2. You need a lateral view. Is it better to rotate the image intensifier
toward you or away from you?
Why is fluoro time a poor indicator of radiation exposure ?
How many Grays of radiation puts the patient at risk for skin
injury?
A 5-second DSA run uses how much more radiation than 5
seconds of fluoro?
A typical embolization procedure exposes the patient to how
many CXRs worth of radiation?
What is the increased cancer risk of such a procedure?
What is the cancer risk to the operator if he does 1 embo procedure
per working day for 30 years?
3. Radiation exposure
Radiation effects
Minimizing radiation to the patient
Minimizing radiation to you
5. X-rays are produced by
accelerating electrons
through high voltage (50-
150 kVp) applied to a
tungsten target in an X-ray
tube
Amount of X-rays produced
are determined by tube
current (mA) and the tube
voltage (kVp)
6. Dose is not administered uniformly throughout the
patient’s body
Radiation field is moved, angled, collimated
Both fluoro and DSA are used
Four metrics are used to estimate patient radiation
dose
Fluoro time
Peak skin dose (not yet measured by equipment)
Reference dose (air kerma)
Dose-area product (DAP)
7. Also called “cumulative dose”
The Air Kerma for the entire
procedure, measured in Gy at a fixed
reference point near the isocenter of the
tube
Does not account that the radiation field
is moved to different areas of the patient
during the procedure
Conservative, generally overstates risk
Measurement is likely accurate to within
+/- 50%
8. Measure of total X-ray
energy absorbed by the
patient
Basically the air kerma
(dose) multiplied by the
area of body exposed
(area)
9. Fluoro time is only a very rough indicator of
radiation dose, affected by:
Patient size
Beam location
Beam angle
Normal vs. high dose rate
Distance of tube from the patient
These can all add up to 10-fold difference in dose
for the same fluoro time!
10. DOSE-AREA PRODUCT (DAP) CUMULATIVE AIR KERMA
Product of the air kerma and the Air kerma = Kinetic Energy
exposed area (in cm2) Released per unit Mass of Air;
basically, how much radiation dose
Good measure of stochastic risk is being delivered at a specific
(cancer risk) because it estimates point (about where the patient’s
total radiation energy delivered to skin is)
a patient
Also known as reference dose or
Poor estimator of skin dose and cumulative dose
deterministic effects
large dose over small area or small Easy to measure, expressed in Gy
dose over large area?
Absorbed dose in tissue will be
Unit of measurement (Gy-cm2) about equal to the air kerma at
does not translate into standard that point
units of dose (hard to use)
Notification threshold = 3 Gy
12. Patients and staff are exposed to radiation, but
only a portion is absorbed into the body
Absorbed dose is measured in Gray or rads
1 Gray = 100 rads
Approximate radiation doses:
Fluoro = 2-10 rads/min
CXR = 0.02 rads
CT abdomen = about 2-10 rads
Natural background radiation = 0.3 rads/year
13. Different forms of radiation (X-rays, alpha
particles, etc) produce different biologic
effects for same absorbed dose
Dose equivalent (rem or Sievert) is used to
measure biologic “harmfulness” of a radiation
dose
For diagnostic X-rays, 1 rem = 1 rad and 1 Gy =
1 Sv
14. Effective dose is the dose equivalent to the
whole body caused by irradiating just a
localized area
This is calculated by multiplying the dose to each
irradiated organ by a weighting factor based on
the radiosensitivity of that organ
Example effective doses:
CXR = ~0.1 mSv
PTA = 10-20 msV
Biliary drainage = 40 mSv
Transcatheter embolization or TIPS = 50-100 mSv
Additional cancer risk = ~5%/Sv
So, a long embolization procedure in a 30 year
old increases risk of developing a fatal cancer
by about 0.5%
15. Fluoro machines operate in automatic
brightness control
When brightness of picture is inadequate, the
ABC automatically increases mA or kVp (or both)
to increase X-ray penetration
Large patients = more dose than small patients (up to
4-10x higher!)
Abdominal fluoro = more dose than chest fluoro
Oblique fluoro = more dose than AP fluoro
16. Direct exposure rate refers to entrance skin
exposure where the X-ray beam enters the
patient
2-10 rads/min for fluoro
~50 rads/min for DSA
30 mins of fluoro = 60-300 rads = 0.6-3 Gy
17. Indirect exposure rate refers to exposure to the
staff from scattered radiation from the patient
~1/1000 of the skin entrance exposure rate at a
distance of 1 meter
Large patients increase scatter radiation
Larger field (not collimated) increases scatter
Scatter much higher on the X-ray tube side of the
patient
▪ For lateral view, stand next to II, not next to tube!
19. Radiation effects with a threshold dose;
effect is not observed unless threshold is
exceeded
22. Early erythema – 3 Gy – 1-2 days –
sunburn
Epilation – 3-7 Gy – 3 weeks – hair loss
Main erythema – 10 Gy - onset 1-4
weeks – burning, itching
If >14 Gy, progresses to dry
desquamation 1 week later
If >18 Gy, progresses to moist
desquamation (blistering, sloughing) 1
week later
Ulceration – 24 Gy – 2-12 months
23. No threshold
Any dose increases the chance of the
effect, with higher doses increasing the
chances
Radiation-induced cancer
24. Approximate additional risk of fatal cancer
for an adult for an examination:
Extremity X-ray: <1/1,000,000
CXR: 1/100,000 to 1/1,000,000
Chest CT: 1/10,000 to 1/1,000
Multiphase abdominal CT: 1/1,000 to 1/500
These risks are additive to the ~25%
background risk of dying of cancer
26. Very small (<10 kg) or very large
(>135 kg) patients
Age (3x risk for newborns, 1x risk at
age 25, 0.2x risk for patients in 60s)
Pregnant patients
Prior radiation exposure within last
2 months
Diabetes, autoimmune
diseases, connective tissue
diseases increase risk of skin
effects
27. Ultrasound instead of fluoro when possible (biliary, arterial
access)
Patient should be as far from tube, and as close to II, as
possible (good to be tall!)
Don’t step on the pedal
Pulse fluoro mode (7.5 or 15 frames/sec instead of 30/sec)
View and save images with “last image hold”
Exclude bone from the image
28. Collimate to smallest field of view possible
Avoid exposure to eyes, thyroid and gonads
Position and collimate without fluoro
5-8% of radiation exposure is delivered during preparation for
imaging, positioning the table and adjusting collimators
Avoid magnification
ABC uses more radiation to brighten and sharpen the image in mag
view
Avoid high-dose or detail modes
Use higher kVp (but can reduce contrast)
Minimize overlap of fields and repeated acquisitions
32. Less time on the pedal
Use last image hold
Pulsed fluoro
Low dose fluoro
33. Inverse square law
Double distance from patient = ¼ the radiation
dose from scatter radiation
Nonessential personnel should be outside a 6-foot
radius from the X-ray source
Step out of room for DSA runs
34. Lead apron (0.5 mm Pb equivalent) blocks
about 95% of scatter radiation
Thyroid shield, leaded glasses are essential
Most radiosensitive organs
Lead drapes and clear leaded glass barriers
36. Record dose in the medical record
If dose exceeded deterministic thresholds
Discuss possible effects and management with
patient
Have patient or family member notify IR if
deterministic effects occur
Institute a clinical follow-up plan for the patient
37. Necessary when large radiation dose was
used
Telephone call at 2 weeks or so
Redness? Blistering? Hair loss?
Location of radiation field
May need follow up for >1 year
39. You need a lateral view. Is it better to rotate
the image intensifier toward you or away
from you?
40. You need a lateral view. Is it better to rotate
the image intensifier toward you or away
from you?
Toward you! Keep the beam away from
you, because most of the scatter occurs at
the point the beam enters the patient
41. Why is fluoro time a poor indicator of
radiation exposure ?
42. Why is fluoro time a poor indicator of radiation
exposure?
Does not include DSA runs
Dose varies greatly for the same fluoro time
Thin or obese patient
AP or oblique views
Magnification
Distance from X-ray source
43. How many Grays of radiation puts the patient
at risk for skin injury?
44. How many Grays of radiation puts the patient
at risk for skin injury?
3 Grays!
45. A 5-second DSA run uses how much more
radiation than 5 seconds of fluoro?
46. A 5-second DSA run uses how much more
radiation than 5 seconds of fluoro?
About 10x more radiation for DSA!
47. A typical embolization procedure exposes the
patient to how many CXRs worth of
radiation?
What is the increased cancer risk of such a
procedure?
What is the cancer risk to the operator if he does 1
embo procedure per working day for 30 years?
48. A typical embolization procedure exposes the
patient to how many CXRs worth of radiation?
About 1000!
What is the increased cancer risk of such a procedure?
About 0.5% for a 30 year old!
What is the cancer risk to the operator if he does 1
embo procedure per working day for 25 years?
100 mSv (patient equivalent dose) x 1/250 (scatter fraction at 18 inches) x 1/20 (fraction of radiation that
gets through the lead) x 5000 (# of procedures) = 100 mSv
A career in IR is probably equivalent to having an embolization
procedure done on yourself (0.5% additional cancer risk)
49. Mitchell E and Furey P. Prevention of radiation injury from
medical imaging. J Vasc Surg 2011; 53:22S-27S.
Miller D, et al. Clinical radiation management for
fluoroscopically guided interventional procedures.
Radiology 2010;257:321-332.
Cousins C and Sharp C. Medical interventional procedures
– reducing the radiation risks. Clin Radiol 2004;59:468-473.
Wagner L. Angiography radiation dose – limiting dose to
the patient while maintaining effective image quality.
http://www.uth.tmc.edu/radiology/RSNA/2008/RSNA_wa
gner_2008.pdf