RADIATION EXPOSURE OF CHILDREN DURING BARIUM MEAL AND
MICTURATING CYSTOURETHROGRAPHY EXAMINATIONS
Canevaro, L.V.[1]; Oliveira, R.R. [1], Daltro, P.A. [2]
[1] Serviço de Física Médica de Radiodiagnóstico e Imagem, Instituto de Radioproteção e Dosimetria, Comissão
Nacional de Energia Nuclear. Av. Salvador Alende, s/n. CEP. 22780-160. Barra da Tijuca. Rio de Janeiro,
Brazil. E-mail: [email protected].
[2] Clínica de Diagnóstico por Imagem – Crianças (CDPI-C) and Instituto Fernandes Figueira. FIOCRUZ. Rio
de Janeiro. Brazil.
Abstract
It is well known the fact that diagnostic radiology examinations on children have a higher risk when compared to
the ones carried out on adults. In Brazil, there are no established diagnostic reference levels (DRL) for
fluoroscopy guided examinations, surveys of patients dose are relatively recent and there are few experimental
data related to the determination and establishment of DRL in adults and no data for examinations in children.
The present work is part of a research project on dose and image quality indicators in conventional and
interventional fluoroscopy that was first started by our group in 2001. One of the aims is to quantify the levels of
exposure on paediatric and adult patients, developing and applying a methodology to obtain enough statistical
information in order to propose initial values of DRL. A second aim is the future assessment of the digital
technology impact on the dose received by the paediatric patients. To quantify the paediatric patients’ exposure,
a kerma-area product (PK,A) meter was used during the accomplishment of barium meal and micturating
cystourethrography examinations. Typical values of fluoroscopy time, number of images and contributions
percentage of fluoroscopy and radiography were also obtained. The third quartile of the corresponding parameter
distribution was adopted to determine these values. They are part of a database that will be taken as a baseline to
suggest DRLs. The relation between the PK,A and the patients’ physical characteristics is also discussed. Five
paediatric radiologists of the hospital’s permanent staff performed the procedures. 33 barium meals and 20
micturating cystourethrographies for patients with ages ranging from 0 to 10 years old were examined. Barium
meal and micturating cystourethrographies were the chosen examinations for being very frequent in children.
Here are presented some preliminary results of this research in a paediatric radiology department. In a long-term
period it will be possible to construct a map of the patients’ exposure in fluoroscopic procedures in Brazil.
Introduction
Diagnostic radiology examinations in children cause higher risks when compared to the ones carried
out on adults; young individuals have a longer life expectancy and their developing tissues are more
radiosensitive. The relative risk of harmful effects after radiation exposure during the first 10 years of
life is 3 to 4 times higher if compared to an exposure at 30 or 40 years old, and 5 to 7 times if
compared to an exposure after 50 years old [1][2]. Other important aspects related to paediatric
radiology are: the need of identifying adequate quantities to express the patients’ exposure levels, the
fact that in developing countries the rate of young population is higher than the adult population.
Besides, the young population is affected by a wider variety of diseases and consequently,
radiologists, radiographers and nurses need special training on paediatric techniques.
The optimization of the patients’ exposure conditions [3][4][5][6] is an extremely up to date subject.
The practical implementation of this principle is only possible when we are provided with the
appropriate tools, such as the patient’s exposure levels and well-defined image quality criteria [7].
Some problems related to radiological protection include the absence of collimation, inadequate
devices for immobilizing, absence of quality control programs and the necessity of having specific
exposure factors for the age based on appropriate anatomic parameters.
In Brazil, the Administrative Rule 453/98 of the Health Office [8], demands the application of quality
control programs that include the determination of the dose rate levels given to the patient as well as
the examination time, or the kerma-area product. However, there are no DRL established for
fluoroscopic examinations, studies on patient doses are relatively recent, there are few experimental
1
data aiming to determine and establish these levels in adults and no data at all for the examination in
children. Moreover, the application of quality control programs is not a routine yet, and the paediatric
fluoroscopic examinations are, generally, carried out in the same way as they are in adults. For this
reason, it is relevant to count on data to qualify each kind of fluoroscopic examination, especially the
paediatric ones.
In Rio de Janeiro there are some antecedents about measurements of patient dose in non-digital
fluoroscopy [9][10][11], in adults, though. In Europe, some studies were performed on radiological
procedures on children [1][12], evidencing, in some cases, a considerable potential of dose reduction.
Some evaluations of the digital technology introduction show that, generally, there is a reduction of
the dose imparted to the patient [13][14].
The present work is part of a research project first started by our group in 2001 on dose and image
quality indicators in conventional and interventional fluoroscopy applied in medical institutions in Rio
de Janeiro [15]. One of the aims is to quantify the levels of exposure in paediatric and adult patients, in
order to propose initial values of DRL. Some preliminary results of this research performed in a
paediatric radiology department are presented here. A second aim is the future assessment of the
digital technology impact on the dose received by paediatric patients during fluoroscopic
examinations.
Materials and methods
To quantify the radiation exposure levels of paediatric patients, a PTW Diamentor E (Freiburg,
Germany) kerma-area product (PK,A) meter was used during the performance of barium meal and
micturating cystourethrography examinations. The PK,A meter was tested before being used. Tests
were about reproducibility, linearity versus fluoroscopic technique, the constancy of response over the
chamber, etc.
The kerma-area product, PK,A, is the most adequate quantity to measure the patient’s exposure level in
fluoroscopy in general and to express the DRL in particular. First, because the PK,A measure is easier
and more practical, since the examination is entirely registered (in terms of the patient’s exposure),
there is little interference in the examination performance and there is no necessity of disturbing either
the patient or the radiologist with the measurements. Second, the PK,A is a quantity more related to the
risks of induction of stochastic effects, because it considers, besides the dose, the irradiated area
(related to the tissue volume and irradiated organs) [1].
The fluoroscopic examinations were performed on a digital Philips DUO DIAGNOSTIC overcouch
unit, with a high frequency generator, and 38, 32 and 21 cm intensifier image diameters, under the
table. The unit has a digital fluorography capability and is also capable of storing last image hold. The
equipment allows working in manual and automatic modes and there is an available alarm device after
5 minutes of irradiation. The equipment is only used to perform paediatric examinations. The
antiscatter grid was not removed. Kerma-area products were measured with a Diamentor E (PTW
Freiburg), attaching the ionization chamber to the collimation system of the X-ray equipment. The
Diamentor was calibrated at diagnostic X-ray qualities using a Radcal 2025 X-ray monitor with a
20X5-60-ion chamber.
Until the present moment, 33 barium meals (17 girls, 16 boys) and 20 micturating
cystourethrographies (12 girls, 8 boys) of patients with ages ranging from 0 to 10 years old have been
evaluated. Barium meal and micturating cystourethrography were the chosen examinations for being
very frequent in children. Barium meal examinations include the assessment of oesophagus, stomach
and duodenum. Five radiologists of the hospital’s permanent staff, following the institution’s medical
protocols, carried out the examinations.
For each examination the following data were collected: the patient’s age, gender, weight and height,
fluoroscopic technique (kVp and mA), time of exposure, radiographic technique (kVp, mAs), total
number of images, focus-to-skin and focus-to-image intensifier distances, total PK,A, PK,A of the
2
fluoroscopic part of the examination, PK,A of the radiographic part and PK,A per image, in screen-film
or digital.
Results and discussion
Characteristic data of patients included in the study is shown in Table 1. Patients were split
into 3 age ranges: 0-1, 1-5 and 5-10 years.
Table 1. Number of barium meal and micturating cystourethrogram patients in study.
EXAMINATION
BARIUM MEAL
MICTURATING
CYSTOURETHROGRAPHY
Age[years]
Number of
patients
Height [cm]
min-max
Weight [kg]
min-max
0-1
1-5
5-10
13
11
9
0,50-0,77
0,73-0,97
0,99-1,46
2,20-5,12
9,3-16,5
13-32
0-1
1-5
5-10
6
8
6
0,54-0,77
0,74-1,08
1,12-1,37
4,0-10,5
8,50-23,5
18-45,7
Table 2 shows the measurements performed. We can notice a wide variety of measurements for each
kind of procedure, proved in the value of the standard deviation of each sample. This happens because
of the different degrees of complexity of each examination and the variation of physical characteristics
among the patients.
Table 2. Measurement performed until now in the paediatric radiology department. (n = number of patients,
SD = Standard Deviation).
Age
Total PK,A
Time
Nº of images
Fluoro
graphy
Fluoro
[years]
[cGy·cm2]
[min]
Digital Screen-film
%
%
BARIUM MEAL (n = 33)
Range
0-1
57-422
0,7-8,5
0 – 37
Mean ± SD
205 ± 116
3,5 ± 2,5
9 ± 12
3rd. Quartile
273
5,0
7
Range
1-5
148-687
1,5-7,3
0 – 12
Mean ± SD
319 ± 171
4,3 ± 1,8
4±5
3rd. Quartile
373
5,2
7
Range
5-10
78-1199
0,8-7,9
0 –24
Mean ± SD
330 ± 335
2,55 ± 2,2
8 ± 10
3rd. Quartile
280
2,8
7
MICTURATING CYSTOURETHROGRAPHY (n = 20)
Range
0-1
54 - 288
1,2 –7,2
0 - 11
Mean ± SD
167 ± 86
2,8 ± 2,2
4,5 ± 4,7
3rd. Quartile
220
2,4
8
Range
1-5
121 - 1496
0,6 – 21,2
1 – 15
Mean ± SD
435 ± 469
4,8 ± 6,8
6,5 ± 4,9
3rd. Quartile
442
3,8
8,3
Range
5-10
231 - 1284
0,6 – 4,1
4 - 27
Mean ± SD
810 ± 460
2,2 ± 1,3
13 ± 8
3rd. Quartile
1169
3
16
0
0
0
-
0-43
10 ± 13
18
0-35
9 ± 12
18
0-22
9±9
18
57-100
90 ± 13
100
65-100
91 ± 12
100
82-100
91 ± 10
100
0-1
0,8 ± 0,4
1
0-1
0,6 ± 0,5
1
0-1
0,1 ± 0,4
0
4 - 40
18 ± 16
30
7 - 39
19 ± 12
25
14 - 59
39 ± 20
57
60- 96
82 ± 16
93
61 - 93
81 ± 12
90
41 - 86
61 ± 20
76
Fluoroscopic techniques ranged from 60 to 80 kVp and 1,3 to 1,9 mA during barium meal and ranged
from 59 to 73 kVp and 0,9 to 1,9 mA during micturating cystourethrography. Besides the digital
images and the screen–film, some images were captured directly from fluoroscopy, that were not
included in Table 2 because their contribution to PK,A was meaningless. These images have less quality
than the digital ones, however they were considered useful for diagnostic.
3
In Brazil, we still cannot count on other measurements performed during paediatric fluoroscopic
examinations that allow us to have comparisons. However, there are data about similar fluoroscopic
procedures in adults [1]. The comparison to internationally available paediatric data [13][16] shows
that the values of this work were always higher. The standard deviations obtained in the number of
images and in the total time of the examination suggest the necessity of a review in the medical
protocols, in order to standardize the procedures. In paediatric radiology, this is not always possible,
especially because the patients do not collaborate.
Kerma-area product, fluoroscopy time and the fluoroscopic and fluorographic PK,A contributions are
shown in Figures 1 to 3. In general, the PK,A was smaller for barium meal than for micturating
cystourethrography (Fig. 1), for the three age ranges, although the fluoroscopic times were higher (Fig
2). This can be explained by the wider use of digital fluorography during the micturating
cystourethrographies (Fig 3). In figures 4 and 5 the distribution of the number of images obtained for
both kinds of examination are presented. A small number of digital fluorographies and no images in
screen–film were performed for barium meal. In both procedures, a great number of fluoro capture
images was acquired, and they were considered as having enough quality for the diagnostic, avoiding
increasing the dose imparted to the patient.
2
PK,A [cGycm ]
1400
BM
1200
MC
1000
800
600
400
200
0
0-1
1-5
5-10
Age [years]
Figure 1. PK,A (3rd. quartile) for barium meal (BM) and micturating
cystourethrography (MC).
Time [min]
6,0
BM
5,0
MC
4,0
3,0
2,0
1,0
0,0
0-1
1-5
5-10
Age [years]
Figure 2. Fluoroscopy time (3rd. quartile) for barium meal (BM) and micturating
cystourethrography (MC).
4
BM - % fluoro
MC - % digital fluorography
MC - % fluoro
Percentage [%]
BM - % digital fluorography
100
80
60
40
20
0
0-1
1-5
5-10
Age [years]
Figure 3. Percentage contributions from fluoroscopy and digital fluorography (mean
values) for barium meal (BM) and micturating cystourethrography (MC).
Number of images
28
24
20
16
12
8
4
0
Digital
0-1
1-5
5-10
Age [years]
Screen-film = 0
Fluoro capture
Number of images
Figure 4. Number of images from digital fluorography, screen-film and fluoro capture
(mean values) for barium meal.
28
Digital
24
Screen-film
20
Fluoro capture
16
12
8
4
0
0-1
1-5
5-10
Ages [years]
Figure 5. Number of images from digital fluorography, screen-film and fluoro capture
(mean values) for micturating cystourethrography.
Correlation between PK,A and weight and between PK,A and age were not found. Paediatric patients at
the same age can present completely different physical characteristics (weight, height). The relation
between PK,A and equivalent diameter [17][18] was studied. The body weight takes the average density
into consideration but does not include the shape. The concept of equivalent cylinder considers the
patient as a cylinder having the same height (H in cm) and weight (W in g) as the body. The
equivalent cylindrical diameter (De) takes the average (unit) density into consideration and it has some
information about the shape of the body. De = 2√(W/Hπ). By normalising to the fluoroscopy time
used, the body size influence becomes even more obvious. Figures 6 and 7 show the normalized PK,A
per minute for barium meal and micturating cystourethrography, respectively.
5
Log(PK,A/time)
2,5
2,0
1,5
1,0
5,0
10,0
15,0
20,0
Equivalent Diameter [cm]
Figure 6. PK,A (normalized to fluoroscopic time) to the patient as a function of equivalent
diameter for barium meal for children aged 0-10 years.
Log(PK,A/time)
3,5
3,0
2,5
2,0
1,5
1,0
5,0
10,0
15,0
20,0
25,0
Equivalent Diameter [cm]
Figure 7. PK,A (normalized to fluoroscopic time) to the patient as a function of equivalent
diameter for micturating cystourethrography for children aged 0-10 years.
For micturating cystourethrography procedures the correlation was better than for barium meal. On the
other hand, the patients’ samples are small, though we can observe that there really is a correlation
between PK,A and the dimensions of the patients through De.
The total energy imparted to a patient can be obtained from a measurement of the total PK,A and
knowledge of the fractional energy absorption (FEA) and an appropriately weighted mean value of
(µen/ρ)air for the X-ray spectrum used:
ε =
∫
(µ
K
ar
dA
en
/ ρ ) ar
. FEA
The energy imparted is a useful quantity to evaluate the radiation risks. Once we have a bigger amount
of data, this relation will be analysed according to our patients’ samples.
Conclusion
This work presents preliminary local values of PK,A for paediatric fluoroscopic examinations of barium
meal and micturating cystourethrography, intended to work as baselines -once other X-ray equipment
and other paediatric radiology departments are evaluated- for us to suggest temporary values for DRL
in paediatric fluoroscopy in Brazil. Obviously, the patients’ samples evaluated are still few to
accomplish this goal. It will be necessary to perform a higher number of measurements to improve the
available statistical information we have up to the present moment. We assume that as our project goes
6
on, in a long term it will be possible to manufacture a map of the patient’s exposure in fluoroscopic
procedures in Brazil. We consider that the DRL for fluoroscopy should be established by measuring a
set of parameters, instead of having only one indicator. The exposure time, the number of images and
the total PK,A are a base of this set.
Monitoring the patients’ exposure -especially children- by means of the installation of kerma-area
product meters during the examinations allows us to analyse the several variables that are part of the
performance of a fluoroscopic procedure and provides the tools for the optimization of the practices.
For instance, the discussion about figures 1 to 5 shows the importance of the rational use of
fluorography during the examinations, especially when we are dealing with children.
Acknowledgements
The authors wish to thank all staff in the X-ray Department of Clínica de Diagnóstico por ImagensCrianças for their help throughout the study. This work has the support of FAPERJ.
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