Chapter 24 - Radiation safety Flashcards
Classification of types of radiation
Nonionizing radiation = US, MR, laser, microwave Ionizing = X-ray, gamma rays, beta rays, electrons
Define Roentgens
measurement for amount of ionization that radiation produces in air Units = 1R = 2.58 x 10^-4 C/kg
Define Curie
Measurement of radioactivity Number of particles/sec from 1 g of radium
Define absorbed dose
Measure of amount of energy in medium by ionizing radiation per unit mass of matter Equal to amoun tof heat generated by radiation per tissue weight in specified material Unit = Gray = 1 J/kg = 100 rad (radiation absorbed dose)
Define Radiation weighting factor
degree of damage by different types of radiation
Define equivalent dose
Measure of radiation dose to tissue taking into account different types of radiation Absorbed dose x W(R) Unit = Sievert = 1 Gy x W = 100 rem (roentgen equivalent man)
Define effective dose
Taking into account of different sensitivity of tissue Tissue weighting factor WT Unit = Sievert = 1 Gy x W = 100 rem (roentgen equivalent man)
Define tissue weighting factor
sensitivity of each tissue type to damage
Weighting factor
combines WR with WT
Two types of effects of radiation on biological tissue
1) Deterministic effects 2) stochastic effects
Define deterministic effects
1) dose-dependent cell death 2) hair follicle, skin, subcu tissue, lens of eye 3) acute events 4) threshold level exceeded 5) higher dose, greater injury
Threshold effective dose for various organs and damages
TABLE 24.2
Acute whole body exposure and consequences of radiation
10-20 Gy high energy = death 0.5-1 Sv = light radiation sickness 1Sv = slight blood changes 2-3 Sv = nausea, hair loss, hemorrhage 3Sv = death in 50% in 30 days > 6Sv = unlikely survival
Define stochastic effects
1) aka probabilistic effects 2) DNA damage to single cells = mutation 3) all-or-none phenomenon 4) probability of occurrence increasing as cumulative radiation exposure increases 5) no established threshold level 6) linear-nonthreshold model of incremental risk
Probability of fatal cancer as result of radiation exposure
4% per 1Sv of lifetime dose 0.004%/mSv < 100 mSv does not cause cancer
Hereditary effect of radiation exposure
0.1% per sievert
Annual average natural background radiation in US
3 mSv/yr
Greatest source of domestic radiation
radon gas 2 mSv/yr
Typical effective dose in common diagnostic procedures
TABLE 24.4
Recommended dose limit to general public
1 mSv/yr
Recommended dose limit to radiation workers
20 mSv/yr average over 5 years < 50 mSv in any year
International commission on radiological protection safety limits for lens, skin, extremity and for fetus
TABLE 24.5
Effective dose of spiral CT and MDCT compared to older scanners
10-30% higher
Effective dose of DynaCT (3 dimentional rotational) compared to SDCT
7-8x less
Voltage and current of the fluoroscopic tube
Voltage = controls penetration and contrast Current = number of photos produced by tube
Ways to limit radiation emission
1) high voltage 2) low current 3) low frame rate 4) pulse fluoroscopy instead of continuous 5) limit mag view (2-3x higher) 6) use collimation and filters (focus radiation for better image) 7) limit DSA (10x more radiation) 8) increase distance (1/d^2) 9) ceiling shields (reduce brain/eye 20x)
What oblique view gives higher exposure
LAO gives 3-5x more radiation than RAO
Patient follow up when
exposed to > 3-5 Gy in 1-2 weeks
With average use and equipment, the average dose exposed to surgeon for body eye and hand are
0.2 0.2 1 below limit
Fetal risk and radiation dose
TABLE 24.6 0.04% mental retardation with IQ loss 2-3 points/mSv
