1. IAEA International Atomic Energy Agency RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY Part 19.03: Optimization of protection in Mammography Practical exercise IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology

2. IAEA 19.03 : Optimization of protection in Mammography2 Overview To be able to apply quality control protocols to mammography equipment To measure the breast entrance surface dose and determine the average glandular dose Interpretation of results

3. IAEA International Atomic Energy Agency Part 19.03: Optimization of protection in Mammography Topic 1: Entrance surface dose (measurements on patients) IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology

4. IAEA 19.03 : Optimization of protection in Mammography4 Entrance surface dose (ESAK) The Entrance Surface Air Kerma (ESAK) free-in-air, i.e., without backscatter, has become the most frequent used quantity for patient dosimetry in mammography ESAK can be determined under reference conditions either with AEC or manual exposure

5. IAEA 19.03 : Optimization of protection in Mammography5 Entrance surface dose (I) (measurements on patients) This simple method of determining ESAK requires dosemeters from a central laboratory to provide first line information on the level of radiation dose being delivered to patients. It is intended for facilities where local resources or expertise are not available.

6. IAEA 19.03 : Optimization of protection in Mammography6 Entrance surface dose (II) (measurements on patients) Select 10 patients with a compressed breast thickness in the range 4 to 6 cm For each patient and for each projection, position one calibrated TLD on the upper inner quadrant of the breast and x-ray the patient normally Remove the TLD and keep it away from radiation

7. IAEA 19.03 : Optimization of protection in Mammography7 Entrance surface dose (III) (measurements on patients) Complete the questionnaire for dosimetry on patient (provided by the central laboratory) When all 10 TLDs have been used, return them together with the completed questionnaire to the issuing dosimetry laboratory Compare the mean value of ESAK with the reference value of 10 mGy.

8. IAEA 19.03 : Optimization of protection in Mammography8 Calibration of output (I) (Purpose) This method of determining ESAK relies on the calibration of the radiation output of the X-ray machine together with a recording of the tube loading on a series of patients It is suitable for X-ray machines which have an AEC system and a post-exposure display or for units with manual exposure control only

9. IAEA 19.03 : Optimization of protection in Mammography9 Calibration of output (II) (Test equipment) Select a dosimeter with a dynamic range from at least 0.5 to 100 mGy Accuracy > ± 10% Precision > ± 5 Calibrate the dosimeter in terms of air kerma free-in-air at an HVL as close as possible to 0.4 mm of Al. Use post-exposure technique readouts (mAs)

10. IAEA 19.03 : Optimization of protection in Mammography10 Calibration of output (III) (test method - patient measurements) Select 10 patients with a compressed breast thickness in the range of 4 to 6 cm For the same view on each patient, record the mAs after exposure value or the value set on units with manual exposure control

11. IAEA 19.03 : Optimization of protection in Mammography11 Calibration of output (IV) (test method - output measurements) Place the dosemeter at the reference point (45 mm above the cassette table, 60 mm from the chest wall side and laterally centred). The compression plate should be in place Set manual exposure mode (same kV, anode, filtration, etc.) as used clinically Record the air kerma readings per mAs for the exposure that covers the range of values recorded on patients.

12. IAEA 19.03 : Optimization of protection in Mammography12 Calculations (I) Calculate the mean value of the mAs for the 10 patients Determine the output, i.e., the air kerma/mAs Calculate the mean value of ESAK corresponding to the mean value of tube loading Calculate the mean ESD by multiplying the mean ESAK by the appropriate backscatter factor if the HVL is known

13. IAEA 19.03 : Optimization of protection in Mammography13 Calculations (II) Backscatter factor as a function of HVL (Jansen et al. 1994) If the information on the HVL is lacking, apply a backscatter factor of 1.09

14. IAEA 19.03 : Optimization of protection in Mammography14 Assessment of results Compare the mean value of ESAK with the reference value of 10 mGy If the mean value of ESAK exceeds 10 mGy per view, it is necessary to investigate the reason and corrective actions must be taken

15. IAEA International Atomic Energy Agency Part 19.03 : Optimization of protection in Mammography Topic 2: Entrance surface dose (measurements with phantom) IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology

16. IAEA 19.03 : Optimization of protection in Mammography16 Entrance surface dose (measurements with phantom) This method is an alternative to the method of placing TLDs on patients where this is not deemed to be acceptable due to interference with patient examination It is intended for facilities where local dosimetry resources and expertise are not available

17. IAEA 19.03 : Optimization of protection in Mammography17 Tests equipment (provided by a central laboratory) TLDs: calibrated in terms of air kerma free- in-air at a HVL as close as possible to 0.4 mm Al. Standard phantom: PMMA (thickness 45  0.5 mm, 150 x 240 mm2) Developed film strip with labelled optical densities Questionnaire

18. IAEA 19.03 : Optimization of protection in Mammography18 Test method (1) Set up the x-ray equipment for a cranio- caudal view with the compression plate present and a cassette loaded in the bucky Position the phantom on the breast table, make sure that it completely covers the AEC device Place the TLD at the reference point

19. IAEA 19.03 : Optimization of protection in Mammography19 Test method (2) Expose the phantom to the same conditions as used clinically for a standard-sized breast Process the film in the normal way Verify that the film density (base + fog included) at the reference point is in the optical density range of 1.20 to 1.80 (densitometer measurement or visual comparison with the film strip provided by the laboratory)

20. IAEA 19.03 : Optimization of protection in Mammography20 Test method (3) Replace the TLD with a second one If the film optical density is in the range 1.20 to 1.80 make a second phantom exposure aiming for a density of 1.50 Finally process a fresh, unexposed film Estimate the density of the background film by visually comparing with the density with a densitometer or with the test strip

21. IAEA 19.03 : Optimization of protection in Mammography21 Test method (4) Complete the questionnaire provided by the central laboratory Return the TLDs together with the three films and the questionnaire to the issuing laboratory Compare the value of ESAK provided by the laboratory to the limiting value of 11 mGy corresponding to a net optical density of 1.00 (for different values of optical density, see table)

22. IAEA 19.03 : Optimization of protection in Mammography22 Limiting values for ESAK as a function of net optical density

23. IAEA 19.03 : Optimization of protection in Mammography23 Calibration of output (Purpose) This method of determining ESAK with a standard phantom gives information on compliance of the technical set-up of the mammographic equipment with guidelines on radiation dose. It is suitable for X-ray machines which have an AEC system and a post-exposure display or for units with manual exposure control only

24. IAEA 19.03 : Optimization of protection in Mammography24 Calibration of output (Test equipment) A dosemeter with a dynamic range from at least 0.5 to 100 mGy Accuracy > ± 10% Precision > ± 5 The dosimeter should be calibrated in terms of air kerma free-in-air at an HVL as close as possible to 0.4mm of Al. A standard phantom: PMMA block of 45 mm; 150x240 mm2 A densitometer (resolution of 0.01 density units)

25. IAEA 19.03 : Optimization of protection in Mammography25 Test method (determination of mAs (1)) Set up the x-ray equipment for a cranio- caudal view with the compression plate present and a loaded cassette in the Bucky Position the phantom on the breast table, make sure that it completely covers the AEC device Expose the phantom at clinically used technique

26. IAEA 19.03 : Optimization of protection in Mammography26 Test method (determination of mAs (2)) Record the mAs Process the film Measure the optical density and verify that it is in the range 1.20 to 1.80 If necessary, adjust the AEC density setting to achieve a suitable optical density and repeat the procedure described above

27. IAEA 19.03 : Optimization of protection in Mammography27 Test method (measurement of output) Remove the phantom and place the dosemeter at the reference point. The compression plate should be in place Set manual exposure mode and mAd determined previously Record the dose measurement. If it is not possible to select the exact mAs, make two exposure that bracket this value

28. IAEA 19.03 : Optimization of protection in Mammography28 Calculations Apply the appropriate calibration factor to the dose measurement Interpolate the results if it was necessary to make two bracketing exposures Express the result as ESAK

29. IAEA 19.03 : Optimization of protection in Mammography29 Assessment of results Compare the mean value of ESAK with the limiting value of 11 mGy corresponding to a net optical density on the film of 1.00. For optical densities deviating from this value see the table If the mean value of ESAK exceeds 10 mGy per view, it will be necessary to determine the cause and corrective must be taken

30. IAEA 19.03 : Optimization of protection in Mammography30 Entrance surface dose Limiting value :  10 mGy for 40 mm PMMA,  12 mGy for 45 mm PMMA,  20 mGy for 50 mm PMMA. Frequency : Annually Equipment : Dosimeter, PMMA block 150x240 mm 2, densitometer

31. IAEA International Atomic Energy Agency Part 19.03: Optimization of protection in Mammography Topic 3: The average glandular dose IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology

32. IAEA 19.03 : Optimization of protection in Mammography32 Determination of average glandular dose (AGD) The AGD cannot be measured directly. It is derived from measurements of the ESAK (with a standard phantom) and HVL. The ESAK is used with tabulated conversion factors (derived from Monte Carlo calculations) to determine the AGD.

33. IAEA 19.03 : Optimization of protection in Mammography33 Average Glandular Dose Table 1: Conversion factors g PB for calculating the AGD for a 50 mm « standard breast D GS » from the ESAK (K a ) measured at the technique as for 45 mm standard PMMA phantom (Dance 1990)

34. IAEA 19.03 : Optimization of protection in Mammography34 Limiting values for AGD as a function of net optical density Table 2

35. IAEA 19.03 : Optimization of protection in Mammography35 Calculations Derive the HVL by interpolation. This may be done by plotting the logarithm of the dose measurements against the relevant Al absorber thickness Derive, if necessary by interpolation, the conversion factor g PB for the measured HVL from table 1. Multiply the measured ESAK, K a, at the mAs determined for the correct exposure of a standard phantom and the relevant g PB to obtain the standard AGD DGS (breast) = g PB x ka

36. IAEA 19.03 : Optimization of protection in Mammography36 Calculations (example) An exposure of the standard phantom in the AEC mode, at 28 kV and Mo-Mo anode-filter combination requires 94 mAs 0.080 mGy/mAs (average of values measured at 90 and 100 mAs) was determined from the calibration of the output at the reference point The measured HVL was 0.32 mm Al, yielding a g PB value of 0.187, derived by interpolation from Table 1

37. IAEA 19.03 : Optimization of protection in Mammography37 Calculations (example) The standard AGD (DGS) is: DGS =94 [mAs] 0.080 [mGy/mAs] 0.187 [mGy/mGy] DGS = 1.4 [mGy]

38. IAEA 19.03 : Optimization of protection in Mammography38 Assessment of results Compare the value of standard AGD with the limiting value of 2.3 mGy, derived from the ESD limiting value for a film optical density of 1.00 Table 2 provides information for other film densities

39. IAEA Where to Get More Information 39 European protocol for the quality control of the physical and technical aspects of mammography screening. http://euref.org/index.php?option=com_phocado wnload&view=category&id=1&Itemid=8 American College of Radiology Mammography Quality Control Manual, Reston VA, 1999. 19.03 : Optimization of protection in Mammography