Key words arteries - angiography - angioplasty - radiation safety
Introduction
Interventional procedures represent fundamental elements of medical diagnostics and
therapy. In particular, vascular interventions require a certain proximity to the
patient in a sterile environment, which means that the examiner is subject to greater
radiation exposure [1 ]
[2 ]
[3 ]
[4 ].
An important element of radiation protection is the monitoring of staff exposed to
radiation during their work. The radiation dose is officially monitored in the medical
field by the use of so-called “badges or TLDs” (film or thermoluminescence dosimeters),
but they only supply data at a later stage (retrospective analysis). For this reason,
in most cases it is no longer possible to determine in which situation increased exposure
occurred and whether it might have been avoidable. Additionally, directly readable
dosimeters can be used, e. g. the rod dosimeter, which only provides limited information
during the examination [5 ]. In the everyday clinical routine, a direct dosimeter ([Fig. 1a–c ]) with an acoustic warning signal might thus be helpful in detecting unnecessary
radiation exposure and learning to avoid it and in training the examiner in radiation
protection [6 ]
[7 ]
[8 ].
Fig. 1 The dosimeter device is flexible with a small sensor a . The sensor was attached to the back of the left hand b , below the sterile glove c .Abb. 1 Das Dosimeter hat einen flexiblen kleinen Sensor a . Der Sensor wurde am linken Handrücken b , unter einem sterilen Handschuh c befestigt.
The aim of our single-center study was to prospectively evaluate if a reduction of
radiation exposure can be achieved using a direct dosimeter with an acoustic warning
signal in the clinical routine.
Material and Methods
A direct dosimeter was used in interventional angiography in the clinical routine
to determine partial-body dose measurements on the left hand. The mean dose (in µSv)
and the mean dose rate (in µSv/s) were established.
Table 1
Number of examinations distributed among the examiners.Tab. 1 Anzahl der Untersuchungen in Bezug auf die Untersucher.
technique
antegrade
retrograde
cross-over
diagnostic
total
examiner
EE
26
3
12
12
53
IE
23
13
6
5
47
BE
31
8
19
25
83
total
80
24
37
42
183
183 patients (male: 110, female: 73; mean age: 68.7) underwent diagnostic angiography
(42/183) or angiography with subsequent angioplasty (141/183). The main reason for
the vascular intervention was peripheral arterial occlusive disease (PAOD: stage II
b to IV according to Fontaine). There was only one case of an inguinal vascular injury
after attempted intravenous drug abuse, with the development of a pronounced false
aneurysm (approx. 5 cm), the reason for contrast medium visualization of the arteries
for planning surgical therapy.
In 24/141 cases treatment of the pelvic area was necessary. 117/141 patients were
treated on the lower limb by an antegrade (80/141) or cross-over technique (37/141).
Examiners
The 3 interventional radiologists were classified according to 3 grades of experience.
The examiner with initial angiography experience and less than 200 examinations was
referred to as a beginner (BE). The examiners with more than 1000 vascular interventions
and more than 5000 interventions were designated as intermediate (IE) and experienced
(EE), respectively. The examination distribution among the examiners was: BE: 83;
IE: 47; EE: 53.
Each examiner used radiation protection clothing with a 0.35 mm lead equivalent and
an additional thyroid shield. Safety glasses were also worn.
Data were included in the study if they provided a complete dataset without interruption,
i. e., if the respective examiner fully completed the intervention. If, for example,
the beginner had to ask for the help of an experienced examiner, who then took over
the intervention, the collected data were discarded.
Angiography
The examinations were conducted on a digital flat detector angiography system (Allura
Xpert FD 20, Philips Healthcare, Da Best, Netherlands) using pulsed fluoroscopy (image
frequency: 15/s).
The common femoral artery was punctured under sterile conditions, using either an
antegrade (80/183) or retrograde technique (103/183). A mechanical contrast medium
injection system was used to prepare serial angiograms for diagnostic pelvis-leg angiography.
Interventions, especially those using an antegrade technique, were usually conducted
with manual contrast medium application.
Dosimeter
In accordance with the guidelines of the European radiation protection and X-ray ordinance
[9 ], official personal dosimetry was conducted under the protective clothing on the
front of the torso. Thermoluminescence dosimeters were used. A finger dosimeter was
also worn. In addition, before the start of the examination, a direct dosimeter (model
EDD-30, Unfors Instruments, Billdal, Sweden) was fixed to the body and the measuring
probe was attached to the back of the left hand.
The sensor has a spherical response with an inaccuracy of ± 6 % at the calibration
point. The dosimeter was calibrated to measure in terms of the personal dose equivalent
at a depth of 0.07 mm (Hp 0.07). The dose rate range was 0.03 mSv/h to 2 Sv/h.
The measurement of the dosimeter starts at a trigger level of 0.054 mSv/h. If the
dose falls below a value of 0.036 mSv/h, the measurement ends until the dose exposure
again reaches the start trigger level.
In accordance with the specifications of the device, the hand could be chosen as a
body part for dose measurement, with specified alarm limits. The alarm limits for
the hand are divided into 4 levels, with signals of different intensity: Level 1 = 1.0 mSv/h,
Level 2 = 5.0 mSv/h, Level 3 = 25.0 mSv/h and Level 4 = 1.0 mSv. The dosimeter gives
immediate audible warnings, beginning with a single beep at level 1 to a constant
beep at level 4.
Statistics
Statistical analysis was conducted using SPSS (version 15.0 for Windows). All values
are given as means ± standard deviation or number of patients and percentage. The
statistical significance of quantitative data was determined by analysis of variance
(ANOVA), in part after controlling for a third variable. The learning effect over
the chronological course was determined on the basis of an analysis of variance. The
graphic presentation of the estimated marginal means, on the basis of the means of
the dose rates of the individual examiners, shows the effect of the factors “examination
technique” and “time point” and thus accentuates the learning effect. A p-value < 0.05
was rated as statistically significant.
Results
Beside 42/183 diagnostic angiographies, 141/183 angiographies were performed with
subsequent angioplasty. A total of 80/141 patients were treated with an antegrade
technique, 24/141 with a retrograde technique and 37/141 with a cross-over technique
([Fig. 2 ]). The highest mean dose rate ([Fig. 3 ]) was found when retrograde angioplasty was performed (1.01 ± 0.56 µSv/s), followed
by cross-over angioplasty (0.46 ± 0.42 µSv/s) and diagnostic angiography (0.76 µSv/s),
while antegrade angioplasty (0.26 ± 0.19 µSv/s) was found to have the lowest exposure.
Fig. 2 Number of examinations distributed among the examiners and approaches.Abb. 2 Anzahl der Untersuchungen in Bezug auf die Untersucher und Technik.
Fig. 3 Mean dose rate (µSv/s) of the different techniques.Abb. 3 Mittlere Dosisleistung (µSv/s) der unterschiedlichen Techniken.
Compared to the mean dose rates, the mean dose ([Fig. 4 ]) showed a different disposition: the highest values were registered in cross-over
angioplasty (373.45 ± 357.83 µSv), followed by retrograde (295.73 ± 151.53 µSv) and
antegrade angioplasty (114.63 ± 109.24 µSv), while diagnostic angiography was found
to have the lowest accumulation (95.49 ± 99.45 µSv). There was no significant difference
in the average BMI for the different groups: beginner: 30.3 ± 4.7; intermediate examiner:
29.5 ± 2.5; experienced examiner: 31.1 ± 3.5.
Fig. 4 Mean dose (µSv) of the different techniques.Abb. 4 Mittlere Dosis (µSv) der unterschiedlichen Techniken.
In accordance with the radiation exposure of the examiner, the highest dose-area product
(DAP) as a method of monitoring patient dose was found in retrograde (107 906 mGycm2 ) and cross-over angioplasty (124 357 mGycm2 ), followed by diagnostic angiography (59 620 mGycm2 ). The lowest patient radiation exposure was found when antegrade angioplasty was
performed (12 703 mGycm2 ).
DAP values were recorded in this study over the 3-month course. There was no major
deviation in the average DAP for the different techniques: for antegrade angioplasty
month 1: 13 812 mGycm2 , month 2: 12 294 mGycm2 and month 3: 12 692 mGycm2 ; for the diagnostic angiography month 1: 57 251 mGycm2 , month 2: 59 391 mGycm2 and month 3: 61 915 mGycm2 ; for cross-over angioplasty month 1: 105 667 mGycm2 , month 2: 88 130 mGycm2 and month 3: 126 234 mGycm2 ; for retrograde angioplasty month 1: 126 920 mGycm2 , month 2: 89 812 mGycm2 and month 3: 141 263 mGycm2 .
Exposure of the operator’s hand is clearly dependent on the experience of the examiner.
On the basis of an analysis of variance (ANOVA), the mean values of dose rate of an
intermediate examiner or of a beginner were 0.14 + 0.38 µSv/s (p = 0.13) or 0.22 + 0.38 µSv/s
(p = 0.008) higher than the average dose of the expert of 0.38 µSv/s ([Fig. 5 ], [6 ]). This means that the beginner had the highest mean dose rate, followed by the intermediate
examiner. The experienced examiner was found to have the lowest.
Fig. 5 Mean dose rates as a function of the examiner’s experience.Abb. 5 Mittlere Dosisleistung in Abhängigkeit der Erfahrung des Untersuchers.
Fig. 6 Mean dose as a function of the examiner’s experience.Abb. 6 Mittlere Dosis in Abhängigkeit der Erfahrung des Untersuchers.
Controlling for a third variable as part of the ANOVA, i. e. controlling for the individual
examination techniques did not show any relevant change in the statistically different
results ([Table 2 ], [3 ]).
Table 2
Dose rate distributed among the examiners.Tab. 2 Dosisleistung in Bezug auf die Untersucher.
mean dose/sec
std. error
sig.
examiner
EE
0.377
0.064
0.000
IE
0.520
0.093
0.129
BE
0.597
0.082
0.008
Table 3
Dose distributed among the examiners.Tab. 3 Dosis in Bezug auf die Untersucher.
dose
std. error
sig.
examiner
EE
106.467
29.572
0.000
IE
208.626
43.136
0.019
BE
224.676
37.854
0.002
Over the 3-month course, an improvement in the average dose of –110 µSv (p = 0.04)
in the second month and –116 µSv (p = 0.03) in the third month and a dose rate improvement
of –0.155 µSv/s (p = 0.246) in the second month and –0.145 µSv/s (p = 0.271) in the
third month can be shown for the intermediate examiner. Analogously, the ANOVA showed
a trend towards a slight drop in the average dose/sec by approx. 0.09 µSv/s (p = 0.40)
for the beginner. For the experienced examiner, a significant difference in dose or
dose rate was not found over the observation period ([Fig. 7 ], [8 ], [9 ]).
Fig. 7 Dose of the different techniques for the experienced examiner (EE) over the course
of 3 months.Abb. 7 Dosis des erfahrenen Untersuchers in Bezug auf die unterschiedlichen Techniken über
einen Zeitraum von 3 Monaten.
Fig. 8 Dose of the different techniques for the beginner (BE) over the course of 3 months.Abb. 8 Dosis des Anfängers in Bezug auf die unterschiedlichen Techniken über einen Zeitraum
von 3 Monaten.
Fig. 9 Dose of the different techniques for the intermediate examiner (IE) over the course
of 3 months.Abb. 9 Dosis des fortgeschrittenen Untersuchers in Bezug auf die unterschiedlichen Techniken
über einen Zeitraum von 3 Monaten.
In comparison to the radiation exposure for the different grades of experiences and
techniques, the beginner had the highest frequency as well as levels of alarms. Up
to 5 audible warnings in level 1 to 3 were observed per intervention. In only two
cases the beginner had to tolerate a constant beep of level 4 in line with the retrograde/
crossover technique.
Discussion
Angiographic interventions mean high radiation exposure for the examiner, even if
this is mainly caused by scatter radiation [10 ]. Exposure can be reduced by actively adhering to the known rules for radiation protection
in accordance with the European radiation protection ordinance and X-ray ordinance
[7 ], by consistently applying the protective measures (lead apron, thyroid protection,
safety glasses, lead lamellae on the examination table, lead glass protection, etc.)
and by constantly improving the interventional techniques (learning curve).
To ensure adequate protection, the shielding effect of the protective clothing must
be verified. For the determination of shielding properties of protection clothing,
DIN EN 61331-1 (measurement in the narrow and broad beam) and DIN 6857-1 (inverse
broad-beam geometry) are available [11 ].
Dose limit values have been established to protect the examiner from the effects of
radiation. Official personal dosimetry is therefore an important part of radiation
protection [8 ]
[9 ].
Official personal dosimetry requires a whole-body dosimeter, which is to be worn under
the protective lead clothing on the front of the torso. However, this dosimeter does
not allow monitoring at the site of unprotected exposure, in particular. Within the
context of optimizing radiation protection, one should not only rely on the data from
dosimeters worn underneath the protective clothing, but also take dose measurements
on other, unprotected parts of the body. For example, an additional finger ring dosimeter
worn on the hand can supply appropriate information [12 ]
[13 ]. However, this information is insufficient to make the examiner aware of unnecessary
radiation exposure and enable him to take immediate protective action during an intervention
with intensive doses of radiation, since these dosimeters are not evaluated until
a later stage. In addition, personal dosimeters that supply direct information are
in use in the medical field, such as the rod dosimeter. However, this has the following
disadvantages: inaccuracy of reading, low resolution, small measuring range and shock
sensitivity [5 ]. Electronic personal dosimeters are also in use. The research group of Wucherer
M et al. [6 ] investigated personal dosimetry in interventional measures using a direct dosimeter
for partial-body dose measurement. Direct dosimetry makes it possible to call up information
about acute radiation exposure during an intervention [8 ]
[9 ].
In our experience there were no restrictions in the framework of the preparation for
the procedure.
An additional acoustic signal when a threshold value has been reached reinforces the
flow of information and can lead to a situational analysis on the part of the examiner,
possibly resulting in a change in behavior. However, the warning signal can be a stressor
with the level of intensity varying on an individual basis. In the case of an audible
warning signal, the shielding was optimized, the position of the examiner was changed
or the image intensifier was moved closer to the patient. In other words, a form of
training takes place with which an improvement in radiation protection can be achieved.
Through a precise knowledge of the exposure, the acceptance and application of additional
protective measures can be influenced [14 ].
The dosimeter used in our study was attached to the back of the left hand under the
sterile glove, since the radiation exposure of the left side of the body and left
hand is significantly higher than that of the right side [15 ]. For the left hand of the interventional radiologist, the paper by Hidajat et al.
describes dose values of 0.92 mSv, which roughly reflect the dose values of an experienced
examiner in the present study (1.06 mSv).
Pecher G et al. [14 ] reported high values of DAP and mean doses in angioplasties of the pelvic area (retrograde
or cross-over), while vascular interventions of the lower limb were accompanied by
low radiation exposure.
In our prospective study, measurement of the partial-body dose of the left hand revealed
that experience represents a form of protection against unavoidable radiation exposure.
In order to achieve this stage earlier, regular training through direct dosimetry
with a real-time flow of information can accelerate this process. This was displayed
over a period of three months, especially for the advanced examiner. A learning effect
was observed, which is reflected by a reduction in dose and is presumably the result
of a change in behavior.
Several limitations have to be considered in this study. Due to the complex statistical
design, the actual number of patients in each subgroup was relatively small, thus
there is the possibility that actual statistically significant differences in radiation
exposure could not be revealed due to a lack of statistical power. Furthermore, a
correlation between the radiation exposure measured by our device and the readings
from the TLDs could not be evaluated as the TLDs were always worn by the participants
and thus also recorded other radiation exposure outside of the angio lab. In conclusion,
the use of a direct dosimeter with an acoustic warning signal is a practicable tool
for sensitizing the interventional radiologist to unavoidable radiation exposure,
with the aim of reducing the dose.
“Real-time” dosimetry represents a sensible extension of the indirect protection of
the radiation-exposed angiography examiner, in particular for the intermediate examiner,
and less definitively for the beginner.
