Dexa – The forgotten Survey

Paul Charnock, Fergus Dunn, James LoweIRS Ltd, Liverpool

• Should Level B QA be performed on Dexa?

• Who does anything on Dexa?

• Should guidance on QA & methods be included in any update to IPEM 91?

Questions for the Audience

• Dual (Energy) X-ray Absorbtiometry– Osteoporosis

– Bone Mineral Density determination

• Patient dose ~0.01 to 0.1mSv

• But...– (From IRR99) any practice involving medical

exposure of patient should have a suitable QA programme

QA in Dexa

• QA Guidance IPEM 91 (prev. IPEM 77)

– No Dexa

• Should it be included?

• Is there any guidance available?

QA in Dexa

• Commissioning & QA for Dexa

(Sheahan et al, RPD 2005)

• QA/Acceptance Testing of Dexa

(Larkin et al, RPD 2008)

• Patient doses in bone mineral densitometry

(Huda et al, BJR 1996)

QA in Dexa

QA in Dexa

Manufacturer / Model

Units

GE Lunar Prodigy

4

HologicDiscovery QDR

7

DMS StratosDR

1

12

• Scatter dose

• Reference Dose

• Patient Dose

• BMD

• Field Size

• HVL

• Cone/Fan Size

QA in Dexa

• BMD

Level A QA use a local, manufacturer specific phantom

Measure BMD for (usually) spine, plot against a baseline

Sometimes results clear, sometimes simple PASS/FAIL

QA in Dexa

QA in Dexa

• BMD

Level B – Take pelvis image of standard phantom

QA in Dexa

QA in Dexa

QA in Dexa

• Reference Dose

– Some systems display a dose

– Some are DAP, others (assumed) ESD

– One unit displays mrem

– How to measure?

QA in Dexa

QA in Dexa

Model Measured Dose Displayed Dose WBED

Lunar Prodigy Pro 131.8 µGy 146 (no units) 2.3 µSv

Lunar Prodigy Pro 200.2 µGy 146 (no units) 3.4 µSv

Discovery QDR 70.9 µGy No displayed 1.2 µSv

Discovery QDR 79.9 µGy No displayed 1.4 µSv

Discovery QDR 72.35 µGy No displayed 1.2 µSv

Stratos DR 50.3 µGy No displayed 0.86 µSv

QDR 4500W 208.9 µGy 3.5 cGycm2 3.6 µSv

Discovery Wi 173.4 µGy 3.5 cGycm2 3.0 µSv

Discovery Wi 151.9 µGy 3.5 cGycm2 2.6 µSv

Lunar Prodigy 68.56 µGy 3.7 mrem?? 1.2 µSv

• Field Size

– LBD equivalent

– Image a cassette (could use detector, gafchromicfilm etc)

– Is radiation constrained to the stated area?

• Issues?

– If no bone detected, some systems stop

QA in Dexa

QA in Dexa

Field size given is 10 cm by 15 cm

QA in Dexa

Scan field is given as 180 mm by 180 mmScan actually stops at 160 mm by 160 mm

• BMD Baseline is easy

– Some systems allow simple comparison with previous survey, even 1 yr later

– Supplements local QA

• Field size also easy

– Result show good indication

Conclusions

• Dose indication– Variable results

– Would like to discuss methodology

• Patient Dose– Can establish a baseline

– Conversion factors may not be appropriate

• HVL– Only at commissioning

– Only possible with Al

Conclusions

• Should Level B QA be performed on Dexa?• Yes

• Who else does anything on Dexa?• Send method / results to:

paulcharnock@irs-limited.com

ipem.evidence.based.qa@gmail.com

• Should guidance on testing be included in any update to IPEM 91?

Questions for the Audience