1. Radiation Protection
RTMR 284
CHAPTER 21

2. Units Of Exposure Rad Rem The unit of absorbed dose..
Patient radiation dose is measured in units of rad
Rem
The unit of effective dose..
Dose to the whole body measured in units of rem
Basis of dose limits

3. Units Of Exposure mRAD Gray - Gy Sievert –Sv
The millirad is equal to one one-thousandth of a rad
Gray - Gy
The SI unit of absorbed dose equal to an energy deposition of Joule/kg = 10,000 ergs/gm
(1 Gy = 100 rads).
Sievert –Sv
The SI unit of effective dose.

4. 5 Ways Photons Interact with Matter
Classical /Coherent scattering (occurs at < 10keV)
Compton effect
Photoelectric effect
Pair production (occurs at 1.02 MeV)
Photodisintegration (occurs at >10 MeV)
Reference Chapter 7 for more details

5. Compton Effect
Moderate-energy X-rays interact with outer- shell electrons
This interaction
scatters the X-ray (up to 180 degrees)
reduces its energy (retains up to 2/3rds energy)
ionizes the atom
Compton effect occurs more above 80 kVp
Compton effect occurring does not depend on the atomic # of the atom involved

6. Compton Effect
Scattered X-rays provide no useful information on the image
Compton-scattered X-rays produce fog
Compton effect is the source of exposure to radiographers
Radiation (large amounts) can be scattered from the patient, especially during fluoroscopy

7. Photoelectric Effect
Diagnostic range X-rays undergo ionizing interactions with inner-shell electrons
The X-ray is absorbed

8. Photoelectric Effect Photoelectric effect occurs more with:
high atomic number material
low energy X-rays
Photoelectric effect occurs more below 80 kVp
Name two materials that would result in more photoelectric effect occurring.

9. Atomic numbers or Z #’s Lead 82 Iodine contrast 56 Barium 56 Bone 14
Soft tissue/air
Fat 6

10. Comments
Most of the photons (going through the patient) will interact & be absorbed by the tissue. Only ~5% of the incident photons will emerge from the patient to form the image
~50 % of the total number of photons reaching the image is from scattered radiation

11. 4 Factors Affecting Scatter Radiation
kVp (Kilovoltage peak)
part thickness
field size (area exposed, large coning)
tissue density
Scatter radiation is greatest with:
high kVp
large fields (open cone) - most important factor
thick body parts
dense tissue

12. Advantages of High kVp  skin entrance dose to the patient
shorter exposures ( motion and blurring)
increased radiographic latitude
improved control of radiographic contrast
tube not heated up as much due to better X-ray production efficiency at higher voltages
The next slide is for your comprehension only – will not need to reproduce!

14. Factors Affecting Differential Absorption
Higher atomic number (Z)
PE absorption greater in absorbers with higher Z
Compton scatter unaffected by Z number
Increased kVp
PE absorption decreases sharply
Compton scatter remains proportionally greater
Increased mass density
PE absorption increases
Compton scatter increases

15. ALARA As Low Reasonably Achievable
What can we do as technologists to reduce radiation exposure???

16. Basic Principles of Radiation Redux
Cardinal Principles:
Time
Distance
Shielding
How do we use these principles in our daily jobs as technologists?

17. Dose Limits Limiting Occupational exposure. Whole body: 5 rem / 50 mSv
Quarter: 1.25 rem / 12.5 mSv
Cumulative Effective Dose Limit E = N x 10 mSv, where N is the age in years.
Study Table 21.3 in textbook.

18. Protective Apparel Type Pb Atten. Apron 0.50 mm 99.9%
Gloves mm %
Thyroid mm 99%
Glasses mm 99%
Drape mm 99%
Holding Pt. Comments?

19. Patient Dose Reduction
Techniques
Repeats
Shielding
Flat contact
Shadow
Radiation Dose
ESE – Skin entrance exp.
Pediatrics Patients
What exams have a high ESE???

20. Pregnant Radiographer & Patient
Technologist:
Have a choice to declare her pregnancy.
Dose limit 0.5 mSv/mo.
5 mSv for pregnancy
Baby Badge
Wrap around apron
Stay away from high dose procedures
Patient:
10-day rule for patients.
Ask EVERY TIME
Keep dose low
Talk to Radiologist if you feel the exam is unnecessary and the physician is insisting.