1. Rad T 110
Sherer
Ch. 3

2. Discovery of X-rays
November 1895
Crooke’s tube

3. Injuries Dally Early awareness of effects First American fatality 1904
Radiodermatitis
Lead to cancerous lesions
Aplastic anemia
Leukemia

4. Investigation into Safety
1921 – British X-ray and Radium Protection Committee
Had the idea and ‘recognized’ the dangers but did not have the technology to establish or measure guidelines.

5. Skin Erythema dose 1900 -1930 Used to measure exposure
Does not account for individual differences or tolerance of dose.
Inaccurate

6. Tolerance Dose
Based on keeping exposure below threshold dose for acute or early effects
The idea being that nothing bad was going on before early effects were noted.
Still resulted in a tremendous dose however
In 1934, tolerance dose limited to 0.2 R daily
1936, tolerance further reduced to 0.1 R daily.
This was in response to the observation that late effects also occurred.

7. Roentgen
In 1937 became the internationally accepted measure for exposure to x-ray and gamma radiation.

8. Modern Era of Rad Protection
In the 50s, Maximum Permissible Dose (MPD) replaces tolerance dose.
REM
Allows for comparison between different types of radiation.

9. Traditional units of exposure
Roentgen – unit of exposure
2.58 X 10-4 coulombs/kg of dry air
Basically, how much air is being ionized
REM – radiation equivalent man
Any exposure that produces the same biologic effect as 1 rad of x-radiation
Rad – absorbed dose
100 ergs per gram of tissue

10. SI units of exposure Roengten is a roengten 100 rads = 1 Gray (Gy)
100 rem = 1 Sievert (Si)

11. Absorbed dose
Each tissue in the body has different absorption characteristics.
Based on
Effective atomic number, tissue or mass density, and part thickness
Produces differential absorption
Subject contrast

12. LET
High LET radiation deposits a large amount of energy in a small area.
This would be bad, thereby producing more damage
X-rays are a low LET form of radiation

13. Quality factors X-ray photons, beta particles, and gamma photons – 1
Thermal neutrons – 5
Fast neutrons – 20
Alpha particles – 20
Based on LET

14. Equivalent Dose
Takes into account that different types of radiation are more dangerous than others and applies a radiation weighting factor to them.
Radiation weighting factor is based on RBE.

15. Radiation weighting factors
Electrons, x-ray photons, gamma photons – 1
Neutrons < 10 keV – 5
Neutrons 10 keV – 100 keV – 10
Neutrons >100 keV – 2 MeV – 20
Protons – 2
Alpha particles - 20

16. Effective Dose
This uses the equivalent dose and then factors in the types of tissue that have been irradiated.
Some tissues are more sensitive than others; thereby, potentially causing more damage.

17. Weighting Factors
We will focus on Equivalent Dose using weighting factors.