Prospective Systematic Intervention to Reduce Patient Exposure to

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Urolithiasis
Prospective Systematic Intervention to Reduce Patient
Exposure to Radiation During Pediatric Ureteroscopy
Paul J. Kokorowski,* Jeanne S. Chow, Keith J. Strauss, Melanie Pennison,
William Tan, Bartley Cilento and Caleb P. Nelson
From the Division of Urology, Children’s Hospital Los Angeles (PJK), Los Angeles, California, Departments of Urology (MP, WT, BC, CPN)
and Radiology, Boston Children’s Hospital, Harvard Medical School (JSC), Boston, Massachusetts, and Department of Radiology,
Cincinnati Children’s Hospital and Medical Center (KJS), Cincinnati, Ohio
URS ¼ ureteroscopy
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Accepted for publication March 1, 2013.
Study received institutional review board
approval.
Supported by the Pediatric Loan Repayment
Program through the National Institutes of
Health (PJK) and National Institute of Diabetes
and Digestive and Kidney Diseases Grant K23DK088943 (CPN).
* Correspondence: Division of Urology,
Children’s Hospital Los Angeles, 4650 Sunset
Blvd., No. 114, Los Angeles, California 90027
(telephone: 323-361-2247; FAX: 323-361-8034;
e-mail: [email protected]).
da
SSD ¼ source-to-skin distance
iza
ESD ¼ entrance skin dose
MLD ¼ midline absorbed dose
or
DAP ¼ dose area product
ut
AP ¼ anterior to posterior
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ALARA ¼ as low as reasonably
achievable
Purpose: After prospective measurement of radiation exposure during pediatric
ureteroscopy for urolithiasis, we identified targets for intervention. We sought to
systematically reduce radiation exposure during pediatric ureteroscopy.
Materials and Methods: We designed and implemented a pre-fluoroscopy quality
checklist for patients undergoing ureteroscopy at our institution as part of a
quality improvement initiative. Preoperative patient characteristics, operative
factors, fluoroscopy settings and radiation exposure were recorded. Primary
outcomes were the entrance skin dose in mGy and midline dose in mGy before
and after checklist implementation.
Results: We directly observed 32 consecutive ureteroscopy procedures using
the safety checklist, of which 27 were done in pediatric patients who met study
inclusion criteria. Outcomes were compared to those in 37 patients from the prechecklist phase. Pre-checklist and postchecklist groups were similar in patient
age, total operative time or patient thickness. The mean entrance skin dose and
midline dose were decreased by 88% and 87%, respectively (p <0.01). Significant
improvements were noted among the major radiation dose determinants, total
fluoroscopy time (reduced by 67%), dose rate setting (appropriately reduced dose
setting in 93% vs 51%) and excess skin-to-intensifier distance (reduced by 78%,
each p <0.01).
Conclusions: After systematic evaluation of our practices and implementation of
a fluoroscopy quality checklist, there were dramatic decreases in radiation doses
to children during ureteroscopy.
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Abbreviations
and Acronyms
Key Words: kidney, nephrolithiasis, ureteroscopy,
radiation dosage, checklist
MEDICAL radiation exposure is a major
concern in the United States and it
represents the most rapidly increasing
source of radiation exposure.1 Children have a longer remaining life span
and more radiosensitive tissues, making them particularly vulnerable to
the long-term effects of ionizing radiation.2 The United States National
Council on Radiation Protection and
1474
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www.jurology.com
Measurements advocates the ALARA
principle when using ionizing radiation for medical purposes and the
Alliance for Radiation Safety in Pediatric Imaging recently released the
“Image Gently” campaign to bring
attention to the need for judicious use
of radiation in pediatric patients.3,4
We recently reported a systematic
investigation of radiation exposure
0022-5347/13/1904-1474/0
THE JOURNAL OF UROLOGY®
© 2013 by AMERICAN UROLOGICAL ASSOCIATION EDUCATION AND RESEARCH, INC.
http://dx.doi.org/10.1016/j.juro.2013.03.006
Vol. 190, 1474-1478, October 2013
Printed in U.S.A.
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INTERVENTION TO REDUCE PATIENT EXPOSURE TO RADIATION DURING URETEROSCOPY
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After receiving institutional review board approval, we
prospectively monitored all URS procedures done by
6 pediatric urologists (surgeons) at our institution from
September 2009 to December 2010. Specific data collection methods were previously described in detail.5 Briefly,
a trained research assistant was present for each URS
procedure in its entirety who collected data on patient
characteristics, operative factors, fluoroscopy settings and
radiation exposure.
Based on the findings of this project, we designed a prefluoroscopy checklist with collaborative input from multiple stakeholders. This was tested during several procedures before undergoing subsequent revisions. The final
checklist included 6 items and was pilot tested on several
additional procedures before laminated copies were fixed
to the fluoroscopy machines (see Appendix). In addition, a
radiation physicist gave a 50-minute didactic session to
the urology department. No other protocol changes were
made by the department during this period.
After incorporating the checklist in regular clinical
use, we again prospectively obtained data from June 2011
to June 2012 on the same surgeons, collected variables,
personnel (a radiation technologist activated imaging
according to standard practice at this center) and equipment (BV Pulsera mobile units, Phillips, Best, The
Netherlands) as during the initial study period with
additional information on checklist use. The same criteria
were used for inclusion/exclusion as in the prior report,
limiting patients to those younger than 21 years undergoing unilateral URS for urolithiasis.5 Distinct from the
pre-checklist procedures, surgeons and operating room
staff were informed about checklist components and primary project aims.
Our primary outcome measure was the patient radiation dose, calculated as ESD and MLD. ESD estimates
radiation dose to the skin, which is the organ that receives
the maximum dose, while MLD is a better approximation
of the average dose received by all irradiated tissue. Doses
were indirectly measured from the dosimeter of the fluoroscopy unit (air kerma) at 70 cm from the radiation
source. To calculate ESD, air kerma is adjusted for
backscatter by a factor of 1.2, bed/pad attenuation
measured as 0.40 at 70 kV and observed SSD using the
inverse square law. MLD at the midpoint of the patient
umbilical AP diameter, measured with calipers by the
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METHODS
surgeon, researcher or staff, was estimated from the
calculated ESD by applying appropriate tissue attenuation factors for a 70 kV beam from a mobile fluoroscope.
SSD was calculated from direct measurement of the
patient, table height and fluoroscopy unit. In this study
we added DAP as an additional dose index, corrected for
table attenuation. The DAP in mGy m2 considers collimation, a process by which peripheral or iris-type radiation barriers are used to block radiation delivery to the
periphery of the field of view. This results in a smaller
portion of the patient body exposed to the direct beam and
can significantly decrease the total radiation delivered.
All dose calculations were performed under the supervision of a radiation physicist (KJS).
Known determinants primarily responsible for radiation
exposure in the setting of fluoroscopy include patient AP
diameter, total fluoroscopy time, SSD and the dose rate
setting of the fluoroscope, eg voltage and tube current.
Differences in these determinants between the pre-checklist
and postchecklist cohorts were compared by univariate
tests of association, including the t or Wilcoxon rank sum,
chi-square or Fisher exact test based on data characteristics. Multivariate linear regression was used to control for
potential confounding when sufficient data points per outcome group were available. For the fluoroscopy time outcome items identified as potential predictors at p 0.1 in
our prior study5 were included on multivariate analysis. Log
transformation was performed on skin entrance dose and
DAP outcomes to allow for parametric analysis. All analyses
were performed using SASÒ, version 9.2. All tests were
2-sided with p 0.05 considered statistically significant.
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levels in pediatric patients undergoing URS at our
institution.5 Of the major determinants of radiation
exposure total fluoroscopy time was most important,
followed by dose rate setting, patient thickness and
skin-to-source distance. Data obtained from direct
observation of procedures as part of a quality
improvement project were used to identify opportunities for reducing radiation without prohibiting
safe, effective completion of the procedure.
We designed and implemented a pre-fluoroscopy
surgical checklist meant to decrease radiation exposure during URS in pediatric patients with stones.
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RESULTS
We observed 32 URS procedures using the fluoroscopy checklist, of which 5 were excluded from study
due to patient age greater than 21 years, leaving
27 patients. We compared the characteristics of
this group to those of the pre-checklist cohort of
37 patients (table 1). The groups were similar in
age, AP diameter, preoperative stent in place, postlithotripsy stenting, ureteral access sheath and
safety wire use, retrograde pyelograms and trainee
role. Time required to complete the checklist was
anecdotally noted to be less than a minute.
Table 2 lists radiation dose outcomes in the prechecklist and postchecklist groups. Compared to the
pre-checklist group, mean ESD was decreased in
the postchecklist group by 88% from 46.4 to 5.7 mGy
(p <0.01). Similarly, mean MLD was reduced by 87%
from 6.2 to 0.8 mGy (p <0.01). DAP was decreased
by 88% from 0.82 to 0.10 mGy m2 (p <0.01). After
adjusting for the effect of small differences in patient
thickness, reductions in primary dose outcomes
remained significant (changes in ESD, MLD and
DAP after vs before checklist each p <0.01).
Significant improvements were noted among
the major radiation dose determinants. Total fluoroscopy time was decreased by 67% from 2.68 to
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INTERVENTION TO REDUCE PATIENT EXPOSURE TO RADIATION DURING URETEROSCOPY
model, significant reductions in total fluoroscopy
time were still seen in the postchecklist compared to
the pre-checklist group (e2 minutes, 95% CI e1.3
to e2.7, p <0.01).
An appropriate or decreased dose rate setting was
used in 93% of postchecklist vs only 51% of prechecklist cases (p <0.01). In 12 of 27 cases (44%) a
lower than maximum allowable setting was used in
the postchecklist group compared to only 1 of 37 (3%)
in the pre-checklist group. The average excess skinto-intensifier distance was reduced by 78% from 12.3
to 2.7 cm (p <0.01). The effect was an increase in the
average SSD from 67 to 76 cm and an average 22%
decrease in the radiation dose. Collimation was used
in only 1 case (3%) in the pre-checklist cohort and in
6 of 27 (22%) in the postchecklist cohort. The
reduction in the exposure field secondary to collimation was not directly measured.
Table 1. Descriptive information
16.0 4.0
2
(7)
2
(7)
4
(15)
19
(70)
17.8 3.7
76 39
15
22
(41)
(59)
12
15
(44)
(56)
31
6
(84)
(166)
24
3
(89)
(11)
26
11
(70)
(30)
19
8
(70)
(30)
32
5
(86)
(14)
25
2
(93)
(7)
31
6
(84)
(16)
27
0
(100)
4
33
(11)
(89)
0
27
(100)
3
30
4
(8)
(81)
(11)
2
22
3
(7.5)
(81.5)
(11)
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14.8 4.0
0
7
(19)
2
(5)
28
(76)
18.6 4.3
73 45
DISCUSSION
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0.88 minutes (p <0.01). The mean reduction by individual surgeon was 69% (range 45% to 89%). Total
stone volume, assuming spherical shape (p ¼ 0.13),
and ureteroscope type (semirigid in 13 cases and
flexible in 51, p ¼ 0.20) were not significantly
associated with fluoroscopy time. Cases with complications had a higher average fluoroscopy time
(p ¼ 0.01). However, they accounted for only 8% of
reduced fluoroscopy time in the postintervention
group and did not alter results when added to the
multivariate model. After adjusting for access
sheath use, retrograde pyelography and postlithotripsy stent placement in a multivariate
Table 2. Primary pediatric URS dose outcomes before and after
implementing fluoroscopy checklist (p <0.01)
Before
Intervention
After Checklist
Mean SD primary outcomes
(range):
ESD (mGy)
46.4 (2.7e223) 5.7 (0.4e34.4)
MLD (mGy)
6.2 (0.7e17.1) 0.8 (0.07e3.1)
2
0.82 (0.01e8.88) 0.10 (0.01e0.57)
DAP (mGy m )
Modifiable dose determinants:
Mean SD total fluoroscopy 2.68 1.8
0.88 0.8
time (mins)
No. higher than recommended 18
(49) 2
(7.4)
dose rate setting (%)
Mean SD skin exit to
12.3 6.7
2.7 4.9
intensifier (cm)
The use of medical radiation is an especially important issue in the pediatric population. Children are
up to 3 to 10 times more radiation sensitive than
adults because of a longer life span and relatively
higher radiosensitivity.6 Collaborative efforts of clinicians, radiation physicists, public health officials
and industry have promoted the ALARA principle7
and there is widespread agreement that decreasing
radiation exposure is a public health priority.4,8
The Pause and Pulse initiative from the Image
Gently Campaign of the Alliance for Radiation Safety
in Pediatric Imaging specifically addresses the use
of fluoroscopy in young patients.3 With respect to
genitourinary related procedures, there are reports
of significant variations in the number of images,
fluoroscopy time and total radiation dose for the
same type of procedure.9 This variation suggests that
a common protocol may assist in decreasing radiation
doses, in keeping with the ALARA principle.
A number of published reports describe efforts to
reduce radiation exposure in patients with genitourinary conditions. Some focused on diagnostic
procedures such as voiding cystourethrography
for congenital abnormalities10,11 or computerized
tomography to identify urolithiasis.12,13 Others looked
at ways to decrease radiation exposure during
endourological procedures by specific protocols and
technical modifications.14 An example of such a
protocol standardized how many images and which
types would be typically performed during urodynamics, yielding a 71% reduction in fluoroscopy
time (40.9 to 11.7 seconds per procedure), a 73%
reduction in mean air kerma (15.48 to 4.25 mGy)
and a 71% reduction in mean DAP (518.90 to
150.28 mGy m2).15 Another study of cystogram
protocols showed that adjusting machine settings
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or
No. pts
Age (yrs):
Mean SD
No. less than 6 (%)
No. 6-10 (%)
No. 10-12 (%)
No. greater than 12 (%)
Mean SD AP thickness at umbilicus (cm)
Mean SD total operative time (mins)
No. preop stent (%):
Yes
No
No. postop stent (%):
Yes
No
No. ureteral access sheath (%):
Yes
No
No. retrograde pyelogram (%):
Yes
No
No. safety wire (%):
Yes
No
No. complication (%):
Yes
No
No. % surgeon trainee role (%):
Less than 50
50
Greater than 50
After
Checklist
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Before
Intervention
%
Change
88
87
88
67
85
78
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INTERVENTION TO REDUCE PATIENT EXPOSURE TO RADIATION DURING URETEROSCOPY
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The results of our analysis should be interpreted
in light of their limitations. This study was done in
patients treated at a single tertiary center and patient characteristics, surgical practices and other
factors in this setting may not apply to other settings. Although we compared procedures with and
without the checklist, this study was not a randomized trial. Therefore, differences in outcomes
between the pre-checklist and postchecklist groups
may have been due to factors other than initiation of
the checklist, such as changes in procedure techniques or equipment, or greater general awareness
of radiation safety issues. However, we believe that
the magnitude of the reductions in observed exposure was such that it is highly unlikely that such
ancillary factors would have had such an impact.
Furthermore, it is possible that the findings were
due in part to the Hawthorne effect, that is surgeons
and operating room staff were aware that they were
being observed and altered their behavior as a
consequence.24 However, notably surgeons and staff
were aware that they were being monitored during
the pre-checklist and postchecklist periods. Thus,
while overall exposure levels measured during the
study course may have been decreased by the
Hawthorne effect, this would have done little to
explain the differences between the study periods.
We also cannot comment on the long-term effectiveness of the checklist to maintain these reduced
exposure levels.
Finally, as in our prior report, we used indirect
methods to calculate patient dose outcomes from
measured exposure levels. Despite a strong correlation between indirect and direct methods, estimated patient doses always include some error.
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has the potential to decrease radiation without
compromising study quality.16
Taking a cue from the aerospace and other high
risk industries, checklists have been introduced into
the operating room environment and evidence suggests that use can significantly improve outcomes
and reduce the incidence of errors.1719 Video monitored investigations of operating room personnel
showed that critically important steps are 6 times as
likely to be performed when a checklist is available.20
In addition to the performance of key process
measures, checklists are associated with fewer
complications and with improvement in clinician
perceptions of teamwork and the safety climate.17
However, Simply constructing and mandating a
thorough safety checklist is not sufficient to achieve
successful long-term radiation reduction goals.
A more holistic, systems based approach is clearly
needed to achieve maximal effectiveness, safety and
quality.21 Efforts to explain the rationale behind
the checklist, commitment by surgical staff and
training in the proper use of the checklist are critical
to success.22 Our anecdotal experience confirms the
need for training. The checklist first had to be initiated by the research assistant and specific steps,
such as patient and fluoroscope positioning, had to
be demonstrated. We also solicited input from surgeons, radiation physicists, radiologists, radiation
technologists and nursing staff when designing the
checklist and determining logistics for the timing
of key steps and the location of equipment.
While a checklist helps achieve the lowest
reasonably achievable doses, other strategies may
also be important. Lower total exposure time has
been achieved when there is routine documentation
of fluoroscopy time in official reports (40%), or when
feedback is provided (24%).10,23 In addition, specialized equipment such as laser guided c-arms and a
dedicated radiological technologist familiar with the
nuances of pediatric URS may also be important
components of an overall dose reduction program.14
Finally, the introduction of new technologies may
decrease doses in the future, as shown by the success
of pulsed fluoroscopy and digital imaging.
Fluoroscopy machines have various exposure
settings, including continuous and pulsed modes as
well as reduced dose rate settings that allow for
maintained image quality with lowered radiation
exposure. The final checklist enabled the lowest
dose rate setting to be used at the start of the procedure as a default when patient thickness measurements were not available. When the initial
positioning images were of insufficient quality, the
dose rate setting could then be increased. Interestingly, surgeons were content with image quality at
the lowest setting in almost every case and typically
completed the case using the lower setting.
1477
CONCLUSIONS
Using a pre-fluoroscopy checklist resulted in a significant decrease in fluoroscopy time and the overall
radiation dose delivered to pediatric patients undergoing URS for urolithiasis. Additional system
changes may provide further reductions. Efforts
must be made to ensure the durability of these
effects.
ACKNOWLEDGMENTS
Michael Demers assisted with the study.
APPENDIX
Pre-fluoroscopy checklist
The included portions represent key factors identified using data from the initial
data collection period and input from stakeholders. The primary goal was
simplicity and attention to safe performance of the procedure first, eg surgeon
comfort for item 2, followed by important radiation reduction maneuvers.
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1478
1)
2)
3)
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INTERVENTION TO REDUCE PATIENT EXPOSURE TO RADIATION DURING URETEROSCOPY
Are the patient’s arms to the side?
Is the table height OK?
Has intensifier been brought to within one fist of patient?
What is the patient thickness? Has the dose rate setting been adjusted for
patient size?
a) Toddler: AP diameter less than 12 cm
b) Child: AP diameter 12 to 20 cm
c) Adult: AP diameter greater than 20 cm
Notes:
Standard Accepted Terminology:
“Live Fluoro”
“Spot Fluoro” or “Single X-ray”
“Off” or “Stop”
“Save”
“High Resolution” or “High Dose”
Repeat back to surgeon
Collimate when deemed appropriate, ie if only working on right side, collimation
on the left
Feedback at the end of case, ie fluoroscopy time and radiation dose
**If patient thickness has not been measured, set to “toddler” for first image
5) Is the exposure mode set to digital?
6) Is everyone wearing lead?
REFERENCES
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of patients with urinary lithiasis: minimizing radiation exposure. Curr Urol Rep 2010; 11: 80.
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6. United Nations Scientific Committee on the
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7. Slovis TL: The ALARA concept in pediatric CT:
myth or reality? Radiology 2002; 223: 5.
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cystourethrography. Br J Radiol 2007; 80: 731.
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dose computerized tomography for detection of
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4. Strauss KJ and Kaste SC: The ALARA (as low
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to keep radiation doses as low as possible during
fluoroscopy of pediatric patientsda white paper
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reduction during voiding cystourethrography.
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3. Hernanz-Schulman M, Goske MJ, Bercha IH
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2. Preston DL, Cullings H, Suyama A et al: Solid
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1. Scientific Committee 6-2 on Radiation Exposure
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