A Basic Investigation of Cancerous Breast Microwave Ablation
Using Opened-tip Applicator and Ex Vivo Experiment.
A. Sanpanich 1,2, P. Phasukkit 1, D. Sueaseenak 3, Y. Kajornpreedanon 2, K. Hamamoto 4, and C. Pintavirooj 1
1

1

Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang, THAILAND
2
Institute of Molecular Biosciences, Mahidol University, THAILAND
3
Faculty of Engineering, Srinakharinwirot University, THAILAND
4
School of Information and Telecommunication Engineering, Tokai University, JAPANIntroduction

Cancer in female breast was realized as one of the mainhealth hazard that threatening women around the world formany year [1]. Besides from a conventional intervention
surgery, thermal ablation in microwave frequency range waswidely accepted as an another alternative medical treatment due
to its minimal invasive maneuver and using only bipolar antennaprobe technique [2,3]. Some research groups propose theirstudies both in simulation phase and only a few with a realexperiment [2-5]. In this research, we propose an analysis of
FEM and a valid ex vivo real experiment of an opened-tip
microwave antenna for using in breast cancer ablation.
Consideration to a tissue destructive shape, we intently design
our microwave applicator as a conventional opened-tip antenna[6, 7]. At first, materials, dimensions and characteristic in termof VSWR of this antenna was investigated. Then, a complicatedCAD model of cancerous breast tissue was originally proposedby our group in this research in which compose of a tumor cellin a multi-layer mammalian tissue. By using FEM of COMSOL
solver, we have analyzed a distribution pattern of SAR,
temperature and estimated destructive breast tissue region withrespect to bioheat effect and phenomenon of an electric field in
living tissue. These all implementations were able to show intrue full 3D tissue space. Furthermore, we also confirm oursimulation by an ex vivo real ablation of female swine breast
with enhancing an applicator insertion by ultrasound-guidedimage. During ablation process, temperature generated frommicrowave heat was also monitored and finally a burning lesionof swine tissue was declared.

Table 1. Dimensions and materials of opened-tip applicator
Dimension/material
Dimension/materialsizesize
Diameter of outer conductor – D1
3.581
Length of antenna (L1)
60(Silver plated copper clad steel)mm.
mm.
Diameter of dielectric – D2
2.985
Length of outer (L2)40(Solid PTFE)mm.
mm.
Diameter of inner conductor - D3
0.912 Length of open slot (L3)20
(Silver plated copper clad steel)
mm.
mm.

2.2

Cancerous Breast ModelIn this research, cancerous breast phantom model which
originally created by our research group was designed by using
CAD program. We introduced an ideal to insert a small size (1.5centimetres in cubic shape) of maglinant tumor in between amulti-layer of female breast tissue [8]. As a preliminary model,
this tumor was located at approximately 2 centimetres below
breast tissue surface. Then, our opened-tip type applicator was
supposed to be inserted through the middle of this tumor. Figure
3 shows subdomain geometry of CAD breast phantom model
while meshing refinement is shown in Fig. 4. Table 2 showsmain physical properties of breast tissue and materials for FEM
simulation [8, 9].
Applicator
Skin – 0.3 cm.
Fat – 2 cm.
Glandular tissue – 2 cm.
Muscle – 1 cm.

2Finite Element Analysis Implementation

The implementation of FEM was primarily performed to anapplicator design then following by cancerous breast phantom
modelling and definition of governing control equation.

Tumor – 1.5 cm.

Fig. 3. Cancerous breast
tissue subdomain geometry model.

Table 2. Physical parameters of breast tissue and applicator for
FEM simulation
Tissue /Conductivity
Permittivity
Material( ⁄ )
( ⁄ )
Skin
1.464
38.007
Fat0.10452
5.2801Glandular tissue
1.967957.201
Muscle1.738852.729Tumor
450
Dielectric
0
2.03

2.1

Opened-tip Applicator Design
Coaxial opened-tip antenna type (COT) was selected as anapplicator in our microwave ablation since its propagation
pattern is quite predictable to a desire destructive area. Figure 1
shows an antenna structure while the dimensions and materials
are shown in Table 1. Return loss factor was also simulated at
microwave frequency range and show voltage standing wave
ratio (VSWR) response in Fig.2.
L2

L3

2.3

L1
outer conductor
dielectric
inner conductor

Fig. 4. Breast modelling andmeshing refinement.

D1

D2

D3Fig. 1. Applicator structure.

Fig. 2. VSWR of COT
applicator.

Governing Equation
All governing equation in our FEM analysis was strictly
derived with respect to bioheat effect, SAR criteria andmicrowave phenomenon in living tissue. These solutions werepresented in (1,2) [7] as following.
·1
Where is a conductivity of tissue ⁄ ,is an electric⁄field ⁄and is a density of tissue. This term
generally used to indicate a heating ability of microwave
antenna or imply as heat generated by an electric field in livingtissue. In this research, SAR can be applied as an external heatsource in bioheat consideration and derived into heat equation
as shown in (2).
···Ablation Experimental Results
To clarify our simulation proposal, we have implemented an
ex vivo real ablation of our opened-tip applicator to a piece offemale swine breast with our in-house microwave ablation
prototype system and Bird site analyzer SA-6000EX as shownin Fig.8. The applicator insertion into swine breast wasenhanced by using ultrasound-guided viewing (Aloka SSD-1700
Dynaview). Figure 9 shows tissue ablation lesion using 50 Watts
at 2.45 GHz for 180 seconds. Rising of heat temperature inswine tissue was also monitored continuously from 2 observedsites by using Fluke 54 II thermometer as shown in Fig. 10.

2

Where is a specific heat of tissue ⁄, is a thermal⁄
conductivity of tissue,
is a temperature of tissue° ,is a blood temperature ° andis a convective heat⁄transfer coefficient.
2.4

FEM Analysis
In this research, we use COMSOL Multiphysics (version3.5a) solver to implement FEM analysis. Simulation module
was selected on RF module with a harmonic propagation andalso heat transfer module of living tissue. Microwave frequency
was preset at 2.45 GHz according to ISM criteria. Thesimulation was truly performed in full 3D tissue space on Corei5 2.5 GHz desktop computer and 16 GB RAM.
3

3.2

Simulation and ex vivo experimental results

The simulation and real experimental results in this researchwere presented as following.
3.1

Simulation Results
In this simulation, a number of meshing elements wascompromisingly refined at 55,396 elements in tetrahedral shapewith 334,905 degree of freedoms and the solution time is about
755 seconds. Figure 5, 6 and 7 shows SAR, temperature
distribution pattern and estimated destructive tissue shape atopened-slot site in full 3D space after 180 seconds of 2.45 GHz
microwave ablation at 50 Watts.

Fig. 9. Ablation of female swine
breast by the bending applicator using
2.45 GHz at 50 Watts for 180
seconds.

4

References
[1]
[2]

[4]

[5]
Fig. 6. Temperature distribution
pattern.
[6]
Desktop PC

Temperature
meter

Microwave
source 2.45
GHz MCTsystem[7]

MWWatts
meter

Swinebreast

Fig. 7. Estimation ofdestructive breast phantom modelin 3D tissue space.

Fig. 8. Ex vivo real ablation
experimental setup.

Discussion and Conclusion

By using FEM, we propose a design of opened-tip antenna
and a complicated cancerous breast phantom model in an
investigation of breast cancer ablation. Validation of oursimulation is also performed with ex vivo real ablation in female
swine breast. From this proposed research, these outputs not
only show a promising result of both simulation and realexperiment but also encourage us to develop an advancemicrowave ablation system for using in breast cancer
hyperthermal treatment in near future.

[3]

Fig. 5. SAR distribution pattern.

Fig. 10. Monitored temperatureduring microwave ablation.

[8]
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