3 Modern Dose Sensor Diversity Solid State Multi-sensors (dose, kV, time, hvl, filt)Ion Chambers (nGy – kGy 10keV – MeV)Solid State Dose only
4 Radcal’s Mfg. and Calibration Laboratory CertifiedISO 9001:2008 (TUV since 1995)IEC ISO/IEC 17025:2005ANSI/NCSL ZAll products CE markedDirect traceability toNIST (USA) – Air KermaPTB (Germany) – Air KermaSwedish National Laboratory – High VoltageProficiency Tested – NIST & Secondary Labs
5 Dose Calibration Chain National LaboratoryRadcal PrimaryIon Chamber StandardsWorking/Secondary StandardsStd1Std2Std3Std4Std5Std6
6 Proficiency Testing National Laboratory Transfer Standard Secondary Lab- Lab calibrates transfer std.- Ship to Radcal for calibration- Radcal calibrates & issues report- Return to lab for re-calibration- Lab Issues proficiency reportRadcalCal Lab
7 Customer Traceability Chain National LaboratoryRadcalCertificate of ConformanceCertified CalibrationCustomer
8 Radcal Certificate of Conformance MotivationVerify equipment meets published specificationsPreserve component interchangeabilityProcessTest electronics (control unit) – verify performance and accuracy over full dynamic rangeIndependently test sensors with reference standard electronics for accuracy and energy dependenceVerify sensor & electronics combination, but do not adjust.
9 Air Kerma Uncertainty Budget NIST & PTBNational Standard~1%Radcal (1s)Transfer measurements0.50%Long-term stability1.00%Short-term reproducibilityTemperature: 0.25 ºC0.08%Pressure: 1mB0.10%Geometry & positioning0.20%Charge: 0.5%Beam quality*0.25%Quadrature Sum1.5%Total UncertaintyRadcal@ 95% Confidence (2s)2.9%(1)NIST and PTB uncertainties vary depending on the type of measurement. The value listed is the worst case with a 95% a confidence level (2s).*Radcal ion chambers have documented energy response functions of <5% over their specified range of use. For x-ray beams, hvl can be determined to < 5% uncertainty. The resulting error for ion chamber calibration is < 0.25%. For non-Radcal chambers, which may have up to 20% energy response, the associated uncertainty is <1%. Note: this influence quantity only applies to x-ray measurements and is not present in 60Co or 137Cs measurements.
10 TUR (test uncertainty ratio) Note: desirable TUR is >4Implies RMS <1.25%
11 Beam standardizationGeometry – IEC “Radiation conditions for use in the determination of characteristics”.Collimator 1Trans Chamber 1Added FiltCollimator 2LaserBeam SplitterPrisimHVL Filters.Collimator 3Trans Chamber 2
12 Radcal Air Kerma Standards 3-terminal guarding< 5e-15 A leakage with 300 VDC biasNegligible stem effects< ±5% energy dependence over rated energy range2nGy to >20 GyRates from nGy/s to >mGy/sEnergies from 10 keV to 2 MV
15 Ion Chamber Response for low energy x-rays American College of Radiology:±1% mm Al hvlThe 6M ion chamber was designed specifically for the mammographic energy range . It’s response characteristics have been demonstrated to be completely independent of spectra from all anode filter combinations.
16 Mammographic Energy Response Radcal 10X5-6M (DeWerd et al.) ±2%
17 Diode Energy ResponseLet’s take a look at how a bare diode responds to conventional Mo-Mo 30u beams. Compensation can dramatically improve this response.
18 Diode Energy ResponseExpanding the y-axis of the previous graph shows the detail of the compensated response.
19 Diode Energy ResponseAdding other Anode filter combinations shows the effect of these different spectra on the Mo-Mo compensation.
20 Diode Energy ResponseIf we apply different correction factors for each anode-filter condition, we have a much better result.
21 Diode Energy Response – Auto Corrected via kV & hvl Finally if we use additional sensors to determine kVp and filtration, we can have a very good result for dose diode energy response.
22 Equipment Tolerances IEC – “Dosimeters with ionization chambers and/or semiconductor detectors as used in x-ray diagnostic imaging"Performance CharacteristicsLimit of VariationAir Kerma Reproducibility1%Resolution<Stabilization2%Leakage currents (<1%/min)---StabilityAccumulated dose stabilityRMS3%
23 Equipment Tolerances IEC – “Dosimeters with ionization chambers and/or semiconductor detectors as used in x-ray diagnostic imaging"Influence QuantitiesLimit of VariationRadiation Quality5%Air Kerma Rate2%Incidence angle (± 5°)3%Operating VoltageAir PressureTemperature and HumidityEMCField sizeRMS9%
24 Equipment Tolerances IEC – “Dosimeters with ionization chambers and/or semiconductor detectors as used in x-ray diagnostic imaging"
25 Summary Select dose sensors to match your requirements Acceptable uncertainty - QA checks vs. acceptance testingEnergy range – Mammography vs. conventional,Geometric response - fluoro backscatter, CT & tomoEnergy response – acceptable uncertaintyDynamic Range - scatter & leakage vs. pulsed fluoro
26 Summary Understand the sensor & associated electronics Trigger thresholds – minimum dose rateMaximum dose rate – pulsed fluoroOpaque – interfere with AECLinearity over the range of applicationUse of automatic vs. manual temp & pressure correctionsTime to come to thermal equilibrium
27 Thank You! Paul Sunde Radcal Corporation Monrovia, California USA ISO/IEC 17025:2005ANSI/NCSL ZAccreditedISO 9001:2008 CertifiedPaul SundeRadcal CorporationMonrovia, California USA