Final Flashcards
Helps determine structure’s radiation tolerance
Alpha beta ratio (a/B)
Radiosensitivity of cells/nonrepairable
Alpha (a)
Repairable portion of radiation damage
Beta (B)
Larger B = _______ ratio = _______ repair and _______ shoulder
Small
Increase
Broad
Law stating that ionizing radiation is more effective against cells that are actively mitotic, undifferentiated, and have a long mitotic future
Law of Bergonie and Tribondeau (B&T)
Mature/well differentiated cells with less division/mitotic activity (A) = _______ radioresistant
More
Sensitivity of cells is ______ proportional to mitotic A and _______ proportional to differentiation
Directly, inversely
Environmental conditions can affect radiosensitivity, especially if stressed
Law of Ancel and Vitemberger
2 parts that affect the Law of Ancel and Vitemberger
Biological stressor on cells
Environment: in poor environment (less oxygen) cells have more time to repair because they’re less likely to move into mitosis (M)
What is the biologic stressor on cells?
Mitotic A/division
Cells that divide _______ damage earlier
Quickly
3 cell populations
Stem cell
Transit
Static cell
Cells that provide/divide for its and other populations, undifferentiated
Stem cell
2 examples of stem cells
Basal cells
Bone marrow
Cells that go from one place to another, may or may not divide; red blood cells (RBCs)
Transit cell
Fully differentiated and mature cells, no or limited mitotic A
Static cell
2 examples of mitotic cells
Adult nervous tissue
Muscle
5 cell population categories
Vegetative intermitotic cells (VIM) Differentiating intermitotic cells (DIM) Multipotential connective tissue cells Reverting postmitotic cells (RPM) Fixed postmitotic cells (FPM)
Most radiosensitive cell population, rapidly dividing undifferentiated with short life spans
Vegetative intermitotic cells (VIM)
___% of VIM undifferentiated, ___% mature leukocytes
95%, 5%
3 examples of VIM
Basal cells
Crypt cells of intestines
Erythroblasts
Immature RBCs
Erythroblasts
Second most radiosensitive cell population, actively mitotic but more differentiated; more specialized
Differentiating intermitotic cells (DIM)
4 examples of DIM
Type B spermatogonia
Urinary bladder
Lens of eye
Mucous membranes of of lung
Intermediate/moderate radiosensitivity cell population
Divide irregularly and are more differentiated than VIM and DIM cells
Multipotential connective tissue cells
2 examples of multipotential connective tissue cells
Endothelial cells
Fibroblasts
Cells of the cavity of the heart and vessels
Endothelial cells
Cell in connective tissue that produces collagen and other fiberes
Fibroblasts
Cell population doesn’t divide normally unless stimulated, live longer and are more differentiated than other groups
Radioresistant
Reverting postmitotic cells (RPM)
3 examples of RPM
Liver cells
Mononuclear cells in blood and lymph
Mature lymphocytes
Most radioresistant cell population, don’t divide and highly differentiated; may or may not be replaced when they die
Long living mature cells
Fixed postmitotic cells (FPM)
2 tissue organizations
Parenchyma
Stroma
Contains characteristics of cells of that organ, functional unit of cell; VIM, DIM, RPM, and FDM
Parenchyma
Connective tissue and vasculature intermediate radiosensitivity
Supporting structures; blood vessel, nerves, etc.
Stroma
Function of tissues’ most sensitive cell it contains
Radiosensitivity
Lethal dose that kills 50% of population in 60 days
LD50/60
3 modifying tissue responses
Physical factors
Chemical factors
Biological factors
High LET curves _______, no _______; cells show quick response, linear
Steeper, shoulder
HDR produce more damage, _______ shoulder on LDR graph
Broad
Rate at which radiation is delivered
Dose rate
_______ LET and LDR allow cells to repair
Low
2 chemical factors
Sensitizers
Protectors
Enhance killing effect of radiation, used to make tumor cells more sensitive
Best known ex: molecular oxygen
Must be in cell environment at time of exposure
Oxygen must be 0-20 mm of mercury, over 20 has no effect
Sensitizers
Decreases cellular response
Protectors
Dose _______ with oxygen
Decreases
Low LET oxygen = _______ radiosensitivity 2-3 times = shoulder gets _______/_____ broad = _______ Do
Increases
Smaller
Less
Decrease
Magnitude of oxygen effect, compares response with radiation without the presence of oxygen
More pronounced with low LET because whether or not oxygen is present with high LET (average = 1.2-1.7) there’s no healing
Oxygen enhancement ratio (OER)
OER for mammalian cells
2-3
OER formula
OER = dose without oxygen/dose with oxygen > 1 gives same biologic effect
Chemicals that protect normal cells from effects of radiation
Act as free radicals that compete with oxygen in body
Ex: sulfhydryls (1.5-2) contain free sulfur atom in their structure
Present during exposure
Used to protect esophagus, parotids and military; give 15-20 mL before radiation
Dose reduction factor (DRF) Protection factor (PF)
DRF/PF formula
DRF/PRF = dose with protector/dose without protector
2 problems with DRF/PFs
Amount needed to protect from whole body exposure usually lethal
Decreases blood pressure (BP)
4 biologic factors
Position in cell cycle to phase in cell cycle
Intracellular repair
Age: very young and old more sensitive
Sex
Synthesis (S) phase more _______, G2-M most _______, and G1 ______
Resistant
Sensitive
Moderate
Cells can repair _______ damage, _______ don’t repair as well
Sublethal
Hypoxic
2 factors intracellular repair takes in
LET
Extrapolation/n number
3 reasons females are 5-10% more resistant to radiation than males
Nutrition
Lipid/fat count greater
Work environment
Dose of permanent sterility
15-20 Gy
Most sensitive trimester
First, 1-3 months
Why are younger patients more sensitive to radiation?
Less differentiated cells
4 stages to radiation syndromes
Prodromal
Latent
Manifest
Recovery or death depending on dose and radiation type
Symptoms correlate to dose and can be gastrointestinal, neurologic, or both
Prodromal
Period in which victim appears to have no symptoms
Latent
Effects of exposure return typically worse than before correlated with dose
Manifest
3 radiation syndromes
Hematopoietic syndrome/bone marrow syndrome
GI
CNS
Syndrome at 1-10 Gy that affects blood, females more resistant
4-6 weeks 3-5 Gy = death
Hematopoietic syndrome/bone marrow syndrome
Survival and death dose for hematopoietic syndrome
Survival = under 2 Gy Death = over 10 Gy
At 100-1000 Gy; nausea and vomiting within hours lasts two days
Hematopoietic prodromal stage
Bone marrow and stem cells dying, blood counts decrease in a few days to 3 weeks
Hematopoietic latent stage
Anemia and serious infection 3-5 weeks after exposure
Hematopoietic manifest stage
2 causes of death from hematopoietic syndrome
Hemorrhage
Infection
Loss of crypt cells in small intestine at 1,000-10,000 cGy
Death by bone marrow loss leads to infection, dehydration, and electrolyte imbalance
100% mortality rate without medical support; average survival = 3-10 days, 2 weeks with medical support
Latent period 2-10 days after prodromal or absent
GI syndrome
GI syndrome threshold
10-50 Gy
Nausea, vomiting, cramps and diarrhea within hours
GI prodromal stage
Symptoms reappear after 5-10 days
Severe diarrhea by 6th day leads to dehydration; bacteria enters blood stream and leads to sepsis
Blood forming organs show severe radiation damage
GI manifest stage
Caused by gamma or neutrons, external whole body exposure at 20-50 Gy
Death in several days
Final stage
Latent period several hours long
Cause of death: intracranial pressure before other two syndromes
Over 10,000 cGy
CNS syndrome
Rapid dehydration, lethargy, nervousness, confusion, severe nausea, vomiting, and burning sensation within minutes to hours
CNS prodromal stage
Coma and death in 5-6 hours, death 2-3 days past 50 Gy
CNS manifest stage
3 criteria for occurrence of total body radiation syndromes
Whole body exposure
Exposure to gamma rays, neutrons, or x-ray externally; not isotopes
Exposure must have occurred acutely, within minutes
