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Dosimeters, calibration and uncertainty Radcal Corporation Paul Sunde Monrovia, CA.

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Presentation on theme: "Dosimeters, calibration and uncertainty Radcal Corporation Paul Sunde Monrovia, CA."— Presentation transcript:

1 Dosimeters, calibration and uncertainty Radcal Corporation Paul Sunde Monrovia, CA

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3 Modern Dose Sensor Diversity Ion Chambers (nGy – kGy 10keV – MeV ) Solid State Multi-sensors (dose, kV, time, hvl, filt ) Solid State Dose only

4 Radcals Mfg. and Calibration Laboratory o Certified o ISO 9001:2008 (TUV since 1995) o IEC ISO/IEC 17025:2005 o ANSI/NCSL Z o All products CE marked o Direct traceability to o NIST (USA) – Air Kerma o PTB (Germany) – Air Kerma o Swedish National Laboratory – High Voltage o Proficiency Tested – NIST & Secondary Labs

5 Dose Calibration Chain National Laboratory Radcal Primary Ion Chamber Standards Working/Secondary Standards Std1 Std2 Std3 Std4Std5Std6

6 Proficiency Testing National Laboratory Transfer Standard Secondary Lab Radcal Cal Lab - Lab calibrates transfer std. - Ship to Radcal for calibration - Radcal calibrates & issues report - Return to lab for re-calibration - Lab Issues proficiency report

7 Customer Traceability Chain National Laboratory Radcal Customer Certificate of Conformance Certified Calibration

8 Radcal Certificate of Conformance o Motivation o Verify equipment meets published specifications o Preserve component interchangeability o Process o Test electronics (control unit) – verify performance and accuracy over full dynamic range o Independently test sensors with reference standard electronics for accuracy and energy dependence o Verify sensor & electronics combination, but do not adjust.

9 Air Kerma Uncertainty Budget NIST & PTB National Standard ~1% Radcal (1 ) Transfer measurements0.50% Long-term stability1.00% Short-term reproducibility0.50% Temperature: 0.25 ºC0.08% Pressure: 1mB0.10% Geometry & positioning0.20% Charge: 0.5%0.50% Beam quality*0.25% Quadrature Sum 1.5% Total Uncertainty 95% Confidence (2 ) 2.9%

10 TUR (test uncertainty ratio) Note: desirable TUR is >4 Implies RMS <1.25%

11 Beam standardization Geometry – IEC Radiation conditions for use in the determination of characteristics. Collimator 1 Trans Chamber 1 Added Filt Collimator 2 HVL Filters. Collimator 3 Trans Chamber 2 Laser Beam Splitter Prisim

12 Radcal Air Kerma Standards o 3-terminal guarding o < 5e-15 A leakage with 300 VDC bias o Negligible stem effects < 5% energy dependence over rated energy range o 2nGy to >20 Gy o Rates from nGy/s to >mGy/s o Energies from 10 keV to 2 MV

13 Recent Standard Chamber Set

14 Diagnostic Energy Response (RQR & RQA)

15 Ion Chamber Response for low energy x-rays American College of Radiology: ±1% mm Al hvl

16 Mammographic Energy Response Radcal 10X5-6M (DeWerd et al.) ±2%

17 Diode Energy Response

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21 Diode Energy Response – Auto Corrected via kV & hvl

22 Equipment Tolerances IEC – Dosimeters with ionization chambers and/or semiconductor detectors as used in x-ray diagnostic imaging" Performance CharacteristicsLimit of Variation Air Kerma Reproducibility1% Resolution<1% Stabilization2% Leakage currents (<1%/min)--- Stability2% Accumulated dose stability1% RMS3%

23 Equipment Tolerances IEC – Dosimeters with ionization chambers and/or semiconductor detectors as used in x-ray diagnostic imaging" Influence QuantitiesLimit of Variation Radiation Quality5% Air Kerma Rate2% Incidence angle (± 5°)3% Operating Voltage2% Air Pressure2% Temperature and Humidity3% EMC5% Field size3% RMS9%

24 Equipment Tolerances IEC – Dosimeters with ionization chambers and/or semiconductor detectors as used in x-ray diagnostic imaging"

25 Summary o Select dose sensors to match your requirements o Acceptable uncertainty - QA checks vs. acceptance testing o Energy range – Mammography vs. conventional, o Geometric response - fluoro backscatter, CT & tomo o Energy response – acceptable uncertainty o Dynamic Range - scatter & leakage vs. pulsed fluoro

26 Summary o Understand the sensor & associated electronics o Trigger thresholds – minimum dose rate o Maximum dose rate – pulsed fluoro o Opaque – interfere with AEC o Linearity over the range of application o Use of automatic vs. manual temp & pressure corrections o Time to come to thermal equilibrium

27 Paul Sunde Radcal Corporation Monrovia, California USA Thank You! ISO/IEC 17025:2005 ANSI/NCSL Z Accredited ISO 9001:2008 Certified


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