Evaluation of various diagnostic x-ray measuring devices

1. Evaluation of various diagnostic x-ray measuring devices MDCH Radiation Safety Section Don Parry, CHP

2. Evaluation of X-ray Measuring Devices • Evaluation Criteria – (Don) • Accuracy • Reliability • Range of Application • Durability • Ease of Use • Cost

3. Evaluation of X-ray Measuring Devices • Evaluation Criteria – (Don’s Bosses) • Cost • Durability • Reliability • Range of Application • Accuracy • Ease of Use

4. Evaluation of X-ray Measuring Devices • Evaluation Criteria – (Don’s Staff) • Ease of Use • Reliability • Range of Application • Durability • Accuracy • Cost

5. Evaluation of X-ray Measuring Devices • Types of Devices • Ion Chambers • Solid State Detectors

6. Evaluation of X-ray Measuring Devices Ion chambers • Advantages • Flat Energy Response • History of Reliability • Disadvantages • Weight • Chambers can be fragile

7. 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

8. 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)

9. 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)

13. 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)

18. Evaluation of X-ray Measuring Devices • Comparison • Ion Chambers vs. Solid State Detectors • Do not use any detector outside it’s specified energy range

20. All the solid state detectors showed under response at low energies

21. 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)

27. 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.

28. 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

30. 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

32. Evaluation of X-ray Measuring Devices - Range of Applicability • Field Data IC 1 versus SS 3

33. 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

34. 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

35. 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.