronal and sagittal planes, together
with a 3D segmented image. Any deviation from the tumour
margins can be manually adjusted by either cropping or
adding to the target volume. The target point (centre of the
tumour volume) was then defined by the radiologist on the
treatment plan. The entry point (needle puncture site on the
skin surface) was determined by taking into consideration any
critical structures in the needle path. This was done by
scrolling the axial images manually on the treatment plan
and ascertaining if the needle path traverses any critical struc-
tures, as the software is not able to reconstruct an obliquity to
see the entire needle path in one image. If critical organs were
involved, the entry point needed to be modified to change the
needle trajectory. The operator then input the choice of abla-
tion device (RFA or microwave), including the length of the
probe that was going to be used. The workstation determined
the orbital and cranio-caudal angulations as well as the min-
imum length of the probe required to complete the ablation
(refer to Fig. 4b). The system allows up to six probes to be
planned at one time. Figure 4c shows an example of treatment
plans for two different tumours. The simulated ablation maps
of different probes were then displayed as an overlay on the
original tumour volume, as shown in Fig. 4d. The plan was
carefully checked by the radiologist to avoid critical organs or
bone across the trajectory prior to confirming the plan. If the
margins were inadequate, the target point or the entry point
could be modified.
Robotic-assisted needle placement
Once the treatment plan was confirmed, the patient was posi-
tioned at the exact coordinate as determined in the treatment
plan. The patient’s skin in the intended region was prepared
for the procedure. The skin and liver capsule along the
projected path of the ablation probe was infiltrated with
10 ml of 1 % lignocaine. The robotic arm was then activated
and moved automatically to the desired location. Once the
robotic arm was completely halted at its position, the radiol-
ogist placed an appropriate bush (a plastic needle holder) that
had a diameter matching the diameter of the ablation probe at
the end-effectors of the arm. The function of a bush is to
minimize deviation of the needle entry point from the treat-
ment plan, by guiding the needle along the planned trajectory.
The radiologist then inserted the ablation probe through the
bush and generally deployed the probe completely (in one go)
to the end of the bush (Fig. 5). Upon completion of the
Fig. 1 Key components of the
Maxio robotic system
Fig. 2 InstaReg
TM
docking system for the Maxio. The alphabet “R”
indicates that the robot is docking at the right side of the CT gantry at
which the tumour is more conveniently accessed from the right of the CT
248 Eur Radiol (2015) 25:246–257
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insertion of the probe, the end effectors were detached from
the probe and the robotic arm was returned to its original
position.
A CT fluoroscopy check examination was performed to
ascertain the location of the ablation probe within the target
volume (Fig. 6). Ablation therapy was then started. For mul-
tiple lesions, the process of needle insertion was repeated as
determined by the treatment plan. The completeness of the
ablation was determined by using multiphasic contrast-
enhanced CT immediately after the ablation (Fig. 7).
Patient respiratory motion control
To optimize tumour localization, the baseline CT, CT fluoros-
copy check and post-ablation contrast-enhanced CT were all
performed at the end expiration of the patient, with the airway
disconnected from the ventilator. To minimise liver and hence
ablation probe excursion between the end expiration (when
needle placement was carried out) and the inspiration, the tidal
volumes were set at a high respiratory rate and high O
2
level
considered safe by the attending anaesthetist. Muscle relax-
ants were used regularly (especially when doing multiple
placements) to minimise spontaneous breathing of the patient
so that the end expiratory phases were consistent. Otherwise,
the loss of muscle paralysis would impair the end tidal volume
and place the liver at a much lower level.
Data collection and analysis
The orbital and cranio-caudal angulations of the robotic arm
were recorded for each lesion targeted in all patients. The
numbers of adjustment of the needle to achieve satisfactory
positioning within the desired tumour volume were docu-
mented. Deviations of the tip from the centre of the targeted
location were also recorded.
The performance level of the overall procedures was
assessed on a five-point scale (refer Table 1for the description
of the scoring scheme) by the interventional radiologist for
Fig. 3 Operational flow of the Maxio robotic system for interventional procedures
Eur Radiol (2015) 25:246–257 249
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each robotic-assisted thermal ablation. Any complications
related to the use of the robot or the procedures were also
recorded.
The CT fluoroscopic dose (DLP) received by the patients
during the probe placement and ablation was recorded. The
total CT dose from the whole procedure including the multi-
phasic CT studies was also recorded. The doses were then
compared with a random historical control group of 30 pa-
tients (48 lesions) who had liver radiofrequency or microwave
ablation performed by the same radiologist, but without using
the assistance of a robot for probe placement. Statistical anal-
ysis was performed using independent samples T-test with a
95 % confidence interval.
Results
Thermal ablation was successfully completed in 20 patients
with 40 lesions, and confirmed on multiphasic contrast en-
hanced CT. No complications related to either the use of the
robot or the thermal ablation were noted in this study. How-
ever, there was a single case of residual disease after the
ablation. Table 2demonstrates patient demography and treat-
ment protocols for all the patients.
The total number of lesions treated in each session ranged
from one to a maximum of five lesions (mean of 2±1). The
deepest lesion was 169 mm, while the shallowest was 40 mm
from the skin’s surface. The diameter of the lesions ranged
Fig. 4 Treatment planning and simulation on the Maxio’s workstation. a
Identification and segmentation of the first lesion (labelled as Tumour 1).
The CT images are displayed in axial (middle panel), coronal (top right
panel) and sagittal (bottom right panel) planes, while the 3D simulated
diagram is shown in the left panel of the treatment plan. bThe entry point,
target point, type of probe and targeted ablation volume were defined by
the interventionalist in the treatment plan. The pink straight line indicates
the trajectory of the ablation probe from the skin surface (entry point)to
the centre of the target volume (target point). The ablation volume is
calculated automatically by the software and indicated in the treatment
plan (shown as green spheres covering the tumour). cSegmentation and
treatment planning for the second lesion (labelled as Tumour 2). The
same planning procedures as for Tumour 1 are repeated. The simulation
for Tumour 1 can still be seen on the plan as reference. The indigo straight
line indicates the trajectory of the ablation probe for the second lesion. d
A complete plan for all the three lesions targeted in the same patient. The
simulated needle trajectories are shown in the images and carefully
checked through by the interventionalist prior to the RFA procedures
250 Eur Radiol (2015) 25:246–257
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from 5 to 49 mm (mean diameter 19×23 mm). The lesions
were all targeted successfully with the assistance of the robotic
device. The orbital angulations of the robotic arm ranged from
-49.4° to 65.1° (mean positive angulation was 25.1±17.8°;
mean negative angulation was -28.5 ± 16.0°). The cranio-
caudal angulations remained 0° in 24 lesions (15 patients),
while the remaining 16 lesions (five patients) had cranio-
caudal angulations that ranged from −11.9° to 36.8°
(mean positive angulation was 4.3±8.4°; mean negative
angulation was −10.3± 2.2°).
Readjustments of the probe were required in 12 of the 20
patients, with only a single repositioning in each of the lesions.
The average number of needle readjustment was 0.8 ± 0.8.
There were no cases of needle reinsertions required. The mean
performance level rated for the robotic-assisted ablation pro-
cedure was 4.4±0.6.
The total DLP per patient for the entire robotic assisted
thermal ablation was 1382± 536 mGy.cm, while the CT fluo-
roscopic dose per lesion was 352± 228 mGy.cm. When com-
pared with historical data from our standard ablation
procedure without the assistance of the robotic device, the
total DLP per patient (n=30) was 1611±708 mGy.cm, while
the CT fluoroscopic dose per lesion was 501± 367 mGy.cm.
Although the dose reduction was not statistically significant
different (p> 0.05), the total DLP, and CT fluoroscopic dose
per lesion were reduced by 14 and 30 %, respectively. Table 3
shows the comparison of patient radiation dose for robotic-
assisted versus non-robotic assisted thermal ablation
procedures.
Discussion
Percutaneous CT-guided intervention is an effective method
for image-guided biopsy and tumour ablation. However, the
accuracy of CT-guided needle or probe placement, which is
critical for good diagnostic yield, is highly dependent upon
physician experience. Additionally, the presence of vulnerable
anatomy (such as bowel, nerves or vessels in proximity to the
target) in the needle path has low tolerance for errors in needle
placement. With conventional techniques, challenging tumour
targeting frequently mandates multiple needle adjustments
and intra-procedural imaging, which can prolong procedure
duration as well as increase patient radiation exposure and
procedural risk [6,7]. Recent advances in robotically guided
interventions have been successful in assisting placement of
needles or related instruments for surgery and interventional
procedures [8–13].
For small tumours, such as HCC that are <3 cm, RFA has
been shown to achieve results comparable to surgical resec-
tion. However, its efficacy is reduced for larger tumours [14,
15]. This may in part be attributable to the complexity of
multi-probe placement (simultaneous or sequential), which
is prone to human error, as well as the greater heat sink effect
with larger, more perfused tumours. Accurate probe place-
ment is thus critical for successful large volume composite
ablation and a tumour-free margin [1,16].
Fig. 6 CT fluoroscopy check examination to verify the location of the ablation probe within the target volume for (a) Tumour 1 (b) Tumour 2
Fig. 5 The intervention radiologist inserted the RFA probe to the target
tumour through the bush located at the end-effector of the robotic arm
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Navigational software and robotic assistance may offer a
tailored solution to physicians confronting a technically chal-
lenging biopsy or ablation target. Early phantom and clinical
experiences with robotic navigation systems suggest proce-
dural accuracy, reduced procedure time and reduced patient
radiation exposure compared with freehand techniques
[3,4,17].
The robot used in this study was a CT-compatible 3D
tumour targeting and needle positioning system for interven-
tional radiology procedures. It is an improved version of its
predecessor, ROBIO Ex (Perfint Healthcare, Florence,
Oregon, USA), which only allows 2D visualization of the
axial images and single needle or probe access per treatment
plan. Additionally, the planning software has a multiplanar
capability, ensuring that better delineation of the centre of the
lesion can be achieved. The system calculates coordinates on
DICOM images from the CT console and guides the
placement of the needle accurately within the body using a
stereotactic device. The depth of needle placement is pre-
determined by the system, but the operator still has the option
of varying this for increased safety. The system can be used for
tumour targeting for abdominal and thoracic interventions,
including biopsy, fine needle aspiration cytology (FNAC),
tumour ablation, pain management and drainage.
While MR-compatible robots have also been developed
and provide many advantages such as non-ionizing
multiplanar imaging with hepato-specific contrast agents and
have the highest liver tumour contrast compared to CT and
ultrasound, they are, however, expensive and require all MR-
compatible equipment and accessories. Hence, access may be
limited and the robots currently only useful for lesions that are
not accessible by other methods [18,19].
Localisation and navigation systems performed with op-
tical or magnetic localisation spheres require multiple skin
markers to be broadly placed prior to imaging [20]. In
addition, pre-procedure import and processing of the 3D
data to the robot’s workstation can be complex and time
consuming and occupy a lot of space in the operation room.
Devices that are time consuming in terms of pre-arrangement
and usage are economically unattractive and are therefore not
likely to be used in daily routine. In contrast, the Maxio
requires minimal effort to be mounted and registered to the
CT device using the InstaReg™technology. The system is
motorised and can be operated by one person. These fea-
tures reduced the complexity of the robotic-guided proce-
dure. We found the overall satisfaction with the performance
of the system to be high. Furthermore, the planning software
on the Maxio system allows the segmentation of the tumour
and subsequent selection of the ablation probe (RFA or
microwave) with the pre-determined ablation volumes to
be overlaid on the target tumour. This adequacy of the
ablation can be checked in all three planes to determine
successful ablation. If this is found to be inadequate, the
tip of ablation needle can be repositioned or a different
probe selected.
Fig. 7 Comparison of (a) Pre-RFA contrast enhanced baseline CT; b
Post-RFA multiphasic contrast-enhanced CT. The ablated volume (red
dashed line) can be clearly seen on the multiphasic contrast-enhanced
scan to verify the completeness of the ablation; and (c) 3-month post-RFA
follow up showing reduction of the coagulation necrosis
Table 1 Scoring scheme for evaluation of the performance level of
robotic-assisted thermal ablation
Score Criteria
5•Successful ablation
•No needle repositioning
•Superior to the manual needle insertion technique
4•Successful ablation
•1 to 2 needle repositionings
•Superior to the manual needle insertion technique
3•Successful ablation
•3 to 4 needle repositionings
•Equivalent to the manual needle insertion technique
2•Successful ablation
•More than 4 needle repositionings or reinsertion of needle is
required
•Inferior to the manual needle insertion technique
1•Ablation could not be completed due to needle positioning error
•Unsuccessful needle insertion
•Inferior to the manual needle insertion technique
252 Eur Radiol (2015) 25:246–257
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Tab l e 2 Patient demography and treatment protocols of the robotic-assisted CT-guided thermal ablation for liver tumours (20 patients, 40 lesions)
ID Age Sex Diagnosis Thermal Ablation Treatment Baseline contrast- enhanced
CT scan (Yes or No)
Size of lesion (Short
Axis × Long Axis)
Depth of Lesion
from the surface
(mm)
Angulations (Degree)
Short axis (mm) Long axis (mm) Orbital (+) Orbital (−)cc(+)
1 74 M Low rectal cancer post-anterior resection
with liver metastases at segments V,
VI and VI
RFA using RITA system for
all the tumours
No 21 21 78 45.7
20 21 119 45.8 0.0
32 37 116 61.7 6.0
2 66 M Colorectal liver metastases at segments
VII, II, III and I
RFA using RITA system for
all the tumours
Yes 5 9 126 23.0 5.9
812 8926.2 3.2
16 24 43 20.3 0.0
6 6 153 40.8 0.0
3 74 M Colorectal liver metastases at
segments III
RFA using RITA system Yes 21 21 122 23.3 0.0
4 56 M HCC at segment IVa RFA using RITA system No 16 20 77 29.3 9.7
5 64 M HCC at segments VI, VII and VIII RFA using Cool-tip system
for all the tumours
No 27 35 116 22.8 0.0
23 29 152 44.7 0.4
21 43 104 35.8 0.0
6 61 M HCC post segmental hepatectomy,
new lesions at segments IVb and VIII
RFA using Cool-tip system
for all the tumours
No 11 13 112 22.5 0.0
13 14 81 49.4 0.0
14 14 94 30.8 17.3
7 55 F HCC at segment VII RFA using RITA system No 35 43 141 8.6 6.5
8 46 F Endometrial carcinoma with liver
metastases at segment VII
RFA using RITA system No 22 30 169 9.0 0.0
9 66 M Colorectal liver metastases at segments
V, VI, IIX, I and II
i. RFA using RITA system
for lesion V, VI, IIX and I
ii. RFA using Cool-tip system
for lesion II
Yes 1 9 2 3 71 5 . 5 0. 0
15 21 112 21.0
25 30 128 24.9 0.0
21 22 53 30.6 0.0
16 20 108 24.7 0.0
10 66 M Recurrent multicentric HCC at
segments III, VI and II
RFA using RITA system for
all the tumours
Yes 11 15 79 3 9 . 9 0. 0
32 38 105 6.8 3.3
10 11 128 1.8 0.0
11 41 F Breast metastases to the liver at
segments III, VI and VIII
RFA using RITA system for
all the tumours
No 12 12 40 2.1 0.0
20 23 86 35.2 0.0
17 19 68 0.8 26.1
12 32 F Multiple liver metastases from
gastrointestinal stromal tumour
at segments VII and V/VI
RFA using RITA system for
all the tumours
No 20 23 52 8.6 0.0
19 21 99 29.9 20.2
13 80 F Liver metastases at segments
VII and III
RFA using RITA system for
all the tumours
No 13 14 117 25.6 0.0
12 14 126 0.0 36.8
8 9 73 48.2 0.0
14 60 F Liver metastases at segment IV RFA using RITA system No 25 42 104 36.0 11.7
15 46 M HCC at segment VI/VII Microwave ablation using
Avecure 14G single cycle
Yes 45 49 98 11.5 4.6
16 54 M HCC at segment IIX/VI Microwave ablation using
Avecure 14G single cycle
No 26 38 92 20.4 0.0
17 56 F HCC at segment III RFA using Cool-tip system No 10 13 47 2.2 0.0
18 53 M HCC at segments VII/VIII Microwave ablation using
Avecure 14G single cycle
No 28 32 88 1.7 12.8
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Tab l e 2 (continued)
ID Age Sex Diagnosis Thermal Ablation Treatment Baseline contrast- enhanced
CT scan (Yes or No)
Size of lesion (Short
Axis × Long Axis)
Depth of Lesion
from the surface
(mm)
Angulations (Degree)
Short axis (mm) Long axis (mm) Orbital (+) Orbital (−)cc(+)
19 60 F Colorectal liver metastases
at segment III
Microwave ablation using
Avecure 14G single cycle
No 16 18 108 65.1 0.0
20 71 M HCC at segment V Microwave ablation using
Avecure 14G single cycle
Yes 22 23 86 44.1 0.0
Mean 19 23 99 25.1 28.5 4.3
Standard Deviation 8 11 31 17.8 16.0 8.4
Min 5 6 40 0.0 0.8 0.0
Max 45 49 169 65.1 49.4 36.8
ID Angulations (Degree) Number of
Needle
Insertions
Number of
Repositioning /
Readjustment
Performance Level (1
to 5, refer to scoring
scheme in Table 1)
CT Fluoroscopic Dose
(DLP, mGy.cm)
Tot al CT D ose
(CTDI
vol
,mGy)
Tot al C T Dos e
(DLP, mGy.cm)
CT Fluoroscopic
Dose, DLP
per Lesion
(mGy.cm)
Outcomes
cc (−)
1 11.9 3 1 4 1083 753 1860 361 Successful ablation
2 4 2 4 1712 1189 2084 428 Successful ablation
3 1 0 5 777 540 1191 777 Successful ablation
4 1 0 5 187 170 1218 187 Successful ablation
5 3 1 4 495 344 1458 165 Successful ablation
6 3 1 4 875 608 1030 292 Successful ablation
7 1 0 5 164 114 815 164 Successful ablation
8 1 1 4 614 426 1725 614 Successful ablation
9 5 3 3 1597 1109 2699 319 Successful ablation
8.8
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Tab l e 2 (continued)
ID Angulations (Degree) Number of
Needle
Insertions
Number of
Repositioning /
Readjustment
Performance Level (1
to 5, refer to scoring
scheme in Table 1)
CT Fluoroscopic Dose
(DLP, mGy.cm)
Tot al CT D ose
(CTDI
vol
,mGy)
Tot al C T Dos e
(DLP, mGy.cm)
CT Fluoroscopic
Dose, DLP
per Lesion
(mGy.cm)
Outcomes
cc (−)
10 3 1 4 717 498 2042 239 Successful ablation
0.0
11 3 1 4 461 320 969 154 Successful ablation
12 2 2 4 1446 1005 1996 723 Successful ablation
13 3 0 5 1136 789 1554 379 Successful ablation
14 1 1 4 284 197 811 284 Successful ablation
15 1 1 4 128 89 851 128 Successful ablation
16 1 0 5 729 508 1142 729 Successful ablation
17 1 1 4 589 1312 701 589 Successful ablation
18 1 0 5 45 31 1018 45 Successful ablation
19 1 0 5 418 290 1080 418 Successful ablation
20 1 0 5 54 37 1391 54 Successful ablation
Mean 10.3 2.0 0.8 4.4 676 517 1382 352
Standard Deviation 2.2 1.3 0.8 0.6 505 396 536 228
Min 8.8 1 0 4 545 31 701 45
Max 11.9 5 3 5 1712 1312 2699 777
F = Female; M = Male; HCC = Hepatocellular carcinoma; RFA = Radiofrequency ablation; CC = Cranial-caudal angle; Min = Minimum; Max = Maximum
Eur Radiol (2015) 25:246–257 255
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As was previously reported [3], the greater control and ease
of needle placement outside the bore of the CT gantry without
exposure to CT fluoroscopy dose was again a tremendous
benefit. This is especially helpful in patients who are large,
as well as for the lesions that require more lateral access of the
needle. Even though none of the patients in this study required
placement of multiple probes simultaneously, we believe this
system will be truly beneficial when multiple probes/needles
are necessary for the treatment, e.g., Cool-tip RFA needles
with a switching controller. Additionally, robotic-assisted in-
terventions would be useful for those who do not have access
to CT fluoroscopy during the procedures.
Although our study showed no significant differences of
patient radiation dose between robotic-assisted and conven-
tional thermal ablation, this may be related to the expertise of
the operatorin this study. Previous studies noted the decreased
accuracy of inexperienced operators when placement of the
needles was performed manually under the guidance of CT
fluoroscopy [21,22]. Certain impreciseness during manual
needle insertion is unavoidable. The continuous reassessment
and repetitive adjustment of the needle orientation under the
guidance of CT fluoroscopy could lead to an increase in
radiation exposure to the patients as well as the attending staff.
With the assistance of the robotic positioning device, the direct
radiation exposure to the interventionist’s hands during needle
insertion could be minimized. The radiation exposure to the
operators was not assessed in this study, but theoretically the
staff dose decreases when the CT fluoroscopy dose decreases.
A randomised controlled study with a larger sample size
would be necessary to confirm this.
A critical part of the capability of the Maxio system is in
ensuring accurate co-registration of the planning data sets with
liver volume at the time of needle insertion, as the system is
still not able to compensate for movements of the target
region, especially those caused by respiration, since the
planned trajectory is based on a static-acquired 3D data set.
This co-registration in our practice was achieved by
performing all procedures under general anaesthesia with
intubation and muscle relaxants at the end of expiration, with
the airway disconnected from ventilator-produced consistent
positing. The muscle relaxants were used regularly, especially
when doing multiple placements. Otherwise, the loss of mus-
cle paralysis would impair the end tidal volume and place the
liver at a much lower level. The baseline CT, needle placement
and post-procedure CT acquisitions were all performed at the
end of expiration once the ventilator was disconnected. Others
have suggested that anaesthetic manoeuvres, such as high
frequency jet ventilation to reduce respiratory motion, signif-
icantly reduce radiation dose [23]. However, these systems are
expensive and require a greater skill set. Additionally, we used
low tidal volumes with high respiratory rate and high O
2
to
minimize liver excursion and needle movement in the cranio-
caudal direction.
The use of robots to assist in thermal ablation may require a
major change to the current workflow, with additional steps to
the procedure. These include docking the robotic system,
importing the images from the CT console into the worksta-
tion, segmenting the tumour, planning the entry and target
points, inputting the length of the needle, and finally sending
the information to the robotic arm. Thus, there would be a
need to redefine the roles of different members of the medical
team with use of robotic assisted thermal ablation. A compre-
hensive work flow chart, with staff being well trained in
operating the robot, also needs to be established.
In conclusion, we present our early clinical experience of
thermal ablation for primary and secondary liver tumours
using an advanced CT-guided robotic system. The system
showed good accuracy for percutaneous needle placement
for ablative therapy, with a radiation dose comparable to the
historical controls. Even though these preliminary data were
promising, the study was not randomised. A randomised
controlled study with a larger sample size comparing robotic
and non-robotic-assisted thermal ablation needs to be carried
out to determine the outcomes.
Acknowledgements The scientific guarantor of this publication is
Basri Johan Jeet Abdullah. The authors of this manuscript declare rela-
tionships with the following companies: Perfint Healthcare Pvt Ltd,
Florence, Oregon, USA. The authors state that this work has not received
any funding. No complex statistical methods were necessary for this
paper. Institutional Review Board approval was obtained. Written in-
formed consent was obtained from all subjects (patients) in this study.
Approval from the institutional animal care committee was not required
because no animal was used in this study. Some study subjects or cohorts
have been previously reported in the European Congress of Radiology
(ECR), Vienna, on 6 March 2014. Methodology: prospective, case-
control study, performed at one institution.
Tabl e 3 Comparison of total
DLP per patient and CT fluoro-
scopic dose per lesion of robotic-
assisted versus non-robotic-
assisted thermal
ablation procedures
Robotic-assisted
thermal ablation
(n=20)
Non-robotic-assisted
thermal ablation
(control group, n=30)
Dose reduction
with robotic
assistance (%)
P-value
Total DLP per patient (mGy·cm) 1382±536 1611±708 14 P>0.05
CT fluoroscopic dose per lesion
(DLP, mGy·cm)
352± 228 501± 367 30 P>0.05
256 Eur Radiol (2015) 25:246–257
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