Patient Dose Estimates. from CT Examinations. Patient Dose Estimates

Transcription

1 Patient Dose Estimates from CT Examinations Patient Dose Estimates from CT Examinations John M. Boone, Ph.D. Professor and Vice Chairman of Radiology Professor of Biomedical Engineering University of California, Davis Chairman, AAPM Science Council Chairman, ICRU CT* Committee Why are we here? Definitions CT dosimetry in the real world Perspectives from the ICRU Committee Summary *Image Quality and Patient Dose in Computed Tomography, ICRU Report 93 www:myhealthfinder.com/hcac/ctreport04.pdf 1

2 emergency room CT scans emergency room CT use rate in press, Journal of the American College of Radiology in-patient CT use rate out-patient CT use rate 2

3 The radiation levels from CT has caught the eye of the public CT scans per patient mean = 2.88 let s go measure the CTDI 100 3

4 Bob Dixon So what s wrong with the CTDI 100? David Brenner Patient Dose Estimates from CT Examinations where it all began. Why are we here? Definitions CT dosimetry in the real world Perspectives from the ICRU Committee Summary 4

5 1 + 7T CTDI = D( z) dz nt 7T 1 + 7T CTDI = D( z) dz nt 7T nt 100 mm 5

6 1 + 7T CTDI = D( z) dz nt 7T 1 + 7T CTDI = D( z) dz nt 7T 1 + 7T CTDI = D( z) dz nt 7T So what s wrong with the CTDI 100? 6

7 So what s wrong with the CTDI 100? So what s wrong with the CTDI 100? ρ 1.0 ρ = cm 32 cm scan length So what s wrong with the CTDI 100? So what s wrong with the CTDI 100? 16 cm diameter PMMA cylinder 32 cm diameter PMMA cylinder 7

8 Patient Dose Estimates from CT Examinations 100 mm pencil chamber Why are we here? Definitions CT dosimetry in the real world Perspectives from the ICRU Committee Summary 8

9 Computation of effective dose (ImPACT of UK) based on Standard patient geometry and Monte Carlo derived tables Patient Dose Estimates from CT Examinations Why are we here? Definitions CT dosimetry in the real world Perspectives from the ICRU Committee Summary ICRU: Image Quality and Patient Dose in CT John M. Boone (US) James Brink (US) Sue Edyvean (UK) Jacob Geleijns (Netherlends) Walter Huda (US) Wolfram Leitz (Sweden) Cynthia McCollough (US) Michael McNitt-Gray (US) ICRU Sponsors: Willi Kalender (Germany) Kunio Doi (US) Peter Dawson (UK) ICRU: Image Quality and Patient Dose in CT A. CT scanner radiation output measurement B. Dose to the Reference Patient -D RP C. Dose to the Individual Patient 9

10 A. CT scanner radiation output measurement A. CT scanner radiation output measurement A-1 CTDI 100 A-2 Rise to Equilibrium (TG-111) A-3 D(z) of CT beam A-4 D(x, z) of CT beam A-1 CTDI 100 A-2 Rise to Equilibrium (TG-111) A-3 D(z) of CT beam A-4 D(x, z) of CT beam A. CT scanner radiation output measurement A. CT scanner radiation output measurement A-1 CTDI 100 A-2 Rise to Equilibrium (TG-111) A-3 D(z) of CT beam A-4 D(x, z) of CT beam A-1 CTDI 100 A-2 Rise to Equilibrium (TG-111) A-3 D(z) of CT beam A-4 D(x, z) of CT beam 10

11 A. CT scanner radiation output measurement A-1 CTDI 100 A-2 Rise to Equilibrium (TG-111) A-3 D(z) of CT beam A-4 D(x, z) of CT beam B. Dose to the Reference Patient -D RP B-1 Definition of the Reference Patient B-1.1 Size Range B-1.2 Standard Scans (D RP-X ) B-2 Dose assessment B-2a Monte Carlo measurements B-2b physical measurements B-3 Utility of D RP-X Size Range Standard Scans thoracic abdomen pelvis > 50 cm (XXL) cm (XL) cm (L) cm (M) cm (S) head 11

12 B. Dose to the Reference Patient -D RP B-1 Definition of the Reference Patient B-1.1 Size Range B-1.2 Standard Scans (D RP-X ) B-2 Dose assessment B-2a Monte Carlo measurements B-2b physical measurements B-3 Utility of D RP-X Monte Carlo Modeling physical dose measurements θ θ abdomen abdomen αx 2 + βy 2 = r Monte Carlo Simulations αx 2 + βy 2 = r TLDs r r = a + bθ + cθ 2 + dθ 3 +. vendor bow tie spectrum etc. r r = a + bθ + cθ 2 + dθ π 1π 1.5π 2π θ 0 0.5π 1π 1.5π 2π θ 12

13 B. Dose to the Reference Patient -D RP B-1 Definition of the Reference Patient B-1.1 Size Range B-1.2 Standard Scans (D RP-X ) B-2 Dose assessment B-2a Monte Carlo measurements B-2b physical measurements B-3 Utility of D RP-X abdomen thorax Doses from XX CT Scanner in Room 4 (mgy per 100 mas) Pediatric Female Male Xs xx yy zz S xx yy zz M xx yy zz L xx yy zz XL xx yy zz Xs xx yy zz S xx yy zz M xx yy zz L xx yy zz XL xx yy zz C. Dose to the Individual Patient Dose metrics Dose units C-1 Doses to patients measured in mgy C-2 Individualized deterministic dose computation average tissue dose (mgy) 13

14 Individualized Dose Estimates DICOM header kvp, mas eff., pixel size, slice thickness, etc. Determination of Primary Dose 14

15 Determination of Scatter Dose CT image primary dose image P S HU CT image primary dose image 1000 bone 0 tissue air S µ µ scatter total S µ µ scatter total HU scatter to primary ratio (per voxel) - SPR 15

16 Dose(x,y,z) = Dose primary (x,y,z) + Dose scatter (x,y,z) CT image primary dose image scatter dose image three dimensional dose distribution Determination of Dose from CT Examinations primary dose Why are we here? Definitions scatter dose CT dosimetry in the real world Perspectives from the ICRU Committee total dose Summary 16

17 average tissue dose (mgy) THE END 17