Rad T 110 Sherer Ch. 3

Discovery of X-rays November 1895 Crooke’s tube

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

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.

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

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.

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

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

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

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

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

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

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

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.

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

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.

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