RADIOPROTECTION AND DOSIMETRY
MEASUREMENT OF THE EQUIVALENT INDIVIDUAL DOSES
FOR PATIENTS IN ANGIOGRAPHY PROCEDURE AND INTERVENTIONAL
RADIOLOGY WITH THERMOLUMINESCENT SYSTEMS
DANIELA ADAM1, ANA STOCHIOIU2
1
Bucharest Emergency University Hospital, Romania
“Horia Hulubei” National Institute for Physics and Nuclear Engineering, IFIN-HH, Bucharest
Reactorului 30, P.O. Box MG-6, Măgurele, Romania
2
Received July 6, 2012
The aspects of radiation injuries in IR were highlighted and the increasing concern
about the high skin dose levels in cardiology and other IR procedures, as it is very
important a close monitoring in order to prevent stochastic effects and, in time,
deterministic effects. The present study reports on investigations that we have
performed to allow the calculation of the individual penetrant radiation dose, Hp(10) in
interventional radiology and also the important results in determining the homogeneity
of the radiation flux. In order to determine the uniformity of large area beams with a
better precision, thermoluminescent matrices of 8 × 12cm size, containing arrays of
chips, uniformly distributed in each row and column of the matrix, were used. From the
measurements we obtained accurate data of the dose received by patients in different
areas of the body. Measurement method using TLD's is net superior to the measurement
with Dap-meter. Due to the potential for stochastic and deterministic effects existing in
interventional radiology, dosimetry information is required to make the interventionalist
aware of the potential for such effects.
Key words: equivalent dose, TLD, DAP.
INTRODUCTION
International standardization in dosimetry is essential for good exploitation of
the X-radiation based technology. International Atomic Energy Agency (IAEA) and
other nuclear activity control bodies initiated different programs regarding
ionisation radiation dosimetry, in order to help the international community,
including the EU member states, to develop standards and measurement capacities
of dosimetry equipments required for applying radiation in medicine. For some
time there was a growing awareness that the amount of the equivalent doses to
patients after performing medical procedures for diagnostic radiology contributes
at growing proportion of the total dose to the population. Interventional radiology
procedures (IR) and interventional cardiology procedures (IC) are registering the
highest radiation doses received by patients within one year of radiological
examinations. Stochastic effects that may result from these investigations are very
important, especially for the young population.
Rom. Journ. Phys., Vol. 58, Nos. 3–4, P. 330–336, Bucharest, 2013
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Measurement of the equivalent individual doses
331
To optimize patient exposure to radiation, the responsible doctor must know
very well the individual penetrant dose, Hp(10), to the radiosensitive organs for
each type of procedure performed. A precise determination would be very difficult
because of exposure to different areas of the body which may overlap in the
investigation. Even when a full protocol of all exposure parameters is used, it can’t
provide a good estimate of the effective dose for each organ exposed to the
radiation field. There are several direct and indirect methods used to determine the
patient's skin dose, but one of the most accurate methods we consider that is
thermoluminescent dosimetry (TLD), allowing for evaluation of the equivalent
dose at various organs. The aim of the study presented in this paper is to measure
the individual penetrant dose, Hp(10), from angiographic investigations with the
TLD method and to determine the homogeneity of the radiation beams.
MATERIALS AND METHODS
For the measurement of the individual penetrant radiation dose equivalent,
Hp(10) values in Sievert, we used the thermoluminescent system, SD-TL type, set
up at the Horia Hulubei National Institute of Physics and Nuclear Engineering,
IFIN-HH, described in detail in [1], whose characteristics are in full agreement
with the requirements of the standard IEC 61066:2006 [2]. It contains the
dosimeters based on the use of LiF:Mg, Cu, P detectors, as chips, commercially
known as GR- 200A and a TLD reader type READER ANELYSER RA’94. The
calibration of the system was done according to the prescriptions of the ICRU
Report 39 [3] in units of Hp (10), using a standard radiation field from a 137Cs
standard source.
To determine the dose in interventional radiology examinations we used a
30 cm, plexiglas phantom calibrated at PTW – Freiburg, Germany, to position the
detector arrays. The irradiations were done using the Integris H5000 angiography
equipment produced by Philips. In order to determine the uniformity of large area
beams with a better precision, thermoluminescent matrices of 8 × 12cm size,
containing arrays of chips, uniformly distributed in each row and column of the
matrix, were used.
The average time for carrying out an investigation by angiography or
interventional cardiology is 20 min. During this time, exposure to radiation is done
in area of interest and adjacent areas of the patient to be investigated. In order to
prevent deterministic effects it is important to measure the surface input dose; to
have the control over stochastic effects is essentially to know deeply absorbed
dose. In this respect, we measured the Hp(10) values at different depths in phantom:
10 cm, 16 cm, 23 cm and 30 cm, as Fig. 1, representing the PTW-phantom, shows.
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Daniela Adam, Ana Stochioiu
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Fig. 1 – Plexiglas Phantom type PTW.
TLD matrices were exposed to an X radiation beam characterized by the
following parameters: Tube high voltage, T = 110 kV; Intensity, I = 14.5 mA; Dose
Area Product, DDAP = 12 Gy cm2. Several measurement sets were performed: (i)
the first set, 96 chips placed at 10 and 30 cm depths and an exposure time, t = 2
min; (ii) the following sets, with 15 and 11 chips, at 16, 23 and 30 cm depths with
t = 1 min exposure times. After readings we obtained the individual and mean
values per detectors column of dose equivalent Hp(10), with the standard deviation,
σn(col) such as presented in Tables 1–5 .
Table 1
The values of dose equivalent [mSv] for the matrix I, (10 cm depth, t = 2 min).
No. of
chip
1
2
3
4
5
6
7
8
Mean
σn(col)
a
b
c
d
e
f
g
h
i
j
k
l
5.885
5.911
6.217
6.409
6.743
6.289
7.495
6.502
6.651
6.542
7.005
7.086
8.127
7.387
7.838
7.240
6.135
6.408
6.779
7.912
8.401
7.617
7.689
7.565
7.071
7.888
7.070
8.501
8.827
7.720
7.891
7.592
6.417
6.968
7.938
7.386
7.663
9.119
7.739
7.622
6.740
7.406
7.714
7.080
7.898
7.932
7.790
7.552
6.646
7.277
7.896
8.166
8.667
8.665
8.722
7.762
5.536
6.004
7.660
6.932
7.537
7.523
7.594
7.579
4.627
6.464
7.385
7.562
7.120
7.411
7.252
7.217
3.794
4.260
5.305
5.194
5.813
6.128
6.887
7.024
2.898
3.686
4.398
5.183
5.303
5.678
5.668
5.109
2.530
2.792
3.274
3.608
3.770
3.870
3.763
3.625
6.431 7.235 7.313 7.820 7.607 7.514 7.975 7.046
0.516 0.544 0.786 0.617 0.782 0.420 0.742 0.828
6.880
0.968
5.551
1.152
4.741 3.404
1.001 0.496
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Table 2
The values of dose equivalent [mSv], for the matrix II, (30 cm depth, t = 2 min)
No of
chip
1
2
3
4
5
6
7
8
Mean
σn (col)
a
b
c
d
e
f
g
h
i
j
k
l
0.096
0.094
0.105
0.120
0.110
0.120
0.100
0.065
0.113
0.109
0.119
0.111
0.123
0.108
0.105
0.104
0.116
0.135
0.135
0.123
0.122
0.111
0.131
0.126
0.114
0.102
0.117
0.122
0.122
0.127
0.132
0.122
0.113
0.119
0.107
0.126
0.124
0.143
0.112
0.112
0.108
0.109
0.128
0.127
0.112
0.124
0.136
0.105
0.113
0.127
0.108
0.130
0.123
0.135
0.110
0.109
0.120
0.129
0.126
0.137
0.109
0.116
0.113
0.125
0.101
0.113
0.116
0.126
0.116
0.129
0.112
0.120
0.108
0.100
0.112
0.110
0.109
0.126
0.119
0.114
0.100
0.087
0.084
0.097
0.109
0.100
0.110
0.086
0.093
0.089
0.092
0.112
0.098
0.108
0.108
0.105
0.101 0.112 0.125 0.120 0.119 0.119 0.119 0.122
0.017 0.006 0.008 0.009 0.011 0.011 0.010 0.009
0.117
0.008
0.112
0.007
0.096 0.100
0.010 0.008
Table 3
The values of dose equivalent [mSv] for the matrix III, (16 cm depth, t = 1 min)
No
1
2
3
Mean
σn (col)
a
1.626
1.595
1.722
1.648
0.066
b
1.137
1.172
1.172
1.161
0.020
c
0.992
1.028
0.914
0.978
0.058
d
1.630
1.792
1.634
1.354
0.062
e
1.382
1.427
1.322
1.377
0.052
Table 4
The values of dose equivalent [mSv] for the matrix IV (23 cm depth, t = 1 min)
No
1
2
3
Mean
σn (col)
a
0.356
0.425
0.382
0.388
0.034
b
0.346
0.350
0.331
0.342
0.009
c
0.413
0.481
0.430
0.441
0.035
d
0.460
0.475
0.467
0.010
Table 5
The values of dose equivalent [mSv] for the matrix V (30 cm depths, t = 1 min)
No
a
b
c
d
1
0.082
0.080
0.0680
0.0760
2
0.078
0.0793
0.0701
0.0684
3
0.074
0.0765
0.0738
Aver.
0.0786
0.0534
0.0717
0.0728
value
σn (col)
0.004
0.00049
0.00443
0.00391
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Daniela Adam, Ana Stochioiu
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Measurements are also important in determining the homogeneity of the
radiation flux. By plotting the TLD dose equivalent derived from exposures of
1 min and 2 min, we can observe a variation of radiation flux that influences the
radiation dose to the patient skin and collected dose at organs at risk, which are
near the exposed area. In principle, the values depend of radiation flux
homogeneity. Using the data from the upward tables, one represents graphically
minimum and maximum dose distribution on TLD matrix surface, exposed to X
radiation, such as presented in Figure 2, which provides an intuitive image of
uniformity of beam.
Fig. 2 - Equivalent dose distribution on TLD matrix surface, exposed to X radiation.
As we can see in Fig 2. the radiation flux is not uniform on the TLD surface.
Table 6 represents the summarized values of dose equivalent value [mSv] of
the 5 matrices of detectors, expressed as mean, minimum and maximum values,
calculated from all columns, corresponding to an exposition time of 1 min.
Table 6
•
Mean, maximum and minimum values of individual penetrant dose rate H p (10) , mSv/min
Depths
(cm)
Average value
(mSv/min)
Min value
(mSv/min)
Max value
(mSv/min)
10
16
23
3.314 ±0.194
1.304±0.025
0.331±0.009
1.702±0.248
0.914±0.058
0.297± 0.00311
4.064±0.272
1.792±0.627
0.467±0.010
30
0.0690± 0.0012
0.0570±0.006
Mean: 0.063±0.007
0.053±0.008
0.048±0.005
Mean: 0.051±0.003
0.068±0.004
0.066±0.004
Mean: 0.067±0.004
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Measurement of the equivalent individual doses
335
RESULTS INTERPRETATION
As first conclusion from tables, as expected, the central part of the beam has
the maximum intensity; the last two columns contain lower values; regarding the
matrices’ lines, the differences are lower. For the 30 cm, the second line values,
calculated from a measurement time of 2 min are in agreement with the 1 min
results, what means that for these short intervals the generator parameters remained
constant.
The graph below, Fig.3, represents the average value data from Table 6.
•
Fig. 3 – Individual penetrant dose rate H p (10) , mSv/min, as function of the depth, d.
The mathematical fitting of the data, represented by the continuous line in Figure 3,
results in a relation of variation of the equivalent dose rate, mSv/min, as function of
the depth d, in cm, of the type:
•
H p (10)[mSv/min] = (8.089 ± 0.672) − (0.589 ± 0.074)d + (0.0108 ± 0.018)d 2
This relation approximates satisfactory the variation of equivalent dose rate
with the depth and allows the calculation of the value for each depth, inclusively at
the entrance surface, d = 0. One can deduce that the exposure times of 20 minutes
result in significant equivalent dose values.
It is very important a close monitoring in order to prevent stochastic effects
and, in time, deterministic effects. The aspects of radiation injuries in IR were
highlighted and the increasing concern about the high skin dose levels in
336
Daniela Adam, Ana Stochioiu
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cardiology and other IR procedures were mentioned in Publication 85 of the ICRP
[3]. The two main causes mentioned for radiation injuries were: a) the use of
suboptimal equipment, and b) procedures performed by individuals inadequately
trained in radiation protection.
CONCLUSIONS
– Measurements with TLDs give a good estimation of the dose rates for
various exposition times and depths. Dose Area Product (DAP), is a
multiplication of the dose and the area exposed, often expressed in Gy.cm2.
– Total DAP is not always a good estimator of the risk of radiation. Using the
method of measurement with TLD one can have a better overview of doses
at different distances and times.
– From the above measurements we can obtain accurate data of the dose
received by patients in different areas of the body. Measurement method
using TLD's is net superior to the measurement with Dap-meter.
– A potential for stochastic and deterministic effects exists in interventional
radiology. Dosimetry information is required to make the interventionalist
aware of the potential for such effects. Also, for the purposes of tracking
doses to patients after IR procedures, it is necessary for details of the
patient’s dosimetry to be available within the patient record. Radiation
protection for patients and staff is one of the main issues for IR .
Acknowledgement. Thanks for assistance in achieving this article to Mrs. Prof. Dr. Maria
Sahagia and Eng. Ion Tudor from “Horia Hulubei” National Institute for Physics and Nuclear
Engineering, IFIN-HH, Bucharest.
REFERENCES
1. A. Stochioiu, F. Mihai, F. Scarlat. A new passive dosimetric system with thermoluminiscent
LiF:Mg, Cu, P detectors applied in individual radiation monitoring. Journal of Optoelectronics
and Advanced Materials. Vol. 8, No 4, pp. 1545–1551 (2006).
2. International Standard, International Electrotechnical Commission, IEC 61066:2006.
Thermoluminescent dosimetrical systems for the survey of environment and personnel.
3. International Commission for Radiation Units, ICRU Report 39. Determination of dose equivalents
resulting from external radiation sources, ICRU, 1985.