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]
