DOSIMETRY FOR MEDICAL APPLICATION OF IONIZING RADIATIONS: Calibration requirements and clinical applications 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]Vinca Institute of Nuclear Sciences Radiation and Environmental Protection Laboratory www.vinca.rs
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DOSIMETRY FOR MEDICAL APPLICATION OF IONIZING RADIATIONS: Calibration requirements and clinical applications Olivera Ciraj-Bjelac, Milojko Kovacevic, Danijela.
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DOSIMETRY FOR MEDICAL APPLICATION OF IONIZING RADIATIONS:
Calibration requirements and clinical applications
Olivera Ciraj-Bjelac, Milojko Kovacevic, Danijela Arandjic, Djordje LazarevicVinca Institute of Nuclear SciencesRadiation and Environmental Protection DepartmentLaboratory for Radiation MeasurementsBelgrade, [email protected]
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Content
Global trends in medical exposures Dosimetric quantities and units Dosimetry in diagnostic radiology
Metrology and calibration requirements Clinical application
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Medical exposure contributes 99% of man-made radiation exposure to humans
The concept of risk is used to quantify possible detrimental effects
Medical exposure to ionizing radiation
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0.61
0.0020.005
0.0020.005
mSv
Medical
Nuclear weapons
Occupational
Chernobyl
Atmospheric nuclear tests
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
Dose?
Medical exposure to ionizing radiation
The role of dosimetry is to determine the amount of radiation received by a person from the radiological examination
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
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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
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Depends on the examination type Variations for the same type of procedure
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
Effects
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Radiation injuries
10
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ICRP 85
Basic metrology elements
International Measurements System (IMS)
Framework for dosimetry in diagnostic radiology
Consistency in radiation dosimetry
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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
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Traceability chain
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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
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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
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Journal of the ICRU Vol 5No 2 (2005) Report 74
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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
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Dosimetric quantities
Basic dosimetric quantities Application specific dosimetric quantities
Quantities for risk assessment
Conversion coefficient for tissue and organ dose assessment
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Energy fluenceUnit:J/m2
KermaUnit:J/kg, Gy
Absorbed doseUnit:J/kg, Gy
dadR
trtr
dmdE
K
en
dmd
D
Basic dosimetric quantities
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Basic dosimetric quantities
Charged-particle equilibrium Absence of bremsstrahlung losses
trenDK
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Application specific dosimetric quantities
Quantity Symbol Unit Equation
Incident air kerma Ki Gy
Entrance -surface air kerma Ke Gy
Air-kerma area product PKA Gym2
Air-kerma length product PKL Gym
X-ray tube output Y(d) Gy/As
BKK ie
A
KA dxdyyxKP ),(
L
airKL dzzKP )(
Ita PdKdY /)()(
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Application specific dosimetric quantities: computed tomography
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Quantity Symbol Unit Equation
CT air-kerma index (free in air) Ca,100 Gy
CT air-kerma index (in standard phantom)
CPMMA, 100 Gy
Weighted CT air kerma index Cw Gy
Normalized weighted CT air kerma index nCw Gy/As
Air-kerma length product PKL Gym
Application specific dosimetric quantities: computed tomography
pPMMAcPMMAW CCC ,100,,100, 231
50
50100, )(
1dzzK
TCa
It
VOLVOLn
WWVOL
PC
C
pC
INT
CC
j
ItjjVOLjnKL PlCP
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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
quantityionnormalisat
quantitydosimetricc
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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
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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
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Dosimeters in diagnostic radiology
Tube voltage 20-150 keV, various A/F combinations, various modalities
Ionization chambers
Accurate
Good energy dependence
Design for different application (cylindrical, parallel-plate, different volumes..)
Semiconductor dosimeters
Compact
Energy dependant
Others
TLD
OSL
Film (radiochromic)
Scintillation
(kVp meters)
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PSDL/SSDL user
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
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Requirements for dosemeters
User IEC 61674 Ionization chambers Semiconductor
detectors
SSDL Ionization chamber of
reference class
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Calibrations in diagnostic radiology
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 V
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Calibration in diagnostic radiology
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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
Calibration of dosimeters in the conditions that are similar to the clinical environment, in terms of air kerma kerma-area product kerma-length product V
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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 Milos Jovanovic, technician Nikola Blagojevic , technician