oscopy were determined for all 571 electrophysiology procedures performed in a single electrophysiology laboratory
from January 2010 to December 2010. Data from 205 procedures performed by one interventional electrophysiolo-
gist, who instituted a practice of routinely collimating to the minimum required visual fluoroscopy field on a case-by-
case basis, were compared with data from 366 procedures performed by the three other experienced interventional
electrophysiologists using the laboratory who continued their existing practice of ad hoc collimation. Significant
reductions in radiation exposure were seen with the practice of routine maximal collimation. The largest reductions
were seen during ‘simple’ ablation procedures.
A practice of routinely collimating to the minimum required visual fluoroscopy field results in significant reductions in
radiation exposure when compared with a usual approach to collimation. This may have important implications for
risk of malignancy in patients and operators.
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Radiation † Fluoroscopy † Collimation † Catheter ablation
Impact of collimation on radiation exposure
during interventional electrophysiology
Tomos E. Walters1,2, Peter M. Kistler2,3, Joseph B. Morton1,2, Paul B. Sparks1,2,
Karen Halloran1,2, and Jonathan M. Kalman1,2*
1Department of Cardiology, Royal Melbourne Hospital, Melbourne, Australia;2Department of Medicine, University of Melbourne, Melbourne, Australia; and3The Alfred Hospital
and Baker IDI, Melbourne, Australia
Received 6 March 2012; accepted after revision 19 March 2012; online publish-ahead-of-print 19 April 2012
Fluoroscopy remains a cornerstone imaging technique in contemporary electrophysiology practice. We evaluated
the impact of collimation to the ‘minimal required field size’ on clinically significant parameters of radiation
Radiation dose measured by dose area product (DAP) and radiation dose rate measured by DAP per minute of fluor-
Over the last two decades catheter ablation has played an increas-
ing role in the management of both simple and more complex
cardiac arrhythmias. Despite the use of sophisticated three-
dimensional (3D) mapping systems and technologies such as
intracardiac echo, fluoroscopy remains the cornerstone imaging
technique for catheter guidance. Indeed, it is not uncommon for
reported fluoroscopy times for more complex procedures to
remain in excess of 60 min,1–4and this may represent a clinically
significant dose of radiation. Prior studies of the risk of radiation
exposure from electrophysiology procedures estimated each
hour of fluoroscopic imaging to be associated with an excess life-
time risk of developing a fatal malignancy of between 0.048 and
0.1%,5,6with the average risk for genetic defects determined to
be one per million births.6
Beyond a simple reduction in total fluoroscopy time, a number
of approaches may be used to minimize the amount of ionizing ra-
diation exposure received by patient and operator. X-ray tube
current and kilovoltage are typically controlled by the automatic
brightness control mechanism of contemporary fluoroscopy
units. Use of low fluoroscopy pulse rates,7short fluoroscopy
pulse durations,8and soft radiation filtration8,9are strategies that
have been demonstrated to reduce radiation exposure and
which in modern fluoroscopy systems are frequently pre-
programmed to low settings for electrophysiology procedures.
Removal of anti-scatter grids7,10and the use of lead glass
screens9are examples of more operator-dependent strategies
that have also been demonstrated to reduce radiation exposure.
In the current study, we evaluated the impact of collimation to
the ‘minimal required field size’ on total radiation dose and dose
per unit time during a range of interventional electrophysiology
* Corresponding author. Tel: +61 3 9342 7133; fax: +61 3 9347 2808, Email: firstname.lastname@example.org
Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 2012. For permissions please email: email@example.com.
Europace (2012) 14, 1670–1673
by guest on September 13, 2015
procedures. We hypothesized that the simple practice of minimiz-
ing the irradiated and thus the imaged field through collimation
would significantly reduce radiation exposure.
Over the course of a single calendar year, one of four experienced
interventional electrophysiologists using a single electrophysiology la-
boratory instituted a practice of routinely collimating to the
minimum required visual field on a case-by-case basis. The other
three interventional electrophysiologists continued their existing prac-
tice, which we have termed as usual collimation (Figure 1). The labora-
tory is equipped with a Philips Allura Xper FD20 fluoroscopy system
(Philips Medical Systems, Eindhoven, The Netherlands) which uses
automatic brightness control to select tube current and kilovoltage,
and includes selectable copper beam filtration. Pulse fluoroscopy
rates were pre-programmed for electrophysiology procedures and
did not differ between the four electrophysiologists.
The Philips system has real-time measurement of fluoroscopy time
and radiation dose area product (DAP). These data were examined
for all electrophysiology procedures performed in the laboratory
from January 2010 to December 2010. Procedures were grouped
according to those performed with collimation to the minimum
required visual field and those with usual collimation. The DAP and
DAP rates (DAP per unit fluoroscopy time) were compared
between the groups. The two groups were further subdivided into
diagnostic electrophysiology procedures, a ‘simple’ ablation group
(ablation of atrioventricular nodal reentry tachycardia, accessory path-
ways, and typical atrial flutter), and a ‘complex’ ablation group (ablation
of atrial tachycardia, atrial fibrillation, and ventricular tachycardia) and
the same data were compared.
Continuous data were tested for normality. Continuous data that
were not normally distributed are reported with a median and
interquartile range. The significance of differences between such
data sets was assessed using the Wilcoxon rank-sum test. Continu-
ous data that were normally distributed are reported with a mean,
a standard deviation, and a 95% confidence interval. The signifi-
cance of differences between such data sets was assessed using un-
paired Student’s t-tests. Continuous data that were not normally
distributed were transformed to a normal distribution to allow
comparison between multiple data sets through analysis of vari-
ance. A value of P , 0.05 was considered significant.
Five hundred and seventy-one procedures were performed
between January 2010 and December 2010. Three hundred and
sixty six were performed with usual collimation and 205 with col-
limation to the minimum required visual field. Forty eight were
diagnostic electrophysiology studies, 228 were classified as
‘simple’ ablation procedures, and 295 as ‘complex’ ablation proce-
dures according to the above definitions. Mean patient age was
56+16 years and 60% were male.
Overall, there was a significant 60% reduction in the total radi-
ation dose as measured by the DAP for procedures performed
with collimation to the minimum required visual field (median
11 199 vs. 27 759 mGy cm2, P , 0.0001) (Table 1). The most
marked difference was a 64% reduction in radiation dose during
‘simple’ ablation procedures (median 6923 vs. 19 286 mGy cm2,
P , 0.0001).
Although total fluoroscopy time was shorter during procedures
performed by the operator using collimation to the minimal
required visual field for all procedures taken together and for
‘simple’ ablation procedures, the radiation dose per unit fluoros-
copy time remained significantly lower with maximal collimation
for both these groups. Overall, there was a 23% reduction in
the radiation dose rate (median 1065 vs. 1390 mGy cm2/min,
P , 0.0001) whereas there was a 37% reduction in the dose
rate for ‘simple’ ablation procedures (788 vs. 1256 mGy cm2/min,
Figure 1 (A) Routine collimation: coronary sinus and His catheters are shown in the right anterior oblique projection, with a mapping cath-
eter in the atrioventricular junction region. (B) Maximal collimation: coronary sinus and His catheters are shown in the right anterior oblique
projection, with a mapping catheter in the slow pathway region.
Impact of collimation on radiation exposure
by guest on September 13, 2015
P , 0.0001) (Table 2). There was no significant difference in fluor-
oscopy times for ‘complex’ ablation procedures, yet there was a
significant 12% reduction in the radiation dose rate with collima-
tion to the minimum required visual field (median 1366 vs.
1551 mGy cm2/min, P ¼ 0.03). There was no significant difference
in either fluoroscopy time or the radiation dose rate (median 1148
vs. 1139 mGy cm2/min, P ¼ 0.64) for diagnostic electrophysiology
Normalization of radiation dose per unit time demonstrated a
significantly lower rate of radiation dose accumulation for all pro-
cedures performed by the electrophysiologist using collimation to
the minimum required visual field when compared with those per-
formed by each of the other three electrophysiologists individually.
Even in the current era of sophisticated 3D mapping systems fluor-
oscopy remains a cornerstone imaging technique in interventional
electrophysiology. It is not uncommon for reported fluoroscopy
times for more complex procedures to be in excess of 60 min.
In this study, we demonstrate that a strategy of collimation to
the minimum required field significantly reduces radiation expos-
ure when compared with a usual approach. Although this result
may seem obvious, it has been our experience that this approach
of tight collimation is infrequently used in clinical electrophysiology
These data emphasize the importance of maximal collimation in
minimizing radiation exposure in electrophysiology (EP) proce-
dures. A reduction in radiation exposure with collimation was
seen for all EP procedures with the exception of short diagnostic
studies and was most marked during simple compared with
complex procedures. We observed that in simple procedures
such as slow pathway, atrial flutter, and accessory pathway ablation
the field size required to monitor catheter movement during abla-
tion could be small indeed. In more complex procedures requiring
mapping and ablation over extensive regions, the required field size
was larger and hence the impact of collimation was smaller.
Fluoroscopy in interventional
Fluoroscopy exposes patients to both the deterministic and sto-
chastic effects of ionizing radiation, and health care workers to
its stochastic effects. The underlying principle of medical radiation
is that the dose should be kept as low as reasonably achievable. A
range of strategies available in contemporary fluoroscopy units
have previously been demonstrated to reduce radiation exposure
to both patients and health care workers.
Radiation exposure may be measured by the DAP, a product
of the radiation dose to air and the cross-sectional X-ray beam
area at any given distance from the X-ray source. Dose area
product has been shown to correlate well with the total ionizing
energy imparted to a patient and therefore to the risk of stochastic
effects such as malignancy.11–14The DAP and the DAP rate have
been shown to correlate with scattered dose and scattered dose
rate at any given point in the laboratory, and so are also markers
of cumulative stochastic risk to health care workers.15–17Thus, a
reduction in these parameters would be expected to reduce the
lifetime risk of malignancy in both patients and health care workers.
Collimation of the X-ray beam reduces its cross-sectional area
at any given distance from the source and hence reduces the
DAP. It is the only radiation reduction strategy with the potential
to both reduce radiation exposure and to improve image quality.
It is our observation, however, that collimation of the X-ray
beam is not maximally pursued in many EP laboratories.
Fluoroscopy time (min): median (IQR) 22 (21)
Radiation dose (mGy cm2): median (IQR)27 759 (44 536)
Dose rate (mGy cm2/min): median (IQR)1390 (1015)
Table 1 Median and interquartile range for fluoroscopy time, radiation dose, and dose rate
Usual collimation Maximal collimation% Reduction
11 199 (29 712)
All procedures (diagnostic EP studies, ‘simple’ ablation, and ‘complex’ ablation) are grouped together. IQR, interquartile range.
Diagnostic EP study: median (IQR)1139 (693)
Simple ablation: median (IQR)1256 (890)
Complex ablation: median (IQR)1551 (1120)
Table 2 Radiation dose rate measured by dose area product per unit fluoroscopy time according to the type of EP
Usual collimationMaximal collimation% Reduction
Unit is mGy cm2/min.
T.E. Walters et al.
by guest on September 13, 2015
Prior studies have evaluated the effect of various radiation reduc-
tion strategies in electrophysiology procedures. Wittkamp et al.9
studied the effect of increasing X-ray beam filtration and reducing
fluoroscopic pulse frequency on radiation exposure to patients
during electrophysiology procedures. There was a .50% reduc-
tion in patient skin dose rate with beam filtration and a 50% re-
duction with a decrease in pulse frequency. Davies et al.8studied
the effect of increasing X-ray beam filtration and reducing fluoro-
scopic pulse width during electrophysiology procedures, with
DAP and DAP rate per minute of fluoroscopy recorded as an
index of patient radiation exposure. For diagnostic EP cases
DAP was reduced by 87% and for ablation cases by 84%.
Rogers et al.7assessed the effect of removal of the secondary ra-
diation grid and the use of ultra-low fluoroscopy pulse rates in
631 simple and 376 complex electrophysiology ablation proce-
dures. Dose area product rate was reduced by 63% for ‘simple’
ablations and by 46% for ‘complex’ ablations. These reductions
occurred without a decrease in fluoroscopy time or in proced-
ural success rate. These reductions were determined to equate
to .50% reduction in the excess risk of fatal malignancy. With
institution of collimation to the minimum required visual field
we observed a 60% overall reduction in median DAP. The
current study emphasizes a further simple approach to minimize
radiation exposure in interventional electrophysiology through
The reduction in fluoroscopy times in the procedures performed
by the operator employing collimation to the minimum required
visual field might suggest that observed differences in radiation ex-
posure were due to an overall heightened attention to radiation
dose minimization by this operator rather than specifically to
routine maximal collimation. The significant reductions observed
in the rate of radiation dose accumulation do, however, point to
a specific benefit from collimation itself.
This is a retrospective study in which information required for
calculation of equivalent organ dose and thus excess risk of malig-
nancy was not available. However, it would have been ethically dif-
ficult to construct a prospective study where some patients
receive maximal collimation and others do not. The emphasis of
this study is to demonstrate that a careful approach to collimation
can result in significant reductions in radiation exposure compared
with what might be viewed as the current standard or usual
A practice of routinely collimating to the minimum required visual
fluoroscopy field results in highly significant reductions in radiation
exposure when compared with a usual approach to collimation.
This may have important implications for risk of malignancy in
patients and operators.
Conflict of interest: none declared.
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Impact of collimation on radiation exposure
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