1. Patient exposure trends and problems in implementing ALARA
Barry Wall
Medical Exposure Department
Radiation Protection Division
Health Protection Agency
Chilton, UK

2. Uses of radiation in medicine
Medical radiology
X-ray imaging for diagnosis
X-ray imaging to guide therapeutic interventions
Radionuclide imaging (nuclear medicine)
Radiotherapy
Together  99% of man-made population dose

3. Medical X-ray Imaging Radiography Effective dose Cancer risk 10 µSv
<1 in a million
Radiation
doses
&
risks
increasing
Fluoroscopy
Computed
Tomography
20 mSv
~ 1 in 1000

4. X-ray examinations in 4 dose bands
Effective dose Typical % of total % of total
range (mSv) x-ray exams no. of exams collective dose
< Radiography of
chest, limbs, teeth
Radiography of
head, neck, joints
Radiography of spine,
abdomen, pelvis
CT, angiography,
contrast studies of GI,
biliary & urinary tracts

5. Course Introduction (RADSAFE)
Typical Effective Doses
from X-ray Procedures
Chest
Skull
Abdomen
Pelvis / hip
Lumbar spine
IVU (urinary tract)
Ba meal (stomach)
Ba enema (colon)
CT body
Angiography
Interventional
Thoracic spine
CT head 5 10 15 20
Effective dose, mSv
Typical values of E per procedure for developed countries
Mean values range from 0.1 to 20 mSv, but significant variations in practice for given type of exams between different x-ray departments and individual patients
Quite low doses for many common exams: fractions of a mSv for chest, head, limbs and joints
1-2 mSv for exams of the abdomen, pelvis, lumbar or thoracic spine
Larger doses for urography and barium meal (4 mSv), barium enema (6 mSv)
CT - 2 mSv for head, but about 10 for body
Complex angiography and intenventional procedures typically between and 10 and 20 mSv
Highest dose band

6. Conventional Radiography
Course Introduction (RADSAFE)
Conventional Radiography
Images of bones obtained on film sandwiched between intensifying screens in cassette below patient couch

7. Course Introduction (RADSAFE)
Conventional
Fluoroscopy
Ba study of colon
Fluoroscopy provides real-time images, move collimated x-ray beam and electronic image intensifier, images on TV monitor
Used for example in barium studies of gut, meals and enemas where barium introduced into stomach or colon to enhance contrast
Image intensifier

8. Course Introduction (RADSAFE)
Single slice axial CT

9. Recent developments in medical imaging
Digital radiography
Storage phosphors or
flat-panel detectors
 static digital images
Amorphous selenium coating over TFT matrix
Digital fluoroscopy
Image intensifier or flat panel detector
 moving digital images
and DSA

10. Recent developments in medical imaging
Multi-slice helical CT
Up to 64 rows of detectors across beam
0.5 s rotation time
 3D images with 0.6 mm isotropic spatial resolution

11. Image from 64 slice CT scanner

12. Recent developments in medical imaging
Increasing use of
fluoroscopy-guided
key-hole surgery by
non-radiology clinicians
(eg. cardiologists)
Prolonged fluoroscopy
with static x-ray beam
can produce
tissue reactions

13. Patient Dose Measurement Methods Radiography Fluoroscopy CT
Entrance surface dose
(ESD)
Direct
measurements
can only be
made in x-ray
beam outside
the patient
Fluoroscopy
Dose-area product
(DAP) CT
CT dose index
(CTDI)
38507, 29033, 29037

14. Calculation of organ doses
Simulate x-ray exams on mathematical phantoms and follow tracks of millions of x-ray photons through phantom
Calculate energy deposited in each organ & external dosemeter to derive coefficients relating organ doses to the measurable dose quantities (ESD, DAP or CTDI)
Conventional X-ray exams
CT examinations
Family of phantoms
Baby 1y 5y 10y 15y Adult

15. 1983 NRPB Patient Dose Survey Abdomen AP Frequency
Entrance surface dose per film, mGy 10 15 30 45 60 20 40
Abdomen AP
Best hospital
Worst hospital
22834

16. Radiation protection principles for medical exposures
Justification
Optimisation
But no dose limits

17. Optimisation of medical exposures
X-ray equipment and techniques should be selected to ensure that patient exposures are ALARA consistent with obtaining the required diagnostic information
How?

18. DRLs - the first step to ALARA
Patient exposures cannot be reduced indefinitely without impact on image quality
Radiologists subjectively assess the adequacy of their images every time they report on them but they cannot intuitively assess the patient dose (particularly with modern digital systems)
DRLs provide a means for alerting radiologists when their patient doses become unusually high

19. DRLs - the first step to ALARA
Concept of DRLs recognised in:
- ICRP Publications 60 (1991) & 73 (1996)
- IAEA BSS (1994)
- EC Medical Exposure Directive (1997)
DRLs usually set at 3rd quartile of dose distributions seen in national patient dose surveys
Hospitals with mean doses > DRL should investigate why and take corrective action, if not clinically justified
DRLs are ‘investigation levels’ triggering further optimisation where most urgently needed.

20. DRLs - the first step to ALARA
On exceeding DRL, the subsequent investigation will involve detailed analysis of existing routine performance tests on the x-ray equipment (that include simple image quality checks) [e.g. IPEM Report 91]
and reference to international guidance on good imaging techniques:-
e.g. in European Guidelines on Quality Criteria for adult and paediatric radiography and CT

21. Trends in UK DRLs for radiographs (1985 - 2000)
Course Introduction (RADSAFE)
Trends in UK DRLs for radiographs ( )
Radiograph Entrance Surface Dose (mGy)
Skull AP/PA
Skull LAT
Chest PA
Chest LAT
Thoracic spine AP
Thoracic spine LAT
Lumbar spine AP
Lumbar spine LAT
Lumbar spine LSJ
Abdomen AP
Pelvis AP
Average 2000/1985 = 0.56

22. Trends in UK DRLs for exams (1985 - 2000)
Course Introduction (RADSAFE)
Trends in UK DRLs for exams ( )
Examination Dose-area product, Gy cm2
___________________________________
IVU (urinary system)
Ba meal (stomach)
Ba enema (colon)
2000
1985
Average
= 0.48

23. Trends in doses for CT (UK 1991 - 2003)
1991 (SSCT) (MSCT)
CT exam DLP E DLP E
(mGy cm) (mSv) (mGy cm) (mSv)
Head *
Chest *
Abdomen *
Pelvis
Abdo+pelvis
Chest+abdo+pelvis
* 2003/1991 =

24. Future problems in implementing ALARA
Although doses are coming down for ‘old routine’ CT exams scanning speeds have increased and whole trunk scans (with higher doses) are becoming the ‘new routine’.
Only radiologists can decide whether these increasing patient doses are ‘reasonable’ in relation to the extra diagnostic information obtained.
BUT they need to be reminded regularly to consider if the doses are ALARA - through the use of DRLs.
The major problems arise in trying to keep abreast of all these rapid developments in medical imaging and their impact on patient exposures, so that appropriate DRLs can be established to implement ALARA - ASAP