4.1 - Radiation Biology Flashcards by Marian Pacho

biologic effects of radiation

radiographs made with ionizing radiation
interaction with xrays with biologic macromolecules

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risk for cell damage is ___ but never ___

SMALL but never ZERO

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what does ALARA stand for

as low as reasonably achievable

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[low OR high] energy xrays are completely absorbed by the body (photoelectric absorption)

LOW

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when do low energy xrays interact with biologic macromolecules? what does it look like on xray?

completely absorbed by body (photoelectric absorption) and appears radio-opaque

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what is the release of fast-moving secondary electrons that can cause further biologic interaction when interacting with biologic macromolecules

compton scattering

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[low or high] energy xrays are a major interaction

HIGH

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high energy xrays are a major site of biologic damage to what

DNA

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___: the photon directly interacts with and ionizes a biologic macromolecule,
the free electrons produced by the ionization interaction (secondary electrons) may also
interact DIRECTLY with biologic macromolecules

Direct Action

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1/3 [direct/indirect]
2/3 [direct/indirect]

direct = 1/3
indirect = 2/3

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what do direct actions produce

unstable free radicals

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what do indirect actions produce

unstable free radicals

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___: the secondary electron interacts with, for example, a water molecule to
produce a hydroxyl RADICAL (OH-) which in turn produces the damage to the DNA

Indirect Action

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indirect actions mostly involve what

electrons interacting with water

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what refers to how water dissociates into H and OH when irradiated

radiolysis of water (type of indirect action)

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what is the time between when energy is absorbed and the damage is done to when signs and symptoms are visible

latent period

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what does latent period depend on

amount of radiation and the particular type of damage

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cancer from radiation has a long or short latent period

long

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cells are MOST sensitive to radiation during what phase

G2 and M

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cells are LESS sensitive to radiation in what phase

G1 phase

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cells are least sensitive to radiation in what phase

S phase

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what happens if DNA strand break occurs before chromosomal duplication (late G1, early S) the break is replicated and both sister chromatids will carry the damage

chromosome abberations

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what happens if DNA strand break occurs AFTER chromosomal duplication (late S, G2) only one of the sister chromatids will carry the break)

chromatid aberrations

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what is damage to DNA in reproductive cells (sperm or ova) and damage can be passed onto future offspring

genetic mutation

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what is damage to body cell (somatic cell, non-sperm/ova) and damage passed onto other cells of same time in that person, not to future offspring

somatic mutation

what is the most likely effect of stochastic effects

carcinogenesis

what is radiation that modifies DNA

gene mutation

what can be an initiator, promotor, or may convert premalignant cells into malignant ones

gene mutation (radiation modified DNA)

do radiation effects increase with dose

yes

is there a safe level of exposure?

no! dental doses are low but not zero

what are deterministic effects of cells

1. nucleus more sensitive than cytoplasm 2. causes of cell death from radiation

what is the most sensitive site of cell

DNA in chromosomes (nucleus is more sensitive than cytoplasm)

what happens when damaged cells released molecules that kill adjacent cells

bystander effect

what can induce programmed cell death

apoptosis

most sensitive cells are cells that:

1. divide rapidly over many generations 2. primitive or immature 3. undifferentiated

what are the most sensitive cells (ranked)

1 . Small lymphocytes 2. Bone marrow 3. Reproductive cells 4. Intestine 5. Mucous membranes

least sensitive cells are those that

1. divide rarely 2. are mature 3. are specialized

least sensitive cells ranked

1. muscle and nerve cells 2. lungs 3. kidneys 4. liver 5. salivary glands MartiN LUthe KIng LIkes Salivary glands

what are the types of acute radiation syndrome with Gy level

prodromal (1-2 Gy) hematopoietic (2-7 Gy) GI (7-15 Gy) Cardiovascular and CNS (>50 Gy)

can you cause acute radiation syndrome with dental diseae

symptom and Gy of: prodromal

1-2 Gy nausea, vomiting, diarrhea

symptom and Gy of: hematopoietic

2-7 Gy damage to bone marrow, infection, bleeding, anemia

symptom and Gy of: GI

7-15 Gy damage to lining of GI tract, ulceration, septicemia, death

symptom and Gy of: cardiovascular and CNS

>50 Gy die

what are late effects of low dose

cataract formation

dental dose is ___ lower than threshold

1250 times

effects of low doses on fetal w/ day

1. preimplantation (0-9 days) 2. organogenesis (10 days to 8 weeks) 3. early fetal period or later organogenesis (8-25 weeks) 4. late fetal period

describe stage and days: preimplantation

1. Preimplantation (0-9 days): most sensitive stage for lethal effect; threshold for effect is 100 mGy

describe day and stage: organogenesis

2. Organogenesis (10 days to 8 weeks): mental retardation, microcephaly, growth retardation

describe day and stage: early fetal period or late organogenesis

3. Early fetal period or late organogenesis (8-25 weeks): mental retardation

describe stage: late fetal period

4. Late fetal period: excess absolute risk is about 6%/Gy for early child cancer

what does it mean if small volume of tissue exposed

fewer cells damaged

how does oxygen affect radiation

hypoxia decreases the effect

how does LET affect radiation

higher LET causes more double-strand breaks

what radiation treatment is administered as many daily small doses

fractionation

benefits of fractionation

- Increased cellular repair of surrounding normal tissues that are unavoidably exposed - Repopulation of surrounding normal cells - Increases the mean oxygen tension (reoxygenation) in an irradiated tumor, rendering the tumor radiosensitive - Reassortment of the tumor cells to be in the most sensitive part of the cell cycle

process of radiotherapy involving the oral cavity

- 2 Gy is delivered daily for a weekly exposure of 10 Gy - Radiotherapy course continues for 6-7 weeks until a total of 60 to 70 Gy is delivered

what is the golden window

lowest risk of ORN (4 months after radiotherapy) highest risk (4-12 months post therapy)

xerostomia can be radiation induced by what

apoptosis of salivary acinar cells

what can cause rampant cares from radiotherapy

decreased salivary flow

3 types of radiation caries

1) Lesions that affect the cervical aspect of the teeth extending along the CEJ 2) Demineralized and worn occlusal surfaces 3) Color changes in the dentin along with occlusal wear patients may present with any combination of the above lesions

does radiotherapy affect mature and developed teeth

how can radiotherapy affect developing teeth

- May completely destroy tooth bud - Arrest the growth potential that a bud may have - Result in malformations of the tooth - Eruptive mechanisms of the teeth ARE NOT affected

ORN Gy levels

- 1-4 Gy - 10 Gy - 20 Gy - 60-70 Gy

what happens at 1-4 Gy

sitmulatory effects on osteoblasts - new bone formation

what happens at 10 Gy

death of chondroblasts and osteoblasts

what happens at 20 Gy

single dose in a young child = irreversible growth retardation and short stature

what happens at 60-70 Gy

radiation damage to mature, intact bone (a more radioresistant tissue)

what happens to musculature from radiotherapy

- Fibrosis and scarring (limiting function) - If muscles of mastication (usually masseter and temporalis) are affected it may result in TRISMUS (reduced opening of the jaw)