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International Journal of Engineering & Technology IJET-IJENS Vol: 12 No: 06
109
An Attempt to Establish National Dose Reference
Levels for Head CT-Scan Examinations in
Indonesia: Preliminary Results from Malang
Hospitals
Johan Andoyo Effendi Noor and Indrastuti Normahayu

Abstract— CT-scanners are becoming more and more popular
imaging modality amongst medical practitioners as their tools
for diagnostic practices. Yet, since CT-scanners employ ionizing
x-ray beam as the source of imaging light, protection against its
damaging effects must be observed closely to ensure that the
harmful effects to patients are minimum. Our study involved
three Departments of Radiology in three major hospitals in the
city of Malang, East Java, Indonesia. We took at least 100 (50
males and 50 females) patients who were sent to the department
CT facility to have non-contrast head CT examination in each
hospital. The effective dose of each patient was calculated using
the CTDosimetry version 1.0.4 dose calculator software. Our
results reveal that the effective doses received by patients were
in range 1.25 – 2.51 mS v for male patients and 1.14 – 2.39 mS v
for female patients. In general, male patients received more
doses than the female counterparts as predicted.
Index Term—
CT-scanner, ionizing x-ray beam, radiodiagnostic, medical imaging
I. INT RODUCT ION
X–RAYS are invisible rays at a frequency band between 3 ×
1016 Hz to 3 × 1019 Hz and an energy band between 100 eV to
100 keV in the spectrum of electromagnetic waves. With such
energy x-rays are capable of penetrating objects and ionized
the objects in its path. X-rays have been used in many fields,
including the military, security, indus trial, and health.
In medical world x-rays are used in the field of diagnostics
(radiodiagnostic) and therapy (radiotherapy). In the field of
diagnostic x-rays are used to image internal organs of human
body (medical imaging) and in the field of therapy x-rays are
used to kill cancer cells (such as with a linear accelerator
machine). Overall, x-rays share over 70% of ionizing radiation
J.A.E. Noor is with the Department of Physics, Faculty of
Mathematics and Natural Sciences, Brawijaya University, Jl. Veteran 2,
Malang 65145, Indonesia (corresponding author, phone:+62 -341575833; fax:+62-341-575834; e-mail: jnoor@ ub.ac.id).
I. Normahayu is with the Department of Radiology, Faculty of
Medicine, Brawijaya University, Jl. Veteran 2, Malang 65145 and the
Department of Radiology, Dr Saiful Anwar Public Hospital, Malang
65122, Indonesia (e-mail: [email protected]).
used in medical field globally.
In further developments, along with the development in
computer technology and programming algorithms, in the
1970s, Sir Godfrey N. Hounsfield, a British engineer invented a
computed tomography (CT) scanner to make a tomographic
image of the human body interior transversely using x-ray. The
first image was generated from the CT scan of brain on
1October 1971 and presented to the public on 20 April 1972 at
the 32nd Congress of the British Institute of Radiology [1] and
later published in 1973 [2-4]. At the same time Allen McLeod
Cormack, a South African American, wrote an algorithm for CT
image reconstruction [5].
The advent of computed tomography (CT) has
revolutionized diagnostic radiology. Since its inception in the
1970s, CT has been used intensively and demand for this
imaging modality has increas ed rapidly. It is estimated that
more than 62 million CT scans per year currently take place in
the United States, including at least 4 million in pediatric [6]. By
its nature, CT involves larger radiation doses from the more
common x-ray conventional imaging procedures (Table I).
Thus the risk of cancer in patients as a consequence of the use
of ionizing radiation is also elevating. Although the risk for
everyone is small and not uniform, the increased radiation
exposure to public becomes health concern, now and in the
future.
The radiation dose received by the patient depends on the
magnitude of the x-ray intensity and duration of exposure.
Typical radiation dose for adult posterior-anterior (PA) chest
radiography is about 0.02 mSv (2 mrem) and 0.04 mSv (4 mrem)
for lateral imaging, with dose received by the lung is given in
Table II. While in CT scanning, the effective dose received by
patients undergoing chest examination is about 7 mSv [7],
which is about 175-350 times higher than the conventional xray radiography. Low-dose radiation carries cancer risk to
patients receiving it [7-13] and the possibility of deterministic
effects, such as skin injury [14], temporary bandage-shaped
hair loss [15], as well as leukemia and brain tumors [16].
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T ABLE I
T YP ICAL ORGAN RADIATION DOSES FROM VARIOUS RADIOLOGICAL
STUDIES.
T ype of Study
Relevant Organ
Relevant Organ
Dose*
(mGy or mSv)
0.005
0.01
Dental Radiography
Brain
Posterior-anterior chest
Lung
radiography
Lateral chest radiography
Lung
0.15
Mammography screening
Breast
3
Adult abdominal CT
Stomach
10
Barium enema
Colon
15
Neonatal abdominal CT
Stomach
20
* Radiation dose, a measure of the ionizing energy absorbed per unit of
mass, expressed in gray (Gy) or milligray (mGy), 1 Gy = 1 joule per
kilogram. T he radiation dose is often expressed as an equivalent dose in
unit of sievert (Sv) or millisievert (mSv). For x-ray radiation, which is
the type of radiation used in CT scanners, 1 mSv = 1 mGy..
From the technology side, CT-scanner has experienced rapid
development, both in the aspect of hardware and software. All
the developments are intended to minimize the dose received
by the patient while accelerating the process of data
acquisition and image reconstruction. In addition, in radiation
protection the principle of ALARA (As Low As Reasonably
Acceptable), the principle of minimizing the radiation dose
while maintaining the produced image quality, must always be
observed [17].
The first CT scanner was capable of producing a single slice
image with 2 minutes scan time and 20 minutes image
reconstruction. Improvements were made to reduce gantry
rotation time of only 2 seconds for a complete rotation (360º).
In the latest development CT-scanner has employed a MSMD
(multi-slice multi-detector) technique [18] and AEC (Automatic
Exposure Control) that is able to work under 2 minutes to
produce an image up to 128 slices and reducing the dose by
10-60% [19-21]. The difference between the doses received by
patients undergoing conventional scanning (fixed tube
current) and scanning using AEC is illustrated in Fig. 1.
Fig. 1. Illustration of dose profiles generated by a fixed current machine
compared to dose generated by a scanner with an automatic exposure
control (taken from reference [20]). In total, the dose of AEC scanner
is smaller than the dose of a conventional scanner.
The use of CT scan procedure is to obtain the internal image of
the object of interest for diagnostic and treatment purposes.
Reconstructed image quality depends on a number of factors
110
that will determine the level of dose received by the patient.
Thus, in the end there is a need to optimize the dose level while
keeping the image quality acceptable [22-24]. Many studies
have been conducted to determine the safe doses for both
local and national standards [25-36].
Effective dose (ED) is a measure to express and compare the
radiation dose given to patients of various CT-scanner
machines introduced by the ICRP in 1977 [37] and is defined as
the sum of weighted dose to the tissue known to be sensitive
to radiation as
(1)
H E   wT  HT
with wT is the specific tissue or organ weighting coefficient (T),
HT is the equivalent dose to tissue T, and HE is the sum of the
product wT • HT. In the publication number 102, ICRP provides
an estimate for the effective dose using the relationship [37,
38],
(2)
DE  k  DLP
–1
–1
with k (mSv.mGy .cm ) is an empirical weighting factor, which
is independ on the type of machine and specific to a particular
area of the body. This formulation is also used in the dose
calculation software CTDosimetry version 1.0.4 created by the
imPACTscan group [39] which was used in this study. The
software calculates the dose using Monte Carlo simulation
techniques [40-42].
This paper discusses the results of our study in estimating
the doses received by patients undergoing CT imaging
examination procedures at three major hospitals in Malang that
operate single slice CT-scanners with fixed current mode and
automatic mode as well as a multi slice scanner, to see if the
doses received by patients were below the recommended value
of the ICRP (International Commission on Radiological
Protection) published in its Publication No. 103 [12] and the
Indonesian Government Regulation No. 63 year 2000 on
Occupational Safety and Health in Utilization of Ionizing
Radiation, article 5, paragraph 1 that states: "If there are
multiple nuclear energy facilities in a single location, the
employers must observe lower dose level for each installation,
so the cumulative dose does not exceed the threshold dose".
II. SUBJECT S AND M ET HODS
Patients
Routine head CT scans are common examinations performed
in hospitals. We have collected CT data of three groups of 100
patients (50 males and 50 females) sent to the Departments of
Radiology in three major hospitals in Malang. The data used
in this study were obtained from patients having head CT
procedures from April up to October 2011 in the participating
hospitals. The age of the patients ranged from 17 to 87 years of
age.
Imaging Techniques
The CT examinations were performed with a General Electric
(GE) HiSpeed DX/i system in Hospital A, a Siemens Somatom
Spirit in Hospital B, and a Siemens Somatom Emotion6 in
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Hospital C.
Dosimetry Data
Dosimetry data were obtained from image headers of the
image series. The information extracted included: acquisition
date and time, manufacturer and model name, study
description, patient age and sex, tube voltage (kVp), protocol
name, series information, slice thickness (mm), tube current
(mA), exposure time (s), scan length (cm), CTDIvol (mGy), and
DLP (mGy.cm).
CT organ doses were obtained using the ImPACT
CTDosimetry software package ver. 1.0.4 (27/05/2011) [39] that
calculates dose for irradiation of a mathematical head phantom
as depicted in Fig. 2 which uses CT dosimetry data generated
by the National Radiological Protection Board [40-42]. See Fig.
2 for the phantom model used in the ImPACT calculation.
111
currents also vary. The CTDI values were averaged from the
MSAD (Multiple Scan Average Dose). The MSAD is an
average dose parameter in CT examination. The BAPETEN
(The Indonesia Nuclear Energy Regulatory Agency) set the
threshold of an adult MSAD to 50 mGy. The average CTDI for
male patients were 43.35 mGy and 40.48 mGy for female
patients. Therefore the CTDI values in Hospital A Malang are
below the threshold.
Fig. 3. Chart relating patients’ age to CT DIvol (mGy) for Hospital A.
The effective dose for each age group is charted in Fig. 4. The
effective dose is the radiation exposure received by the patient
during the CT examination procedure. The effective dose was
calculated using the CTDosimetry spreadsheet and referred to
the ICRP (International Commission on Radiological
Protection) publication No. 103. The average effective dose
was 1.32 mSv and 1.21 mSv for male and female patients,
respectively.
Fig. 2. T he ImpACT scan CT Dosimetry software showing the phantom
set up used in this study. T he scan was made to the head, started at 80
cm and ended at 94 cm (within the pink shaded area). T he effective dose
calculation can be selected using the organ weighting scheme of ICRP -60
or ICRP-103.
III.
RESULT S AND DISCUSSION
Analyses were conducted over a 100-patient group having
head scans between April 2011 and October 2011 in each
participating hospital. The results from each hospital are
discussed below.
Hospital A
The GE CT scanner installed in Hospital A utilizes an
adaptive tube current technique. The current supplied to the xray tube and the CTDIvol calculations for the patient age group
are presented in Fig. 3. The CTDIvol ranged from 38.93 mGy to
45.54 mGy.
It is shown that the CTDI values vary since the tube
Fig. 4. T he bar chart of the average effective dose (mSv) received by the
patients in the age group in Hospital A.
Hospital B
The CT-scanner employed in Hospital B is a Siemens
Somatom Spirit. Unlike the machine in Hospital A that utilizes
an adaptive current supply, the Siemens used a fixed current
mode. In this mode, the magnitude of the current supplied to
the scanner is constant throughout the examination, which is
240 mA. Therefore the CTDIvol also is constant, 47.5 mGy. The
effective dose calculation used the similar software and ICRP
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112
recommendation. The results are graphed in Fig. 5. The
average effective doses are 1.38 mSv and 1.32 mSv for male and
female patients, respectively.
Fig. 6. T he bar chart of the average effective dose (mSv) received by the
patients in the age group in Hospital C.
Fig. 5. T he bar chart of the average effective dose (mSv) received by the
patients in the age group in Hospital B.
T ABLE II
COMP ARISON OF THE AVERAGE EFFECTIVE DOSE FOR MALE P ATIENTS IN
THE THREE P ARTICIP ATING HOSP ITALS VALCULATED ACCORDING TO THE
ICRP RECOMMENDATION NO . 103
Hospital C
The CT-scanner in Hospital C is of the same manufacturer as
the Hospital B, only the type is different. The scanner in
Hospital C is Siemens Somatom Emotion6 that capable of
reconstructing six slices of image in one single rotation. The
tube current used in the head examination is 140 mA and 2 s
rotation time. This makes the mAs parameter of the scanner 280
mAs and gives a constant CTDIvol of 47 mGy. The calculation
of the effective dose also used the ICRP recommendation 103.
The results are provided in Fig. 6. The average effective doses
are 2.06 mSv and 1.93 mSv for male and female patients,
respectively.
Effective Dose Comparison
The scanners employed in the three participating hospitals
are categorized into two groups: fixed current, that is
represented by the scanners of Siemens Healthcare and
adaptive current that is represented by the scanners of General
Electric (GE) Healthcare. The fixed current system uses a
constant current to the x-ray generator tube, whilst the
adaptive current system adjusts the current supplied to the
tube according to the thickness of the object being imaged.
The latter system is aimed to reduce the radiation exposed to
the patients, thus reducing the radiation effects. The effective
doses from the three scanners investigated in the research are
tabulated in Tables II and III for male and female patients,
respectively.
Age (y.o.)
Hosp A
1.34
1.41
1.25
1.34
1.25
1.25
≤30
31-40
41-50
51-60
61-70
>71
Effective Dose (mSv)
Hosp B
1.40
1.36
1.39
1.38
1.38
1.34
Hosp C
2.21
2.31
2.39
2.51
2.23
2.14
T ABLE III
COMP ARISON OF THE AVERAGE EFFECTIVE DOSE FOR FEMALE P ATIENTS
IN THE THREE P ARTICIP ATING HOSP ITALS VALCULATED ACCORDING TO
THE ICRP RECOMMENDATION NO . 103
Age (y.o.)
≤30
31-40
41-50
51-60
61-70
>71
Hosp A
1.25
1.14
1.15
1.17
1.24
1.20
Effective Dose (mSv)
Hosp B
1.28
1.32
1.34
1.32
1.33
1.33
Hosp C
1.92
2.39
2.38
2.36
2.28
2.31
It is revealed that the GE scanner produced a lower dose
compared to the Siemens scanners. It shows that the adaptive
current scanner is safer that its counterparts that utilize fixed
current technique.
IV.
CONCLUSION
Our study reveals that, as predicted, the multislice machine (i.e.
of Hospital C) produces higher dose to patients (2.06 mSv and
1.93 mSV for male and female patients, respectively) than that
of single slice (i.e. 1.32 mSv and 1.21 mSV for male and female
patients, respectively in Hospital A and 1.38 mSv and 1.32 mSV
for male and female patients, respectively in Hospital B); and
the fixed current machine (i.e. of Hospital B) emits higher
radiation than that of adaptive current machine (i.e. of Hospital
A). We also found that, in general, female patients received
lower dose than male patients.
The recommendation we would like to propose is the use of 2.0
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mSv threshold as the local dose reference for CT head
examinations in hospitals in Greater Malang district. Further
research is required to extend the area coverage in order to
establish a national reference.
A CKNOWLEDGMENT
This research was funded by the Directorate General of
Higher Education (DGHE), Ministry of Education and Culture
through the DIPA of Brawijaya University Rev. 1 No: 0636/02304.2.16/15/2011 R, dated 30 March 2011 and the letter of DP2M
DGHE No: 121/D3/PL/2011 dated 7 February 2011. The authors
would like to thank radiographers at the participating hospitals
for the supply of the image data.
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