An Overview of Radiation Monitoring
Programs in Radiology
Edward Wong
Chief Radiographer, HKSH
16 April 2011
Nuclear Plant Leakage
Radiation Horrors
• No Color, no Smell
• Deterministic effects
– Threshold dose
– Redness of skin
• Stochastic effects
– Younger affect most
– Exposure to 1 Sievert of
radiation is estimated to
increase the lifetime risk
of fatal cancer by around
5% (Atomic Bomb Study)
Radiation Horrors
• No Color, no Smell
• Deterministic effects
– Threshold dose
– Redness of skin
• Stochastic effects
– Younger affect most
– Exposure to 1 Sievert of
radiation is estimated to
increase the lifetime risk
of fatal cancer by around
5% (Atomic Bomb Study)
Radiation Horrors
• No Color, no Smell
• Deterministic effects
– Threshold dose
– Redness of skin
• Stochastic effects
– Younger affect most
– Exposure to 1 Sievert of
radiation is estimated to
increase the lifetime risk
of fatal cancer by around
5% (Atomic Bomb Study)
Public Awareness
Working 200
hours before
CRT monitor
Eat 130
Bananas
CXR (0.1mSv)
2 months Background
Radiation in Hong Kong
Smoking
7 Cigarettes
Travel 10
hours
by Plane
Educational Pamphlet
Educational Pamphlet
Accuracy of dose
information ?
What is the
examination dose
level of your institute ?
Dose Measurement
Quantity
Unit
Determination
Exposure
Coulombs (C) Measure the amount of ionization produced in air
/Kg
Absorbed
Dose
Gray (Gy) or
J/Kg
Measure the radiation energy absorbed by the patient
Equivalent
Dose
Sievert (Sv)
Multiply Absorbed Dose by a quality factor (QF) to show
harmful effects, e.g.
X-ray & Gamma: QF=1; Alpha particle: QF=20
Effective
Dose
Sv
Multiply Equivalent Dose by a tissue weighting (TW)
factor, i.e. Colon: TW=0.12; Skin: TW=0.01; Whole Body:
TW=1 (ICRP 2007)
Example: 100mSv to skin = Effective dose of 1mSv
Device for measurement
Film
badge
TLD
DAP and
printer
Various detectors
and Phantoms
TLD-100
chips
(Harshaw)
Dose Area Product Meter
• Reading includes SID
variation
• Reading includes
Collimation factors
• DAP do not measure
backscatter
• DAP do not measure
wedge or added filters
• mGy/cm2
Monte Carlo simulations
• The assessment of conversion factors
began more than 30 years ago
• Use tissue-equivalent plastic body
phantoms containing organs into which
dosimeters are inserted and Monte
Carlo simulations are applied
• Common available standard includes
an adult with a body mass of 70 kg;
children aged 15, 10, 5, 1 year and
newborns
• Effective dose: can’t measure routinely
• Entrance Skin Dose is commonly used
Effective Dose Calculation
The geometry of patient exposure is
less predictable and varies during the
procedure
X-ray
Fluoro
CT
The fundamental radiation dose parameter in
CT is the CT dose index (CTDI & CTDIvol). To
assess patient dose exposure after scanning a
certain distance use dose-length product
(CTDIvol × scan length)
Verdun F R et al. Radiographics 2008;28:1807-1816
Use ESD & DAP to calculate the
Effective Dose
HartD, Jones DG, Wall BF. Estimation of effective dose in diagnostic radiology from entrance dose and
dose-area product measurement (NRPB-R262). Chilton, England: NRPB, 1994.
Dose Reference Levels (DRL)
• Introduced by ICRP
• Dose level for typical exams for group of
standard-sized patients
• DRL are typically set at
the 3rd quartile of dose
distribution from a
survey
DRL for monitoring
Calculation of Entrance Skin Dose (ESD) for
Supine and Erect Abdomen in Digital
Radiography for HA hospitals
ESD = (DAP*BSF/FieldSize)*(SID/FSD)^2
FSD, focus-to-skin distance = SID - 25 cm
BSF, backscatter factor estimated from
NRPB SR262 (e.g. 80kVp = 1.458)
Information from DICOM Header
kVp = 110
Protocol = Chest
SID = 1800mm
FSD = 1750mm
FOV (collimation) =
35.1cm x 37.1cm
mAs = 3.376
DAP = 1.5766 mGy/cm2
Position = PA
Mapping to PACS
database is required
Results of DRL
A
B
C
D
E
Hospitals
F
G
Usage of DRL
Complied by ACR for Appropriateness Criteria
CR vs DR
• CR: no kVp and mAs
data
• Vendors have their own
calculation of Exposure
Index (EI) which give
feedback about detector
dose level
• AAPM try to standardize
the EI
• Complicated by
collimation detection and
post processing
Freeware for CT dose
• Image Server
• PHP/mySQL
• OCR
Move dose info to Database
• Difficult to handle more than one scanner
• Need mapping ?
Fluoroscopy ?
DICOM Structure Report
& IHE enhancement
• Store Dose Information - Similar to
Images Stored
• Query Dose Information
• Retrieve Dose Information
• Submit Dose Report
Dedicated Dose Monitoring
Reports and Alerts
LA Law: 5 Gy collective dose over 18
months or 4 Gy single examination !!!
IAEA Smart Card Project 2009
•
•
•
•
•
•
Tracking life time dose record for patient
eHR for recording or Radiation Passport
Access anywhere by digital signature
Data for monitoring public radiation level
Refine existing standard on dosimetry
Enhancement in DICOM & IHE-REM for
dose report and dose information
communication
Thanks
www.pacs.hk
[email protected]
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Radiation Dose Monitoring in Radiology