www.nrpa.no

Metode for estimat av absolutt risiko fra

radiologiske undersøkelser

HPA-CRC-028 Radiation risks from Medical X-ray Examinations (2011)

Hilde M. Olerud, Dr.ing.

Seksjonssjef Statens strålevern

1.Amanuensis II Fysisk institutt, UiO

www.nrpa.no

… learning objectives

• Status of the

knowledge about

dose and risks from in

ionising radiation

• How to estimate organ

doses in diagnostic

radiology

• A method to estimate

absolute risks as input

to cost-benefit

analysis

How would you rate the absolute

risk of radiation induced cancer?

1) Yearly dental X-ray screening

2) Follow up cancer testis «wait

and see» patients every third

month with CT of pelvis,

abdomen and chest

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History, status and challenges

Five goal areas :

1. More user-oriented cancer care

2. Vanguard nation for good

patient progress through the

system

3. Vanguard nation within cancer

prevention

4. More people shall survive and

live longer after cancer

treatment

5. Best possible quality of for

patients and relatives

New National Cancer

Strategy 2013 - 2017

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Bildediagnostikk ved utredning og kontroll

av kreftsykdommer • Første møte i Helsediraktoratet

6.12.2012

• Fokus på mandat & arbeidsform

• Møtet 24. januar

• Lungekreft

• Møtet 21. mars

• Ca. testis

• Møtet 12. juni

• Ca.testis – Prostata

• Møtet 25. september

• Prostata, nyre

• Møtet 12. desember

• Status – videre arbeid?

• Middag

• Strålevernets innspill i arbeidet

– Strålefysikk, dose-risk

– Fra KVIST faglige anbefalinger

4

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Referral guidelines for use of radiology

Input to cancer action plans • Does the radiological procedure provide added value to the

decision making process about further treatment?

• What modality is the best to answer the clinical question?

– Xray – CT – MR – US – NM (PET/CT, PET/MR…)

• The issues about costs: Use of common resources in a

socio democratic community as in the Nordic countries.

– Aim: Equal health services to people across the country

– Alternative costs: How could we better use the money?

• The issue about radiation risks

– Vulnerable groups of patients; pediatrics, young adults,

chronic diseases, follow up patients, screening…

– Risks into perspective – other kinds of (bigger) risks

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The order of magnitude of radiation doses

Radiotherapy

- external, NM

Radiological examinations

- Xray, CT, nuclear medicine

Staff exposures

- Operators *)

Gy/Sv mGy/mSv mGy/mSv

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Late effects of moderate and low doses

Increased risk of cancer

• No other cancer types, just increased incidence

• A certain latency period – takes time before the cancer shows clinical symptoms

– leukemia 5-7 years

– solid cancer 20-30 years

Hereditary effects in later generations

• congenital deformity, malformation

STOCASTIC EFFECTS

• Since the probability increase with increased dose

• When it occurs it manifest similar

Starting

devision

Cancer cell

Mis repair

Normal

cell

Radiation

event

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ICRP 103 Cancer risk for low doses

• Risks of radiation induced

cancer and hereditary effects

are extracted from the

Japanese Life span study

– LSS – Hiroshima/Nagasaki .

– High doses over short time

• Risk factors are reduced from

LSS with a factor 2 (DDREF-

factor) to estimate the risk for

low doses (< 100 mSv) over

along time

• (A187): ”On this basis it is recommended that the LNT model, combined

with a judged value of DDREF for extrapolation from high doses, remain

a prudent basis for the practical purposes of radiological protection at

low doses and low dose rates”.

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Excess cancer risk associated with CT of children leukemia and brain cancer – a cohort of 350.000 barn i UK

Pierce M. Lancet 2013; 380(9840): 499 – 505

• Relative risk x 3 for age<15y from repeated CT scans of children

– Brain, leukemia

• Support the linear no threshold model (LNT) for doses > 1mSv

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Understanding the dose parameters Dose quantity

• Air kerma/dose to water

• CTDIvol measured in 16cm

and 32 cm PMMA phantoms

• DLP (dose-length product)

• CTDIvol and DLP

• Organ absorbed dose (mGy)

• Effective dose (mSv)

• Collective effective dose

Used for

• Physical quantity you measure

• Estimates the organ doses in the

CT scan region (mGy)

• Monitor total dose burden (mGycm)

• Basis for diagnostic reference levels

in CT and optimisation. Stored as

part of the DICOM header in PACS.

• For risk assessments, and in the

calculation of effective dose

• For comparison of various exposure

situations (RG versus CT)

Say something about the risk for

late effects from a radiation

protection point of view, but NOT to

be used in risk assessments

TT T HwE

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ICRP 103 Organ- and tissue weigthing factors

Risk coefficients (% per Sv)

www.nrpa.no

Excess cancer risk as function of dose and

age at exposure

• Graph shows lifetime

attributable cancer mortality

risks per unit dose as a function

of age at a single acute

exposure as estimated by

• National Academy of Sciences

BEIR (Biological Effects of

lonizing Radiations) committee

(solid line)

• and in ICRP (International

Commission on Radiological

Protection) report 60 (dotted

line)

• Note rapid increase in lifetime

risk with decreasing age at

exposure.

Children more

radiosensitive –

and have longer

life expectancy

www.nrpa.no

How to do radiation risk estimates Healt Protection Agency (HPA) in UK; Report HPA-CRCE-028 (2011)

1. National surveys of local examination procedures (exposure- and

scan parameters) for current equipment in selected room and

laboratories (Xray radiography&fluoroscopy, CT, nuclear medicine)

2. Calculations of organ absorbed doses using commercially available

software; the basis is simple dosimetry parameters but advanced

simulations of the different examination procedures (Monte Carlo

simulations of the interaction between radiation and matter)

3. Estimates of total lifetime cancer risk for age groups of patients

using published age-, sex- and organ specific risk factors published

by ICRP

4. Calculations of effective dose (ICRP 103) for the most common

examinations, so that the estimated risk can be normalised to

the effective dose (total lifetime cancer risk given in % per Sv)

www.nrpa.no

Dose survey methods: the “practical dose parameters”

• For radiography and fluoroscopy the practical dose parameter is the dose area product, DAP

• for mammography it is the calculated “mean glandular dose”

• while for CT it is the weighted and pitch corrected CTDIvol and the dose length product, DLP

• FUTURE: data collection from picture archiving and communication system (PACS)

Radiography and fluoroscopy Mammography CT

DAP

MGD

Dair

CTDIw

CTDIvol

DLP ESD

www.nrpa.no

Monte Carlo simulations in Xray and CT

• Theoretical simulations of the photons

interactions in patients/biological tissue

by means of a computer

• Define a mathematical phantom where

radiation sensitive organs and tissue are

given certain coordinates

• The Xray energy spectrum must be

known (kV, anode, filtration) as well as

the fluence of photons from the Xray

tube, the irradiation geometry, distance,

etc

• The irradiation is simulated while we

keep track of all energy deposits in

various parts of the phantom. We may

simulate Xray radiographs and

fluoroscopy, mammography, CT

scans…

• Provides conversion factors between

measurable quantities (DAP, ESD,

CTDI) and doses to organs in the body

MATEMATICAL PHANTOMS

• Simple models based on geometrical figures

• VOXEL phantoms based on CT or MR uptake of real patients

Glandular tissue/fat

50% / 50%

www.nrpa.no

CT dose calculator http://www.impactscan.org/index.htm

Input parameters

• Scanner model

• kV

• Head/body FOV

• Scan region

• mA og rotation time

• ”collimation”

• Pitch

The calculation of

• Organ doses

• CTDIw – CTDIvol

• DLP – effective dose

Scanner Model: Acquisition Parameters:

Manufacturer: Tube current 260 mA

Scanner: Rotation time 0,6 s

kV: Spiral pitch 0,984

Scan Region: mAs / Rotation 156 mAs

Data Set MCSET20 Effective mAs 158,5366 mAs

Current Data MCSET20 mm

Scan range Rel. CTDI 0,858196 0,86 at selected collimation

Start Position 4 cm CTDI (air) 30,008 30,0 mGy/100mAs

End Position 44 cm CTDI (soft tissue) 32,1 mGy/100mAs

nCTDIw 9,5111 9,5 mGy/100mAs

Organ weighting scheme

CTDIw 14,8 mGy

CTDIv ol 15,1 mGy

DLP 603 mGy.cm

Organ wT HT (mGy) wT.HT HT (mGy)

Gonads 0,08 10 0,81 Adrenals 18

Bone Marrow 0,12 8,1 0,97 Small Intestine 21

Colon 0,12 19 2,2 Kidney 24

Lung 0,12 3 0,36 Pancreas 18

Stomach 0,12 21 2,6 Spleen 19

Bladder 0,04 21 0,84 Thymus 0,52

Breast 0,12 0,71 0,085 Uterus / Prostate (Bladder) 21

Liver 0,04 19 0,77 Muscle 8,2

Oesophagus (Thymus) 0,04 0,52 0,021 Gall Bladder 22

Thyroid 0,04 0,062 0,0025 Heart 3,7

Skin 0,01 6 0,06 ET region (Thyroid) 0,062

Bone Surface 0,01 11 0,11 Lymph nodes (Muscle) 8,2

Brain 0,01 0,0022 0,000022 Oral mucosa (Brain) 0,0022

Salivary Glands (Brain) 0,01 0,0022 0,000022 HT (mGy)

Remainder 0,12 12 1,5 Eye lenses 0,00075

Not Applicable 0 0 0 Testes 1,5

Total Effective Dose (mSv) 10 Ovaries 19

Uterus 20

Prostate 21

ImPACT CT Patient Dosimetry CalculatorVersion 1.0.4 27/05/2011

Scan Description /

Comments

Remainder Organs

Collimation

Other organs of interest

Update Data Set

Look upGet From Phantom Diagram

Look up

Look up

www.nrpa.no

www.nrpa.no

Organdose i CT

www.nrpa.no

Age- sex and

organ specific risk

factors

• Organisations like BEIR

and ICRP provide such

data based on

UNSCEAR macro

updates of research

• Radiosensitive organs

are identified

• All risk estimates should

preferably be based on

individual dose

estimates for organs at

risk, and patients age-

and sex

HPA-CRC-028 Radiation risks from Medical X-ray Examinations (2011)

www.nrpa.no

Total lifetime risk %

per Sv

• Merk at risk for indusert

cancer er normalisert til

effektiv dose (ICRP 103)

• Men det underliggende er

kunnskap om:

• beregning av organdoser

for spesifikke radiologiske

prosedyrer (scan

protokoll)

• Og bruk av organ- alder-

og kjønn spesifikke risk

faktorer

www.nrpa.no

How to rate risk

HPA-CRCE-028

• «Negligible» or «minimal»

– Xray of extremities

– All planar Xray and fluoroscopy

of people > 50 years

• «Very low» or «low» risk

– Xray and fluoroscopy in trunk

region

– CT examinations of middle age

and elderly

• «Moderate» risks

– patients suffering from chronic

diseases or having a cancer

follow-up regimes with many

extensive CT scans of the trunk

– Multiple Pediatric CT’s

www.nrpa.no

Example: Follow up Ca.testis male 20-29 yr BASED ON HPA (2011) methodology

• Table 27: Total life time cancer risk from a typical CT of abdomen-pelvis is

in the order of magnitude 1/1000 (average age and sex)

• Table 20: For male in the age group 20 – 29 yr the risik factor is stated as

520 per 10-6 from a typical CT of abdomen-pelvis.

• Tabell 29: Total life time cancer risk for male in the age group 20 – 29 is

stated as 7,5 % per Sv from CT in the abdomen-pelvis region.

• Based on a local protocol dedicated to the particular patient the effective

dose is calculated to 11 mSv (ICRP103, Impact dose calculator). For the

actual CT procedure the life time cancer risk is then calculated as

0,075/1000mSv*11 mSv=0,000825 or 825 per 10-6. This estimate is valid

for the particular CT scanner, protocol and patientgroup.

• If you presume that radiation risk risiko increases lineary with cumulative

dose for an individual patient, the lifetime risk can be estimated from the

cumulative effective dose (mSv) considering different follow-up regimes

• Ten repeated CT examinations in certain intervals during three years

would in case give a risk of 825 per 10-5 for this patient (1/100)

www.nrpa.no

Interactive RadioEpidemiological Program

NIOSH-IREP v.5.5.2

For Estimating Probability of Cancer Causation for

Exposures to Radiation

NIOSH-IREP was created for use by the Department of Labor for adjudication of claims in accordance with the Energy Employees' Occupational Illness Compensation Program Act of 2000 (EEOICPA). NIOSH-IREP was adapted from the National Institutes of Health's (NIH)

Interactive RadioEpidemiological Program (IREP) developed by the National Cancer Institute (NCI) to update the NIH Radioepidemiological Tables of 1985. (The version of IREP

developed by NCI is known as NIH-IREP.)

NIOSH-IREP v.5.5.2, introduced on June 13, 2007, increases the capabilities of the Multiple Primary Cancer calculation from being able to handle 12 primary cancers to being able to

handle up to 120 primary cancers. The PC results from v.5.5.2 are identical to those calculated using the previous version of NIOSH-IREP. Click here for more details about the

modifications made to version 5.5.2 and to other recent versions. Comments and suggestions should be communicated directly to NIOSH.

ABOUT SSL CERTIFICATES

www.nrpa.no

EXAMPLE

• Claimant Information Used In Probability of Causation Calculation:

• Birth Year: 1948

• Year of Diagnosis: 1997

• Cancer Model: Stomach (151) N/A

• General Exposure Information:

• Exposure Year : 1977

• Organ Dose : 22 mSv

• Exposure Rate : Acute

• Radiation Type : photons E=30-250keV

• Probability of Causation (PC)

• 1st percentile 0.00 %

• 5th percentile 0.01 %

• 50th percentile 0.69 %

• 95th percentile 8.45 %

• 99th percentile 16.27 %

www.nrpa.no

ICRP 103 Annex A - state of the art health risk

www.nrpa.no

ICRP 103 Letal doses

www.nrpa.no

ICR

P 1

03

– A

nn

ex A

Se

x s

pe

cific

ca

nce

r risk

www.nrpa.no

ICRP-103 - Annex A

Sex averaged cancer risk

www.nrpa.no

ICRP 103 Annex B - dosimetric quantities

Effective dose

• ”the primary use of effective dose is for demonstrating complience with dose limits, i.e. for regulatory purposes. E should not be used for epidemiological purposes or assessment of cancer probability”

• ”The assessment and interpenetration of effective dose from medical exposure of patients is problematic when organs and tissues receive only partial exposure or of very heterogeneous exposure, which is the case especially with diagnostic and interventional procedures.”

Collective effective dose

E = wT H T