WHT A MEDICAL PHYSICST CAN DO TO IMPROVE THE CHANCES OF EARLY DETECTION OF BREAST CANCER

1. WHT A MEDICAL PHYSICST CAN DO TO IMPROVE THE CHANCES OF EARLY DETECTION OF BREAST CANCER Dr. Nabil Maalej Physics Dept., KFUPM 21-10-2004

2. Outline • Image Formation in Mammography • Image Quality • Contrast • Scatter and Scatter Reduction • Quality Assurance • Breast Dose • Entrance Skin Exposure Measurement • Glandular Dose Measurement in Mammography

3. Breast Cancer (Highest)

4. Breast Cancer (Highest) • For the total Saudi population, the most common ten cancers are (1994-1996 Cancer Registry): • Female breast cancer (8.8%), • Liver cancer (7.5%), • Leukemia (7.5%), • Non-Hodgkin's lymphoma (7.3%) • Colo-rectum cancer (5.5%). • Thyroid cancer (5.2%), • Lung cancer (4.7%) • Nervous system cancer (3.9%) • Stomach cancer (3.8%) and • Urinary bladder cancer (3.5%)

5. Image Formation

6. Mammography Machine

7. What Can We do to Get Best Image? X-ray Source X-ray Beam Compression Paddle Compressed Breast Table Chest Wall Grid Image Detector

8. X-Ray Tube

9. IMAGE CONTRAST

10. Imaging Quality Parameters CONTRAST RESOLUTION NOISE

11. Contrast • Image Contrast is a measure of difference between regions in an image • Good image contrast is particularly important when imaging low-contrast objects such as breast cancer

12. Mammography Contrast • Image contrast is due to the difference in linear attenuation coefficient of different types of tissue in the breast (adipose tissue (fat), fibro-glandular, tumor).

13. Attenuation Coefficient Contrast decreases toward higher energies  the recommended optimum for mammography is in the region 18 - 33 keV depending on tissue thickness and composition.

14. Mammography Spectrum

15. I I Ib Ib It It S Contrast Degradation with Scatter

16. Scattered Radiation and Contrast

17. Photoelectric Interaction (Primary) T h hν = T + BEelectron

18. Compton Scattering (Scatter) T h h’ hν = T + BEelectron + hν’

19. How Can We Reduce Scatter? • Use an Anti-Scatter Grid • Use and Air Gap between the breast and the detector • Line Scanning System • Capillary optics

20. Anti-scatter grid breast leadsepta detector

21. Anti-scatter grid Scattered Rays Primary Rays Grid Septa Image Receptor

22. Grid Parameters Primary Transmission Scatter Transmission

23. Grid Parameters Total Transmission Bucky Factor

24. Contrast Improvement Factor This equation states that for a given transmission factor, the contrast can only be improved when the absorbed dose in the breast is also increased by a Bucky factor B.

25. MEASURING CONTRAST

26. Contrast Detail Analysis • Contrast detail analysis: an observer reports the size of the smallest object he or she can perceive at a certain contrast level and with a given noise level in the image.

27. Measuring Contrast Detail Curve

28. Measuring Contrast Detail Curve

29. Measuring Contrast Detail Curve

30. RMI 156 Phantom

31. RMI 156 Phantom ACR minimum score is 4 visible fibers, 3 speck groups and 3 masses

32. RMI 156 Phantom ACR minimum score is 4 visible fibers, 3 speck groups and 3 masses

33. Importance of Image Quality

34. Radiation Dose to The Breast

35. Risk of Radiation Induced Breast Cancer

36. The Nationwide Evaluation of X-ray Trends (NEXT) • The Nationwide Evaluation of X-ray Trends (NEXT) is a U.S. national program conducted annually to measure the x-ray exposure that a standard patient receives for selected x-ray examinations

37. Mean Glandular Dose • The mean, or average, dose to the glandular tissue within the breast • 3 mGy per view is the federal and ACR dose limit for an average-size patient

38. Entrance Skin Exposure • The entrance skin exposure is the amount of radiation delivered to the patient skin at the entrance point of the X-ray

39. SETUP For Entrance Skin Exposure Measurement X-Ray Tube Ionization Chamber Breast Equivalent Phantom X-Ray Film Table Film

40. Entrance Skin Exposure Measurement Dosimeter Mammography Phantom

41. Conclusion • Using the Contrast Detail phantom or ACR phantom allows medical physicists to evaluate the image quality. This will ensure good image quality and reduce the chances of miss-diagnosis • Using the simple measurement of the entrance skin exposure and breast dose and comparing them with recommended ranges will ensure safer levels of radiation to the patient • Saudi hospitals should implement such quality control and radiation protection procedures to provide quality care for the patients

42. THANK YOU

43. X-Ray Production Cathode(-) e- Current (mA) Voltage (KV) e- h h Anode (+) • Electrons are accelerated from cathode to anode. • When high energy electrons hit atoms of heavy metals, the atoms produce X-ray photons.

44. Exposure Factors • Tube Voltage (kVp) • Tube Current (mA) • Time of exposure (s)

45. Exposure • Exposure due to radiation is the measurement of amount of charge generated by the radiation per unit mass of air [C/kg or R=2.5810-4 C/kg] • Exposure  Tube current (mA) • Exposure  Time (s) • Exposure  Tube Voltage 2 (kVp 2) • Exposure  (1/distance 2) Exposure in Air [C/kg or R]  (kVp)2(mA.s)/d2

46. Radiation-Induced Skin Injuries Figure from [17] • Skin “burns” are rare but possible for prolonged fluorocardio & other interventions • FDA has received 60 reports of burns since 1994  ~ 8.6 reported burns per year • How many radiation burns are not reported? 8