Eye Lens Dosimetry Workshop · 2017-11-16 · •Overview of dosimetry concepts and methods...

Eye Lens Dosimetry Workshop

Renato Padovani

ICTP, Trieste

Conference on Physics in Medicine: From Diagnosis to Treatment

"Enhancing safety and quality in radiation medicine".

KFMC, Riyadh

7-9 November 2017

• To know methodologies for eye lens dosimetry

• To be able to discuss factors affecting eye lens doses, to know typical correction factors from protective devices,

• To be able to discuss the sources of uncertainties in the assessment of eye lens dose

• To be able to properly design a monitoring protocol aiming to assess also eye lens doses

Learning Objectives

Conference on Physics in Medicine: From Diagnosis to Treatment, Riyadh, 7-9 Nov 2017 2

• Effects of radiation on eye

• Epidemiological evidences

• Levels of eye exposures in IR

• Overview of dosimetry concepts and methods

• Monitoring protocol

• Eye protections and efficacy

• EURALOC study on dose-effect relationship

• New ICRP recommendations

Content


Cataract and lens opacity

• A cataract is an opacity of the normally clear lens which may develop as a result of aging, metabolic disorders, trauma, heredity or……RADIATION!


Cataract

• Starts with lens opacities

• Types of cataract: nuclear, cortical, posterior subcapsular

– Damaged cells in lens

• Radiation: cortical, posterior subcapsular (but not exclusively)


• Eye lens is highly radiosensitive.

• Coagulation of proteins occur with doses greater than 2 Gy.

• There are 2 basic effects: - Detectable opacities

- Visual impairment (cataract)

Effect of radiation on eye


Degree of opacity and likelihood proportional to dose

– Latency period inversely proportional to the dose, typically 1 year

– Doses up to 2 Gy rarely cause cataracts; doses> 7 Gy always produce cataracts

– The exposure in chronic reduces the likelihood

Cataract


Epidemiological studies on humans for medical occupational exposures

• Medical occupational exposure

– Number of studies show increased risk of cataracts for hospital based workers • Milacic (2009), Ciraj-Bjelac et al (2010), Mrena et al (2011), Dauer

et al (2010), Anastasian et al (2011), Vano et al (2010),…

• O-Cloc study (Jacob, 2012), IRSN, France

– 100 cardiologists + control group

– Clear increased prevalence in cardiology group

– No clear dose relationship


Epidemiological studies on humans for medical occupational exposures

• Vano et al., 2013:

– 58 physicians, 69 nurses and technicians during congress

– Unexposed match control

– Lens doses roughly estimated from questionnaire

– Dilated slit lamp eye examination

– Posterior subcapsular lens changes (not cataract, but opacities) were found in 50% of the cardiologists, and 41% of nurses and technologists

– Less then 10% in controls


ICRP Recommendation: reduced eye lens annual dose limit for lens exposure

• Consistency between all studies: Relative Risk (RR) at 1 Gy > 1

BUT

• No sound confirmation on threshold dose

• Do not exclude the absence of a threshold dose

Studies are too small


• ICRP 103 (2007): • threshold dose of 2 Gy (acute exposure) and 5 Gy (protracted exposure) • occupational eye lens dose limit: 150 mSv/year

• ICRP 118 (2012):

• threshold dose of 0,5 Gy • occupational eye lens dose limit: 20 mSv/year

High level of eye exposure in medical practice

Interventional radiology and cardiology, guided by fluoroscopy images, have the potential to deliver high cumulative doses to staff

In nuclear medicine: manipulation of therapeutic beta sources

Staff involved in interventional procedures work next to the patient

close to the X-ray beam

• ISEMIR (IAEA 2014): 730 IC workers, 26 facilities, 16 countries – Eye lens dose to ICs from reported data:

32±70 (max 700) Sv/proc (nurses 10±12, max 32) – Only 37% of ICs claim to always use all protective tools

– Over apron dose as an indicator of the eye exposure – Many Ics over the new dose limit

– From ISEMIR surveys: • use of protective tools and personal dosimeters are uneven • quality of occupational dose monitoring is poor • knowledge about actual doses is limited. • This has implications for the professionals, hospital

management, and regulatory bodies.

Eye lens exposures in IR


Evidences of high level of eye exposure of IR/IC/EF physicians (Italy)

• Annual dose over the protective apron (eye dose) in a sample of IC and IR facilities, Italy 2011

0.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

CI CI CI CI CI EF EF EF IN IN IN IN NI NI RI RI RI RI RI RI TE TE TE

Maximum/Mean Over apron Annual Dose/Hospital

max

Large fraction of interventionalists are receiving lens doses over new

EU BSS eye lens dose limit

CI: int. cardiologist, EF: electrophys, IN: nurse, NI: neuroradiol, RI: int. radiologist, TE: radiographer


EYE LENS MONITORING


• There are three fundamental challenges related to occupational exposure monitoring:

1. Need for a simple, easily implemented and consistent approach to monitoring that does not require frequent analysis of what to do.

2. Need for converting one or more dosimeter readings into effective dose and equivalent dose for specific tissues.

3. Need for compliance by the staff with monitoring procedures and proper and regular use of the dosemeters.

Staff monitoring challenges


Recommendations of ICRP 103 (2007) have revised the dose quantities that allow to evaluate the radiation-induced effects with regard to late stochastic and genetic effects

Radiation protection dose quantities

EQUIVALENT DOSE

J/Kg = Sv HT = wR∙DT

wR expresses the biological effectiveness of a given

type of radiation.

Type of radiation and energy interval

Wheighting factor wr

Photons ( all energies)

Electrons ( all energies)

Neutrons ( < 10 KeV)

Neutrons (da 10 KeV a 100 KeV)

Neutrons ( da 100 KeV a2 MeV)

Neutrons ( da2 MeV a 20 MeV)

Neutrons ( > 20 MeV)

Protons ( > 2 MeV)

particles

1

1

5

10

20

10

5

5

20

EFFECTIVE DOSE

E = ∑ HT ∙ wT J/Kg = Sv

HT is the averaged equivalent dose for reference male and

female, wT represent the relative contribution of that organ or

tissue to the total detriment. In brackets the weighting factors

of ICRP 60 modified in ICRP 103 (2007)

Organ or tissue Wheighting factor wt

Gonads

Colon

Red bone marrow

Lungs

Stomach

Bladder

Breast

Liver

Esophagus

Thyroid

Bone surface

Skin

Remaining organs and tissues

(0.20) 0.08

0.12

0.12

0.12

0.12

0.05

(0.05) 0.12

0.05

0.05

0.05

0.01

0.01

0.05

• The radiation protection dose quantities (equivalent dose and effective dose) are not measurable

• Operational quantities are therefore used for the assessment of effective dose or equivalent doses in tissues or organs

• They are often used in practical regulations or guidance.

Operation dose quantities

• Where doses are estimated from area monitoring results, the relevant operational quantities are:

– ambient dose equivalent H*(d)

– directional dose equivalent H*(d,)

• For individual monitoring, is recommended the use of the

– personal dose equivalent Hp(d) • Hp(10) – penetrating radiation

• Hp(0.07) – non-penetrating radiation skin equivalent dose

• Hp(3) – eye lens dose

Operational Quantities

• The calibration of dosimeters is performed under simplified conventional conditions, on an appropriate phantom.

• The quantity Hp(d) may be used to specify the dose equivalent at a point in a phantom representing the body.

• If a dosimeter measures Hp(d) correctly at a point in such a phantom, it is assumed that it measures Hp(d) with sufficient accuracy in the body of any person.

ISO phantoms used in the calibration of (a) whole-body, (b) bracelet and (c) ring dosimeters

Calibration of individual dosimeters


Relationship of dosimetry quantities

Primary physical quantities

Fluence, f

Kerma, Ka

Absorbed dose, D

Protection quantities Operational quantities Ambient dose equivalent, H*(d)

Directional dose equivalent, H'(d,W )

Personal dose equivalent, HP(d)

Calculated using Q(L) and simple

phantoms (sphere or slab)

validated by measurements and

calculations

Compared by measurement and

calculations (using wT, wR ) and

anthropomorphic phantoms

Monitored quantities:

Instrument responses

Related by calibration and

calculation

Calculated using wR, wT

and anthropomorphic

phantoms

Organ absorbed dose, DT

Organ equivalent dose, HT

Effective dose, E


• Can be performed with:

– a specifically designed dosimeter worn at the level of the most exposed eye (usually on the left side) and calibrated in term of Hp(3)

– or, from the Hp(0.07) reading of a whole-body dosimeter worn at the collar level over protective garments

Eye lens dose assessment

21

Conference on Physics in Medicine: From Diagnosis to Treatment, Riyadh, 7-9 Nov 2017

ICRP 116 (2011) : Operation quantities vs. Eye lens dose

For IR x-ray qualities: Hp(10) or Hp(0.07) can substitute Hp(3)


ICRP 116

ICRP 116 (2011) : CONVERSION COEFFICIENTS FOR RADIOLOGICAL PROTECTION QUANTITIES FOR EXTERNAL

RADIATION EXPOSURES. APPENDIX F.

Equivalent eye dose/ air kerma Average values for the 2 eyes

R. Behrens, PTB, Germany , ORAMED Workshop, Barcelona 2011


ICRP 116 (2011): EYE DOSE VS. AIR KERMA

R. Behrens, PTB, Germany , ORAMED Workshop, Barcelona 2011

Right different from Left eye dose ICRP 116


ORAMED: Dosimeter position (Gaber,2011)

• MEASUREMENTS IN CLINICAL SITES: DOSIMETER POSITION VS LENS DOSE

• Dose at measurement sites relative to the Lens Dose (left) from phantom measurements


Position of dosimeter Absorbed dose as a percentage of the dose to the left lens

Measurements Simulations

Left side of head 106 (103-109) 86-96

Right side of head 20 (16-23) -

Over le left eye (eyebrow) 87 (55-108) 95

Centred between the eyes 80 (75-84) 88

ORAMED: Eye dose per type of procedure normalised to patient KAP (Vanhavere,2011)

LENS DOSE VS PATIENT DOSE

Wide variation of lens dose:

• between procedures: mean 3.10-6 - 6.10-5 mSv/µGym2

• for the same procedure F. Vanhavere et al, Measurements of eye doses in Interventional Radiology and cardiology,

Rad. Measurements . 46 (2011), 1243-1247


• Several factors are influencing eye dose: – Position of the operator, X-ray projection

– Dosimeter position: • Left side (on the side of the x-ray tube)

• Alternative: dosimeter at the neck over the apron • Different studies are providing corrective factors

from 0.4 to 0.9

Summary

Operational quantity:

• Hp(3)

• Hp(0.07) or Hp(10)can be properly

used


From collar dosimeter to eye lens dose


• European ELDO project (funded by DoReMi network) “Correlation between eye lens dose and whole body dose”

• Measurement of eye lens doses and whole body doses in clinical conditions – Measurements above the lead apron

• Eye, Collar, Chest, Waist level

• Left – middle – right side

– Clinical conditions

• Different x-ray beam projections and x-ray qualities

• Different operator positions

• Mono-plane and bi-plane

– Without protection equipment (ceiling suspended screen and lead glasses)

Conversion coefficients from Hp(10) over the apron doses to eye lens dose


• Hp(3)/Hp(10) distribution for each position of the whole body dosemeter vs. X-ray projection

A wide (again) distribution of the coefficients

Conversion coefficients from Hp(10) over the apron doses to Eye lens dose

European ELDO project


• The collar left or central positions are giving the lower standard deviations

Conversion coefficients from Hp(10) over the apron doses to Eye lens dose

Ratio of average left eye lens dose and Hp(10) measured at different locations, considering all projections and access routes.

Collar

L

Collar

M

Collar

R

Chest

L

Chest

M

Chest

R

Waist

L

Waist

M

Waist

R

Ratio 3.3 2.1 11.5 0.8 1.2 2.5 1.5 1.8 8.0

Standard

deviation 42% 48% 81% 90% 73% 100% 159% 143% 147%

Ratio of average right eye lens dose and Hp(10) measured at different locations, considering all projections and access routes.

Collar

L

Collar

M

Collar

R

Chest

L

Chest

M

Chest

R

Waist

L

Waist

M

Waist

R

Ratio 2.7 1.7 8.6 0.7 0.9 5.7 1.3 1.6 6.2

Standard

deviation 42% 45% 73% 90% 58% 473% 164% 153% 155%


Effect of shielding

• Not only monitoring is important: reducing and avoiding doses

• Shielding: – Lead glasses

– Ceiling suspended shield

– RP cabin,….

• How effective is such shielding?

• Many different influence factors

• Type of glasses, position, kVp, projection, …


Effect of protective eyewear

Radiation direction Dose transmission factor (%)

1 2 3 4 5 6 7 8

Frontal, left lens 18 14 27 26 23 14 16 20

Frontal, right lens 17 13 25 26 24 17 19 17

Below, left lens 72 43 78 85 86 22 35 70

Below, right lens 98 89 97 94 97 89 88 92

When radiation is coming from below, great difference between models due to

the gap created between the eyewear and the cheek and the nose T. Geber, Eye Lens Dosimetry for Interventional Radiology, Rad. Meas. 46 (2011)

Design and individual fit is decisive. Design should minimise gaps


Small lenses Large lenses (x 2.5 larger)

90 kVp, 3 mm Al, 0 mm Cu

Field size at image intensifier = 20 cm diameter

Left eye

Ratio with/without glasses

PA CRA20

No lead glasses 1 1

Small lens (0.5 mm Pb) 0.30 0.28

Large lens (0.5 mm Pb) 0.15 0.14

Small and thick lens (1.0 mm Pb) 0.26 0.25

Large and thick lens 0.14 0.13

LEAD GLASSES (ORAMED)


Lens thickness >0.5 mm Pb does not improve the protection of the eye lens significantly

Large lenses that cover better the eyes are preferred

Ceiling shield

Ceiling shield

19 different configurations considered (rotated/straight shield, above patient/next to operator’s head, touching patient/10 cm above, mono-tube/biplane etc.)

Values in this table = ratio doses With/Without ceiling shield

Config. Left eye Right eye Collar L Collar M Collar R Chest L Chest M Chest R Waist L Waist M Waist R

Rotated + touching

patient + PA proj.

0.34 0.19 0.41 0.26 0.18 0.42 0.24 0.25 0.66 0.58 0.62

Rotated + touching patient +

LLAT proj.

0.88 0.84 0.88 0.86 0.85 0.81 0.58 0.67 0.97 0.94 0.96

Straight + touching patient +

LLAT proj.

0.12 0.20 0.09 0.17 0.27 0.27 0.52 0.51 0.98 1.0 0.97

Observation: Inappropriate positioning of the ceiling shields may decrease their protection efficiency

Result: Mean correction coefficient to account for the ratios to account for the use of ceiling shield for any interventional procedure and tube configuration Left eye = 0.53 (71%)


• Protection factors for eye lens and head (expressed in term of Dose Reduction Factor - DRF):

– Ceiling suspended screen: • from different clinical studies: 2 to 10 (Vano, 2015), 1.3 to 7

(Vanhavere, 2012), 0.7 to 2.5 (Jacob, 2013), 5 (Magee, 2014)

• from simulations: 8.5 to 17.6 (Galster, 2013)

• with careful placement: 19 (Maeder, 2006)

It gives better protection of lead glasses, also to the head and neck

Suggested a DRF range 2 to 3

Summary and recommendations (2017 draft ICRP)


• Protection factors for eye lens and head (expressed in term of dose reduction factor - DRF):

– Lead glasses: • Several not recent papers: 2 to 10

• Today after measurements and simulations: 1.8 to 5.8 (Galster, 2013), 3 to 4 (Cousin, Vanhavere and others)

• Conventional glasses with lateral protection have larger gaps between glasses and head. Better wraparound glasses. Important to check

Measurements are recommended (but not DRF > 4)

Where no measurements a DRF of 2 is recommended

Summary and recommendations (2017 draft ICRP)


A retrospective epidemiological study


European epidemiological study on

radiation induced lens opacities among

interventional cardiologists Lara Struelens

Belgian Nuclear Research Centre (SCK•CEN)

40

http://www.ru.nl/english/

EURALOC concept

• Goal:

– Investigate the relationship between the dose received to the lens of the eye and the occurrence of lens opacities

• Challenges:

– Recruitment of interventional cardiologists (ICs) in different countries

follow the same protocol

Pooling the data: Increase the cohort size

Provide a distribution of possible eye lens doses for each IC single dose estimate

detailed and quantitative investigation of the impact of cumulative eye lens dose on lens opacity occurrence

Define adequate strategy to deal with complex statistical design represented by the ophthalmological data

addressing the correlation between pairs of eyes in the same individual


Methodology

Recruitment of interventional cardiologists &

controls

• 11 countries

• 393 ICs

Additionally, 106 IC from France and 19 IC from Finland

Identified: 1628 + 41 German cardiology departments

Contacted: 1560

Eligible: 562 (82%)

Responded: 684 (44%)

Consented: 318 (57%)

Questionnaire: 314 Eye examination: 268

No response: 876

Declined: 244

Two questions: 150

Not eligible: 97


Methodology

Recruitment of interventional cardiologists &

controls

1. Completion of questionnaires

2. Ophthalmological examinations

1a. General & medical quest.

1b. Occupational quest.

Confounding factors

Eye lens doses

Lens opacities

Dosimetry methodology

APPROACH 1: Eye lens dose data from literature + individual working history

APPROACH 2: Conversion from whole body dose to eye lens dose

Lens opacities

Slit lamp imaging scoring density according LOCSIII scale

Scheimpflug imaging quantitative scoring in continuous way


Retrospective dosimetry

Dosimetry methodology

APPROACH 1: Individual working history +

eye lens dose data from literature

APPROACH 2: Conversion from whole body

to eye lens dose

• Direct eye lens dose measurements

• Individual occupational history • Evolution over the years • Consider the number of procedures

• Large spread in available eye lens dose data • even for similar working practices

• Confidence in self reported info from early years

• Use of personal dose information of recruited cardiologist

• Conversion to eye lens dose • Availability of Hp(10) values

above the apron • Very low confidence in correct use of

whole body dosimeter in early years!


Retrospective dosimetry approach 1

• Based on available literature data

– Individual measured dose values from 7 papers and 4 unpublished studies

– Creation of eye lens dose Probability Density Functions (PDF) for different exposure configurations

• 500,000 x sampling frequency histograms from literature data, including measurement uncertainty

• kernel density estimates

zyxjD ,,,• j: type of procedure • x: lead glasses • y: ceiling suspended

screen • z: type of x-ray system

CA –

ceiling screen –

monoplane C-

arm


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Eye Lens Dosimetry Workshop · 2017-11-16 · •Overview of dosimetry concepts and methods...

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