Chapter 24 - Radiation safety

Question 1

Classification of types of radiation

Answer 1

Nonionizing radiation = US, MR, laser, microwave Ionizing = X-ray, gamma rays, beta rays, electrons

Question 2

Define Roentgens

Answer 2

measurement for amount of ionization that radiation produces in air Units = 1R = 2.58 x 10^-4 C/kg

Question 3

Define Curie

Answer 3

Measurement of radioactivity Number of particles/sec from 1 g of radium

Question 4

Define absorbed dose

Answer 4

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)

Question 5

Define Radiation weighting factor

Answer 5

degree of damage by different types of radiation

Question 6

Define equivalent dose

Answer 6

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)

Question 7

Define effective dose

Answer 7

Taking into account of different sensitivity of tissue Tissue weighting factor WT Unit = Sievert = 1 Gy x W = 100 rem (roentgen equivalent man)

Question 8

Define tissue weighting factor

Answer 8

sensitivity of each tissue type to damage

Question 9

Weighting factor

Answer 9

combines WR with WT

Question 10

Two types of effects of radiation on biological tissue

Answer 10

1) Deterministic effects 2) stochastic effects

Question 11

Define deterministic effects

Answer 11

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

Question 12

Threshold effective dose for various organs and damages

Answer 12

TABLE 24.2

Question 13

Acute whole body exposure and consequences of radiation

Answer 13

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

Question 14

Define stochastic effects

Answer 14

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

Question 15

Probability of fatal cancer as result of radiation exposure

Answer 15

4% per 1Sv of lifetime dose 0.004%/mSv < 100 mSv does not cause cancer

Question 16

Hereditary effect of radiation exposure

Answer 16

0.1% per sievert

Question 17

Annual average natural background radiation in US

Answer 17

3 mSv/yr

Question 18

Greatest source of domestic radiation

Answer 18

radon gas 2 mSv/yr

Question 19

Typical effective dose in common diagnostic procedures

Answer 19

TABLE 24.4

Question 20

Recommended dose limit to general public

Answer 20

1 mSv/yr

Question 21

Recommended dose limit to radiation workers

Answer 21

20 mSv/yr average over 5 years < 50 mSv in any year

Question 22

International commission on radiological protection safety limits for lens, skin, extremity and for fetus

Answer 22

TABLE 24.5

Question 23

Effective dose of spiral CT and MDCT compared to older scanners

Answer 23

10-30% higher

Question 24

Effective dose of DynaCT (3 dimentional rotational) compared to SDCT

Answer 24

7-8x less

Question 25

Voltage and current of the fluoroscopic tube

Answer 25

Voltage = controls penetration and contrast Current = number of photos produced by tube

Question 26

Ways to limit radiation emission

Answer 26

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)

Question 27

What oblique view gives higher exposure

Answer 27

LAO gives 3-5x more radiation than RAO

Question 28

Patient follow up when

Answer 28

exposed to > 3-5 Gy in 1-2 weeks

Question 29

With average use and equipment, the average dose exposed to surgeon for body eye and hand are

Answer 29

0.2 0.2 1 below limit

Question 30

Fetal risk and radiation dose

Answer 30

TABLE 24.6 0.04% mental retardation with IQ loss 2-3 points/mSv