Week 1: Radiation

sources of radiation exposure (3)

-anthropogenic sources (man-made): medical devices, electricity produced by nuclear reactors, used to kill/extend the shelf-life of foods, radioluminescence (glow-in-the-dark), heat generation in deep space missions

-primordial (largest source of radiation exposure): from when Earth was formed, radiation is in layers of ground (Radon gas is biggest contributor)

-cosmogenic: from space/atmosphere (increased risk of radiation if living at a higher altitude)

what is fluoroscopy + examples (4)

-continuous or pulsing x-ray beam that creates a live image on a monitor to guide a surgical procedure

-EX: C-arm in cath lab, ERCP, IR, pain management

atomic value/symbol meanings

-main, large number is the symbol of element

-small, top number to the left is mass # (protons + neutrons)

-small, bottom number to the left is atomic # (# of protons)

radiation definition

when the nucleus of a radioactive atom (radionuclides) decay, they emit energy waves (EMR)/subatomic particles that crash into other molecules and knock out an electron (can then continue on into more molecules)

why does radiation occur when nuclides split apart d/t instability?

protons repel each other with such force that is creates an unstable nucleus and radioactive decay

particle size relationship to speed and energy

-smaller particles = increased speed = increased energy/potential for damage

-larger particles = decreased speed = decreased energy/potential for damage

two main forms of radiation

ionizing and non-ionizing

non-ionizing radiation (definition + examples)

-waves/particles do not have enough energy to remove tightly bound electrons

-EX: visible light, microwaves

ionizing radiation (definition + examples)

-waves/particles DO have enough energy to remove tightly bound electrons (called “ionizing”)

-EX: medical radiation (gamma, x-rays for EMR; alpha/beta decay for non-EMR sources of radiation)

**more dangerous than non-ionizing radiation

ionizing forms of medical radiation from least to most damage (4)

-alpha particles (stopped by skin/paper but dangerous if inhaled/digested)

-beta particles (go through paper but blocked by aluminum; can cause skin burns)

-x-rays, including fluoroscopy and CT (goes through paper/body/steel)

-gamma rays, including PET scan (goes through paper/body/steel/concrete)

**MRI does not emit radiation as it uses magnets to create cross-section images

examples of how ionizing radiation causes somatic (biological) damage (3)

-if it damages one strand of DNA, it might be able to repair itself; if it damage both strands of DNA then this is permanent damage that can lead to death and mutations

-RNA damage, disrupted lipid membrane, enzyme deactivation

-causes radiolysis of water which generates free radicals such as hydroxyl ions

2 classifications of biological (somatic) effects of radiation exposure

-deterministic effects (threshold): only occur above a specific threshold of radiation exposure; increased effect severity with higher doses of radiation

-stochastic effects (probability): no safe threshold; instead, effect happens with the radiation dose

examples of deterministic (threshold) effects (4)

-cataracts if >0.5 Gy

-radiation sickness if >1 Gy

-skin burns if >2 Gy

-fetal malformations, sterility, hair loss

examples of stochastic (probabilistic) effects

CA, DNA mutations (influenced by patient age, sex, and body part exposed)

regulatory implications for fluoroscopy

time >1 hr or 5,000 mGy require follow-up

max regulatory standards for radiation exposure to body parts (4)

-if pregnant: 5 mSv or 0.5 rem over course of pregnancy

-whole body: 50 mSv/yr or 5 rem

-lens of the eyes: 20 mSv/yr

-skin/extremities: 500 mSv/yr

what is latency?

CA caused by radiation that may not appear for years after initial exposure

alpha vs beta decay

-alpha: emission of alpha particles (helium nucleus) and kinetic energy

-beta: atomic number changes but mass number stays the same which causes nucleus to emit a beta particle (electron)

why is it important to understand half-life of radioactive material/medicine?

tells you the duration of exposure for the radioactive substance to decay

how does radioactive decay work?

parent nucleus with high energy changes into a daughter nucleus with less energy

what is radiation exposure defined as + unit of measurement

-radiation in the air

-Roentgen (R); 1 R = equals 2.58 x 10^-4 C/kg

what is radioactivity defined as + unit of measurement

-rate of radioactive decay

-Becquerel (Bq) in SI units and Curie (Ci) in Imperial units (1 Bq = 2.703 × 10^-11 Ci)

what is radiation absorbed dose defined as + unit of measurement

-energy deposited per mass, tells us the dose within a material

-Gray (gy) in SI units or rad in Imperial units (1 Gy = 100 rad = 1 J/kg)

what is radiation dose equivalent defined as + unit of measurement

-biological effect of dose based on dose of radiation and absorption by human tissue

-Sievert (Sv) in SI units or rem in Imperial units (1 Sv = 100 rem)

**this is what is used to set regulatory limits for radiation safety

linear energy transfer (LET)

-amount of energy lost by the ionizing radiation and transferred to the matter it affected

-radionuclides can deposit a large amount of energy into a very small volume, which causes a large energy density

steps to convert Gy to Sv (absorbed dose to equivalent dose)

-1st step) multiply the absorbed dose in Gy by the radiation weighting (Wr) factor (equals to the dose that each organ receives)

-2nd step) multiply the absorbed dose in Gy by the tissue weighting (Wt) factor (equals to the dose the whole body receives)

-3rd step) add the answers from Steps 1 and 2 together in order to get the effective dose in Sv

**need to know that gamma and beta particles have a Wr of 1, while alpha particles have a Wr of 20

what factors affect tissue sensitivity to radiation? (5 R’s)

-repair (can be more at risk depending on how well cells are able to repair DNA)

-repopulation (regeneration)

-redistribution (can be more at risk depending on cell cycle phase at time of radiation exposure)

-reoxygenation (highly oxygenated cells are more at risk)

-radiosensitivity (rapidly dividing cells AND very slow dividing cells are more at risk)

During fluoroscopy, patient receives 40 mR of radiation at a distance of 1 foot. How much radiation does the anesthesia provider receive at a distance of 5 ft?

what organs are the most sensitive to radiation? (4)

bones, thyroid, lens of eyes, gonads (breasts, testes/ovaries)

what organs are moderately sensitive to radiation?

skin, GI

what organs are most resistant to radiation?

muscles, nerves

what are special populations that are at risk for serious effects of radioactivity? (5)

pregnant, fetuses in the womb, pediatric, geriatric, immunocompromised

why are children more sensitive to radioactivity?

their tissues are still growing/rapidly changing and they have a longer lifespan ahead of them which gives CA more time to mature

why do electromagnetic waves (EMR) exist?

electricity and magnetism always go together (direct proportional relationship), and can actually travel as particles AND waves (part of Quantum theory) at the speed of light (3.00 × 10^8 m/s)

**no mass, pure energy

examples of EMR (7)

radio waves, microwaves, infrared radiation, visible light, UV radiation, x-rays, gamma rays

EMR vs sound waves

-EMR has velocity that can exist in a vacuum; transverse waves that are perpendicular to propagation

-sound waves cannot exist in a vacuum and must pass through a medium; longitudinal waves that are parallel to propagation (e.g., why US needs gel to create a medium, or why you can’t hear someone scream in space)

trough

lowest point

peak

highest point

what is the most dangerous MRI zone?

Zone 4, as this is the area with highest magnetic force that can cause ferrous objects to have large amount of kinetic energy

where is most of the mass in an atom?

nucleus, which contains protons and neutrons

what determines the element of an atom?

number of protons

nuclide

general term for any atom type

isotope

atoms which have the same number of protons but different amount of neutrons; chemical behavior is similar

isotone

atoms that have the same number of neutrons, but different number of protons; chemical behavior is NOT similar

isobar

atoms that have the same mass number but different atomic numbers

what happens if O2 is ionized?

free radicals are created

parts of a C-arm (3)

-the bottom part of the C is the X-ray tube, which shoots radiation up

-the top part of the C is the image intensifier, which converts the waves into images

-collimator: focuses the beam, which then creates less exposure to radiation and a crisper image (e.g., think of a cone narrowing)

determinants of radiation exposure (2)

-time is directly proportional to radioactive exposure

-distance is inversely proportional to radioactive exposure (based on inverse square law, which states if you are at least 6 feet (2 m) away from the source of radiation, you are given ¼ exposure to the radiation)

**6 feet/2 m reduces radiation exposure 75-90%

what is the most effective way to protect yourself against radiation in the OR?

shielding (e.g., lead aprons, thyroid shields, leaded glasses, table skirt)

**lead better than concrete

why does shielding work?

attenuation

dosimeter use

wear a dosimeter to measure radiation exposure on a clip that is placed at the level of the collarbone, facing the radiation source, and outside a lead apron

rules for wearing a dosimeter if pregnant

-in addition to the dosimeter at level of neck, also need to wear a fetal dosimeter at level of waist and under the lead apron

-also do double shielding and ask for reassignment if possible

how often are dosimeters read?

monthly or quarterly

ALARA Principle (as low as reasonably possible)

-staff strategies (4): limiting time near radiation sources, standing as far away as practical from radiation source, using long extension tubing for IVs, stand on the image intensifier side of the C-arm and do not place body parts in the primary beam

-patient strategies (6): only perform if medically necessary, use pulse instead of continuous fluoroscopy, use last-image hold, limit the number of images taken, shield sensitive organs as able, dose adjustments if pediatric/underweight

what are common errors that increase radiation exposure in the OR? (4)

-failing to properly wear shields/dosimeters

-standing too close to radiation source/beam side

-unclear communication with radiation staff

-underestimating cumulative low-dose exposure