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Rad T 110

Rad T 110. Sherer Ch. 3. Discovery of X-rays. November 1895 Crooke’s tube. Injuries. Dally First American fatality 1904 Early awareness of effects Radiodermatitis Lead to cancerous lesions Aplastic anemia Leukemia. Investigation into Safety.

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Rad T 110

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  1. Rad T 110 Sherer Ch. 3

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

  3. Injuries • Dally • First American fatality 1904 • Early awareness of effects • 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. • These are the same values presented in last weeks hand-out

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