nanotechnology 148-21may

Investigation of Nanoparticle Properties in Enhancing Hyperthermia

Treatment

Maged A. Aldhaeebi, Mohammed A. Alzabidi, and Ibrahim Elshafiey

Abstract—Nanoparticles attract the attention due to their

potential of enhancing energy localization in hyperthermia

cancer treatment. The electrical properties of the tumor can be

controlled by introducing nanoparticles into the tumors.

Investigation is provided here of the effect of tumor properties

on the specific absorption rate (SAR) inside the tumor at

various frequency values. The study considers the electrical

and magnetic conductivity values, in addition to the dielectric

and magnetic properties of the tumor. Computational analysis

is performed under SEMCAD X environment of four antipodal

Vivaldi antennas surrounding a human phantom. The results

reveal that the specific absorption rate (SAR) is increased as

the permittivity is decreased. Moreover, SAR is increased as

the electrical conductivity increased in the range up to 10 S/m

before starting to decrease. The SAR is shown to be maximized

when the magnetic conductivity equals to electrical

conductivity.

I. INTRODUCTION

Hyperthermia is an emerging therapeutic plan that is

used to enhance cancer treatment using temperature increase

in the range 40–45°C to damage tumor cells. In spite of the

potentials of this modality to enhance cancer treatment and

reduce the side effects associated with the chemotherapy and

radiotherapy, various challenges still face the development of

hyperthermia. First, energy delivery to deep tumors non-

invasively using exterior applicators is a major challenge.

Confining thermal energy to tumor regions to reduce the side

effects on healthy tissue is also a challenge that hinders the

progress of hyperthermia.

Heating mechanisms based on the electromagnetic fields

EM are attractive for hyperthermia treatment. The EM

energy used in hyperthermia is usually classified by

frequency as either microwave energy or RF energy. The

most commonly used microwave frequencies are the ISM

(industrial, scientific, and medical) frequency values of 433

and 915. Common RF frequencies are 13.56 and 27.12

MHz. With limited penetration in human tissue, frequencies

higher than 2450 MHz have no practical value.

EM energy is very effective in heating cancerous

tumors, because tumors typically have high-water content.

Such tissue heats very rapidly when exposed to high-power

microwaves. Furthermore, EM can be delivered to tissue by

special-purpose antennas that are located adjacent to the

patient’s body.

Depending on the tumor size and location in the body,

one or more microwave antennas can be used to treat the

tumor. Localizing EM energy to tumor location can be

obtained by Placing the seeds in a deep tumor may be

difficult and Application of magnetic materials in hyper-

thermia was introduced by Gilchrist [1].

Hyperthermia therapy based on nanoparticle (NP) has

been developed as a promising therapeutic approach for

cancer treatment [2]. As therapeutic delivery systems,

nanoparticles allow targeted delivery and controlled release.

For diagnostic applications nanoparticles allow detection on

the molecular scale: they help identify abnormalities such as

fragments of viruses, precancerous cells, and disease markers

that cannot be detected with traditional diagnostics [3].

Magnetic nanoparticle were used to perform heat therapies

since 1960s. With a frequency value of usually hundreds of

kilohertz, magnetic nanoparticles can be used for localizing

heating of nanoparticle-containing tissue [4].

Nanoparticles thus form the most promising approach to

enhance the performance of electromagnetic hyperthermia

[5]. Application of nanoparticles brings hope to enhance use

of hyperthermia during the upcoming decade, providing the

attractive features. First, nanoparticles provide the capability

of achieving highly localized heating of the tumor, which

allows to preserve the integrity of the surrounding healthy

tissue. Second, they provide minimally invasive techniques

by which the nanoparticles can be delivered to the tumor,

such as intra-tumoral injection or biochemical targeting [6]

and [7].

The variety of nanoparticles types brings hope to

expedite the progress of EM hyperthermia. Microwave

heating was investigated at 2.45 GHz for six types of

nanoparticles [8]. The use of magnetic nanoparticles can

overcome the difficulty in spatial adjustment of power

absorption by cancerous tissue and magnesium nanoparticles

were also proposed for enhancing cancer hyperthermia

therapy, due to their high heat conductivity and uniquely

perfect biodegrade-bility [9].

This paper aims to investigate the possible role of

nanoparticles in hyperthermia treatment by studying the

effect of tumor properties on the SAR values. Various

material parameters are investigated include the relative

permittivity, relative permeability, the electrical conduc-

tivity, and the magnetic conductivity. The simulation is

performed using the SEMCAD X environment [10]. The

paper is organized as follows: Section II introduces the

basics of the specific absorption rate. Section III discusses

the phantom model and antenna design. Section IV

discusses the results. Finally, conclusions are provided in

Section V.

This research work is supported by the National Plan for Science and

Technology, Kingdom of Saudi Arabia, under project no: 10-ELE996-02

[email protected],[email protected] and ishafiey @ksu.edu.sa, Department of Electrical Engineering, King Saud University,

Riyadh, Saudi Arabia

mailto:[email protected]




II. SPECIFIC ABSORPTION RATE (SAR)

SAR is a quantity that describes the amount of absorbed

radiated effect for a specific material at a certain frequency

[11]. The specific absorption rate (SAR) is an index that

quantifies the rate of energy absorption in biological tissue. It

is the power absorbed per unit of volume, P in a tissue

normalized to its density to have the ratio of power absorbed

per unit mass of tissue, and it is proportional to the ratio

between conductivity and density of the exposed tissue as

shown in the equation:

(1)

Where P is the power absorbed in the tissue [W]; is the

mass density of the medium [kg/ m3], is the electrical

conductivity [S/m], and |E| is the rms magnitude of the

electric field strength vector [V/ m] [12].

III. ANTENNA DESIGN

An Antipodal Vivaldi Antenna is used as hyperthermia

applicator in this research. The antenna is created on a

dielectric substrate with two-sided metallization. Feeding

part is a microstrip line, followed by a microstrip to balanced

strip line (twin line) transition. This strip line serves as a

feed to the antipodal exponentially tapered fins. Fins are

arranged in such a way, that from a point of view

perpendicular to the substrate plane, they create a flared

shape [13]. The antenna has inner and outer edge of the

tapers which are defined according to the following

equations:

(2)

(3)

The overall size of the antenna is of 82x94x1.6 mm

which are fed by SMA connector. The substrate has

dielectric permittivity 4.3. Teflon is used as coaxial isolation

of SMA connector. The simulation is performed under

SEMCAD-X [10]. Figure 1 shows illustration of the antenna.

A model a considered with four antennas surrounding a

cylindrical phantom. The spherical model is considered for

the tumor with a diameter of 10 mm. The overall model

structure is shown in Figure 2.

Figure1 . Structure of the designed UWB antenna. Dimensions in mm.

Figure2 . Illustration of the proposed model.

IV. RESULTS

To investigate the possible effect of nanoparticles on the

tumor, various values are used of the relative permittivity

( = 28, 33, 38, 43 and 48), and electrical the electrical

conductivity ( = 0.3, 0.5, 1, 2, 10, 20, 50, 200, 500, and

1000). Figures 3 to 6 present the SAR values at frequency

values of 250MHz, 500MHz, 750MHz, and 900 MHz

respectively. The figures reveal that the SAR is highly

affected by the electrical conductivity while minimal effect is

observed for the permittivity variation. Table 1 presents the

nominal, and maximum obtained SAR values. The nominal

values were obtained for relative permittivity of 38 and

electrical conductivity of 0.5 S/m. The maximum SAR

values were found to occur at relative permittivity of 28,

electrical conductivity of 2 S/m for frequency values of 250

MHz, 500 MHz, and 750 MHz. For 900 MHz the maximum

SAR was found to occur at relative permittivity of 48, while

the conductivity remained at 2 S/m.

Figure3 . SAR levels for various values of relative permittivity, and electrical conductivity at f=250MHz.

Figure4 . SAR levels for various values of relative permittivity, and

electrical conductivity at f=500 MHz.


electrical conductivity at f=750 MHz

b


electrical conductivity at f=900 MHz.

TABLE I. NOMINAL, MAXIMUM AND PERCENTAGE SAR AT DIFFERENT

FREQUENCY VALUES.

Frequency

[MHz.]

Nominal

SAR (w/kg)

Max.

SAR(w/kg)

Percentage

SAR Increase

250 9.02901 17.8343 97.522

500 2.66368 6.54564 145.74

750 0.425977 1.22105 186.65

900 0.261675 0.782 198.84

Since the electrical conductivity were found to be

effective in enhancing SAR values, its effect was further

investigated as shown in Figures 7 to 10. Gradual increase

of SAR was noticed with increasing the electrical

conductivity up to a value of equal 2 S/m, and then the SAR

values start to decrease. Minimal effect is noticed for the

relative permittivity with slight enhancement of SAR

obtained as the relative permittivity decreased.

Figure7 . Relationship between SAR, relative permittivity, and electrical

conductivity when the relative permeability = 1, and zero magnetic

conductivity for=250MHz.


conductivity when the relative permeability = 1, and the magnetic conductivity is zero for=500MHz.


conductivity when the relative permeability = 1, and the magnetic conductivity is zero for=750MHz.


conductivity when the relative permeability = 1, and the magnetic

conductivity is zero for=900 MHz.

Fig. 11 illustrated the effect of larger values of electrical

conductivity, where the SAR approached asymptotically a

low value.


conductivity when the relative permeability = 1, and the magnetic

conductivity is zero for=250 MHz.

Fig.12 shows the relationship between the relative

permeability and SAR at different frequency values. The

maximum value of SAR is obtained as expected at the lowest

frequency value of 250MHz. The magnetic conductivity is

investigated and the results are shown in Figure 13. An

interesting result is to find that the optimum value of SAR is

obtained when the magnetic conductivity is equal to the

electrical conductivity.

Figure12 . SAR vs. relative permeability. The relative permittivity is 38,

the electrical conductivity = 0.5 S/m, and the magnetic conductivity

=0 (S/m)-1.

Figure13 . SAR vs. magnetic conductivity where the relative permittivity = 38, the electrical conductivity = 0.5(S/m), and the relative

permeability = 1.

Figures 14 to 18 show the distribution of the SAR inside

the tumor for both nominal values of relative permittivity

and electrical conductivity (r=38, and =0.5 S/m). The

distribution obtained for maximum SAR values are shown in

Figures 19 to 21.

The SAR distributions shown in the figures clearly reveal

the effect of frequency value on achieving better penetration.

However, at 500 MHz good distribution of the energy is

obtained which is related to the better interference of the

field obtained from the four source antennas.

Figure14 . Nominal SAR distribution in dB when the relative permittivity=

38, the electrical conductivity = 0.5 S/m and f=250MHz. 0 dB

corresponds to 9.03 W/kg. Distance dimensions are in m.


38, the electrical conductivity = 0.5 S/m and f=500 MHz. 0 dB



38, the electrical conductivity = 0.5 S/m and f=750MHz. 0 dB



38, the electrical conductivity = 0.5 S/m and f=900 MHz. 0 dB


Figure18 . Maximum SAR distribution in dB when the relative

permittivity= 28, the electrical conductivity = 2 S/m and f=250 MHz. 0 dB corresponds to 17.83 W/kg. Distance dimensions are in m.


permittivity= 28, the electrical conductivity = 2 S/m and f=500 MHz.

0 dB corresponds to 6.55 W/kg.



0 dB corresponds to 1.22 W/kg. Distance dimensions are in m.



0 dB corresponds to 0.78 W/kg. Distance dimensions are in m.

V. CONCLUSION

In this paper, the potentials of using nanoparticles in

enhancing hyperthermia treatment of cancer are investigated.

From the results the tumor electrical properties are shown to

be essential in controlling the deposited EM energy and

achieving high SAR values. In particular, the electrical

conductivity is found to increase the SAR values when they

are optimally chosen. Moreover, the magnetic conductivity is

also found to play an important role in controlling the SAR

values. Identifying the optimum values of tumor electrical

properties can help guide the choice of nanoparticles to be

used in localizing the EM energy in tumor location and thus

enhance the hyperthermia treatment plans.

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nanotechnology 148-21may

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