Breast CT and Dosimetry

Transcription

1 2013 ICTP/IAEA Training Course on Radiation Protection of Patients Trieste Breast CT and Dosimetry John M. Boone, Ph.D., FAAPM, FSBI, FACR Professor and Vice Chair (Research) of Radiology Professor of Biomedical Engineering University of California Davis Medical Center Sacramento, California

2 Breast CT and Dosimetry Breast CT Background Technical Development Initial Clinical Results Dose Issues in Breast CT Summary

3 Mammography: Standard of Care CC MLO CC MLO 3

4 Breast CT Mammography ~ mm mm 230 mm 250 mm ~0.50 mm 3 70 mm 70 mm 50,000 mm 4

5 Dedicated Breast CT

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7 Computed Tomographic Mammography--CTM John J. Gisvold, Philip R. Karsell, David F. Reese Mayo Clinic 1975 Fall sec scan in water bath 116 kvp, 300 mas 10 mm slice thickness 1.56 x 1.56 mm pixels 4 to 6 10 mm slices per breast 256 shades of gray (8 bit)

8 CTM: 1.56 x 1.56 x 10 mm voxels Voxel volume: over 900 times smaller Special thanks to Cynthia McCollough and John Gisvold for providing this information

9 Breast CT and Dosimetry Breast CT Background Technical Development Initial Clinical Results Dose Issues in Breast CT Summary

10 Computer aided design / computer aided manufacture (CAD/CAM) Albion 2003 Bodega 2007 Cambria 2011 Doheny 2012

11 Albion 2004 Bodega 2007 Cambria 2012 Doheny 2013

12 UC Davis Medical Center Albion Bodega Cambria Doheny 12

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14 Cambria 2011

15 Components (Albion and Bodega) Varian 4030CB 194 mm pixels 2x2 388 mm 1024 x 768 x 30 FPS Kollmorgen Servo Motor Propulsion Bearing Angle Encoder Comet 1 kw Tube 15

16 Components (Cambria and Doheny) Varian 4030CB Yaskawa Servo Motor Propulsion Bearing Angle Encoder Varian 11.3 kw Pulsed Tube M-1500 Dexela mm pixels 26 FPS / CMOS 70 2x2 16

17 Half Cone Beam CT Geometry

18 calibration, corrections, reconstruction Flat Field Correction I corr g I I raw grain I r offset I g offset Geometric Calibration

19 FDK Reconstruction Code >100x ~42 minutes ~35 minutes ~20 seconds

20 Spatial Resolution: Modeled & Measured MTF s g( t) f A a (1 exp( t / T )) a (1 exp( t / T )) a (1 exp( t / T )) Albion & Bodega Cambria (2 x 2) [388 mm pixels] Cambria (1 x 1) [194 mm pixels] Doheny 3X Spatial Resolution 20

21 Phantom Imaging

22 Phantom Imaging

23 Phantom Imaging

24 Breast CT and Dosimetry Breast CT Background Technical Development Initial Clinical Results Dose Issues in Breast CT Summary

25 Patient Imaging Radiologist Observers Over 600 patients imaged at two sites

26 296 second volunteer imaged: January

27 first breast cancer imaged: January

28 True 3D Display! 28

29 2008

30 bct (no injected contrast) 30

31 PRE CONTRAST POST CONTRAST bct (with contrast) PRE CONTRAST POST CONTRAST 31

32 2010 AUC DHU = 0.87

33 mass lesion microcalcifications

34 Prospective Clinical Trial 105 patients /103 lesions (BIRADS 4 or 5) imaged on VCO mammo / tomo / CE-bCT all biopsied malignant microcalcifications 31 masses 27 Shadi Shakeri, M.D. benign total Radiologists Rated Lesions using a 0 to 10 Conspicuity Score 0 = not seen 10 = excellent one-way ANOVA with correction for multiple comparisons

35 mammo tomo CE-bCT mammo tomo CE-bCT mammo tomo CE-bCT mammo tomo CE-bCT

36 Computer (Mathematical) Observer

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39 # observations pre-whitened matched filter computer observer (f i I i ) = dꞌ lesion absent lesion present filter dꞌ inserted lesion inserted non-lesion breast CT image (actual images are used)

40 Breast CT 46% mammo mass lesions only / results do not reflect microcalcifications

41 Breast CT and Dosimetry Breast CT Background Technical Development Initial Clinical Results Dose Issues in Breast CT Summary

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43 Radiation Dose from Breast CT? size matters

44 breast circumference diameter compressed breast thickness

45 25 20 N = 200 Frequency Diameter (cm)

46 Breast Diameter (cm) r = CB Thickness (cm)

47 Mean Glandular Dose in Mammography two-view mammography dose versus CB thickness Two-View Mean Dose (mgy) Average of 4 mammo systems Compressed Breast Thickness (cm)

48 Monte Carlo Assessment of Dose Deposition monoenergetic functions 50 breast modeled as a cylinder ugy per million photons cm dia 18 cm dia SIC=45 cm FOV=20 cm 50% glandular/50% adipose X-ray Energy (kev) JM Boone, N. Shah, and T.R. Nelson, A Comprehensive Analysis of DgN CT Coefficients for Pendant-Geometry Cone-Beam Breast Computed Tomography, Medical Physics 31: (2004)

49 X-ray spectral model for bct beams 1.2e+7 1e+7 1.2e+7 Photon Fluence (mm -2 ) 1.0e+7 8.0e+6 6.0e+6 4.0e+6 2.0e+6 60 kv 8e+6 80 kv Photon Fluence (mm -2 ) 6e+6 4e+6 2e+6 Photon Fluence (mm -2 ) 1.0e+7 8.0e+6 6.0e+6 4.0e+6 2.0e kv X-ray Energy (kev) X-ray Energy (kev) X-ray Energy (kev) Attenuation (%) model meas. data JM Boone and JA Seibert, An accurate method for computer-generating tungsten anode x-ray spectra from 30 kv to 140 kv, Medical Physics 24; , Thickness (mm Al)

50 Converting m-dgn to p-dgn using spectral weighting polyenergetic functions 1.1 ugy per million photons Photon Fluence (mm -2 ) 1e+7 8e+6 6e+6 4e+6 2e X-ray Energy (kev) Dose per Kerma (mgy/mgy) cm dia 18 cm dia Tube Voltage (kvp) X-ray Energy (kev) JM Boone, N. Shah, and T.R. Nelson, A Comprehensive Analysis of DgN CT Coefficients for Pendant-Geometry Cone-Beam Breast Computed Tomography, Medical Physics 31: (2004)

51 Probability (%) A B C D DD Bra Cup Size Probability (%) A B Bra Cup Size C D DD Breast Diameter (cm)

52 Comparison of breast dimensions X = 13.4 cm = 2.0 cm Median = 13.6 cm 2008 assessment on bct images (N = 137) 2001 tape measure results (N = 200) 52

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54 actual and modeled x-ray spectra were tuned measured values spectral model 1.2e+7 1e+7 1.2e+7 Photon Fluence (mm -2 ) 1.0e+7 8.0e+6 6.0e+6 4.0e+6 2.0e+6 Photon Fluence (mm -2 ) 8e+6 6e+6 4e+6 2e+6 Photon Fluence (mm -2 ) 1.0e+7 8.0e+6 6.0e+6 4.0e+6 2.0e X-ray Energy (kev) X-ray Energy (kev) X-ray Energy (kev)

55 X-ray system output carefully measured

56 Trans (%) 14 iso mr/mas HVL E ave (ent) E ave (exit) BH factor F/mGy

57 MGD(t) in two-view mammography Relationship between bct(d) and mammo(t)

58 MGD (mgy) as a function of air kerma at isocenter (mgy) 10 cm 0% 18 cm 0%

59 isocenter to yield same dose as 2V mammography 18 cm 16 cm 14 cm 12 cm 10 cm

60 isocenter to yield same dose as 2V mammography ~0.113 mgy / mas / = 39.3 mas

61 mas (on our scanner) to yield same dose as 2V mammography

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63 Dose assessment repeated by Thacker/Glick Thacker S and Glick S, PMB 2004,

64 Other Considerations

65 Average Glandular Dose (mgy) kvp 100 kvp 120 kvp Compressed Breast Thickness (cm)

66 Mammography a a b = high dose area b = low dose area

67 Breast CT 26 kvp Glandular Dose (mgy) a b c a b c Position (cm)

68 Other Considerations (2) DgN s used in mammography probably underestimate dose: Skin Thickness Issue Glandular Density Spectrum Quality factor for E < 25 kev 1.3

69 Breast CT and Dosimetry Breast CT Background Technical Development Initial Clinical Results Dose Issues in Breast CT Summary

70 Breast CT and Dosimetry: Summary Breast CT has strong clinical potential MGD levels are comparable to mammography MC Methods modern x-ray dosimetry When dosimetry methods are not available, you have to develop them yourself!

71 Breast Tomography Project University of California Davis Acknowledgements: California BCRP 7EB-0075 California BCRP 11I-0114 R01 CA R01 EB (BRP) R01 CA (RDB) P30 CA (CCSG) Susan G. Komen Foundation University of Pittsburgh

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