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Vinca Institute of Nuclear Sciences Radiation and Environmental Protection Laboratory www.vinca.rs. Olivera Ciraj-Bjelac , Milojko Kovacevic, Danijela Arandjic, Djordje Lazarevic Vinca Institute of Nuclear Sciences Radiation and Environmental Protection Department

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Olivera ciraj bjelac milojko kovacevic danijela arandjic djordje lazarevic

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Olivera Ciraj-Bjelac, Milojko Kovacevic, Danijela Arandjic, Djordje Lazarevic

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Department

Laboratory for Radiation Measurements

Belgrade, Serbia

[email protected]

DOSIMETRY FOR MEDICAL APPLICATION OF IONIZING RADIATIONS: Calibration requirements and clinical applications


Content

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Content

  • Global trends in medical exposures

  • Dosimetric quantities and units

  • Dosimetry in diagnostic radiology

    • Metrology and calibration requirements

    • Clinical application


Medical exposure to ionizing radiation

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Medical exposure to ionizing radiation

  • Medical exposure contributes 99% of man-made radiation exposure to humans

  • The concept of risk is used to quantify possible detrimental effects

Total dose from man-made sources of radiation> 0.61 mSv

Medical: 0.6 mSv (> 99.97%)

Source: United Nations Scientific Committee for Effect of Atomic Radiation (UNSCEAR), 2010


Medical exposure to ionizing radiation1

Medical exposure to ionizing radiation

Dose?

The role of dosimetry is to determine the amount of radiation received by a person from the radiological examination


Dosimetry in diagnostic radiology

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Dosimetry in diagnostic radiology

  • Patient dose assessment

  • Establishment of Diagnostic Reference Levels (DRL), optimisation of protection

  • Assessment of x-ray equipment performance

  • Standards of good practice

  • Assessment of radiation detriment


Global trend

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Global trend

  • 3,6 billion radiological examinations in the period 1997-2007

  • Increase of 50% compared to previous decade

  • Significant increase of CT practice:

    • Examination frequency

    • Dose per examination

  • Interventional procedures


Dose to patient

Depends on the examination type

Variations for the same type of procedure

Dose to patient

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

  • 2 mSv

  • 100CxR

5-20 mSv

400- 1000 CxR

0.02- 0.05 mSv

50 chest radiographies= annual natural background radiation dose


Proble ms

Problems

Dose for the same examination type varies up to 2 orders of magnitude

Increased utilization of high-dose procedures

CT

Interventional procedures

Increase of probability for stochastic effects, in particular in the case of the repeated examinations

Possible radiation injuries in high-dose procedures

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Effects


Olivera ciraj bjelac milojko kovacevic danijela arandjic djordje lazarevic

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs


Radiation injuries

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Radiation injuries

ICRP 85


Basic metrology elements

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Basic metrology elements

  • International Measurements System (IMS)

  • Framework for dosimetry in diagnostic radiology

  • Consistency in radiation dosimetry


International measurements system ims

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

International Measurements System (IMS)

  • Bureau International des Poids et Mesures (BIPM)

  • National Primary Standard Dosimetry Laboratories (PSDL)

  • Secondary Standards Dosimetry Laboratories (SSDL)

  • Users performing measurements


Traceability chain

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

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Traceability chain


Metrology and traceability

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Metrology and traceability

  • Dosimeters used to determine doses received by individuals

  • Measurements need to be traceable though an unbroken chain of comparisons to national and international standards

  • Traceability is needed to ensure accuracy and reliability

  • Legal and economic implications


Role of the ssdl

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Role of the SSDL

  • The prime function: to provide a service in metrology

  • Designated by the competent national authorities

  • SSDL-Secondary standards, calibrated against the primary standards of laboratories participating in the IMS


Olivera ciraj bjelac milojko kovacevic danijela arandjic djordje lazarevic

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Journal of the ICRU Vol 5

No 2 (2005) Report 74


Dosimetric quantities in units in diagnostic radiology

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Dosimetric quantities in units in diagnostic radiology

  • Basic dosimetric quantity: Air kerma

    • Easy to measure

  • Calibration:

    • Dosimeters calibrated in terms of air kerma

  • Clinical application:

    • Quantities derived from air kerma for different imaging modalities


Dosimetric quantities

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Dosimetric quantities

  • Basic dosimetric quantities

  • Application specific dosimetric quantities

  • Quantities for risk assessment

  • Conversion coefficient for tissue and organ dose assessment


Basic dosimetric quantities

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Basic dosimetric quantities

  • Energy fluence

    Unit:J/m2

  • Kerma

    Unit:J/kg, Gy

  • Absorbed dose

    Unit:J/kg, Gy


Basic dosimetric quantities1

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Basic dosimetric quantities

  • Charged-particle equilibrium

  • Absence of bremsstrahlung losses


Application specific dosimetric quantities

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Application specific dosimetric quantities


Olivera ciraj bjelac milojko kovacevic danijela arandjic djordje lazarevic

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs


Olivera ciraj bjelac milojko kovacevic danijela arandjic djordje lazarevic

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Application specific dosimetric quantities: computed tomography


Olivera ciraj bjelac milojko kovacevic danijela arandjic djordje lazarevic

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Application specific dosimetric quantities: computed tomography


Quantities describing risk

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

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Quantities describing risk

  • Organ and tissue dose

  • Equivalent dose

  • Effective dose

  • Dose-conversion coefficients for assessment of organ and tissue doses


The use of effective dose e

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

The Use of Effective Dose (E)

  • E is a risk-related quantity and should only be used in the low-dose range

  • Primary use:

    • to demonstrate compliance with dose limits

    • in regulation, for prospective planning of radioprotection

  • Not for:

    • detailed retrospective dose and risk assessments after exposure of individuals

    • epidemiological studies, neither in accidents.

    • In the last cases: organ doses are needed !

ICRP 103, ICRP 105


Effective dose in medical exposure

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Effective Dose in Medical Exposure

  • The relevant quantity for planning the exposure of patients and risk-benefit assessments is the equivalent dose or the absorbed dose to irradiated tissues.

  • The assessment and interpretation of E is very problematic when organs and tissues receive only partial exposure or a very heterogeneous exposure (x-ray diagnostics)

  • E can be of value for comparing doses from

    • different diagnostic procedures

    • similar procedures in different hospitals and countries

    • different technologies for the same medical examination.

ICRP 103, ICRP 105


Dosimeters in diagnostic radiology

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Dosimeters in diagnostic radiology

PSDL/SSDL

user


Dosimetry standards in diagnostic radiology

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Dosimetry standards in diagnostic radiology

  • IEC 61674: Dosimeters with ionization chambers and/or semi-conductor detectors as used in X-ray diagnostic imaging

    • Diagnostic dosimeter: detector and measuring assembly

  • IEC 60580: Dose area product meters


Requirements for dosemeters

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Requirements for dosemeters

User

SSDL

Ionization chamber of reference class

  • IEC 61674

  • Ionization chambers

  • Semiconductor detectors


Calibrations in diagnostic radiology

Calibrations in diagnostic radiology

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

  • Air kerma:

    • Radiography and mammography

  • Kerma-length product

    • Dosimeters in CT

  • Kerma-area product

    • Radiography and fluoroscopy

  • PPV: kVp meters

  • Frequency: according to national regulations


Calibration in diagnostic radiology

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Calibration in diagnostic radiology

  • SSDL with relevant measurement capabilities

  • General requirements: beam qualities, tube voltage and filtration measurements

  • Dosimeter of reference class (with electrometer)

    • Calibrated

    • Quality control

    • Traceability for all beam qualities

  • Auxiliary equipment: electrometers, thermometers, barometers…

  • Environmental conditions


Equipment

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Equipment

Dosimetry

Radiation source

X-ray generator, 50-150 kVp, 20-40 kVp

Ripple less than 10% for radiography and less than 4% for mammography

Beam qualities according IEC 61267

“Shutter” mechanism

Filters and attenuators

Tube voltage meter (ppv, ±1.5%)

  • Ionization chambers

  • Position system

  • HV supply for monitor and reference class ionization chamber

  • Electrometer


Reference class dosemeter

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Reference class dosemeter


Specification of the x ray beam

Spectrum

X-ray beam quality:

First half-value layer (HVL1)

Second half-value layer (HVL2)

Homogeneity coefficient:

Tube voltage

Total filtration

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Specification of the x-ray beam


Radiation beam qualities iec 61267

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Radiation beam qualities (IEC 61267)


Typical calibration set up

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Apertures

X-ray tube window

Focal

spot

Test point

Additional filtration

Shutter

Monitor chamber

Typical calibration set up


Calibration procedures

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

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Calibration procedures

  • Procedures before calibration (acclimatization, positioning, stabilization…)

  • Calibration procedures (methods, number of measurements, interval between measurements…corrections…

  • Procedures following calibration (uncertainty budget, certificate…)


Dosimetry formalism

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

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Dosimetry formalism

  • Air kerma:

  • Reference conditions: set of influencing quantities

  • Influencing condition: quantities that are not subject of mesusremst but have an impact on the result

  • Air density correction:

  • Beam quality correction:


Calibrations of dosemeters for ct

Calibrations of dosemeters for CT

Traditionally, irradiation of the whole volume

Contras:

Information on chamber response only

Size on active volume only assumed

Far from real situation

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs


Calibration for ct air kerma length product

Calibration for CT: air kerma length product

Aperture

Ionization chamber

Monitor chamber

Focal spot

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

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w

da

dr

Cylindrical chamber, 100 mm

Non-uniform irradiation

Uniform response

RQT 9 (120 kVp, HVL: 8.5 mm Al)


Olivera ciraj bjelac milojko kovacevic danijela arandjic djordje lazarevic

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Ref. chamber

Film

10 cm

10 cm

Calibration for fluoroscopy: air kerma area product

  • In laboratory (SSDL)

  • Fieldcalibration

Cekerevac at al, Poster B3


Calibration in terms of practical peak voltage

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

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Calibration in terms of practical peak voltage

  • X-ray tube voltage measurements

  • PracticalPeakVoltage (ppv):

  • Property of the whole exposure cycle

  • Related to image contrast

  • Invasive or non-invasive measurements

  • Voltage divider


Olivera ciraj bjelac milojko kovacevic danijela arandjic djordje lazarevic

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Uncertainty budget

  • Uncertainty of the reference standard

  • Uncertainty of user’s instrument

  • Uncertainty due to calibration set up

  • Uncertainty of the evaluation procedure


Uncertainty budget

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Uncertainty budget

  • Air kerma: ± 2.7 %

  • Air kerma length product: ± 3.0 %

  • Air kerma area product: ± 15 %

  • Non-invasive tube voltage measuring devices: 2.5 %


Quality management system

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Quality Management System

  • Goal: minimal uncertainty

  • Assurance and control of traceability

  • Quality manual: technical details, methods, traceability, uncertainty budget, QC, safety….

  • Continuous improvements and reviews

  • External peer review/audit


Patient dose assessment

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Patient dose assessment


Clinical dosimetry

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Clinical dosimetry

  • Direct measurement on patients or phantoms

  • Indirect measurements on patients or phantoms

    • Output of the X-ray tube, scaled for exposure and geometry


Dosimetric quantites

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

BSF

Dosimetric quantites

KAP

Ke

Quantities

incident air kerma, entrance surface air kerma and kerma-area product (radiography);

kerma-area product and entrance surface air kerma rate (fluoroscopy);

incident and entrance surface air kerma (mammography); and

kerma-length product (computed tomography)


Patients and phantoms

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Patients and phantoms

Patient

Phantoms

Objects that simulate real patients in terms of interaction of radiation with matter

Easy to perform

Standardized

  • Real situation


Radiography

Radiography

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs


Fluoroscopy

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Fluoroscopy


Mammography

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Mammography


Computed tomography

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Computed tomography


Patient dose levels

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Patient dose levels


Uncertainty of clinical dose assessment

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Uncertainty of clinical dose assessment

  • Radiographers taking the x-ray images

  • Determining tube output

  • Calculation of individual patient doses

  • Determining dose to an average patient

  • Use of k=2 for expression of uncertainty of dose assessment

  • Typically >10% and close to 25%*

*if correction for beam quality and for individual patient is not applied


Form measurements towards risk assessment

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Form measurements towards risk assessment

  • Conversion coefficients

    • Conversion of measured quantity into organ doses and effective dose

    • Ratio of the dose to a specified tissue or effective dose divided by the normalization quantity

    • Measured using phantoms or calculated using computer models

    • Voxel phantoms based on images of human anatomy


Organ dose assesment

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Organ dose assesment


Olivera ciraj bjelac milojko kovacevic danijela arandjic djordje lazarevic

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

  • ICRU 74


Optimization of protection

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Optimization of protection


Application of drls

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Application of DRLs

  • Values of measured quantities above which some specified action or decision should be taken

    • Values must be specified

    • Action must be specified

  • DRLs will be intended for use as a convenient test for identifying situations where the levels of patient

    dose are unusually high.

    Quantities that are easily measured!


Diagnostic reference levels

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Diagnostic Reference Levels

Doses to patients from radiographic and fluoroscopic X-ray imaging procedures in the UK—2005 review. HPA RPD-029, HPA; 2007.


Re cap

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

Re-cap

  • Diagnostic radiology is major contribution to total dose from man-made sources of radiation

  • Dose measurements: population dose assessment, optimization of practice

  • Application-specific dosimetric quantities (patients, phantoms)

  • Calibration of dosimeters in the conditions that are similar to the clinical environment, in terms of

    • air kerma

    • kerma-area product

    • kerma-length product


Olivera ciraj bjelac milojko kovacevic danijela arandjic djordje lazarevic

Vinca Institute of Nuclear Sciences

Radiation and Environmental Protection Laboratory

www.vinca.rs

  • Olivera Ciraj-Bjelac, PhD, research associate, dosimetry and radiation physics

  • Milojko Kovacevic, MSc, Head of MDL, radiation physicist

  • Danijela Arandjic, MSc, PhD student, dosimetry and radiation physics

  • Djordje Lazarevic, MSc, PhD student, dosimetry and radiation physics

  • Dragana Divnic, technician

  • MilosJovanovic, technician

  • Nikola Blagojevic , technician


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