radio bio 3

66% of radiation-induced damage is due to _____________________ the high water content in the body allows free radicals to travel freely to other sites to damage tissue remote from original radiation site

hydroxyl free radicals OH*

a. LINEAR ENERGY TRANSFER (LET) refers to _________________ The amount of permanent biological damage that occurs directly corresponds to _____________________________

the average amount of energy deposited per unit path length (keV/micron) the number of ionizations produced in tissue & the amount of energy absorbed per each micron of tissue

b. RELATIVE BIOLOGICAL EFFECTIVENESS (RBE) relative biological effectiveness describes____________________ Low LET radiation and high LET radiation with the same energy level produce a different amount of biological effect RBE is tied to the QF (quality factor or weighing factor), which is used to determine _____________________ 1. QF for x‑rays & gamma rays = _______ QF for beta particles and free electrons =____ QF for alpha particles = _____ NOTE: as LET increases = RBE increases

the capability of different types of radiation to produce a particular biological effect the ability of a dose of different types of radiation to cause biological damage (QF = damage factor) 1 1 20 (20 times more biological damage will occur as compared to equal dose of x‑rays)

c. OXYGEN ENHANCEMENT RATIO (OER) OER helps explain the radio-sensitivity of cells that contain large amounts of oxygen as compared to the relative radio-insensitivity of cells with low amounts of oxygen OER compares _______________________________ Very high energy x-rays & gamma rays (above the diagnostic range) produce damage in cells with high oxygen content; OER of high energy x-rays or gamma rays (low-LET) is_________ When very high energy x-rays (such as those used in radiation therapy) interact with high O2 content cells, the result is ____________________________ High energy alpha particles produce the same amount of damage regardless of the amount of oxygen; OER of alpha particles (high-LET) is __________________ Note: the OER helps explain why some types of cancer cells (example: renal cell carcinoma) are untreatable by way of radiation therapy

the dose required to produce a specific biological response in an oxygen deprived environment vs a normal oxygen environment 2-3 permanent cellular damage 1 (in other words, the presence of oxygen does not enhance or reduce the radiation damage from alpha particles)

Radiolysis of water VERY IMPORTANT CHAD HELP JILL LEARN

x-ray photon strikes H2O = positive water molecule and free electron HOH+ and a free electron can recombine into H2O or HOH+ can split into an H+ Hydrogen ion and an OH* radical The free electron combines with H2O, creating HOH- HOH- splits into OH- (hydroxyl ion) and H* (hydrogen radical) H* and OH- recombine into H20 (2 hydroxyl radicals = hydrogen peroxide ((toxic xxx) hydrogen radical combines with oxygen - hydroperoxyl radical)

immature sperm and ova germ cells (rapidly dividing/unspecialized)

‑‑highly radiosensitive

Cell Radiosensitivity Law of Bergonie' & Tribondeau (developed in 1906) ________________________________ The following increases cell radiosensitivity: unspecialized (undifferentiated) cells _______________ 6 answers Note: undifferentiated cells refers to immature cells haven't taken on the characteristics of the mature cell (stem cells or precursor cells)

"The radiosensitivity of cells is directly proportional to their reproductive activity and inversely proportional to their degree of differentiation (specialization)". (pp 102) increased reproductive activity (rapidly dividing) immature cells increased oxygen content (oxygen enhancement effects) type of cell (see #IV) shorter life span = increased radiosensitivity high LET radiation

3. alpha particles have substantial mass and charge, how many protons and neutrons _____________________ alpha particles pass through tissue ____________ & travel a _______ distance before giving up all energy = more ionizations per micron of tissue increased tissue damage in a localized area (high keV/micron) high or low LET? ___________ NOTE: alpha particles cause tissue damage primarily through direct action; more likely to permanently damage the cell's DNA = Direct Action LET is important in assessing the potential tissue or organ damage

(2 protons and 2 neutrons) slowly short high‑LET radiation

Effects of radiation on different types of Cells 1. Blood Cells a. Types of immature blood cells (stem cells): _________________: most radiosensitive of all blood stem cells ______________; slightly less radiosensitive as compared to erythroblasts ______________________: the most radio-insensitive of the blood stem cells

= overall very radiosensitive erythroblasts: myeloblasts white blood stem cells: megakaryoblasts: platlet stem cells;

3. Results of Indirect & Direct Action in somatic cells ____________ 4 answers 4. Results of Indirect & Direct Action in germ/genetic cells _________________ 1 answers Because ______ of the human body is water, most radiation damage occurs ___________ via free radicals & exposure to toxic substances I

Cancer, impaired function of organs, impaired function of cells (RBC, WBC, etc), organ failure Inaccurate genetic information passed on to future generations = mutations 80-85% indirectly

I. Target Theory ______________

Explains that each cell is controlled by a key molecule (DNA) & damage to that key molecule affects the entire cell If the DNA is destroyed by radiation exposure (either direct or indirectly), the cell will die; no other molecules within that cell can take over the function of the DNA

Reproductive Cells (chad skip)

a. mature sperm and ova (germ) cells are highly specialized & do not reproduce, therefore they are somewhat radio-insensitive b. but in comparison to other mature cells, reproductive cells are relatively radiosensitive, because: even fairly low doses in diagnostic radiology may cause a depressed sperm or ova number OR chromosomal damage and mutations to be passed onto future generations there is a limited number; so if a large number of sperm or ova cells are destroyed, there are fewer remaining to take over function Note: an average female only produces 400-500 ova in her lifetime

Damage is done when _________________________________ the result: ______________________________ the radiographer should have a solid understanding of these effects so that when exposing patients to radiation, he/she can balance the risk vs benefits.

any energy is transferred to atoms within the cells & the atom in disrupted - either partial energy transfer through compton effect or complete energy transfer through photoelectric effect the cell may repair itself or may display harmful/adverse effects

2. Direct Action Involves radiation exposure to vital macromolecules (DNA, RNA, protein or enzymes within cell) Results of Direct Action No permanent damage __________________________________ Cell disruption & repair _________________________________________ Cell disruption & alteration __________________________ Cell death ____________________________________

atom re-stabilizes after ionization most common with low-LET radiation cell's protein repairs cell most common with low-LET radiation cell continues to function but does not carry out function correctly common with high LET radiation OR repeated exposure to low LET radiation

2. Epithelial Cells _________________________________ 3. Muscle Cells _________________________________ 4. Brain Cells ______________________

cells found in the lining of intestines, lining of respiratory tract, lining of blood & lymphatic vessels constantly being regenerated/rapidly dividing highly radiosensitive highly specialized cells; do not divide; numerous muscle cells within body radio‑insensitive highly specialized; do not divide radio‑insensitive

1. Indirect Action _______________________

destructive cell damage in which the DNA, RNA, proteins or enzymes are not initially affected by the radiation Involves Radiolysis of Water (radiation exposure to water) "free radicals" are the immediate result of x-ray exposure to water (H2O) which then could in turn damage the DNA, RNA, proteins & enzymes "indirectly"

Types of mature blood cells: (mature cells are specialized; therefore, radiosensitivity depends primarily on length of life span) leukocytes: mature white blood cells; fights off infection & bacteria (foreign bodies) and assists with tissue repair; there are 3 major subgroups of leukocytes: 1) lymphocytes: _____________________ 2) neutrophils: ____________________________ 3) granulocytes: ____________________ thrombocytes: ___________________________ Note: blood counts are not depressed during routine diagnostic procedures; Exception: lengthy interventional fluoro studies (cardiac cath, etc); affects the # of lymphocytes & may result in chromosomal alteration

fights infection; produces antibodies; 24-hour life span = most radiosensitive of all mature blood cells fights infection; moderately radiosensitive fights bacteria; moderately radiosensitive mature platelet cells; assists with blood clotting; moderately sensitive to radiation; 30-day life span

Ionizing Radiation _______________________________

ionizing radiation can damage cells by removing electrons from the atoms that join together to form cellular molecules

To understand the extent of the energy transferred & the biological damage that may occur in tissue exposed to radiation, 3 concepts should be studied:

linear energy transfer (LET) relative biologic effectiveness (RBE) oxygen enhancement ratio (OER)

5. Nervous Tissue Cells _________________________ Fetal nervous tissue __________________

nerve cells relay messages to and from the brain; found in brain & spinal cord. highly specialized; do not divide radio‑insensitive extremely radiosensitive "window of maximum sensitivity" (most critical time of radiation damage to nerve cells) = 8 weeks (end of neuron organogenesis when neurons are formed from embryonic tissue) to 15 weeks (the fetal period) exposure to nervous tissue during this window could lead to nervous system abnormalities, mental retardation and/or microcephaly

Results of Radiolysis (Radiation Exposure to Water) INDIRECT No permanent damage ______________________ Formation of free radicals _____________________________ Formation of hydrogen peroxide & hydroperoxyl radicals* - toxic substances ____________________________________________ Cell death _____________________________

occurs after an electron is ejected but the water molecule re-stabilizes most common with low-LET radiation common with high LET radiation OR repeated exposure to low LET radiation common with high LET radiation OR repeated exposure to low LET radiation common with high LET radiation OR repeated exposure to low LET radiation

2. beta particles & free electrons (negative charge & small mass) pass through tissue fairly _________________ (due to small size) sparsely ionizing high or low LET?_____________ less likely to __________________________ NOTE: x-rays, gamma rays, beta particles & free electrons causes tissue damage primarily through indirect action (production of free radicals); these types of energy and particles are less likely to interact with the cell's DNA non-interaction with cell's DNA = sub-lethal damage which can be repaired by the cell's protein

rapidly low‑LET radiation interact with the cell's DNA

LET stuff 1. x‑rays & gamma rays (no charge or mass) pass through tissue ____________________ x-rays & gamma rays travel further or shallower? ______________ through tissue so the amount of energy deposited per micron of tissue is small or big? ______________ = high or low LET?_________________

rapidly further small low‑LET radiation

I. Radiation Biology:

refers to the biological sequence of events that occurs after living tissue absorbs radiation energy, the disruption that occurs, and either recovery or adverse effects