1. PRACTICAL APPLICATION OF Diagnostic Reference Levels
Lee O’Hora BSc MSc
RSO UPDATE STUDY DAY BONS SECOURS HOSPITAL GLASNEVIN

2. Concepts
Diagnostic Reference Levels Indicators of central tendency and 75th Percentile A practical overview Establishing local DRLs and national comparison Using dose information locally

3. Diagnostic Reference Level DRL
‘Diagnostic reference levels means dose levels in medical radio diagnostic or interventional radiology practices, or, in the case of radio-pharmaceuticals, levels of activity, for typical examinations for groups of standard-sized patients or standard phantoms for broadly defined types of equipment’
Typically set at 75th Percentile – Nationally –n DRL
Annual comparison to local ‘averages’ –Local – l DRL
Introduced to indicate unusually high patient radiation doses from medical imaging examinations and procedures - NATIONALLY
Council of the European Union. (2013). Council Directive 2013/59/Euratom laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom. Official Journal L-13 of
MERU. Patient Radiation Safety Manual, Section 7, Diagnostic Reference Levels

4. Mean Median and Mode - measures of central tendency
(50th percentile)
Add all values in a set and divide by the number of values
Middle value when numbers are arranged in order of ascendancy
Value that occurs most often
average
middle
most

5. Mean, Median and Dose Distribution
If your dose data is ‘NORMAL’ mean = median either is applicable (CT Brain, Mammo)
Most dose data - right/positive ‘Skewed’ (Generally due to larger patients, Mean doses can be influence upwards by these patients)

6. The 75th Percentile, 3rd Quartile
A percentile (or a centile) is a measure used in statistics indicating the value below which a given percentage of observations in a group of observations fall.
NOT A MEASURE OF
CENTRAL TENDENCY
The 75th percentile dose is that dose for a group of patient doses below which 75% or ¾ of observations (patient doses) fall

7. Consider a group of numbers
The MEDIAN or 50th PERCENTILE (when arranged in ascending order) is the middle number (dividing your data set into upper and lower halves)
The 75th percentile number is the MEDIAN of the upper half

8. A practical demo 12

9. Mean and Median Mean 17.03 Median 11.5
E. Vañó, D.L. Miller, M.M. Rehanic, Overview of ICRP Committee 3 ‘Protection in Medicine’. Annals of the ICRP, vol. 44 (1), pp

10. When checking compliance we compare lDRLs (Median) with nDRLs (75th Per)

11. ? Compare Median with a median…………………
5/12 centers fail

12. ? Compare a 75th with a 75th……………………
6/12 centers fail

13. ? Compare a l DRL (median) with a nDRL (75th)……………………
1/12 center fails
“Introduced to indicate unusually high patient radiation doses from medical imaging examinations and procedures”

14. Establish a local DRL and compare to National DRL

15. What should an RSO/RPO do locally to comply!?!
Target procedures
Local Numbers (Annual common procedures)
High dose work (CT and IR)
Quoted figures from HSE
Start small, create a working model and expand…………..

16. What should an RSO/RPO do locally to comply – Blue Sky!
Target procedures –CT TAP (common and high dose)
Local Numbers – 2000 PA
Quoted figures from HSE - YES
What patients and how many (Sample population and size)

17. Calculating your sample size
Generally a 95% confidence level and 5% Margin of error are ‘gold standard’
Because dose stats are recommended to be reviewed annually, your population size is the annual number of procedures done

18. What should an RSO/RPO do locally to comply – Blue Sky!
323
~27 per month
RANDOM sample of all patients

19. DLP VALUE (Gy.cm)
Mean
402
Median
377
Mode
317¹
25th
312
50th
75th
462

20. First Step
l DRL 377
nDRL 850

22. Now What !?! Recent HSE inspections
Info dissemination (e mail, posters)
Liaise with CS
Dose ‘norms’ readily available for staff
Enable dose optimization by raising awareness of dose
Relatable terms for staff and patients

23. Now What ?!? ? Goal Staff on floor, knowing using
and relating local DRLs
DRLs are produced in the relevant dose metric

24. INJ ACT DLP/CTDI vol MGD/DAP PSD/DAP
Dose metrics
PSD/DAP

25. Each metric above only applies for a certain procedure/body part
MBq
mGy – MGD/Kar/CTDI
µGy.m²
mGy.cm
Each metric above only applies for
a certain procedure/body part
Dose metrics

26. This makes procedure dose comparison difficult
Dose metrics

27. Staff Information CT IR CV GEN MAMMO Readily Available
PROCEDURE
LOCAL MEDIAN DOSE
(DAP, MGD,DLP, ACT)
LOCAL MEDIAN EFFECTIVE DOSE (mSv)
EQUIVALENT PERIOD OF ENVIRONMENTAL RADIATION
EQUIVALENT NUMBER OF CHEST X RAYS
EXTREMITY
(AP and LAT)
2.4 µGy.m²
0.0002
25 Minutes
1/100
PICC line insertion
30 µGy.m²
0.04
3.7 Days 2
Mammo 4 view
4.8 mGy
0.58
1.7 Months 29
CT Brain
668 mGy.cm
1.4
4.2 Months 70
NM Bone Scan
600 MBq 4
1 Year
200 CT IR CV
GEN
MAMMO
Readily Available
Easily accessible
Easy to understand/recall/convey
(01)

28. THANKYOU FOR LISTENING
(01)