2012:15thsession of esmp · lecture presented in archamps(salève building) by : 2012:15thsession...

Lecture presented in Archamps (Salève Building) by :

2012 :15th SESSION of ESMP

Elly CASTELLANO (London)

European School of Medical Physics - Archamps

Patient dosimetry in x-ray imaging and CT

Elly Castellano

2European School of Medical Physics - ArchampsESMP 2011

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 risk-related quantities


Measurable dose quantities• also:

– CTKairIw– CTKairIvol– KLPair

• NB:

– KAP�DAP

– ESAK � ESD

– CTKairIw � CTDIw– KLPair � DLP

IAEA technical report series 457


CT dose indicators

CTDIcCTDIp

head

body CTDIcCTDIp

head

body

( )∫

∞

∞−

= zzCTDI dDT

1

pcw CTDICTDICTDI ,100,100

3

2

3

1+=

p

CTDICTDI wvol =

RCTDIDLP vol ⋅=


Measurable dose quantities

modality measurables

radiography IAK, ESAK, KAPair

fluoroscopy IAK, ESAK, KAPair, screening time, no of acquisitions

dental IAK, KLPair, KAPair

mammography IAK

CT CTKairIw, CTKairIvol, KLPair


Tools for dosimetry: dosimeters

http://www.radcal.com/images/9010_w_9015.jpg

http://www.unfors.com/image/news/img_581.jpg

http://www.ptw.de/typo3temp/pics/5298ee86fc.jpghttp://www.rpdinc.com/assets/images/W155-000-A.gif

calibration

required


Tools for dosimetry: patients

patient

size

target

weight kg

weight

range kg

“newborn” 4 3.5 – 4.5

“1 y” 9 8 – 10

“5 y” 19 16 – 22

“10 y” 32 28 – 36

“15 y” 55 47 – 63

“adult” 70 60 – 80


Tools for dosimetry: phantoms

courtesy: The Phantom Laboratory Inc

• also:

– PMMA slabs

– water phantoms


Practical approaches: references• national protocol for patient dose measurements in DR

• IAEA technical report no 457: Dosimetry in Diagnostic

Radiology


Practical approaches: radiography

• option 1: KAPair 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• kVp2 and mAs

• 1/focus to skin distance2

• option 3: ESAK from patient exposures– TLDs

– IAK scaled by backscatter factor


Practical approaches: fluoroscopy

• option 1: KAPair 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


Practical approaches: dental• intraoral: IAK from patient exposure

parameters

– calibrated ionisation chamber, solid state

detector or TLD at exit cone

• OPG option 1: KLPair from patient

exposure parameters

– calibrated pencil ionisation chamber or

TLD stack at slit

• OPG option 2: KAPair from patient

exposure parameters

– calibrated KAP meter at slit http://www.made-in-china.com/image/xxx.jpghttp://www.kodakdental.com/~/media/images/xxxx


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

• kVpx and mAs

• 1/focus to skin distance2

• option 2: IAK inferred from phantom exposures

– PMMA phantoms

• e.g. 45 mm PMMA for 53 mm breast

– technique as above


Practical approaches: CT• option 1: CTKairIvol inferred from patient exposures

– CTKairIw per 100 mAs

• ionisation pencil chamber

• head or body phantom

• at required filter, kVp, beam collimation

– scaled by

• mAs

• pitch

• option 2: KLPair inferred from patient exposures

– scale CTKairIvol by

• length of irradiated volume

– scan length + slice thickness + overscan


Displayed dose information

modality display measured /

nominal values

radiography KAPair real or nominal

fluoroscopy KAPair, IAK at ref point, screening time, no of acquisitions

real or nominal

dental KAPair nominal

mammography ESAK nominal

CT CTKairIvol, KLPair nominal


Monte Carlo techniques for

estimating organ doses: principles

ESAK or IAK

KAP

particle transport

(Monte Carlo)

CTKI-in-ICRU

muscle


Monte Carlo techniques for

estimating organ doses: phantomsvoxel phantomsgeometric phantoms

e.g. MIRD phantomsnewborn, 1-y, 5-y, 10-y,

15-y / adult woman, adult man e.g. Yale phantom


Practical approaches: radiography

organ doses and effective dose

Monte Carlo source data

phantoms normalisation measurable quantities

NRPB R-262 + XDOSE

adult male MIRD, fixed weight

ESDairDAPair

ESAK, IAK x BSF

KAPair

NRPB R-279 + CHILDOSE

paediatric MIRD, fixed weight

ESDairDAPair

ESAK, IAK x BSF

KAPair

PCXMC MIRD, variable weight

IAK

KAPair

IAK

KAPair

NB kerma ≈ dose at diagnostic energies except in bony tissues


Practical approaches: fluoroscopy


Monte Carlo

source data

phantoms normalisation measurable

quantities

NRPB R-262 + XDOSE


ESDairDAPair

ESDair, IAK x BSF KAPair

PCXMC MIRD, variable weight

IAK

KAPair

IAK

KAPair



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), 2237-2250


Practical approaches: dental

radiography



Practical approaches:

mammography

mean glandular dose

Monte Carlo source data

phantoms normalisation measurable quantities

IPEM report 89 + Dance et al 2009 + NHSBSP 0405

Dance et al 2000

IAK IAK for patient exposures

IPEM report 89 + Dance et al 2009 + NHSBSP 0405

Dance et al 2000

IAK IAK for PMMA phantom exposure NB no 1/r2

correction to surface of equivalent breast model

Dance et al, PMB 45 (2000), 3225-3240

Dance et al, PMB 54 (2009), 4361-4372


Practical approaches: CT


Monte Carlo

source data

phantoms normalisation measurable

quantities

NRPB R-248 to R-250 + ImPACT dose calculator


CTDIICRUmusclefree-in-air

CTKIair free-in-air

CTKIair free-in-air

GSF CT conversion factors + CT-Expo

adult male and female MIRD, Child and Baby, fixed weight

CTKIair free-in-air

CTDIw

CTKairIw



Summary

• practical approaches to measuring dose and estimating risk-related quantities in

– radiography

– fluoroscopy

– dental radiography

– mammography

– CT

2012:15thsession of esmp · lecture presented in archamps(salève building) by : 2012:15thsession...

Documents