ORad Radiation Bio

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Diagnostic Radiography: Radiation doses in diagnostic procedures (FMX of 2 rads or less)
Radiation bio: study of effects of ionizing radiation on living organisms

energy of ionizing radiation is deposited within living tissues
3 effects that may occur when energy is deposited within an atom or molecule: 1. excitation
-temp vibration
-enery is released by
emission of light/heat

2. Ionization
-ionized atom is no
longer electrically
neutral
-becomes chem. reactive

3. breaking of molecular bond
-disrupt and loss of
function
Smallest unit in which chem. rxns occur in life: cell
cell composition: 80% water and 20% various chem

nucleus and cytoplasm
part of the cell that is radiosensitive: nucleus
2 divisions of bio effects of ionizing radiation: deterministic effects

stochastic effects
deterministic effects: severity of response is proportional to dose

threshold level below response is not observed

requires larger dose of radiation
what requires larger dose of radiationi determinist or stochastic effects?: deterministic
examples of deterministic effect of radiation: oral changes after radiation therapy and radiation sickness after whole body irridation, and cataracts
what is threshold dose?: minimum exposure that will produce a detectable degree of a given effect
Stochastic effects: probability of occurrence of the change, rather than its severity is dose dependent

its a all or none response
examples of stochastic effects: spontaneous genetic mutations
or radiation induced cancer
threshold for stochastic effects: none
2 theories of the rxn of ionizing radiation wi living tissue: direct and indirect effect
direct effect: ionizing radiation transfers energy to biologically active molecules (DNA/RNA)

Breakage of molecules occur w/formation of inapprorpiate chem bonds

nonDNA cells regenerate and survive

Direct effect accounts for 1/3 biologic effects of radiation
indirect effect theory: radiolysis of water bc water is 70% of body

interaction of xrays with water leads to ionization
with radiolysis of water, what are some destructive elements produced?: hydrogen
hydroxyl
hydrogen per oxide
hydroperoxyl

free radical produced by radiolysis of water act on organic mol. causing damage

indirct damage occurs with greater frequency
what carries genetic info essential for cell replication and regulation of cell activity?: DNA

DNA is key and it is irreplacable
what is primary mechanism for radiation induced cell death,mutation,and carcinogenisis?: damage to DNA
when is cell most radiosensitive?: during mitosis or just before mitosis
what can occur to chromosome as a result of radiation damge?: breaks or abberations in chrosomes the frequency is proportional to the radiation dose
chromatid abberation: only one arm is broken (this occurs in G2 or late S stage)
Chromosoem abberation: both arms are broken (this occurs in G1 or early S)
somatic cell: not inherited from parent. radiation damage only influences the individual whao has been exposed(muslce, skin, bone, blood)
genetic cell: reproduction cell
radiation damge is passed on to generations (oocyte/sperm)
Radiosensitive cells: cells that are sensitvie to ionizing radiation

developing/immature cells

reproducible cell, fetal cell, blood forming cells, mucus membranes
Radioresistant cells: cells that appear to be less harmed by radiation

fully developed/mature cells

muscle/nerve tissue
optic lens
law of bergonie and tribondeau in 1906: radiosensitive cells are those that
1.have hi mitotic rate
2.undrgo future mitosis
3.primitive in differentiation

although lymphocytes and oocytes are highly differentiated and non dividing they too are radiosensitive
examples of organs that are low radiosensitivity: optic lens
mature erythrocytes
muscle cell
nerves
examples of organs that have hi radiosensity: lymph organs
bone marrow
testes
intestines
mucous membranes
what are host factors that determine damage done by radiation?: species of animal

individual variablity

age

latenet period

type/sensitivty of tissue

rate of cell division
how does species of animal determine damage done by radiation?: diff species have diff sensitivities to lethal radiation effects

most mammels have same radiosensitivity and are sensative to radiation compared to reptiles, insects, bacteria which are all more resistant
how does age determine damage done by radiaon?: children are more susceptible than adults with equal dose bc kids have rapidly dividing cells

elderly are more susceptible than younger adults bc they have less healing ability
How does rate of cell division determine damage done by radiaion?: rapidly dividing cells are more sensitive to radiations

malignant tumors divide more rapidly than normal cell so they are easier to destroy by radiation

nerve cells that dont divide on a regular basis are pretty insensitve to radiation
What are radiation factors?: Total dose and dose rate

type of radiation

oxygen

penetrating ability

acute vs chronic exposure

local area vs whole body
how does dose effect radiation damge: all individuals receiving doses above threshold show damage in proportion to the dose
how does type of radiation effect radiation damage?: xrays and gamma rays are sparsely ionizing radiations that deposit energy in v. seperated energy deposit events

alpha particles are densley ionizing radiations that deposit energy in a short diestance so more radiobiologic effects are produced
Linear energy transfer (LET): amt of energy transferred to tissues per unit distance traveled in the tissue

lo LET are xrays

hi LET are alpha particles

the higher the LET, the more radiation damage can occur
Hoe does oxygen effect radiation damge?: greater cell damage is sustained in the prescence of oxygen due to formation of free radicals like hydrogen peroxide and hydoper oxyl
how does penetrating ability of radiation determine the radiation damage?: the higher the energy, the greater the effects in deeper tissue, the lower the energy, the more radiation is absorbed by superfical layers

dental xrays remove long wavelenght xrays to reduce skin dose
acute exposure vs. chronic exposure: with acute exposure all energy is given off in a v. short period so there are more radiobiological effects

with chronic exposure there is a small amt of radiation given off over a prolonged period so there is less radiobiological effects
what has worse radiobiological effects xrays of local area or the whole body?: exposure of the whole body has worse effects than a small area

dental xrays are local and do not have significant exposure
descibe the accumlative effects of radiation: radiation injury to tissue is followed by repair

many radiation injuries adds to residual damage and is known as accumulative effect of radiation

this is why aging occurs
why is residual injury from diagnostic radiography impossibe to detect?: bc it is masked by aging
why are radiation effects cumulative?: bc cellular repair procedures never completely repair and damage can cause cataracts, cancer, birth defects, or premature aging
what does long term effects of radiation depend on?: fine vasculature

fine vasculature has intermediate radiosensitivty
long term effects of radiation: cancer
leukemia
cataracts
life span shortening
genetic mutations
what does short term effects of radiatin depend on?: extent of cell loss depends on damage to stem cells and cell proliferation rate
wht does short term effects of radiation usualy result in?: mitosis linked cell death

ex: acute radiation syndrome
fractionation: breakin up of total larger dose into many small does to allow for better repair of healthy cells

this allows greater tumor destuction and increases the amt of oxygen in the tumor so the tumor cells get more radiosensitive
what affected by a hi dose of radiation to the head/neck?: oral mucous membranes
taste buds
salivary gland
teeth (caries, ostoradioncrosis)
how are oral mucous membranes affected by hi doses of radiation?: bc mucous membranes contain basal layer composed of radiosensitive vegative and differentiating mitotic cells and these structures are v. effected

get redness and inflam by 2nd week

mucositis by 2-3 wks but it recovers in 2 mos

difficulty eating of week 5

good OH decreases chance of infection
What happens to taste buds with 2 Gy daily dose delivered 5 days a week to head and neck for 5 weeks so all together 50 Gy: extensive degeneration to architecture

loss of taste acuity during 2-3 weeks (like 1000-10000 fold loss!)

type of taste loss depends on location of tongue radiation

recovers wi 60-120 after radiation TX
what salivary gland is most sensitive to radiation?: parotid

radiation decreases flow of salivary glands there is no flow when 60 Gy are reached
What happens if you lose salivary gland due to hi dose radiation?: pH of salive drops to 5.5

changes is saliva flow,pH, and buffering alters micro flora so they are more acidic and cause caries

if some major salivary glands are spared dryness subsides in 6-12 mos by hypertrophy
when are teeth most severetly affected by radiation/: during growth of tooth

if radiation occurs before calcificaiton of tooth, tooth bud can be destroyed

can get shortened roots, eneamel effects, or delayed erruption

Adult teeth are radioresistant but may see fibroatrophy of pulp
radiation caries: rampant caries which occurs following therapy which causes salivary glands to be exposed to radiation

caused by decreased pH of saliva and decreased salivary flow and increased viscosity

decreased flow caused plaque to build up
3 types of radiaton caries: superficail lesion

root caries

darkening and wear of crown
treatment for radiation caries: daily fluride rinses w/5min application of 1% NaF gel

avoid dietary sucrose
pre radiation dental care: extract periodontally or gross carioulsy involved teeth

restoration and dental hygeine insturction
osteoradionecrosis: most serious clinclal impliation

radiation damages vasculature of the periosteum and cortical bone

vasculature is replace with fatty dposits and fibrous tissue
where does osteoradionecrosis most commonly occur?: in the mandible
pretreatment eval of bone: best treatment is to remove all sources of possible infection prior to radiation TX so areas can heal before radiaton
post treatment removal of vasculature invaded by MO in bone: use atraumatic tecniques and provide anibiotic coverage and refer to oral surgeon
Pre radiation dental eval: complete FMX of good quality must diagnose accurately as untreated caries lead to periaplical infection can be v. severe
how long should xrays be delayed after radiation treatmetn?: 6 mos although the radiation in dental offices is negliable compared to radiation TX
acute radiation syndrome: sequence of events following hi level whole body radiation
with acute radiation syndrome, what is manifestation of 1-2 Gy: prodromal period
whith acute radiation syndrome, what is manifestation with 2-4 Gy: mild hematopoieetic symptoms
with acute radiation syndrome, what is manifestation with 4-7 Gy: severe hematopoietic sympotoms
With acute radiation syndromw, what is manifestation with 7-15 Gy?: GI symptoms
With acute radiation syndrome what is manifestations with over 50 Gy?: CV and CNS symptoms
what is prodromel period?: seen w/acute radiation syndrome with 1-2Gy

occurs wi min-hrs

GI disturbance
-anorexia
-nausea
-diarrhea

weakness
the higher the dose, the faster the onset
What is latent perio: time span between exposure to x radiation and obsrevable sign

follows prodromal period and there may be no sign or symptoms

extent is dose related

higher the dose, the shorter the latent period
ARS effects of hematopoietic systems: get hematopoietic syndrome (bone marrow syndrome)

damage occurs at 2-7 Gy

stem cells damaged as they are v. radiosensitive

rapid fall in blood cnt but at varying rates bc mature cells die and are not replaced
stages of hematopoeitic syndrome with ARS: infection
-leukopenia
-granulocytopenia
Hemorrhage
-thrombocytopenia
Anemia
-Erythrocyte depletion

death occurs in 10-30 days
ARS effect on GI: GI syndrome

w/whole body exposure in 7-15 Gy range cause GI destruction

can cause immediate problems but usually not seen in days (latent period)

During latent period basal cells are destroyed from intestinal layer and mucosa is lost and it cant replace itself so absorbtion does not occur
With GI syndrome, what does denuded mucosa cause?: loss of plasma

inability to absorb nutrients

infection from gut microflora

get diarrhea,anorexia,dehydration

death occurs in 9 days

overall effect is immunocomporixed individual with fluid/electrolyte imbalance
CV and CNS syndrome: not surviable

seen with over 50 Gy
death wi 1-2 days

increased intracranial press.

collapse of circulatory sys.

disoreitation, convulsions
What is seen at autopsy with CV and CNS syndrome?: myocardial necrosis and neruon and microvascualr brain damge
2 sources of radiation exposure: 1. natural radiation
-external: cosmic or
terretrial radiation
-internal:radon and other

2. Artifical radiation
-mdical diagnosis
-consumer products
risk assessment for pt: background radation

eye

repro organs

pregnancy

cancer
Risk of background radiation: larges contributor of exposure on daily basis

get 3000microseiverts/year
radiation with 1 FMX with E speed film: 33 uSV this is the same as four days of background exposure
radiation risks to the eye: cataract induction aprox 2 Gy with single dose and more than 5 Gy with multiple exposures
Radiation risks to repro organs: genetic dose for mutaion to occur is 2000mSv or 2 Sv
What gets more radiation male or female repro parts?: ovaries in femals get less radiation bc of attenuation of overlying tissues comppared to male repro organs
Gonadal dose from one FMX: male 1uSv
female .02uSv (50times less)
Radiation risks with pregnancy: embryo and fetus more sensitive to readiation

risk during pregnancy when using lead apron is 0
whn is fetus most sensitive to radiation?: in first three mos.

undectable death of fetus, microcephaly, mental retardation, birth defects, and child cancer can occur
How do gonadal tissues get irradiation from dental Xray?: do to scatter radiation
Risk of getting cancer from radiation: no threshold

radiation increases risk of cancer

could be due to additive effect

children are 2x more radiosensitive than adults
What cancer is at highest risk from radiation in kids?: leukemia and thyroid cancer more common in kids
amt of radiation dentists get per year: 2.3 mSv/year
estimated min does to get skin cancer: 25 simultaneous FMX or 50 simultaneous panos

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