Filip Vanhavere- 09/11/2021 New Dosimetric Techniques: an ...

Filip Vanhavere- 09/11/2021

New Dosimetric Techniques: an overview(including eye lens dosimetry)

ISC: RestrictedReference

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.


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….


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


Different passive dosimetry systems used world wide

• Film dosemeter

• On rapid decline….


• Thermoluminescent detectors

• Different materials: LiF:Mg,Ti – LiF:Mg,Cu,P – Li2B4O7:Cu - …

• Different manufacturers: Harshaw, Rados, Panasonic, …


http://www.google.be/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=http://na.industrial.panasonic.com/products/hvacr-appliance-devices/radiation-measurement-systems/radiation-readers-irradiators&ei=18t1VNi5OfGd7gbfiYGQCw&bvm=bv.80642063,d.ZGU&psig=AFQjCNG7j3qsvfBIxKEJldItAEmKrATS6w&ust=1417092379646769

http://www.google.be/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&ved=0CAcQjRw&url=http://na.industrial.panasonic.com/products/hvacr-appliance-devices/radiation-measurement-systems/radiation-readers-irradiators&ei=18t1VNi5OfGd7gbfiYGQCw&bvm=bv.80642063,d.ZGU&psig=AFQjCNG7j3qsvfBIxKEJldItAEmKrATS6w&ust=1417092379646769


• Optically Stimulated Luminescence detectors

• Different materials: Al2O3:C, BeO

• Different manufacturers: Landauer, Dosimetrics



• Radio Photoluminescence Detectors

• Glass dosemeters

• Chiyuda Technology



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


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


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


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


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….


Extremity and neutron: worse results

• EURADOS IC 2009: extremity dosemeters


• 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


Extremity and neutron: worse results

• EURADOS ICn 2012: neutron dosemeters


• 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


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….


“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


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


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


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)


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


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.


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, …


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


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


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


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


• 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


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


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


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


Monte Carlo

Simulations

Human

Computational

Models

Parallel CPU/GPU

ComputingComputer

VisionMachine

Learning

Exploiting most advanced technologies


• 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


Dose

Calculation

Motion

Tracking

Input

Radiation

Source

Input

Geometry

Input

Dose Simulations Input

Staff movement monitoring and Radiation field mapping


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


• 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


Tracking to computational phantom

Realistic Anthropomorphic Flexible Phantom (RAF)


Animation of RAF phantom


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


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


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


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


Test at UZ-VUB - Brussels


Test at CHU-Liège


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


Procedure Dose Report

Procedure parameters:

• kVp:

- 80 – 125 kVp

• DAP:

- 15935.6 μGy.m2

• Projections:

- 0LAO / 0CRA

- 75RAO / 0CRA

- 27RAO / 0CRA


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

ISC: RestrictedReference50

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


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…


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

Filip Vanhavere- 09/11/2021 New Dosimetric Techniques: an ...

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