Research Journal of Applied Sciences, Engineering and Technology 3(8): 720-724, 2011
ISSN: 2040-7467
© Maxwell Scientific Organization, 2011
Received: April 29, 2011
Accepted: June 10, 2011
Published: August 30, 2011
Preliminary Studies into the Determination of Mean Glandular Dose During
Diagnostic Mammography Procedure in Ghana
1
Irene Nsiah-Akoto, 2Aba Bentil Andam, 2,3Eric KT Adisson and 3Ama Jaben Forson
1
Nuclear Application Centre, National Nuclear Research Institute,
Ghana Atomic Energy Commission, Legon, Accra
2
School of Nuclear and Allied Sciences, University of Ghana, Legon, Accra-Ghana
3
Department of Physics, Kwame Nkrumah University of Science and Technology,
Kumasi, Ghana
Abstract: The objective of this project was to determine the Mean Glandular Dose (MGD) from Craniocaudal
(CC) and Mediolateral Oblique (MLO) views to the breast during diagnostic mammography and the total dose
per woman. The study was conducted at the Mammography Unit of Komfo Anokye Teaching Hospital and
Peace and Love Hospital, Oduom. Data such as age, weight, height, bust size, compressed breast thickness,
time of exposure, milli-ampere second (mAs), kilovoltage peak (KVp) and half value layer (HVL) were
recorded from 440 films from 110 women. The MGD per film was 1.17±0.02 mGy and 1.25±0.03 mGy for the
craniocaudal (CC) and Mediolateral Oblique (MLO) views, respectively. The mean MGD per woman was
1.80±0.03 mGy. The only factors that were found to affect MGD were mAs and the compressed breast
thickness. No significant relationships were seen between MGD per woman with respect to ethnicity and
educational background. The dose values obtained fall within the internationally acceptable dose range of 1-3
mGy. This suggests mammography x-ray generators at the two hospitals are capable of achieving acceptable
dose levels for patient safety and this prompted us to rule out the fact that all other factors considered, they are
not at risk of induced cancer from mammography.
Key words: Compressed Breast Thickness (CBT), Craniocaudal (CC), Half Value Layer (HVL),
Mammography, Mediolateral Oblique (MLO), Mean Gladualar Dose (MGD)
carcinogenesis is increased with such a procedure
(Bushong, 1993; Fung and Gilboy, 2001).
The glandular tissues of the breast are more
radiosensitive than adipose tissues; therefore estimation of
Mean Glandular Dose (MGD) has become an important
area of concern (Faulkner et al., 1995). As direct
estimation of the MGD is not feasible, it is often
estimated from the measurements of the breast entrance
skin exposure and converted to MGD by applying
conversion factors. The average glandular dose cannot be
measured directly, but is calculated under certain
assumptions from the experimentally determined entrance
surface air kerma or entrance surface dose by the use of
conversion factors. (American College of Radiology,
1999; Wu et al., 1991a, b). A numbers of researches have
been done on MGD determination for European females.
(Bulling and Nicoll, 1995; Klein et al., 1997; Moran
et al., 1994; Thilander et al., 1992; Wall and Roberts,
1992; Young and Burch, 2000). No significant research
has been done on the estimation of MGD, the exposure
factor used in mammography, and the Compressed Breast
Thickness (CBT) for Ghanaian women.
INTRODUCTION
The Breast (Fig. 1) is an external symbol of beauty
and womanhood, but it is unfortunate to note that cancer
of the breast is responsible for the deaths of millions of
women worldwide. Breast cancer has become one of the
most common malignancies in women and is the second
leading cause of cancer death (exceeded only by cervical
cancer) (National Cancer Institute, 1997). Breast cancer
patients in Ghana have not survived long enough
compared to their counterparts in more developed
countries who enjoy better survival periods.
Early detection of breast cancer is the key to
successful long-term control of the disease and good
prognosis, while mammography of excellent quality is a
fundamental prerequisite (Miller, 2005). There are two
types of mammography: screening and diagnostic.
Mammography should continue yearly after the age of 40
throughout a woman's life. The breast is a radiosensitive
organ and has a tissue-weighting factor of 0.05
(International Commission on Radiological Protection,
1991). The potential risk of radiation-induced
Corresponding Author: Irene Nsiah-Akoto, Nuclear Application Centre, National Nuclear Research Institute, Ghana Atomic
Energy Commission, P.O. Box LG 80, Legon, Accra
720
Res. J. Appl. Sci. Eng. Technol., 3(8): 720-724, 2011
Fig. 1: The breast
Fig. 2: The mammography x-ray generator of the two hospitals
The objective of this research was to measure the
MGD from CC and MLO views in each breast and total
dose received per patient whilst undergoing
mammography at the two hospitals in the Ashanti Region
of Ghana and also to ascertain if the patients were at risk.
each patient, data on age, weight and height were also
recorded.
CBT was measured to the nearest 0.05 cm using a
tape measure, at a distance of 4 cm from the chest wall, as
the distance between the bottom of the compression plate
and the table upon which the breast rested as shown in
Fig. 2. Measurement of CBT for CC views was made at
left and right sides of the compression plate, and the mean
value was calculated. For MLO views, however,
measurement was made at only one side of the
compression plate, opposite to the patient’s arm. For each
breast, the compression force applied was also recorded.
At both centres radiographers were encouraged to achieve
a firm compression in order to optimize radiographic
image quality, which may account for some of the low
CBT. Figure 3 shows how the breast is compressed before
METHODOLOGY
This study involved 110 women attending
mammography examinations in the two mammography
units, all in the Ashanti Region of Ghana. Data was
collected from women undergoing mammography
examinations over the period from December 2006 to
March 2007.
Patients' identification with a particular ethnic group
was based upon information given by each woman. For
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Res. J. Appl. Sci. Eng. Technol., 3(8): 720-724, 2011
RESULTS AND DISCUSSION
The MGD and CBT were collected from 440 films,
220 films each from projection thus CC and MLO views.
The mean doses per film and their standard errors were
1.17 mGy ±0.02 for the CC projection and 1.25 mGy
±0.03 for the MLO projection (Table 1). Median age of
the study sample was 50 years (range 30-75 years) and
coincides with the age of menopause (median 51 years in
the UK), during which significant changes in composition
of the breast are known to occur. Mean weight of the
study sample was 76.5 kg, which is 16.5 kg greater than
the weight of the standard woman (60 kg). Mean height is
159.5 cm, which is 0.5 cm shorter than the standard height
of 160 cm. 10% of the study sample was in the age range
30-39 years, increasing to 42.1% for the range 40-49, 40%
for the age range 50-59, and 5% for the subsequent
decade, with 2.9% of women 70-years-old and above.
Details of patient information and technique factors can
be found in Table 2.
The mean MGD per film for the MLO (1.25 mGy
±0.03) was 1.5% higher than the CC view (1.17 mGy
±0.02). This could be explained by the presence of
pectoral muscle in the overlying in the MLO projection
causing higher attenuation and hence higher exposure.
Mean CBT for CC and MLO films was 5.01±0.05cm and
5.84±0.07 cm, respectively. These two thicknesses
correspond closely to the standard breast equivalent
thickness as used in the mammography dosimetry
Fig. 3: A diagram showing how the breast is compressed before
exposure
exposure. In some cases, however, firm compression
could not be applied owing to patient discomfort.
The method for estimating the MGD to the breast of
a patient consisted of collecting the data on CBT for each
film with an indication of the tube voltage, and mAs and
target/filter combination for each patient. Medical physics
software developed by Wu and colleagues was used to
compute the radiation dose to the breast consequential to
mammography. The variables the software accepts are
kVp (kilovoltage peak), thickness of the breast, the
glandular fraction, the target/filtration combination. The
radiation dose is given in millirad per roentgen of skin
entrance exposure. The interface of the software is as
shown below in Fig. 4.
Fig. 4: Interface of the Medical Physics software (Wu et al., a, b)
Table 1: Mean glandular dose and compressed breast thickness in each projection
Hospital A (KATH) n = 59
Mean glandular dose (mGy)
Craniocaudal view
1.11±0.02
Mediolateral oblique view
1.35±0.03
Dose per patient
1.79±0.02
Compressed breast thickness (cm)
Craniocaudal view
5.02±0.0.04
Mediolateral oblique view
5.70±0.08
Each data presents mean±Standard Error (SE)
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Hospital B (P L) n = 51
1.12±0.02
1.25±0.02
1.81±0.03
5.12±0.05
5.89±0.06
Res. J. Appl. Sci. Eng. Technol., 3(8): 720-724, 2011
Table 2: Details of patient information and technique factors used in this study. Mean values and Standard errors are given
Patient’s information
Technique factors
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------Age (Yrs)
Weight (kg)
Height (cm)
View
kVp
mAs
Force
49±0.11
159.50 ±0.04
76.5±0.11
RCC
78±0.5
28
105±5
18±1
LCC
75±0.5
28
101±3
18±1
RMLO
131±0.6
28
112±8
18±1
LMLO
124±0.6
28
109±6
18±1
RCC: right craniocaudal; LCC: left craniocaudal; RMLO: right mediolateral oblique; LMLO: left mediolateral oblique; kVp: kilovoltage peak; mAs:
milli-ampere per second
1.8
of adipose to glandular composition. Eklund et al. (1993),
Wall and Roberts (1992), Sookpeng and Ketted (2006)
and Burch and Goodman (1998) have used the same
assumption in their studies and come out with similar
results obtained in the present study. Since women in this
study were from different geographical area, thus the
MGD reported in the present study was lower than that
obtained from some of the previous studies (Burch and
Goodman, 1998; Wall and Roberts, 1992; Sookpeng and
Ketted, 2006).
Doses to CC/mGy
1.6
Dosea in CC/mGy
1.4
1.2
1.0
0.8
0.6
0.4
CONCLUSION AND RECOMMENDATION
0.2
0
0
10
20
30
40
Age
60
70
60
70
The study of the MGDs in the present study revealed
that the mean MGD per film for CC and MLO views were
1.17±0.02 and 1.25±0.03 mGy, respectively, and mean
CBTs were 5.01±0.05 and 5.84±0.07 cm, respectively.
The mean MGD per woman was 1.80±0.03 mGy. A
reference dose for women with breast thickness between
3.0-6.0 cm of 1.5 mGy could be adopted in this part of the
country where the study was conducted without any
compromise in existing image quality. No significant
relationships were seen between MGD per woman with
respect to ethnicity or age. However, two factors namely
mAs of the X-ray beam and CBT had a significant effect
on MGD per woman. Since a constant kVp (28kVp) was
used because of the sensitive nature of the breast no
correlation was seen to affect the doses received. The
mean glandular doses obtained compares favorably with
the international standard dose of 1-3 mGy. This suggests
mammography x-ray generators at the two hospitals are
capable of achieving acceptable dose levels for patient
safety.
It is recommended that further studies should be
conducted for other breast thicknesses in order to make an
appropriate dose reference for all women undergoing such
examinations in this part of the country and also further
studies should be done for all the mammography units in
the country.
80
Fig. 5: Graph of CC doses against age
Doses to MLO/mGy
1.6
Dosea in MLO/mGy
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
10
20
30
40
Age
80
Fig. 6: Doses MLO/mGy against age
protocol. The difference in CBT of 10% between MLO
and CC views is larger than that found in UK (5.4%) and
US (9.1%) based studies for asymptomatic women.
However, the measurement of breast thickness may vary
because there is no standard method for measuring the
thickness of the breast and the values were obtained by
individual practice by each radiation technician.
The MGD per film, CBT and MGD per woman in
CC and MLO projections are shown in Table 1. A Scatter
diagram of craniocaudal and mediolateral oblique doses
against age is shown in Fig. 5 and 6.
MGD estimates in the present study were based on
the assumption that all breasts have a standard 50:50 ratio
ACKNOWLEDGMENT
I would like to extend my profound gratitude to my
Supervisors, Mr. Eric KT Addison and Prof. Aba Bentil
Andam, the Staff at the mammography unit at Komfo
Anokye Teaching Hospital and Peace and Love hospital.
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Res. J. Appl. Sci. Eng. Technol., 3(8): 720-724, 2011
Klein, R., H. Aichinger and J. Dierker, 1997.
Determination of average glandular dose with
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Miller, A.B., 2005. Screening for breast cancer-is there an
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Moran, P., M. Chevalier and E. Vano, 1994. Comparative
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National Cancer Institute, 1997. Cancer Record.
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Also to Dr. Beatrice Wiafe -Addai and to all patients who
willingly participated in our research.
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