estimating cumulated absorbed doses and associated health risks due to occupational exposure to...
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Estimating cumulated absorbed doses and associatedhealth risks due to occupational exposure to ionising
radiation
David Moriña, James Grellier, Adela Carnicer, Eileen Pernot andElisabeth Cardis
May 28th 2015, Barcelona, ICRA 6
Contents
1 Introduction
2 Methods
3 Risk estimation
4 Example
5 Further work
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Introduction
Occupational exposure
• Interventional cardiology (IC) comprises a variety of minimally invasiveprocedures used in the diagnosis and treatment of cardiovasculardisease
• Interventional radiology (IR) forms a key component of the work of theinterventional cardiologist
• Used appropriately to support a variety of procedures, IR representsenormous clinical benefits like minimal invasiveness, reduced pain andrisk, shorter hospital stay and lower cost
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Introduction
Occupational exposure
• Interventional cardiologists and electrophysiologists are occupationallyexposed to ionising radiation
• The clinical benefits of using catheterisation techniques instead of opensurgery have resulted in a considerable increase in workload over thepast two decades
• There is concern that present cumulated doses may result in increasedrisk of brain cancer and cataracts to surgeons
• Effective use of radiation protection measures can reduce these risks byreducing doses to the brain and eye lens
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Introduction
Occupational exposure
• There are some tools for radiation risk assessment already available, butfocused essentially on acute exposures and on cancer related diseases
• Our goal is to estimate doses and associated health risks foroccupational chronic exposures also for other radiation related diseaseslike cataracts
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Introduction
Occupational exposure
• We designed a tool that employs robust estimators of parameters basedon a multiple linear regression of predictors of dose including radiationprotection measures, catheterisation access route, tube configurationand operator experience (derived from data collected in the ORAMEDproject and from the literature) and a user-defined occupational historyto produce distributions of annual and total cumulated absorbed dosesto the targets of interest
• Potential sources of uncertainty are taken into account by means ofMonte Carlo simulation
• Occupational histories can be reconstructed by the user using generaldata derived from existing databases
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Introduction
Occupational exposure
• Changes in imaging equipment available to interventional cardiologistsover the past four decades were taken into account by fitting ametaregression model using results from a literature review, and thecomputed doses are adjusted using these values
• Probability distributions of risk are then calculated on the basis of theresulting cumulated absorbed doses, using estimates of dose-responseand related uncertainties derived from the literature
• In direct support of radiation protection, the tool allows the user tocompare their doses and associated risks with those expected under ascenario where protective equipment is employed to the fullest extentand under a scenario where no protective equipment is employed at all
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Introduction
Occupational exposure
• Outputs of the tool allow population attributable risks of health outcomesto be calculated for specific populations of these health professionals, forwhom group-level occupational histories are reconstructed
• By extension, it allows for estimation of the expected health benefits forthat population associated with use of a variety of radiation protectionmeasures
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Methods
The tool
• The webtool has been developed in R using the shiny package, whichallows to build interactive web applications from R
• The left panel on the website allows the user to enter specific dataconcerning their career (profession, working dates range and number ofannual procedures), while the results are automatically updated andpresented on the right side of the web
• The output part is divided in four tabs, allowing the user to compare theexpected doses in a “standard” career, the expected doses under theuse of all available protection measures and the expected doses underthe usage of none protection measure
• The fourth tab shows the typical behaviour regarding usage of protectionmethods and procedure type distribution per decade
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Methods
The tool
Figure: Screenshot of the tool
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Methods
Underlying model
• The main model considered was a robust linear regression model usingprotection measures as RadPad, table, cabin and screen, the type ofprocedure, the tube configuration and operator experience (high after 4years of work) as predictors of the absorbed dose
• The reduction on the lens dose due to the usage of lead glasses isassumed to follow a PERT distribution with minimal, modal and maximalvalues of 1, 3 and 10 respectively, based on expert opinions
• The obtained estimates were
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Methods
Underlying model
Protection method β̂ (95% CI)Table 0.746 (0.543; 1.026)
RadPad 0.828 (0.485; 1.415)Screen 0.826 (0.604; 1.130)Cabin 0.168 (0.055; 0.518)
Procedure β̂ (95% CI)CA PTCA Ref.
DSA PTA C 0.392 (0.193; 0.794)DSA PTA LL 0.920 (0.612; 1.384)DSA PTA R 0.600 (0.392; 0.906)
Embolisation 0.778 (0.565; 1.070)ERCP 2.166 (1.445; 3.246)
PM/ICD 1.827 (1.265; 2.639)RF ablation 0.965 (0.620; 1.500)
Tube configuration β̂ (95% CI)Above Ref.Below 0.244 (0.164; 0.363)
Biplane 0.230 (0.142; 0.372)Experience β̂ (95% CI)
High Ref.Low 1.063 (0.836; 1.351)
Table: Parameter estimates and confidence intervals
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Methods
Risk estimation
The PERT distribution is a particular case of the Beta distribution,characterized by the density function
f (x) =
{xα−1(1−x)β−1
B(α,β): 0 ≤ x ≤ 1
0 : Otherwise
where B(α, β) is the beta function, defined by
B(α, β) =
∫ 1
0tα−1(1 − t)β−1dt .
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Methods
Risk estimation
• Sampling from the beta distribution requires minimum and maximumvalues (scale) and two shape parameters, α and β
• The PERT distribution uses the mode or most likely parameter togenerate the shape parameters α and β
• An additional scale parameter λ scales the height of the distribution; thedefault value for this parameter is 4
• In the PERT distribution, the mean µ is calculated as
µ =min + max + λmode
λ+ 2
• And it can be used to compute the Beta parameters α and β:
α = (µ−min)·(2mode−min−max)(mode−µ)·(max−min)
β = α·(max−µ)µ−min
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Risk estimation
Risk estimation
• Instead of dosimetry, users may be interested in estimate the cumulatedabsorbed dose has increased their risk of cataracts
• Once the dose is estimated as described before, the associated healthrisk is estimated by means of the PERT distribution with minimal, modaland maximal values derived from the literature
Cataract kind Minimal value Modal value Maximal valueStage 1-5 1.22 1.70 2.38Early PSC 1.25 1.89 2.84
Stage 1 PSC 1.01 1.42 2.00
Table: Minimal, modal and maximal values for cataract risk
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Risk estimation
Risk estimation
• Instead of dosimetry, users may be interested in estimate the cumulatedabsorbed dose has increased their risk of cataracts
• Once the dose is estimated as described before, the associated healthrisk is estimated by means of the PERT distribution with minimal, modaland maximal values derived from the literature
Cataract kind Minimal value Modal value Maximal valueStage 1-5 1.22 1.70 2.38Early PSC 1.25 1.89 2.84
Stage 1 PSC 1.01 1.42 2.00
Table: Minimal, modal and maximal values for cataract risk
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Risk estimation
Report
Figure: Total dose distribution
The user can download a re-port including all the informa-tion regarding estimated dosesand associated risks in a pdfdocument
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Example
Example
For example, we can see how the cumulated absorbed lens doses andassociated health risks changes comparing a “standard” interventionalcardiologist working from 1985 to 2014 and doing about 300 proceduresannually from 1985 to 2000 and then 350 until 2014 to the same workingprofile incorporating the effect of the usage of all available protection methodsor incorporating the effect of the usage of no protection methods at all
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Example
Total dose distributions
Standard career
Dose (mGy)
Den
sity
0 10000 20000 30000 40000
0.00
000
0.00
002
0.00
004
0.00
006
0.00
008
0.00
010
0.00
012
All available protection methods
Dose (mGy)
Den
sity
0 2000 4000 6000 8000 10000
0.00
000.
0005
0.00
100.
0015
No protection method
Dose (mGy)
Den
sity
10000 20000 30000 40000
0.00
000
0.00
002
0.00
004
0.00
006
0.00
008
0.00
010
0.00
012
Figure: Total dose distribution
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Example
Annual dose
The annual absorbed dose for each scenario is also graphically represented
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Example
Annual dose0
100
200
300
400
500
600
Standard career
Year
Dos
e (m
Gy)
1985 1989 1993 1997 2001 2005 2009 2013
050
100
150
All available protection methods
Year
Dos
e (m
Gy)
1985 1989 1993 1997 2001 2005 2009 2013
200
300
400
500
600
700
800
No protection method
Year
Dos
e (m
Gy)
1985 1989 1993 1997 2001 2005 2009 2013
Figure: Annual dose
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Example
Results
• In the case of this example, the total cumulated absorbed lens doseestimated is 4932.79 mGy (685.18, 15046.38) under a “standard”scenario
• If no protection methods are used, these values are increased to11112.62 mGy (6063.63, 22715.79)
• In the scenario under the usage of all available protection methods, theestimated dose is 575.58 mGy (198.02, 1844.93)
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Example
Results
• Regarding the risk of cataracts, the differences between the scenariosare
Cataract kind Scenario Median RR (95% UI)
Stage 1-5Standard
All available protection methodsNo protection methods
8.6 (1.2, 27.1)1.0 (0.3, 3.1)18.3 (9.4, 39.0)
Early PSCStandard
All available protection methodsNo protection methods
9.6 (1.3, 30.8)1.1 (0.4, 3.5)20.4 (10.3, 44.3)
Stage 1 PSCStandard
All available protection methodsNo protection methods
9.6 (1.3, 30.7)1.1 (0.4, 3.5)20.4 (10.3, 43.9)
Table: Cataract risk for the different considered scenarios
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Example
Results
• Obviously, the effect of the protection methods is very relevant for thecumulated absorbed lens dose and for the risk of cataracts as well
• This comparison can also be done to the dose received if no protectionmethods were used at all
• The user can also see the difference between the different protectionmethods usage scenarios on the cataract risk. For example, we can seethe difference in the distribution of relative risk of stage 1-5 cataracts
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Example
Risk of stage 1-5 cataracts
Standard career
RR
Den
sity
0 20 40 60 80
0.00
0.02
0.04
0.06
All available protection methods
RR
Den
sity
0 5 10 15
0.0
0.2
0.4
0.6
0.8
No protection method
RR
Den
sity
20 40 60 80 100
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Figure: RR of stage 1-5 cataracts distribution
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Further work
Further work
• Estimate doses and associated risk for other organs/diseases (inparticular, brain/CNS tumours)
• Use of other health impact measures as• Population attributable fraction• Attributable cases• Lifetime excess risk of cancer• Years of life lost (YLL)• Disability-adjusted life years (DALYs)
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Further work
Live example
The tool is already available onhttp://crealradiation.shinyapps.io/radtool
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Centre for Researchin EnvironmentalEpidemiology
Parc de Recerca Biomèdica de BarcelonaDoctor Aiguader, 8808003 Barcelona (Spain)Tel. (+34) 93 214 70 00Fax (+34) 93 214 73 02