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Evaluation of various diagnostic x-ray measuring devices
MDCH Radiation Safety Section
Don Parry, CHP
Evaluation of X-ray Measuring Devices Evaluation Criteria – (Don)
AccuracyReliabilityRange of ApplicationDurabilityEase of UseCost
Evaluation of X-ray Measuring Devices Evaluation Criteria – (Don’s Bosses)
CostDurabilityReliability Range of Application AccuracyEase of Use
Evaluation of X-ray Measuring Devices Evaluation Criteria – (Don’s Staff)
Ease of Use Reliability Range of Application Durability Accuracy Cost
Evaluation of X-ray Measuring Devices Types of Devices
Ion ChambersSolid State Detectors
Evaluation of X-ray Measuring Devices
Ion chambers Advantages
Flat Energy Response History of Reliability
Disadvantages Weight Chambers can be fragile
Evaluation of X-ray Measuring Devices
Solid State Detectors Advantages
Small and lightweight
Detectors are more robust Disadvantages
More energy dependant Generally not as simple to use
Evaluation of X-ray Measuring Devices Application of X-ray Measuring Devices
Dental X-ray (~ 50 – 90 kVp)Medical X-ray (~45 – 150 kVp)Mammography (~24 – 35 kVp)
Evaluation of X-ray Measuring Devices - Accuracy Ion Chambers – Medical and Dental
Tested at four x-ray “beam codes” M50 (50 kVp ~1.0 mm Al HVL) L80 (80 kVp ~1.8 mm Al HVL) L-100 (100 kVp ~2.8 mm Al HVL) M-100 (100 kVp ~5.0 mm Al HVL) MoMo 25 (25 kVp, Moly target ~0.30 mm Al HVL) MoMo 30 (30 kVp, Moly target ~0.35 mm Al HVL)
0.9
0.95
1
1.05
1.1
1.15
1.2
0 1 2 3 4 5 6
HVL in mm Al
Co
rrec
tion
Fac
tor
IC 1
0.9
0.95
1
1.05
1.1
1.15
1.2
0 1 2 3 4 5 6
HVL in mm Al
Co
rrec
tion
Fac
tor
IC 2
IC 1
0.9
0.95
1
1.05
1.1
1.15
1.2
0 1 2 3 4 5 6
HVL in mm Al
Co
rrec
tion
Fac
tor
IC 1
IC 2
IC 3
Evaluation of X-ray Measuring Devices
Solid State Detectors – Medical and Dental Tested at three x-ray “beam codes”
L80 (80 kVp ~1.8 mm Al HVL) L-100 (100 kVp ~2.8 mm Al HVL) M-100 (100 kVp ~5.0 mm Al HVL)
0.9
0.95
1
1.05
1.1
1.15
1.2
0 1 2 3 4 5 6
HVL in mm Al
Cor
rect
ion
Fact
or
SSD 1
0.9
0.95
1
1.05
1.1
1.15
1.2
0 1 2 3 4 5 6
HVL in mm Al
Cor
rect
ion
Fact
or
SSD 2
SSD 1
0.9
0.95
1
1.05
1.1
1.15
1.2
0 1 2 3 4 5 6
HVL in mm Al
Corre
ctio
n Fa
ctor SSD 2
SSD 1
SSD 3
0.9
0.95
1
1.05
1.1
1.15
1.2
0 1 2 3 4 5 6
HVL in mm Al
Cor
rect
ion
Fact
or SSD 1
SSD 2
SSD 3
SSD 4
Evaluation of X-ray Measuring Devices Comparison
Ion Chambers vs. Solid State Detectors
Do not use any detector outside it’s specified energy range
0.9
0.95
1
1.05
1.1
1.15
1.2
0 1 2 3 4 5 6
HVL in mm Al
Corre
ctio
n Fa
ctor
IC 1
IC 2
IC 3
SSD 1
SSD 2
SSD 3
SSD 4
0.9
0.95
1
1.05
1.1
1.15
1.2
0 1 2 3 4 5 6
HVL in mm Al
Corre
ctio
n Fa
ctor
IC 1
IC 2
IC 3
SSD 1
SSD 2
SSD 3
SSD 4
All the solid state detectors showed under response at low energies
Evaluation of X-ray Measuring Devices Ion Chambers and Solid State Detectors
In Mammography
Tested at two “beam codes”
MoMo 25 (25 kVp, Moly target ~0.30 mm Al HVL) MoMo 30 (30 kVp, Moly target ~0.35 mm Al HVL)
0.9
0.92
0.94
0.96
0.98
1
1.02
1.04
1.06
0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36
HVL in mm Al
Corre
ctio
n Fa
ctor
IC 1
0.9
0.92
0.94
0.96
0.98
1
1.02
1.04
1.06
0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36
HVL in mm Al
Corre
ction
Facto
r IC 1
IC 2
0.9
0.92
0.94
0.96
0.98
1
1.02
1.04
1.06
0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36
HVL in mm Al
Corre
ction
Facto
r
IC 1
IC 2
IC 3
0.9
0.92
0.94
0.96
0.98
1
1.02
1.04
1.06
0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36
HVL in mm Al
Corre
ction
Facto
r
IC 1
IC 2
IC 3
SS Mam 1
0.9
0.92
0.94
0.96
0.98
1
1.02
1.04
1.06
0.29 0.3 0.31 0.32 0.33 0.34 0.35 0.36
HVL in mm Al
Corre
ctio
n Fa
ctor
IC 1
IC 2
IC 3
SS Mam 1
SS Mam 2
Evaluation of X-ray Measuring Devices Some Mammography Machines now use beams with
higher energies
NIST currently does not provide calibration standards for these beams
Since the energy response is typically flat for ionization chambers, no additional corrections should be needed.
Solid state instruments, however, may require appropriate corrections obtained from the instrument manufacturer.
Evaluation of X-ray Measuring Devices Ion Chambers – Reliability
Ion chamber calibrations have historically been very stable.
Ion chambers can be fragile and require appropriate handling by field staff
0.90
0.95
1.00
1.05
1.10
1.15
1.20
0 1 2 3 4 5 6
HVL in mm Al
Co
rrec
tion
Fac
tor
2002
2003
2004
2005
2006
2007
2008
Evaluation of X-ray Measuring Devices Solid State Detectors – Reliability
While reliability has been good, radiation response has drifted or failed on some sensors
Detectors appear more robust and are less often damaged by misuse
SSD Correction Factors Vs NIST beam codes
0.80
0.90
1.00
1.10
1.20
1.30
1.40
1.50
0 1 2 3 4 5 6
HVL in mm Al
CF
127747
128352
128353
128354
128355
128356
131149
131150
131151
131152
131153
131154
Evaluation of X-ray Measuring Devices - Range of Applicability Field Data IC 1 versus SS 3
TypeIC 1mR
SS 3mR
% diff
Dental 190.9 197.9 3.7%
Podiatrist 7.2 7.3 1.4%
Medical 49.8 47.7 -4.2%
Mammo 287.2 296.1 3.1%
Evaluation of X-ray Measuring Devices – Ease of Use IC1- IC3
Care needed in connecting probes SS1
Set up difficult when used on some machines SS2
Detector cable fixed to base SS3
Some felt it was not as simple to use
Evaluation of X-ray Measuring Devices – Our Conclusions Ion chambers exhibit good energy response
over a wide range of beam qualities; new chambers are lighter and smaller
SSDs can be designed to have acceptable energy responses in the diagnostic x-ray range, but know your instruments limitations
Field staff like the small size and light weight of SSD detectors
Evaluation of X-ray Measuring Devices – Our Conclusions Send equipment to an accredited calibration lab
annually to ensure radiation response remains in specification
We use SSD for equipment with known limits on the energy range
We use ion chambers for mammography beams and on x-ray beams in which beam qualities can vary significantly from machine to machine.
