2012 :15th SESSION of ESMP

Transcription

1 2012 :15th SESSION of ESMP Lecture presented in Archamps (Salève Building) by : Elly CASTELLANO (London)

2 Patient dosimetry in x-ray imaging and CT Elly Castellano

3 Objectives measurable dose quantities tools for dosimetry practical approaches to measuring dose displayed dose information Monte Carlo techniques for estimating organ doses practical approaches to estimating riskrelated quantities 2

4 Measurable dose quantities also: CTK air I w CTK air I vol KLP air NB: KAP DAP ESAK ESD CTK air I w CTDI w KLP air DLP IAEA technical report series 457 3

5 CT dose indicators CTDI 1 = D( z) d z T 1 2 CTDI w = CTDI100, c + CTDI 100, 3 3 p CTDI vol = CTDI DLP = CTDI p w vol R body head CTDI c CTDI p 4

6 Measurable dose quantities modality radiography fluoroscopy dental mammography CT measurables IAK, ESAK, KAP air IAK, ESAK, KAP air, screening time, no of acquisitions IAK, KLP air, KAP air IAK CTK air I w, CTK air I vol, KLP air 5

7 Tools for dosimetry: dosimeters calibration required

8 Tools for dosimetry: patients patient size target weight kg weight range kg newborn y y y y adult

9 Tools for dosimetry: phantoms courtesy: The Phantom Laboratory Inc also: PMMA slabs water phantoms 8

10 Practical approaches: references national protocol for patient dose measurements in DR IAEA technical report no 457: Dosimetry in Diagnostic Radiology 9

11 Practical approaches: radiography option 1: KAP air from patient exposures calibrated KAP meter option 2: IAK inferred from patient exposures tube output at 75 cm, standard kvp and filtration ionisation chamber or SS detector scaled by kvp 2 and mas 1/focus to skin distance 2 option 3: ESAK from patient exposures TLDs IAK scaled by backscatter factor 10

12 Practical approaches: fluoroscopy option 1: KAP air from patient exposures calibrated KAP meter additionally: screening time no of acquisitions KAP per acquisition correction for couch attenuation required option 2: ESAK from phantom exposures ionisation chamber 11

13 Practical approaches: dental intraoral: IAK from patient exposure parameters calibrated ionisation chamber, solid state detector or TLD at exit cone OPG option 1: KLP air from patient exposure parameters calibrated pencil ionisation chamber or TLD stack at slit OPG option 2: KAP air from patient exposure parameters calibrated KAP meter at slit

14 Practical approaches: mammography option 1: IAK inferred from patient exposures tube output at 50 cm, for appropriate target / filter combination and paddle ionisation chamber or solid state detector scaled by kvp x and mas 1/focus to skin distance 2 option 2: IAK inferred from phantom exposures PMMA phantoms e.g. 45 mm PMMA for 53 mm breast technique as above 13

15 Practical approaches: CT option 1: CTK air I vol inferred from patient exposures CTK air I w per 100 mas ionisation pencil chamber head or body phantom at required filter, kvp, beam collimation scaled by mas pitch option 2: KLP air inferred from patient exposures scale CTK air I vol by length of irradiated volume scan length + slice thickness + overscan 14

16 Displayed dose information modality display measured / nominal values radiography KAP air real or nominal fluoroscopy KAP air, IAK at ref point, screening time, no of acquisitions real or nominal dental KAP air nominal mammography ESAK nominal CT CTK air I vol, KLP air nominal 15

17 Monte Carlo techniques for estimating organ doses: principles KAP ESAK or IAK particle transport (Monte Carlo) CTKI-in-ICRU muscle 16

18 Monte Carlo techniques for estimating organ doses: phantoms geometric phantoms voxel phantoms e.g. MIRD phantoms newborn, 1-y, 5-y, 10-y, 15-y / adult woman, adult man e.g. Yale phantom 17

19 Practical approaches: radiography organ doses and effective dose Monte Carlo source data phantoms normalisation measurable quantities NRPB R XDOSE adult male MIRD, fixed weight ESD air DAP air ESAK, IAK x BSF KAP air NRPB R CHILDOSE paediatric MIRD, fixed weight ESD air DAP air ESAK, IAK x BSF KAP air PCXMC MIRD, variable weight IAK KAP air IAK KAP air NB kerma dose at diagnostic energies except in bony tissues 18

20 Practical approaches: fluoroscopy organ doses and effective dose Monte Carlo source data phantoms normalisation measurable quantities NRPB R XDOSE adult male MIRD, fixed weight ESD air DAP air ESD air, IAK x BSF KAP air PCXMC MIRD, variable weight IAK KAP air IAK KAP air NB kerma dose at diagnostic energies except in bony tissues 19

21 Practical approaches: backscatter factors national protocol for patient dose measurements in DR IAEA technical report no 457: Dosimetry in Diagnostic Radiology Appendix VIII Petoussi-Henss et al, PMB 43 (1998),

22 Practical approaches: dental radiography organ doses and effective dose 21

23 Practical approaches: mammography mean glandular dose Monte Carlo source data phantoms normalisation measurable quantities IPEM report 89 + Dance et al NHSBSP 0405 IPEM report 89 + Dance et al NHSBSP 0405 Dance et al 2000 Dance et al 2000 IAK IAK Dance et al, PMB 45 (2000), Dance et al, PMB 54 (2009), IAK for patient exposures IAK for PMMA phantom exposure NB no 1/r 2 correction to surface of equivalent breast model 22

24 Practical approaches: CT organ doses and effective dose Monte Carlo source data phantoms normalisation measurable quantities NRPB R-248 to R ImPACT dose calculator adult male MIRD, fixed weight CTDI ICRUmuscle free-in-air CTKI air free-inair CTKI air free-in-air GSF CT conversion factors + CT-Expo adult male and female MIRD, Child and Baby, fixed weight CTKI air free-inair CTDI w CTK air I w NB kerma dose at diagnostic energies except in bony tissues 23

25 Summary practical approaches to measuring dose and estimating risk-related quantities in radiography fluoroscopy dental radiography mammography CT 24