ߘߩઁ⎇ⓥಽᜂ⠪ߩ⊒⴫⺰ᢥ⎇ⓥ⺖㗴ฬ㧦⥄↱㔚ሶ࡟࡯ࠩ࡯ߩᲕ⚦⢩ലᨐߦ㑐ߔࠆ⎇ⓥ⎇ⓥઍ⴫⠪㧦↰ਛ ⦟᣿ (ᣣᧄᄢቇකቇㇱ)(1) ↰ਛ⦟᣿,ᴡ቞ᰴ㇢,ᐔጊ㆏ሶ,೨ᨋବ਽,; "᡼኿✢ᗵฃᕈࠍ㜞߼ࠆߚ߼ߩ⥃ᐥ⊛Ꮏᄦ", ≸ߩ⥃ᐥ,
2000, 46(3), 219-222(2) Hiraoka M, Mitsumori M, Hiroi N, Ohno S, Tanaka Y, Kotsuka Y, Sugimachi K,; "Development of RF
and microwave heating equipment and clinical applications to cancer treatment in Japan", IEEE
Transactions on Microwave Theory and Techniques, 2000, 48(11),1789-1799(3) ㆙⮮ჽᐔ,ự↰ᢘ᳗,㡞ේବᄥ㇢,ᷰㄝ૫ᴦ,ਛ㉿⑲ผ,ᷰㄝஜ৻,㋈ᧁિ,㊁ญ㓶੖,ᧁ↰੫♿,↰ਛ⦟᣿,ᴡ቞ᰴ㇢,;"ㅴⴕਅຜ㗡㨯㗪ㇱ㘩㆏≸ߦኻߔࠆᾖ኿ൻቇ≮ᴺߩᬌ⸛",㗡㗪ㇱ⣲≌,2001,27(1), 1-8(4) Karasawa K, Kaizu T, Niibe Y, Ishikawa H, Okamura T, Tanaka Y,; "Intrathoracic
thermochemoradiotherapy for the treatment of locally-advanced malignant pleural mesotheliomaTreatment protocol and report of the three cases", Jpn J Hyperthermic Oncol, 2001, 17(1), 45-52(5) ⮮੗రᓆ,↰ਛ⦟᣿,ᴡ቞ᰴ㇢,ፉ↰⵨ม,ਛ᧛㆏ሶ,೨ᨋବ਽,ᣧဈ๺ᱜ,ᅏ⇌ᅢቁ,;"࡜ࠗ࠽࠶ࠢߦࠃ
ࠆࠛ࠶ࠢࠬ࠽ࠗࡈࠍ↪޿ߚቯ૏᡼኿✢ᾖ኿ߩ⃻⁁ߣዷᦸ",ᣣᄢකቇ㔀⹹, 2001,60(3), 162(6) Niibe Y, Karasawa K, Kaizu T, Ieki R, Ishikawa H, Tanaka Y,; "Three-dimensional conformal radiation
therapy for lung tumors using a middle fraction size: Preliminary results", J Jpn Soc Ther Raiol Oncol,
2003, 15(1),17-21(7) Karasawa K, Kaizu T, Niibe Y, Igaki H, Shinohara M, Tanaka Y, Matsuda T,; "Rotational 3D-conformal
radiation therapy (conformation therapy) combined with hormone therapy for the treatment of stage
B2/C prostate cancer in Japanese men", Int J Radiat Oncol Biol Phys, 2003, 56(1), 208-212(8) ↰ਛ⦟᣿,; "ේ૕ᾖ኿⊒ዷߩ⿷〔ߣ੹ᓟߩዷ㐿", ᣣ᡼⣲ળ⹹, 15(4), 251-262(9) Niibe Y, Karasawa K, Nakamura O, Shinoura N, Okamoto K, Yamada R, Fukino K, Tanaka Y.; "Survival
benefit of stereotactic radiosurgery for metastatic brain tumors in patients with controlled primarylesions and no other distant metastases", Anticancer Res, 2003, 23(5b), 4157-4159(10) Yokoyama T, Yoshino A, Katayama Y, Watanabe T, Kashima Y, Yoshikawa T, Kawamori J, Tanaka Y,;"Metastatic pituitary tumor from renal cell carcinoma treated by fractionated stereotactic
radiotherapy-case report-", Neurol Med Chir (Tokyo), 2004, 44(1), 47-52⎇ⓥ⺖㗴ฬ㧦㔚ሶ✢ߦࠃࠆㆮવሶ៊்ߦ㑐ߔࠆ⎇ⓥ⎇ⓥઍ⴫⠪㧦⨃ํ ๟ (ᣣᧄᄢቇᱤቇㇱ)(1) Y.NAKAMURA, S.NOSAKA, M.SUZUKI, NAGAFUCHI, T.TAKAHASHI, T.YAJIMA,
N.TAKENOUCHI-OHKUBO, T.IWASE and I.MORO. Dietary fructooligosaccharides up-regulate
immunoglobulin A response and polymeric immunoglobulin receptor expression in intestines of infantmice. Clin Exp Immunol 2004; 137: 52-58(2) Arihiro Iwata, Takashi Iwase, Yoshitaka Ogura, Tomihisa Takahashi, Naoyuki Matsumoto, Toshiyuki
Yoshida, Nobuhiro Kamei, Kunihiko Kobayashi, Jiri Mestecky, Itaru Moro. Cloning and expression of
the turtle (Trachemys scripta) immunoglobulin joining (J)-chain cDNA. Immunogenetics (2002)
54:513-519(3) T. Takahashi, M. Kimura, N. Matsumoto, A. Iwata, Y. Ogura, T. Yoshida, N. Kamei, K. Komiyama, J.
Mestecky, and I. Moro. Cloning of the Chicken Immunoglobulin Joining (J)-Chain Gene andCharacterization of its Promoter Region. DNA and Cell Biology, 21(2), 2002, 81-90

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 48, NO. 11, NOVEMBER 2000

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Development of RF and Microwave Heating
Equipment and Clinical Applications toCancer Treatment in Japan
Masahiro Hiraoka, Michihide Mitsumori, Naotoshi Hiroi, Shinji Ohno, Yoshiaki Tanaka,
Youji Kotsuka, Senior Member, IEEE, and Keizo Sugimachi

Abstract—Development of RF and microwave (MW) heating
equipment for hyperthermia and their clinical applications tovarious cancers undertaken in Japan have been reviewed inthis paper. Originally developed heating devices include an RF
capacitive and RF inductive heating device, an MW heating device
with a lens applicator, an RF intraluminal heating device, an RF
current interstitial heating device, and a ferromagnetic implantheating device. The concept and characteristics of those devices
are described herein. Nonrandomized and randomized trials
undertaken for superficial and deep-seated tumors demonstrated
improved local response with the combined use of hyperthermia.
Furthermore, the complications associated with treatment were
not generally serious, except for chronic bowel damages suggested
in a trial for colorectal cancers. These clinical results indicate thebenefit of combined treatment of hyperthermia and radiotherapy.
With the advancement of heating and thermometry technologies,
hyperthermia will be more widely and safely used in the treatmentof cancers.
Index Terms—Capacitive heating, clinical trial, hyperthermia,
inductive heating, intaluminal heating, interstitial heating.

I. INTRODUCTION

D

URING THE past two decades, hyperthermia in combination with radiotherapy or chemotherapy has been
investigated basically and clinically as a new cancer treatment
modality. Numerous biological experiments demonstratestrong biological rationale for the use of hyperthermia in cancer
therapy [1], [2].
Problems related to the physics and engineering of hyperthermia have also been investigated. Many kinds of heating techniques and methods for accurately measuring temperature inside the human body have been studied, particularly in the past
decade. Most of these efforts seem to have been focused on thedevelopment of an applicator capable of heating deep tumors
with accuracy. However, there are several problems that make it
difficult to achieve deep and accurate heating. These problems
Manuscript received October 30, 1999; revised May 20, 2000.
M. Hiraoka, M. Mitsumori, and N. Hiroi are with the Department of Therapeutic Radiology and Oncology, Graduate School of Medicine, Kyoto University, Kyoto 606-8507, Japan.
S. Ohno and K. Sugimachi are with the Department of Surgery II, Kyushu
University, Fukuoka 812-8582, Japan.
Y. Tanaka is with the Department of Radiology, Nihon University School of
Medicine, Tokyo 173- 8610, Japan.
Y. Kotsuka is with the Department of Telecommunications, Faculty ofEngineering, Tokai University, Kanagawa 259-1292, Japan (e-mail: ykotsuka@keyaki.cc.u-tokai,ac.jp).
Publisher Item Identifier S 0018-9480(00)09529-6.

include skin-depth restriction based on the skin effect and thepresence of insulating materials such as lipid, protein, and bones
in the human body for dielectric-type heating. In addition, eddy
currents cause hot spots in unexpected regions.
As for techniques of measuring temperature, both invasive
and noninvasive methods have been investigated. Invasive thermometers need lead wires to couple them either electricallyor optically to an external monitor. The invasive thermometers must be sterilized prior to insertion into the patient. The
patient tolerance for needle insertion is often low, limiting thenumber of measurement points in the tumor and, thus, limiting
the thermal dose assessment. Among invasive methods, there
are thermometers using thermocouples, thermistor, and fluorescent materials. Noninvasive thermometers include those that explore the use of magnetic resonance imaging (MRI) and microwave (MW) radiometry [3], [4]. These promising methods
are under development.
In Japan, development of heating devices have been intensively investigated, including an RF capacitive and an
microwave heating (MWH) device with a lens applicator,
an RF intraluminal heating device, an RF current interstitialheating device, a ferromagnetic implant heating device, and
MW interstitial heating devices. The former three devices havebeen approved as medical equipment for the clinical use from
the Ministry of Health and Welfare of Japan. Hyperthermic
treatment for cancer using electromagnetic (EM) waves is
now covered by health insurance in Japan, and a large amountof clinical data has been accumulated. In this paper, we will
discuss heating devices developed in Japan, and also describe
the current status of clinical applications in cancer therapy.
II. HEATING DEVICES
Various techniques for producing localized or regional hyperthermia, including annular array using MWs, inductive RF
heating, and capacitive RF heating have been developed. However, each technique has its own inherent advantage and disadvantage, and its use should be chosen based on its clinical site
and tissue composition. Heating methods are divided into external, intraluminal, and interstitial heating.
A. External Heating Devices
1) Dielectric-Type Heating: External heating administers
heat to the tumor through various body structures. Delivery ofheat energy to superficially located tumors is relatively easy.

0018–9480/00$10.00 © 2000 IEEE

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Fig. 1. 430-MHz MW heating equipment with a lens applicator.

MWH is most prevalently used for external heating of superficial
tumors. One of the major problems of MWH is that the depth
penetration is limited by the principle of skin-depth theory in
EM wave. Only tumors located 2-3 cm from the skin surface can,therefore, be heated with a conventional surface applicator [5].
To attain deeper localized heating, metal-plate lens applicators have been developed in Japan that can converge MW energy
in a lossy medium, such as human muscle, with a computer-controlled heating system [6]. Calculation of an electric-field distribution [7] and heating experiment in phantoms and miniature pigs [8] actually demonstrated a maximum heating depthof up to 6 cm with this device, which is approximately twice
as deep as that obtained with a conventional waveguide applicator. This hyperthermia system consists of a 430-MHz MW
generator unit with maximum output power of 500 W, a surface
cooling unit, a thermometry unit, an applicator unit, and microcomputer-controlling system, as shown in Fig. 1. A four-aperture lens applicator with a total aperture size of 212 80 mm
or a two-aperture lens applicator with a total size of 100
50 mm is available. The applicator is covered with a water bag,in which deionized water is circulating. The skin-surface temperature is controlled by changing the temperature of the circulating water from 10 C–50 C. The temperature is measured bya single-point or multipoint thin Teflon-coated copper-constantthermocouple sensor with an outer diameter of 0.8 mm. A multisensor has 3–6 separate thermocouples, with junctions locatedat 6-, 8-, or 10-mm intervals. During hyperthermia, MW poweris switched off for 5 s every 24 s for temperature measurement.
Heat delivery to deep seated is more challenging, and major
efforts have been devoted to the development of external deepheating equipment. The ideal heating device should be capableof raising the whole tumor volume to a therapeutic temperature
without overheating adjacent normal tissues.
Regional heating is the most commonly used deep-heating
method. Since regional heating techniques apply energy to theadjacent deep-seated tumors in an unfocused manner, energy
is also delivered to the adjacent normal tissues. Under suchconditions, selective heating of tumors is only possible whenheat dissipation by blood flow in normal tissue is greater thanthat in tumor tissue. An annular phased-array system delivering
60–80-MHz EM waves and RF capacitive heating apparatus areexamples of regional heating devices. The former system has
the advantage in that subcutaneous fat is not excessively heated
and, thus, it is suitable for obese patients. However, this method
causes systemic symptoms such as tachycardia and malaise,
which result from the use of large-sized applicators. Systemic
stress is reported to be more severe in patients with abdominal
tumors than in those with pelvic tumors or tumors of the extremities [9], suggesting limited usefulness of this heating modality
for tumors in the upper abdomen.
An 8-MHz RF capacitive heating device has been developedwith a grant from the Research Development Corporation ofJapan [10]. The device is schematically illustrated in Fig. 2. Thisequipment was approved as a medical device for thermotherapyof cancer by the Japanese Ministry of Health and Welfare in
December 1984, and is now installed at over 100 hospitals inseven countries. Physical characteristics of this heating method
has been described [11]. It has a self- excited oscillation circuit at 8 MHz and 1.5-kW maximum output power. The RF energy is transmitted from a generator via two coaxial cables totwo disc electrodes. The RF is applied through a pair of electrodes placed on opposite sides of the body and the power isdistributed locally or regionally through interaction of electricfields produced between the parallel-opposed electrodes. To facilitate heating of any site of the body, the gantry with the electrode can be rotated 180 . The adjustable positions of the electrodes and the rotation of the gantry permit heating at different
angles and treatment sites. The treatment couch is motorized forvertical and horizontal movement. A portion of the top panel ofthe couch is opened electrically, and the lower electrode is protruded through the opening when vertical coupling is used. A
pair of electrodes is connected to the pillars of the gantry. The
surface of the metal plate of the electrodes is covered with a flexible water pad. Temperature-controlled water is flowing throughHIRAOKA et al.: RF AND MW HEATING EQUIPMENT AND CLINICAL APPLICATIONS TO CANCER TREATMENT IN JAPAN

1791

Fig. 2. 8-MHz RF capacitive heating device.

the water pad so that excessive heating of the skin and subcutaneous fat can be avoided. This pad makes it possible to smoothly
attach the electrodes to the body surface. Thus, the RF energy
can be supplied relatively homogeneously to an uneven site on
the body. The water temperature is maintained at 30 C–40 C
for superficial tumors and at approximately 10 C for subsurface
or deep tumors. The electrodes vary from 4–30 cm in diameter.
Suitable electrodes are selected according to the size and location of the tumors. This capacitive applicator has a thermometry
system with four Teflon-coated probes of copper-constant microthermocouple. The thermometry system with the microthermocouples connected to an automatic temperature-power feedback controller provides an accuracy of 0.2 C. The high RF
wave filter is inserted in the thermometry system, which is nonperturbed by RF interference and makes it possible to measuretemperature even during heating. Studies made at the Minnesota
University Hospital demonstrated that the measured temperature fluctuation was less than 0.45 C when the RF current was
turned on and off [12]. The temperatures measured at four points
in the heated tissue are continuously displayed both graphicallyand digitally on the computer screen. These data are also continuously recorded on a hard disc drive, and a hard copy canbe obtained on the internal printer. The power absorbed by theheated site is also continuously displayed graphically and digitally, and is recorded. An example of a thermal distribution in ahuman tumor treated with this device is shown in Fig. 3.
The disadvantage of RF capacitive heating is the excessive
heating of subcutaneous fat, and it is shown that a patient with
subcutaneous fat of more than 1.5–2 cm in thickness is difficult to heat with this heating modality [13]. The advantages are
its wide applicability to various anatomical sites and relatively
small systemic stress.
For tumor sites such as the neck region, where only a small
amount of subcutaneous fat is present, localized RF heating will
be advantageous. In dielectric-type RF applicators using a pairof circular conductive electrodes, a large-size electrode is usually needed to deeply heat a tumor uniformly. In the case of acapacitive applicator with a pair of circular electrodes, a diameter of more than 1.5 times the space between both electrodes isneeded to achieve uniform heating inside the human body. For
example, if the height of the heating region is 15 cm, 22.5 cm
is needed as the diameter of the electrode to uniformly heat the

(a)

(b)
Fig. 3. Thermal distribution of an abdominal huge tumor (MHF) treatedwith an RF capacitive heating device. (a) Thin catheter for the guidance of athermometer is demonstrated in the CT image. (b) Thermal distribution was
obtained by pulling out the thermometer by a 5-cm step.

human body in this area. If the diameter is less than this, hotspots will arise and the device cannot heat deeply.

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IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 48, NO. 11, NOVEMBER 2000

Fig. 5. Intralumonal RF electrode.

applicator using a pair of ferrite cores has been developed forbreast hyperthermia [19]. This applicator can regionally heat thebreast, regardless of the size of the breast, without overheating
fat tissue.
Fig. 4.

Construction of new applicator with double electrodes.

To improve this, a capacitive applicator with a double electrode has been developed to achieve local heating, as shown in
Fig. 4 [14]. By introducing a subelectrode consisting of a ferrodielectric material under the main electrode, an electric field
can be concentrated between a pair of subelectrode or ferrodielectric materials. The size of the beam spot is proportional tothe diameter of the semicircular subelectrode. If the semicircularsubelectrode of 5 cm in diameter is used, a 5-cm beam of electric field over a distance of 20 cm between a pair of electrodes
can be obtained.
2) Inductive Heating: Since magnetic fields in RF inductive heating can penetrate an insulating material such as subcutaneous fat, it can heat a tumor without heating fat tissue. A
simple aperture-type applicator has been proposed using a oneturn square column-like coil made of a metal strip [15]. The operating frequency and maximum output power are 6 MHz and
7 kW, respectively. The experiment using living pigs and theclinical trials are investigated in [16] and [17].
Generally, it is difficult to achieve deep inductive heating because the eddy currents are predominantly induced near the surface of the human body. To resolve this problem, a deformed
ferrite core applicator system with auxiliary electrode has beendeveloped [18]. The operating frequency and the output power
are 4 MHz and 850 W, respectively.
Deep local inductive heating can be achieved using an implantmaterial, which generates heat by its interaction with the magnetic field. However, since eddy currents are predominantly induced near the surface of the human body, the result is that boththe implanted region and superficial normal tissue are being
heated. To reduce the heating of normal superficial tissue, an
eddy-current absorber has been proposed [19]. This eddy-current absorber consists of silicon rubber containing a fine carbon
powder. By optimizing material constant of the eddy-current absorber, the eddy currents that arise at unexpected portion of thehuman body can be absorbed.
Knowing that a ferrite core applicator is able to efficiently
heat the inside of a protuberance on the human body, a simple

B. Intraluminal Heating Devices
The second method for deep heating is an intraluminal
heating using hot fluid, MW, or RF. Sugimachi et al. [20]have developed an RF intraluminal hyperthermia system. Very
localized heating is possible with this device by inserting an
endotract electrode into lumens of the human body, such as
the esophagus, rectum, and uterine cervix. A wide counterelectrode is placed on the skin surface of the body so that the RF
flux concentrates around the endotract electrode. Various typesof electrodes are available depending on the size of the lumen
and the site of the lesion. An electrode is connected to the RF
system, which is operated at the frequency of 13.56 MHz with amaximum power of 250 W. The main structure of the electrodeconsists of the following three parts, as shown in Fig. 5:1) transmitter for RF irradiation;2) balloon and cooling system, which eliminates the gap between malignant tissues and the transmitter (60 ml/minof water at the room temperature is circulated to prevent
overheating of the transmitter);3) thermosensor: copper/constant microthermocouples were
fixed to the outside of the balloon.
Recently, a new intraluminal electrode has been developedthat enables us to undertake simultaneous thermoradiotherapy.
A high-dose rate irradiation source (192 Ir) can be introduced
inside this electrode.
C. Interstitial Heating Devices
The third method is interstitial heating, which is divided
into RF current heating, MWH, and ferromagnetic implantheating. The advantages of interstitial heating are: 1) selective
heating of localized tumors and 2) feasibility of combined
use of brachytherapy. On the other hand, the disadvantages
are: 1) invasiveness; 2) difficulty in repeated treatment; and 3)
limitation of applicable sites.
As an interstitial heating devices, a fine coaxial line withsmall slots of about 1 mm in a outer conductor has been developed [21]–[23]. The operating frequency is 430 MHz. Ferromagnetic implant heating is being investigated in Japan. They
have developed an implant heating system (IHS), which consists

HIRAOKA et al.: RF AND MW HEATING EQUIPMENT AND CLINICAL APPLICATIONS TO CANCER TREATMENT IN JAPANFig. 6. Wireless thermometer with implant function using a three-dimensional
MMIC.

of a ferromagnetic implant, induction coil, and generator to produce a high-frequency magnetic field. The implant is made of
Fe–Pt alloy (Fe: 73%, Pt: 27%), and has a Curie temperature of
68 C. This system is being clinically investigated for the treatment of brain tumors [24] and tongue cancers [25].
One of the important problems to overcome in hyperthermia
is to achieve an accurate deep local heating together with exact
measurements of temperature. A wireless-thermometer using amonolithic microwave integrated circuit (MMIC) with an implant function has been proposed from these viewpoints [26],as shown in Fig. 6. As a temperature sensor, a silicone MMIC
with a voltage-controlled oscillator (Si MMIC VCO) has been
introduced. Its size is very small, i.e., 2 2 mm. This has a special feature in that the thermometer is a very simple construction because the Si MMIC VCO acts as a temperature sensor,
thus, the thermometer can be constructed without a transmitteror amplifier. As a wireless thermometer, it can measure the temperature accurately without noise interference induced by a leadwire carrying irradiated EM waves from an applicator.
III. CLINICAL APPLICATIONS: SUPERFICIAL AND SUBSURFACETUMORSA large number of clinical experiences with combined hyperthermia and radiation therapy have been reported for superficial and subsurface tumors. Treatment of superficial tumors offer significant advantage as compared to the treatment of
deep-seated tumors. Well-developed heating devices are available for their treatment, and these tumors are easy to both heatand to place thermometers into. The response of superficial tumors to the combined treatment is relatively easy to assess and,
therefore, they provide a good model to investigate the combined effectiveness of hyperthermia and radiation. Additionally,
several superficial tumors, including malignant melanoma, softtissue tumors, locally advanced tumors, and recurrent tumors
following radiation therapy are still resistant to conventional
treatments. The combined hyperthermia and radiation therapy
offers potential clinical advantages for the treatment of thesetumors.
Usefulness of thermoradiotherapy was initially demonstrated
by several trials, including our trial in patients with two or morecomparable tumors (matched tumors) [27]. Approximately
a twofold increase in local response rates was shown inthermoradiotherapy than in radiotherapy alone. In addition tothese studies, prospective randomized trials have been recently
performed. A trial carried out by the Radiation Therapy Oncology
Group (RTOG) in the U.S. failed to show a difference in1793

the response rate between radiation alone and radiation plus
heat when the tumors treated were analyzed all together [28].
When the tumor response was assessed according to thetumor size, a significantly higher response rate was achieved
with the combined hyperthermia and radiotherapy for tumors
with maximum diameter less than 3 cm, but not for tumors
more than 3 cm in diameter. On the other hand, however,it was pointed out that to evaluate tumor response after thethermoradiotherapy, appearance of low-density area (LDA) on
computed tomography (CT) images are more important than
the actual shrinkage of tumor volume [29]. The combined
treatment also showed a substantially higher response rate
in breast tumors, but not in head and neck tumors or othertumors in comparison with radiotherapy alone. Since smaller
tumors and breast lesions are easier to heat, it is suggested
that heating limitation may be the reason for the lack ofenhanced effects of combined treatment for large tumors andnonbreast lesions.
The other randomized trials including an international trial
for breast cancer [30], a European Society for Hyperthermic Oncology (ESHO) trial for malignant melanoma [31], a JapaneseSociety for Therapeutic Radiology and Oncology (JASTRO)
trial for superficial tumors [32] have clearly demonstrated theimprovement of local control rate with the use of hyperthermia.
Additionally, no enhancement of normal tissue damages by radiation was found. Thus, clinical benefits of hyperthermia combined with radiotherapy appear established for superficial tumors.
IV. CLINICAL APPLICATIONS TO DEEP-SEATED TUMORS
Site-specific trials have been undertaken. A summary of thosetrials is shown in Table I.
A. Trials for Esophageal Cancers
Using an RF intracavitary heating device, Sugimachi etal.have applied hyperthermia in combination with radiotherapy
and chemotherapy to patients with esophageal carcinoma.
The long-term results were compared between two groupsof patients treated with hyperthermo-chemo radiotherapy(HCRT) and those with chemo radiotherapy (CRT). The
five-year survival rates of patients with respectable carcinoma,
given preoperative HCRT or CRT, were 43.2% and 14.7%,). The two-year survival rates of those
respectively (with unresectable carcinoma and receiving HCRT or CRT were
15.5% and 1.2%, respectively [33]. A prospective randomized
trial was carried out to examine the effects of hyperthermia
given preoperatively. Sixty-six patients with esophageal cancer
underwent subtotal esophagectomy following either preoperative HCRT or CRT therapy. The incidence of lack of viable
cancer cells in the resected specimens was 25% in the HCRT
group and 5.9% in the CRT group. The cumulative three-year
survival rate was 50.4% in the HCRT group and 24.2% in the
CRT group [34].
B. Trials for Lung Cancers
It has been shown that RF capacitive heating devices can effectively raise temperatures of invasive lung tumors that were in1794

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. 48, NO. 11, NOVEMBER 2000

TABLE ISUMMARY OF CLINICAL REPORTS FOR DEEP-SEATED TUMORS

contact with the chest walls. We reported clinical results of 20
patients with lung cancer treated by thermoradiotherapy [35].
,, andwas 42.9 C, 41.6 C, and
The mean of
39.7 C, respectively. Of 12 tumors treated by a curative intent,
two (17%) achieved complete response (CR), seven (58%) partial response (PR), and three (25%) no change (NC). The side

effects associated with hyperthermia were pain in 12 patients(60%) and dyspnea in three (15%), all of which resolved aftertermination of treatment.
Improvement of local response rate [36] and survival rate [37]has been demonstrated with the combined treatment of regional
hyperthermia and radiation therapy in nonrandomized trials.

HIRAOKA et al.: RF AND MW HEATING EQUIPMENT AND CLINICAL APPLICATIONS TO CANCER TREATMENT IN JAPAN1795

TABLE I (Continued.)
SUMMARY OF CLINICAL REPORTS FOR DEEP-SEATED TUMORS

C. Trials for Liver Tumors
Heating capability of the 8-MHz RF capacitive device
was evaluated for 77 liver tumors. The maximum tumor
temperature, average tumor temperature, and minimum tumor
temperature in the hepato cellular carcinoma (HCC) werestandard error) 41.2 0.2 C, 40.3 1.3 C, and(mean
40.1 0.2 C, respectively. The same thermometry results for
non-HCC were 42.3 0.2 C, 41.2 0.2 C, and 40.9 0.2 C,
respectively. The maximum and minimum temperatures (41.8
0.2 C and 40.3 0.4 C) in the patients with a CR or PR werehigher than those in the patients with no response (NR) or
progressive disease (PD) (41.2 0.5 C and 39.8 0.4 C), but
the difference was not significant.
Of the 73 cases with HCC who were evaluated by CT, CR
was achieved in 7 (10%), PR in 15 (21%), NR in 37 (51%), and
PD in 14 (19%).
Of the 45 cases involving liver metastases evaluated by CT,
CR was achieved in 3 (7%), PR in 17 (38%), NR in 12 (27%),
and PD in 13 (29%). The one-year cumulative survival rate for
HCC patients was 30.0%, and the five-year survival rate was
17.5%. The one-year survival of non-HCC patients was 32.5%,
and the longest survival was 30 months. The sequelae of hyperthermia included focal fat necrosis in 20 patients (12%), gastriculceration in four (2%), and liver necrosis in one (1%). The sequelae of thermometry were severe peritoneal pain in seven patients, intraperitoneal hematoma in one, and pneumothorax in
one [38].
A number of strategies have been proposed that might leadto an selective heating of tumors. One of these is a manipulation of blood flow by degradable starch microspheres (DSMs).
A DSM is a cross-linked starch microsphere with a mean diameter of 45 m. It is dissolved by a -amylase in the serumwith a biological half-life of 15–30 min. Blood flow in tumors isshown to decrease transiently, leading to an increase in heatingwhen DSM is administered in a feeding artery of tumors duringhyperthermia. The accelerated increase in the liver temperaturein accordance with the administration of DSM in the common
hepatic artery during regional hyperthermia has been demonstrated in an experiment using pigs [39]. A clinical trial showedthat transarterial embolization (TAE) with DSM helped 0.9 C
increase in the maximum tumor temperature [40].
The usefulness of combined treatment of intra-arterial
chemotherapy and hyperthermia have been suggested in several
clinical reports [41].
Complications were mostly related to the chemoembolization
with DSM, which included fever, epigastric pain, and so on [38].
The clinical benefit of combined treatment of hyperthermia
and TAE has been demonstrated in a randomized trial. Twenty
patients were randomly assigned to either hyperthermia plus
TAE or TAE alone. Regional hyperthermia was administeredat tumor temperatures of more than 42.5 C for 40 min twice a
week, to a total of 10–38 sessions. The response rate was 40%
in the ten patients treated by hyperthermia plus TAE and 20%
in the ten patients treated by TAE alone. The patients treated byhyperthermia plus TAE had a tendency to have better survival
rates than those of the TAE group. The main side effects of TAEplus hyperthermia were low-grade fever, localized pain, myelosupression, and liver dysfunction, but these were transient andeventually resolved [42].
D. Trials for Gastric Cancers
The heating capability of Thermotron RF-8 for peritoneally
disseminated tumors from gastric or colorectal tumors was investigated. Tumor temperatures were measured by thin Tefloncoated microthermocouples, which had been implanted underlaparotomy or inserted transcutaneouly under ultrasonography

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into the center of the tumors. Of six tumors heated, tumor temperature could be raised over 43 C in one tumor, 42 C–43 C
in one tumor, and less than 42 C in the remaining four tumors[43].
Hyperthermia in combination with chemotherapy wasapplied to 33 patients with gastric cancer. Hyperthermia wasregionally given twice a week to a total of 6–40 sessions
using an 8-MHz RF capacitive heating device. Chemotherapy
consisted of mitomycin C (MMC) and 5-FU derivatives. Of the
33 patients treated, three (9%) showed CR and ten (30%) PR[41].
Recurrent and/or inoperable gastric cancer has been treatedby thermoradiotherapy at Kyoto University Hospital, Kyoto,
Japan, since 1983. The local response rate (complete regression
plus partial regression/all tumors) was 88.9%, which seemed tobe higher than that of other reports using thermochemotherapy
or radiotherapy alone. The one-year cumulative survival rate
was 39.1% [44].
E. Trials for Colorectal Cancers
The efficacy of RF capacitive heating is high for pelvic tumors, especially for large recurrent colorectal cancers.
We have treated 71 patients with unresectable or locally recurrent colorectal cancer by radiotherapy with or without locoregional hyperthermia [45]. Thirty-five patients were treatedby radiotherapy plus hyperthermia (group I), while 36 patientswere treated by radiotherapy alone (group II), mainly becauseof difficulties with the insertion of temperature probes or the
thickness of the patients subcutaneous fat. The total radiationdose did not differ between groups I and II, but the mean tumor
volume was significantly larger in group I than in group II. The
incidence of freedom from local tumor regression at six months
after the treatment was 59% (17/29) and 37% (11/30) for group
I and group II, respectively. The objective response rate (CRPR) was 54% (19/35) in group I, whereas it was 36% (10/28) ingroup II. A higher response rate of 67% was obtained in the 15
of more than 42 C compared with 47% fortumors with aof less than or equal to 42 C, although
17 tumors with athis difference was not significant. The incidences of obstructive ileus and intestinal fistula were relatively higher in group I(20%, 8.5%) than in group II (3%, 0%).
The usefulness of RF intracavitary hyperthermia combinedwith chemotherapy and radiotherapy as a preoperative treatment for rectal cancer has been investigated [46]. Postoperative
prognoses were compared among 36 patients with carcinomaof the rectum, who were given preoperative HCR therapy
followed by surgery, and 52 patients undergoing surgery alone
without any preoperative therapy. There were significant differences in the prognosis between patients given preoperative
HCR therapy plus surgery and those having surgery alone, andfive-year survival rates were 91.3% and 64%, respectively.
Particularly for patients with tumors invading beyond themuscularis propria and/or with positive lymph node metastasis,a significantly longer survival was obtained with HCR plus
surgery than in surgery alone (86.5% versus 50.9% and 92.9%
versus 51.7%, respectively). However, no significant differences were observed in the postoperative prognosis for caseswith no lymph-node metastasis and/or with tumors limited tothe muscularis propria between these two groups.
F. Trials for Urinary Bladder Cancers
Most trials for urinary bladder cancers were undertaken withthe use of RF capacitive heating devices.
Preoperative radiotherapy or thermoradiotherapy was administered to 49 patients with bladder cancer. Twenty-eight patientswere treated by radiation therapy combined with hyperthermia(group I). Radiation therapy was delivered with 4-Gy per fraction, 3 fractions per week to a total dose of 24 Gy (). The other 21 patients were treated by the same radiation
therapy regimen without hyperthermia (group II). Regional hyperthermia was administered for 35–60 min immediately after
irradiation (two sessions per week to a total of four sessions)using an 8-MHz RF capacitive heating device. Group I was divided into group I (High), in which the average intravesical tem) was above 41.5 C (12 patients), and group I
perature (below 41.5 C (16 patients). The incidence of(Low) with adown-staging for group I (High), group I (Low) and group II was
83%, 38%, and 48%, and that of tumor degeneration was 83%,44%, and 40%, respectively. The differences in response rate
between group I (High) and the other groups were significant). Survival rate tended to be higher in the group I than(in the group II. This trend is more apparent for those cases withT3–4 or Grade-3 bladder cancer for which preoperative treatment is considered to be more indicated [47].
G. Trials for Soft Tissue Tumors
We have treated 31 unresectable and/or recurrent soft tissue
tumors in 27 patients by hyperthermia in combination withradiation therapy. Tumor volume ranged from 3 to 3927 cm ,with a mean of 428 cm . Locoregional hyperthermia wasdelivered once or twice a week for 40–60 min to a total of 2–14
sessions. Radiation therapy was given at doses of 20.8–70 Gy.
,,
was, respectively, 44.0 C,
The mean of
42.3 C, and 40.1 C. Of the 31 tumors treated, 13 (42%)
showed CR, 10 (32%) PR, and 8 (26%) NC. Of 20 tumors inwhich the early response to thermoradiotherapy was assessedby X-CT, massive intratumoral low-density areas reflecting
coagulation necrosis by hyperthermia was shown in six (30%)
tumors. All of these tumors demonstrated a marked responseon follow-up or histopathological examinations. Thermal
parameters were more influential than the total irradiationdose in terms of both tumor regression and the appearance of
intratumoral low-density areas. The five-year survival of 18
patients who had no distant metastases at the start of treatment
was 48% [48].
V. CONCLUSION
Technical and clinical aspects for hyperthermia techniques
used in Japan have been reviewed in this paper. Several
methods of improving the heating characteristics from thevarious heating device have been proposed. Regional heating
can be efficiently achieved by using RF capacitive techniques.
That is because regional heating techniques apply energy toHIRAOKA et al.: RF AND MW HEATING EQUIPMENT AND CLINICAL APPLICATIONS TO CANCER TREATMENT IN JAPANthe adjacent deep-seated tumors in an unfocused manner andenergy is also delivered to the adjacent normal tissue. Thiscondition makes it possible to realize selective heating oftumors when heat dissipation by blood flows more predominant
than in normal tissue. A double-electrode capacitive applicator
has been proposed to attain deep heating locally.
To avoid fat tissue heating, inductive heating is effective.
However, the eddy current has a tendency of distributing near
the surface of the human body due to its inherent nature. As aresult, hot spots arise near the surface of the human body. To
prevent this phenomena, the eddy current was controlled byintroducing an auxiliary electrode and eddy-current absorber.
When using hyperthermia, it is important to establish accurate local and deep-heating techniques and to be able measure
the temperature distribution throughout the heated volume. To
attain this goal, a wireless thermometer with an implant function was proposed, although this is an invasive method. A future
goal is to use MRI and spectroscopic techniques for noninvasive
mapping of the temperature distribution.
Many clinical trials have been introduced with detailed investigation of the response rate.
Nonrandomized trials undertaken in Japan for locally advanced breast cancers, esophageal cancers, lung cancers, liver
tumors, gastric cancers, unresectable, or recurrent colorectal
cancers and invasive urinary bladder cancers demonstrated
higher response rate in thermoradiotherapy than in radiotherapy
alone. Randomized trials have been carried out for esophageal
cancers and gastric cancers, and both of them showed improved local response with the combined use of hyperthermia.
Additionally, the complications associated with treatment
were not generally serious, except for chronic bowel damages
suggested in a trial for colorectal cancers. These clinical results
indicate the benefit of combined treatment of hyperthermia andradiotherapy for various malignancies.
The use of heat in cancer therapy is the subject of an everbroadening multidisciplinary research effort involving the fieldsof biology, physics, engineering, and medicine. There are manyquestions still to be answered regarding biological issues suchas thermotolerance and thermal dose. Major efforts should be
devoted to the development of a device that is capable of raising
the whole tumor volume to therapeutic temperatures without
overheating the adjacent normal tissues. With the advancementof these technologies, hyperthermia will be more widely andsafely used in the treatment of cancers.
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Masahiro Hiraoka was born in Ehime Prefecture,
Japan, in 1952. He graduated from Kyoto University,
Kyoto, Japan, in 1977.
In 1995, he became Chairman and Professorof the Department of Therapeutic Radiology
and Oncology, Graduate School of Medicine,
Kyoto University. His subjects of interest include
radiation oncology (especially breast cancer andgastrointestinal tumors), hyperthermic oncology,
and development of integrated radiotherapy system.
He has been involved with the development ofvarious heating devices, including RF capacitive equipment, MW equipment,ultrasound equipment.

Michihide Mitsumori was born in Osaka Prefecture,
Japan, in 1960. He graduated from Kyoto University,
Kyoto, Japan, in 1985, and received the M.D. degreefrom Kyoto University, in 1994.
His subjects of interest include radiation oncology(especially breast cancer, prostate cancer, andesophageal cancer), clinical hyperthermia using RF
and MW devices, and application of nanoparticles tohyperthermia.

Naotoshi Hiroi was born in Osaka, Japan, in 1965.
He graduated from Fukui Medical University, Fukui,Japan, in 1991.
In 1996, he joined the Department of Therapeutic
Radiology and Oncology, Graduate School of
Medicine, Kyoto University, Kyoto, Japan, where
he is involved in research dealing with the clinicaleffect by brachytherapy and hyperthermia. He has
authored and co-authored six papers in the field ofchemoradiation and clinical hyperthermia.

Shinji Ohno was born in Fukuoka, Japan, in 1958.
He received the Medical License degree in 1984, and
the Ph.D. degree from Kyushu University, Fukuoka,
Japan, in 1992.
From 1989 to 1991, he joined the Division of
Hematology and Oncology, Texas Medical School,
Houston, TX, where he was involved in researchdealing with the effects of whole body hyperthermia
combined with chemotherapy. He has authoredand co-authored 80 papers in the field of oncology.
He is with the Department of Surgery II, Kyushu
University, where he is especially involved with carcinoma of the esophagus,
colon and breast.

Yoshiaki Tanaka was born in 1941. He received the
Medical License degree from the Ministry of Healthand Welfare, Nagoya, Japan, in 1967, and the Dr.
Med. Science degree from the Nagoya University
Postgraduate School, Nagoya, Japan, in 1971.
From 1974 to 1977, he was an Assistant Professor
in the Department of Radiology, Nagoya University
Hospital. From 1977 to 1978, he was Research
Fellow in the Cancer Research and Treatment
Center, University of New Mexico. From 1985 to
1993, he was Chief Director in the Departmentof Therapeutic Radiology, Tokyo Metropolitan Komagome Hospital. He iscurrently a Professor and Chairman in the Department of Radiology, Nihon
University School of Medicine, Tokyo, Japan.
Dr. Tanaka is a Board Certified Fellow of the Japanese Society for Therapeutic Radiology and Oncology of the Japanese Society for Therapeutic Radiology and Oncology.

HIRAOKA et al.: RF AND MW HEATING EQUIPMENT AND CLINICAL APPLICATIONS TO CANCER TREATMENT IN JAPANYouji Kotsuka (M’74–SM’99) was born in
Kanagawa, Japan, on April 30, 1941. He received
the Dr.Eng. degree from the Tokyo Institute ofTechnology, Tokyo, Japan, in 1980.
In 1974, he was a Lecturer at Tokai University,
Tokyo, Japan, and is currently a Professor of telecommunication engineering. From 1995 to 1996, he wasa Visiting Professor at the Harvard University, Cambridge, MA. He has been involved with the development of RF dielectric and inductive applicators fordeep hyperthemia, the development of EM-wave absorbers using ferrites, shield techniques, EM theory on scattering from randomrough surfaces, and propagation in anisotropic media with losses. He was Chairof the Medical Application and Measurement Techniques Committee with Radiated Waves for the Institute of Electrical Engineering, Japan.
Dr. Kotsuka is a member of the Steering Committee of the IEEE Microwave
Theory and Techniques Society (IEEE MTT-S), Tokyo Chapter, and a memberof National Commissions A and K of the URSI.

1799

Keizo Sugimachi was born in Nagasaki Prefecture,
Japan, in 1938. He graduated from Kyushu University, Fukuoka, Japan, in 1963.
In 1985, he became Chairman and Professor in
the Department of Surgery II, Kyushu University.
His subjects of interest include surgical oncology(especially esophageal cancer and gastric cancer),liver diseases (especially liver cancer, portal hypertension, and liver transplantation), and endoscopic
surgery. He has been an editor and co-editor ofmany journals in the field of surgery. Since 1997, hehas been the Chief Director of the Japan Society of Cancer Therapy. He was
President of 99th Japan Surgical Society in 1999.