Filip Vanhavere- 09/11/2021 New Dosimetric Techniques: an ...
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Filip Vanhavere- 09/11/2021
New Dosimetric Techniques: an overview(including eye lens dosimetry)
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Framework for individual monitoring
Individual monitoring of individuals occupationally exposed to external
ionizing radiation should be carried out in order to:
• Control occupational exposure
• Demonstrate compliance with dose limits and the ALARA principle
• Inform workers of their radiation exposure
Individual monitoring may also be carried out:
• For epidemiological investigations
• To demonstrate that radiation protection principles are being followed
• To provide information for the evaluation of doses in the event of accidental exposures.
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Introduction
• Individual dosimetry for external radiation
• Basically still same techniques as in 50’s:
• Point measurement on worker using a dosemeter
• Techniques slowly evolve, something new every 10-20 years
• Pencil dosemeters
• Film dosemeters
• Luminescent dosemeters
• Active dosemeters based on diodes
• No significant improvement on performance
• More changes in quantities and limits than in techniques….
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Personal dosimetry: measuring operational quantity Hp(10)
• Protection quantities
• Effective dose E
• Equivalent dose in organs HT
• Occupational limits expressed in these quantities
• No deterministic effects (tissue effects)
• Limit stochastic effects
• Effective dose E is non-measurable:
• Operational quantities: personal dose equivalent
• Hp(d) with d: 10, 3, 0,07 mm
• Objective of personal dosimetry:
• Measuring Hp(d) for all practical situations, independent of energy, direction, type,… with
an overall prescribed accuracy
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Different passive dosimetry systems used world wide
• Film dosemeter
• On rapid decline….
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• Thermoluminescent detectors
• Different materials: LiF:Mg,Ti – LiF:Mg,Cu,P – Li2B4O7:Cu - …
• Different manufacturers: Harshaw, Rados, Panasonic, …
Different passive dosimetry systems used world wide
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• Optically Stimulated Luminescence detectors
• Different materials: Al2O3:C, BeO
• Different manufacturers: Landauer, Dosimetrics
Different passive dosimetry systems used world wide
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• Radio Photoluminescence Detectors
• Glass dosemeters
• Chiyuda Technology
Different passive dosimetry systems used world wide
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Overall accuracy: ICRP75
• Accuracy required:
• factor 1.5 in either direction for doses
near the limit
• Factor 2.0 for lower doses
• Trumpet curve
• For neutrons a worse accuracy is expected
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Large uncertainties allowed in personal dosimetry
• Factor of 2 is actually not very strict…
• Leads to doubts on performance of dosimetry service by customers
• Most services don’t report the uncertainty on the reports
• What would customer reaction be if on the report is
“In 1 month 200 µSv ± 200 µSv is measured….”
• They would mistrust dosemeter service
• They would pay less attention to the correct use of their dosemeter
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Large uncertainties allowed in personal dosimetry
• Why are such large uncertainties allowed?
• Other large uncertainties involved to get to risk assessment…
• Hp(10) is only estimation of E: large uncertainty
• System of operational quantities as estimation for limiting quantities
• So why should dosimetry service do an effort to get a 5%
better results with their dosemeter?
• Trust in results would improve
• Every uncertainty gained is positive
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How well do dosemeters measure Hp(10)?
• EURADOS intercomparisons give a good image of performance of (mainly
European) service
• IC2012
• 87 participating services
• 1400 irradiated dosemeters
• 6% of data points outside trumpet curve
• 79% of services have no outliers
• 90% of services have maximum 2 outliers (ISO 14146 criterium)
• Overall mean response= 0.98 compared to reference
• In general: personal dosimetry services have no problems in satisfying
trumpet curve
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How well do dosemeters measure Hp(10)?
• Conclusion: good!
• So: no need to improve dosimetry?
• BUT: in intercomparisons only standard fields are used
• No or few mixed fields
• No other influence factors (like environmental influences)
• No high energy and high angles
• Standard fixation on phantom
• No workplace fields….
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Extremity and neutron: worse results
• EURADOS IC 2009: extremity dosemeters
• 59 participating services
• Outliers for gamma irradiations: 10%
• Outliers for beta irradiations: 35%
• The lower the energy, the worse the result
• For Kr-85: 65% of the results were outside the trumpet curve
• Clearly improvements are needed for low energy and high angles
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Extremity and neutron: worse results
• EURADOS ICn 2012: neutron dosemeters
• 34 participating services
• Two steps were needed
• Many systems needed information on neutron spectrum
• Around half of the services could estimate (in step 2) the
real dose within a factor of 2
• Clearly improvements are needed …
S01
S02
S03
S04
S05
S06
S07
S08
S09
S10
S11
S12
S13
S14
S15
S16
S17
S18
S19
S20
S21
S22
S23
S24
S25
S26
S27
S28
S29
S30
S31
S32
S33
S34
0.01
0.1
1
10
Re
sp
on
se
i.e
Hp(1
0) p
art
icip
an
t / H
p(1
0) re
fere
nce
Service ID for exercise
252
Cf - 0.3 mSv
252
Cf - 3.0 mSv
252
Cf - 15 mSv
252
Cf 45 degrees
D2O moderated
252Cf
252
Cf Shadow cone
250 keV
All fields
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Feedback on doses helps
• Active personal dosemeters (APD) give more feedback to worker
• Often used as ALARA or alarm dosemeter
• Mostly in combination with passive dosemeter as Dose-of-Record
• More feedback (on-line)
• Better use and care on dosemeters by workers
• Makes dosimetry more “useful”
• Use of APD will continue to increase
• Smaller and more sensitive devices
• Also now possible connected to smartphones
• New development: dosemeters in between active and passive….
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“Recent” development: direct ion storage detector
• Dosemeter between passive and active
• No alarm, no immediate read-out
• But can be consulted whenever needed via intermediate device
• Communication with iPAD, iPhone, pc….
• No return to dosimetry service for read-out anymore
• “read-out” is done in dosemeter
• Change of wearer possible on day to day basis
• Long stand alone battery life
BUT: approval, QC and calibration important
• Not stand alone use…. Still need of approved dosimetry service
• Background subtraction
• Temperature dependence
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Can APDs be used as legal dosemeter?
• APD’s have clear advantages
• ALARA, Alarm, higher sensitivity
• Present APDs: technologically suited as legal dosemeter
• Reliability is ok
• Less loss of results if dosemeter fails or gets lost
• Radiological characteristics are ok
• Comparable and even better than passive dosemeters
• BUT: approval, QC and calibration important
• Not stand alone use…. Still need of approved dosimetry service
• Regular calibrations needed
• May be less suited for some fields, like some hospital fields
• Low energies (RX)
• Beta (NM)
• Pulsed fields
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Using APD’s in interventional procedures
• Clear attention needs to be made for the energy range of the APDs
• Especially for low energies: <60 keV (scattered radiation)
• APDs have problems with pulsed fields:
• Will have large influence in direct beam
• In most situations will have smaller influence
• above table tube, close to tube, ….
• Important: point measurement is highly inhomogeneous field gives
rise to large uncertainties
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Eye lens dosimetry
• Cataract: “loss of transparancy of the lens of the eye”
• Cataract: most frequent cause for blindness worldwide• Genetic component
• Age related effect
• Additional risk factors include
• Sunlight, alcohol intake, nicotine consumption, diabetes, use of
corticosteroids
• Also induced by RADIATION…
• New eye lens limit: 20 mSv per year(averaged over 5 year, with not more than 50 mSv/year)
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Quantities: how to measure the eye lens doses?
• Dose limit: 20 mSv/year
• for HT, eyelens : equivalent dose at the eye lens
• Not directly measurable
• Need for operational quantity: Hp(3)
• Hp(3): Equivalent dose at 3 mm depth
• Operational quantity > limiting quantity
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Monitoring levels
• The following monitoring levels are recommended:
• 3/10th of the limit, as recommended in European BSS
• For the lens of the eye: if there is a reasonable probability to
receive a dose in a single year greater than 15 mSv or in
consecutive years greater than 6 mSv per year.
• For dose levels expected to be lower than the recommended
monitoring levels, a survey, demonstrating that the levels are
not exceeded, should be sufficient.
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Assessment of dose levels prior to monitoring
• Prior to routine monitoring, it is important to assess the dose levels
in a workplace field situation in order to decide if routine
monitoring is necessary.
• The doses obtained should be extrapolated to annual doses and
compared with the monitoring levels
• From literature, from confirmatory measurements, …
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Whole body monitoring: collar dosemeter
• Some studies suggest estimating the dose to the lens of the eye from a well-
placed dosemeter at collar level• Generally: this might be acceptable in homogenous fields with higher energy radiation, but not
recommended in other fields
• Not when dosemeter is used under protective clothing
• For example, for interventional radiology different correction factors have been published to
convert collar doses to doses to the lens of the eye for interventional procedures
• Such correction factors are very dependent on the type of procedure, personal habits, the
exact place of the above apron dosemeters and the protection measures taken, so they
cannot be applied to all routine cases.
• Such a system can however provide good indications of when dedicated eye
dosimetry is required
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Review of studies reported in literature
0
0.5
1
1.5
2
Ra
tio
of
eye
do
se
/ c
oll
ar
do
se
Third quartile
1.0
• Monte Carlo simulations suggest:
eye dose = 0.75 × collar dose
• Conservative assumption:
eye dose = collar dose
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Relationship between eye dose (Sv) and KAP (Gy cm2)
0
0.5
1
1.5
2
2.5
Efitha
thop
oulos et
al 2
003
(CA/P
TCA)
Dom
iniek et
al 2
011
(LL
R)
Dom
iniek et
al 2
011
(lower
lim
b)
Pra
tt & S
haw 1
993
(CA/P
TCA)
Kou
kora
va e
t al 2
011
(DSA lim
bs)
Dom
iniek et
al 2
011
(DSA C
ereb
ral)
Kicke
n et
al 1
999
(PTA 1
)
Efitha
thop
oulos et
al 2
006
(CA/P
TCA)
Kicke
n et
al 1
999
(PTA 2
)
Dom
iniek et
al 2
011
(em
bolis
ation)
Kicke
n et
al 1
999
(Abd
ominal A
rterio
gras
phy)
Kou
kora
va e
t al 2
011
(Ste
nt)
Lie
et a
l 200
8
Dom
iniek et
al 2
011
(CA/P
TCA)
Kicke
n et
al 1
999
(Cer
ebra
l arte
riogr
aphy
1)
Kou
kora
va e
t al 2
011
(DSA C
ereb
ral)
Kou
kora
va e
t al 2
011
(Nep
hros
tom
y)
Kou
kora
va e
t al 2
011
(Liver
che
moe
mso
lisat
ion)
Kou
kora
va e
t al 2
011
(Bra
in e
mbo
lisat
ion)
Dom
iniek et
al 2
011
(ERCP)
Kicke
n et
al 1
999
(Cer
ebra
l arte
riogr
aphy
2)
Dom
iniek et
al 2
011
(pac
emak
er)
Ra
tio
Eye d
ose/K
AP
(u
Sv/G
y c
m2) • An assumption:
KAP vs Eye dose
1 Gy cm2 1 Sv
• is reasonable for risk
assessment
• Not recommended for
monitoring purposes
Median
0.5
3rd quartile
0.9
Literature data: link with patient dose
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Application of correction factors: eye lens dosimetry
• Eye lens dosemeter positioning:• as close as possible to the eye
• if possible in contact with the skin
• faced to the radiation source
• dosemeter shall be worn preferably behind protective lead glasses
• In practical situations, dosemeters are often placed in various positions:
above the eyes, at the forehead, at the side of the head, between the
eyes, at collar,….• Use of correction factor
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• The dose reduction factor (DRF) of the eyeglass lenses is not an adequate descriptor• Maybe a factor of 100
• Protection from leaded eyewear reported on literature depends on several
parameters: model, fitting of the glasses, geometry,…
Hp(3)
r
efEye lens
Lens of the glasses
• A DRF of 2 could be applied to dosimeter results for
any lead glasses
• A DRF of 3 could be applied for better designs
Application of correction factors: eye lens dosimetry
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Example: EURADOS intercomparison of eye lens dosemeters
• Main objective: check the performance of eye lens dosemeters used
in routine in the medical field
• 2015
• 20 participants – 15 countries
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0
0,5
1
1,5
2
2,5
S-Cs, 0°, Low S-Cs, 0°, High S-Cs,60° N-40, 0° N-60, 0° N-80, 0° RQR6, 0° RQR6, 45° RQR6, 75° Realistic field
Resp
onse
Good results in intercomparison
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Personal Dosimetry: what brings the future?
• Workers don’t like to wear dosemeters….
• May be no need for physical dosimeters?
• Suppose we can use Monte-Carlo simulations to calculate on-line all doses
• Advantages:
• No more need for physical dosimeter
• No more loosing dosimeters
• No more need for operational quantities
• No more worries for changing quantities/weighting factors
• Doses to all organs can be known
• Personalized dosimetry possible
• Better accuracy possible
• Faster feedback to workers
• ….
mSv
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Monte Carlo
Simulations
Human
Computational
Models
Parallel CPU/GPU
ComputingComputer
VisionMachine
Learning
Exploiting most advanced technologies
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• Euratom project: CONCERT 2nd Call
• 24 months, 2018-2020
• 7 partners: SCK•CEN (Belgium), UPC (Spain/Catalunya), HMGU (Germany), LU (Sweden),
PHE (UK), EEAE (Greece), SJH (Ireland)
• Improve occupational dosimetry via an online dosimetry application
using computer simulations: without the use of physical dosemeters
• Apply and validate the methodology for two situations where
improvements in dosimetry are urgently needed: neutron workplaces
and interventional radiology
FEASIBILITY STUDY
PODIUM: Personal Online DosImetry Using computational Methods
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Dose
Calculation
Motion
Tracking
Input
Radiation
Source
Input
Geometry
Input
Dose Simulations Input
Staff movement monitoring and Radiation field mapping
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Storing XYZ coordinates or send to a cloud
Real-time processing
Depth Image
Staff Motion Tracking
Skeleton Tracking
Tracking system based on single depth camera
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• Polygonal Mesh Boundary Representation
• Organ and tissue masses adjusted according to
ICRP 89
• Computational model with 2900 tissues
segmented
• Dosimetric validation in comparison with ICRP 116
RAF: Realistic Anthropomorphic Flexible Phantom
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Tracking to computational phantom
Realistic Anthropomorphic Flexible Phantom (RAF)
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Animation of RAF phantom
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Geometry Input
Define of the workplace geometry for the calculations
Complex geometries can be prepared by:
Scanning of the workplace
Converting CAD files to different formats
Modeling and tracking of important moving objects (shielding)
is also needed
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Interventional Radiology and Cardiology Parameters
Parameter Range
High Voltage 60-120 kVp
Intensity 5-1000 mA
Inherent filtration 3-6 mm Aleq
Additional filtration 0.2-0.9 mm Cu
Energy range of scattered spectra 20 keV – 100 keV
X-Ray spectrum
• Tube potential (kVp value)
• Tube current
• Added filtration
• Target material
• Voltage waveform
Tube Angulation
• C-arm projections
Input
• Radiation dose structured report (RDSR)
extracted from the X-ray machine
• Time synchronization with tracking
• DAP meter for normalization
Radiation Source Input: Radiology Case
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Computational dosimetry … the solution?
Challenge: Make Monte Carlo calculations fast enough
PENELOPE/penEasyIR
MCGPU-IR
Look-up tables
approach
GOAL: MC simulation times:
20-30 s per irradiation eventFast Monte Carlo methods for
interventional procedures
MCGPU-IR
Based on MC-GPU (2009) a MC code for the
simulation of photon transport in restricted
geometrical set-up’s
PENELOPE/penEasyIR
Based on PENELOPE v2014, a standard
multi-purpose MC code
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NPSProjection
DAP
Distance
[X, Y, Z]
SID Filter
kVp
Field
diameter
Shield
[Y , N]Projection
DAP
Distance
[X, Y, Z]
SID Filter
kVp
Field
diameter
Shield
[Y , N]
Optimization Algorithm
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Test at UZ-VUB - Brussels
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Test at CHU-Liège
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Validation Case: Angioplasty Procedure
• Measurement of accumulated dose Hp(10) of operators with Thermo EPD Mk2.3
• Estimation of dosimeter location by the tracking system
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Procedure Dose Report
Procedure parameters:
• kVp:
- 80 – 125 kVp
• DAP:
- 15935.6 μGy.m2
• Projections:
- 0LAO / 0CRA
- 75RAO / 0CRA
- 27RAO / 0CRA
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Results from CHU-Liège case 4
Validation Case
Simulations
Accumulated
Hp(10)
Measured EPD
Accumulated
Hp(10)
EndoVasc CHU-Liège Case 4
(PCI)39 μSv 23 μSv
• Difficulties for comparison
• Low doses
• Exact dosemeter position is not known
• Use of protection screens
• Strong dose gradient on the body
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ALARA planning and training tool
• Accurate MC simulations using flexible phantoms
• Planning and analysis dosimetry tool visualizing
data in Virtual Reality environment
• Neural Network based framework for optimizing
dose calculations
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Conclusion
• Present passive personal dosemeter perform well in measuring Hp(10)
• Within ICRP required trumpet curve
• Factor 1,5 to 2…
• Improvement is however needed
• To increase trust in dosimetry results
• Extremity and neutron dosimetry
• Fast feedback on doses helps
• Active personal dosemeter
• Can be used a legal dosemeter, within approval requirements
• Careful for some applications, like pulsed fields
• New dosemeter types: between active and passive: no more monthly exchange…
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Conclusion
• Eye lens dosimetry
• Good dosemeters are available
• Seen as burden and not very practical
• Indirect methods (whole body, collar, patient dose): very large uncertainties
• When lead glasses are used: correction factor needed
• Future developments: More use of computational methods?
• Improvement compared to point measurements
• For specific high dose workplace fields
• Increasing contribution from AI and ML
• “prediction” of doses instead of simulating….
• Important aspect of visualisation of radiation
• ALARA and training tool