radiation biology Flashcards
interactions of x radiation with matter
ionization
radiation injury
a. direct vs indirect
b. dose response curves
c. deterministic vs stochastic risk
d. somatic vs genetic effects
e. sequence of radiation injury
dose units for radiation measurement:
1. exposure dose
2. absorbed dose
3. equivalent dose
4. effective dose
- exposure dose: R vs. coulombs/kg
- absorbed dose: RAD vs. Gray (G)
- equivalent dose: REM vs. Sievert (Sv)
- effective dose: REM vs. Sievert (Sv)
ionize air
exposure
traditional unit: R
SI unit: air kerma
energy absorbed by tissue
absorbed dose
traditional unit: rad
SI unit: Gy
modified by radiation weighting factor
equivalent dose
traditional unit: rem
SI unit: Sv
modified by tissue weight factor
traditional unit: rem
SI unit: Sv
measure of the capacity of radiation to ionize air
exposure
exposure traditional unit
R roentgen
and air kerma in metric (kinetic energy released in matter)
absorbed dose:
rad
radiation absorbed dose
100 radiation energy in 1 gram of absorbed material
use to compare the biological effects of different types of radiation
equivalent dose (I)
radiation weighing factor (Wr) depends on the type and energy:
of the radiation involved
Ht (equivalent dose)= Dt (absorbed dose) x Wr (radiation weighing factor)
measure of the biological effectiveness of a radiation to ionize matter
equivalent dose
the quality factor for x-radiation is
1
equivalent dose unit is REM that stands for
roentgen equivalent in man
equivalent dose is equivalent to
RAD x QF
(absorbed dose x Wr)
since QF for x-radiation is 1, the RAD units for x-radiation are ____to REM units
equal
effective dose calculation
E= SUM(Z) Wt x Ht
E= Z (tissue weight factor) x (dose equivalence to tissue)
this measure is used to specifically calculate risks of radiation to human tissues on a common scale
effective dose
product of the sum of dose equivalence to the specific tissues or organs exposed and the biological tissue weighting factor
effective dose
**used to assess risk of non-uniform radiation to localized part of body and degree to which this would increase a person’s whole body risk of:
effective dose
- cancer induction and or
- induction of genetic mutations
area exposed is related to the
maximum size of the beam
1 of 4 things can happen when you expose an object to x-radiation
- no interaction (pass right thru) 9%
- coherent scattering (heat and no ionize) 7%
- photoelectric absorption 27%
- compton scattering 57%
two ionizing effects are
- compton (incoherent) scatter
- photoelectric effect
mechanism of injury from xray interaction with matter (ionization)
radiation injury
ionization from ionizing radiation exposure sets off multiple direct and indirect molecular reactions in ____secs
enzymatic repair or further deleterious molecular changes occur in
deterministic and stochastic effects take place over time from
< 1 second
in mins to hours
months to decades to generations
x-ray photon enters object (patient or other tissues) and exits with no change in its energy
no interaction 9%
x-ray photon collides with an orbital electron and loses its energy.
-ejected photoelectron loses its energy and results in an atom with an altered electric state ( example: + charge)
photoelectric interaction
30% of all interactions
in this interaction, the ionized matter is unstable and seeks a more stable configuration.
the new configuration may include new ionic bonds, different covalent bonds, etc.
if the degree of photoelectric effect is significant, this may affect:________
these effects are often deleterious biologic changes, like altered metabolic function or malignancy
photoelectric interaction AND compton interaction/scatter
affect biologic structure, function or both
- xray photon collides with an outer orbital electron losing some energy
- xray photon continues in different direction with less energy creating more scatter until all the energy is lost
- results in an atom with an altered eletric state (ex: + charge)
compton interaction/scatter
62% of interactions
- xray photon of low energy interacts with an outer orbital electron and changes direction
- no photoelectron produced
- no ionization occurs
coherent interaction
8% of interactions
with direct and indirect radiation injury, both:
- effects occur quickly
- take hours to decades to become evident
- result of ionization
this ionizes biologic maromolecules
contributes to ~1/3 of biologic effects
direct effect
xray photons absorbed by H2O-> free radicals-> biologic damage
contributes to ~2/3 of biologic effects
indirect effect
radiation strikes biologically active molecule= biologically active
direct effect
damaged molecule no longer capable of proper function= molecular death
radiation damage theory (bioloically active equals this)
3 outcomes of direct effect of UV light on skin DNA
- repair (healed)
- inaccurate repair (mutation)
- no repair (death)
method of cell damage from radiolysis of water caused by x-radiation
primary
indirect effect
indirect effect.
photon + ____-> H2O-> OH+H
H2O
free atom or molecule carrying an unpaired orbital electron in the outer shell
free radical
free radical formation
xray photons interact with water in cells
ionization occurs
resulting in free radical formation
highly reactive and unstable
lifetime=10^-10 seconds
free radical formation
free radicals seek a more stable configuration which results in formation of
toxic substances
(dose) amount of radiation is correlated with response or damage
dose-response curves
curves are ______for diagnositic xradiation
theoretical
threshold non-linear curve,
small exposures to a substance (does/does not) produce measurable change
doesn’t
what must be reached for exposure to produce measurable change
must meet threshold before changes are observed
most biologic effects are (linear/non-linear)
non-linear
dose is proportional to the response
-no matter how small dose, there is some damage or risk
linear non-threshold curve
no threshold
-minimal damage at first with increased rate of damage with increased dose
nonlinear nonthreshold curve
determinisitic risk/effect
- have threshold
- severity is proportional to the dose
examples:
erythema
xerostomia’cataract
fertility
alopecia
*fetal development
fetal effective dose
OMR imaging, 0.01mGy
threshold radiation erythema dose (TED)
250 rads
average radiation erythema dose
500 rads
maximum radiation erythema dose
750 rads
- have no dose threshold
- probability of occurrence is proportional to dose
- severity of effects does not depend on dose
stochastic effect
genetic mutations cause malignancy (stochastic effect)
to somatic cells
genetic mutations cause heritable effects
(stochastic effect)
to germ cells
radiation-induced cancer is not seen in doses _____10 mGy
throughout pregnancy
<
no affect on parent, affects future generation
genetic injury
affects parent and no effect on future generatiion
somatic injury
all those except reproductive cells
somatic cells
seen in the person irradiate
and NOT transmitted to future generations
(induction of cancer, leukemia, cataracts)
somatic effects/mutations
not seen in person irradiated
passed on to future generations
genetic effects/mutations
sequence of radiation injury
- latent period
- period of injury
- recovery period
time that elapses between exposure and appearance of clinical signs
latent period
latent period can be short or long depending on
total dose and dose rate
shorter latent period if
- increased amount of radiation
- faster dose rate
genetic effects of latent period
may be generations before clinical effects are seen
- Cell death
- Changes in cell function
- Breaking or clumping of chromosomes
- Giant cell formation
- Cessation of mitotic activity
- Abnormal mitotic activity
period of injury
- full recovery for a large percentage of
individuals from a few weeks up to two years
after exposure
recovery period
No recovery period i.e, death likey at higher does of
>1.2 Gy (120 Rads).
> 1.2 Gy (120 Rads).
factors modifying effects of x-radiation
- Total dose
- Dose rate
- Oxygen
- Area exposed
- Cell type and function
- Age
increase total dose:
increase damage
increase dose rate
decrease cellular repair which increases damages
increase oxygen content
increase radiosensitivity
increase tissue damage
young, immature, rapidly growing and dividing, least specialized
(what cell type)
radiosensitive
mature, specialized cells
(what cell type)
radioresistant
____ more sensitive than reptiles, insects, bacteria
Mammals (species)
Mitotic activity
increase frequency of cell division = ___sensitivity
increase sens
Mitotic activity
Immature cells/not highly specialized = ___sensitivity
increase sens
Cell metabolism
increase metabolism = ___sensitivity
increase sens
tissues/organs
1. high sens to radiation
2. least radioresistant
Blood cells
Small lymphocyte – most sensitive
Bone marrow
Reproductive cells
Intestinal mucosa
Mucous membrane
tissues/organs
Intermediate sensitivity to radiation
Connective tissue
Breast (women)
Small blood vessels
Growing bone and cartilage
Salivary gland
tissues and organs
Fairly low sensitivity to radiation
Thyroid gland
Skin
tissues/organs
Low sensitivity to radiation
Most radioresistant
Muscle
Nerve
Mature bone
