radiation biology Flashcards
why do we learn radiation bio?
protecting the public and to have knowledge for controling risk
Dose Units for
Radiation Measurement
- Exposure Dose
- Absorbed Dose; RAD vs. Gray (G)
- Equivalent Dose; REM vs. Sievert (Sv)
- Effective Dose; REM vs Sievert
exposure dose
amount produced by machine
absorbed dose
amount absorbed by tissue (about the same as exposed dose)
equivalent dose modified by?
modified by radiation weighing factor
effective dose modified by what factor?
modified by tissue weight. factor
expsoure
- A measure of the capacity of radiation to ionize air
units of exposure:
traditional unit and metric equivalent
Traditional unit: roentgen (R)
Metric equivalent unit (S.I.) : air kerma
Absorbed Dose
* acronym?
* Metric equivalent (S.I.)? Conversion?
Absorbed Dose
* RAD - acronym for
Radiation Absorbed Dose
* 100 ergs or radiation energy in 1 gram of absorbed material
* Metric equivalent (S.I.) - Gy (gray) is Joule/Kg
Conversion; 1 Gy=100 RAD
0.0 1 Gy= 1 RAD
* 1R = 0.903 RAD
used for? weighing factor? calculation?
equivalent dose
- To compare the biological effects of different types of radiation
- Radiation weighing factor (WR) depends on the type and energy of the radiation involved
❖X-ray = 1
❖High energy radiations >1 - high energy protons = 5 - alpha particles = 20
quality factor of equivalent dose
- Quality Factor(Q.F)- is a measure of the biological effectiveness of a radiation to ionize matter
- the QF for x-radiation = 1;
calculated how? xrays value/conversion?
REM?
- REM- acronym for Roentgen Equivalent in Man
- equivalent to RAD x Q.F.
- Since the QF for X-radiation = 1;
- RAD units for x-radiation are equivalent to REM units
equivalent dose SI unit and conversion
- S.I. unit = Sv (sievert)
- Conversion: 1 rem = 0.01 Sv
1 Sv = 100 rem
- Diagnostic x-radiation is usually measured in?
- Diagnostic x-radiation is usually measured in
millirems (mRem)
used to measure? calculation?
effective dose
- This measure is used to specifically calculate risks of radiation to human tissues on a common scale.
- The calculation is a product of the sum of dose equivalence to the specific tissues or organs exposed and the biological tissue weighting factor.
Use of the ________ dose allows
comparisons of different imaging
techniques to be made on a common
scale.
Use of the effective dose allows
comparisons of different imaging
techniques to be made on a common
scale.
does the whole body need to be exposed for effective dose
- The value is an estimated measure of all somatic and genetic radiation-induced risk even if the entire body is not uniformly exposed.
effective dose used for?
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
1. cancer induction and/or
2. induction of genetic mutation
what tissue have high weight factors
gnads and hematopoetic
low weight factor tissues
skin and cortical bone
what benefit do solid state sensors have with effective dose?
much lower than film and PSPP
area exposed related to?
size of beam (affected by collimination)
possible interactions of xrays with matter
examples?
stochastic effects?
sublethal DNA damage
gene mutation
replication of mutated cells
Examples: leukemia, thyroid cancer, salivary gland tumors and heritable disorders
examples?
deterministic effects?
Lethal DNA damage
cell death
decreased tissue/organ function
examples: xerostomia, osteoradionecrosis, cataracts, etc.
Mechanisms of Injury
from x-ray interaction with matter
what interactions produce secondary electrons
what is the majority of xrays interaction with matter
compton scattering which can cause biological changes
no interaction by x rays
X-ray photon enters object (eg. patient
or other biologic tissues) and exits with
no change in its energy
Photoelectric Interaction
% interaction?
mechanism?
- Accounts for 30% of all interactions
- X-ray photon collides with an orbital
electron and loses its energy - Ejected photoelectron loses it energy
- Results in an atom with an altered
electric state, i.e., “+” charge - (similar orbital electron reaction to characteristic
radiation production but no x-radiation is produced)
Photoelectric Interaction consequences
unstable/seeks?
new configuration?
if the degree of the effect is significant what can be altered?
alterations often cause?
- The ionized matter is unstable and seeks a more stable configuration.
- The new configuration may include new ionic bonds, different covalent bonding, etc…
- If the degree of photoelectric effect is significant, this may affect, biologic structure, function or both.
- These effects are often deleterious biologic changes; e.g. altered metabolic function, malignancy, etc…
compton scatter
mechanism?
%interactions?
- accounts for 62% of interactions
- X-ray photon collides with an outer
orbital electron losing some energy - X-ray photon continues in different
direction with less energy creating more
scatter until all the energy is lost - results in an atom with an altered
electric state, i.e., “+” charge
compton scatter consequences
unstable/seeks?
new configuration?
if effect significant what can be altered?
alteration often lead to?
- The ionized matter is unstable and seeks a more stable configuration.
- The new configuration may include new ionic bonds, different covalent bonding, etc…
- If the degree of photoelectric effect is significant, this may affect, biologic structure, function or both.
- These effects are often deleterious biologic changes; e.g. altered metabolic function, malignancy, etc…
SAME AS PHOTOELECTRIC
Coherent Interaction
* accounts for __% of all interactions
* mechanism
Coherent Interaction
* accounts for 8% of all interactions
* X-ray photon of low energy interacts
with an outer orbital electron and
changes direction
* no photoelectron produced
* no ionization occurs
direct and indirect xray injury similarites
– Both effects occur quickly
– Both effects take hours to decades to become evident
– Both are a result of ionization
direct effect
➢ Directly ionizes biologic maromolecules
➢ Contributes to 1/3 of biologic effects
indirect effect
➢ X-ray photons absorbed by H2O →
free radicals →biologic damages
➢ Contributes to 2/3 of biologic effects
direct DNA damage flow chart
Outcome of Direct Effect of UV Light on Skin DNA
- Repair (healed)
- Inaccurate repair (mutation)
- No repair (death) 1
2
Indirect Effect Primary method of cell damage from?
- Primary method of cell damage from
radiolysis of water caused by x-radiation
radiolysis of indirect effect
toxins from free radicals
Free radicals seek a more stable
configuration which results in formation of toxic substances
Dose-Response Curves
- Dose (amount) of radiation is correlated with the
response or damage - Curves are theoretical for diagnostic x-radiation
Threshold Non-Linear Curve
Threshold Non-Linear Curve
* Small exposures do a substance do not produce measurable changes
* A threshold must be reached before
changes are observed
* Most biologic effects are non-linear
Linear Non-Threshold Curve
- Dose is proportional to the response
- No matter how small the dose, there is some damage or risk
XRAYS BELIEVED TO BE THIS
Nonlinear Nonthreshold Curve
- No threshold
- Minimal damage at first with increased rate of damage with increased dose
threshold? severity proportional to? curve?
Deterministic risk/effect
- Have a threshold
- severity is proportional to the dose
*ex: Erythema, xerostomia, cataract ,osteoradio-necrosis, fertility, fetal devel-opment, alopecia
Radiation Erythema
Radiation Erythema
* Side-effect of head &
neck cancer treatment
dose threshold? severity of effects depends on? somatic/germ cells?
Stochastic effects
- Have no dose threshold- Probability of occurrence is proportional to dose
- Severity of effects does not depend on dose
1. To somatic cells -genetic mutations cause malignancy
2. To germ cells - genetic mutations cause heritable effects
stoichastic effects potential curves
genetic vs somatic effects
examples?
somatic effects/mutations
– Somatic cells –all those except reproductive cells
– Seen in the person irradiated
– NOT transmitted to future generations
* Induction of cancer, leukemia, cataracts
Genetic effects/mutations
– NOT seen in the person irradiated
– Passed on to future generations
sequence of radiation injury
- Latent period
- Period of injury
- Recovery period
Latent Period
* Time?
* May be short or long depending on:
* Shorter latent period if:
* Genetic effects?
atent Period
* Time that elapses between exposure and appearance of clinical signs
* May be short or long depending on:
– Total dose
– Dose rate
* Shorter latent period if:
– Increased amount of radiation
– Faster dose rate
* Genetic effects –may be generations before clinical effects are seen
Period of Injury potential events
cells?
cell function?
chr?
what can form?
what cellualr activity can be impacted? how?
Period of Injury
* Cell death
* Changes in cell function
* Breaking or clumping of chromosomes
* Giant cell formation
* Cessation of mitotic activity
* Abnormal mitotic activity
FACTORS MODIFYING EFFECTS
OF X-RADIATION
- Total dose
- Dose rate
- Oxygen
- Area exposed
- Cell type and function
- Age
dose effect on damage
increased dose= increased damage
dose rate and damage
oxygen and damage
area exposed and damage
increased area=increased damage
radiosensitive and radioresistant cells
Radiosensitive –young, immature, rapidly growing
and dividing, least specialized
Radioresistant –mature, specialized cells
spp and radiosensitivty
◦ Mammals more sensitive than reptiles, insects, bacteria
cellular activity and radiosensitivity
◦ Mitotic activity
^ frequency of cell division = ↑ sensitivity
◦ Mitotic activity
Immature cells/not highly specialized = ↑ sensitivity
◦ Cell metabolism
^ metabolism = ↑ sensitivity
least radioresistant tissues
most radioresistant tissues
Pediatric Patients at risk
Pediatric Patients at risk
* Rate of cellular and organ growth puts tissues at greatest level of radiosensitivity
* Greater life expectancy puts children at 2-10 greater risk of being afflicted with a radiation induced cancer
ACUTE RADIATION SYNDROME
- A collection of signs and symptoms
following acute whole-body radiation
exposure
acute radiation syndrome radiation level exposure
higher doses effect on latent period and symptoms
shorter latent with severe symptoms
sAcute radiation syndrome
syndromes/ tissues involved
- Prodromal period
- Hematopoietic syndrome
- Gastrointestinal syndrome
- Central nervous system and
cardiovascular syndrome
(CNS/CVS syndrome)
prodromal period dose
<200R; <2Gy
hematopoetic syndrome dose
(200- 1,000R; 2-10 Gy)
Gastrointestinal syndrome dose
(1,000 – 10,000R; 10 – 100Gy)
- Central nervous system and
cardiovascular syndrome dose
> 10,000R; 100Gy
PRODORMAL SYNDROME
- Shortly after exposure to whole-body
radiation, an individual may develop
nausea; vomiting;
diarrhea; anorexia;
Causes general malaise, fatigue,
drowsiness and listlessness
Symptoms resolve after several weeks
ACUTE RADIATION SYNDROME lethal and sublethal exposure ranges
injury to? infection? hemmorhage? anemia? death?
HEMOPOIETIC SYNDROME
- irreversible injury to the proliferative capacity of the spleen and bone marrow with loss of circulating peripheral blood cells
- infection from the lymphopenia and
granulocytopenia - hemorrhage from thrombocytopenia
- anemia from the erythrocytopenia
- Death within 10 - 30 days.
GASTROINTESTINAL SYNDROME
damage to what systems?
injury to what cells? leads to?
loss of?
signs?
death in?
- extensive damage to the GI system (in addition to the hemopoietic system)
- There is extensive injury to the rapidly proliferating basal epithelial cells of the intestinal villi which leads to atrophy and ulceration
- loss of plasma and electrolytes
- hemorrhage and ulceration
- diarrhea, dehydration, weight loss
- Infection
- Death in 3 - 5 days
CARDIOVASCULAR
and
CENTRAL NERVOUS SYSTEM
SYNDROME
- radiation induced damage to neurons and fine vasculature of brain
- Intermittent stupor, incoordination, disorientation, and convulsions from extensive CNS damage
- irreversible damage with death in a few minutes to 48 hours
RADIATION TREATMENTS TO THE
ORAL CAVITY
- Combined surgical, radiation and chemotherapy often provides the optimum treatment for cancers
- Oral tissues are subjected to high doses of
radiation during the treatment of malignant
tumors of the soft palate, tonsils, floor of the
mouth, nasopharynx, and hypopharynx
- Oral tissues are subjected to high doses of
- Total radiation doses to treat malignanttumors ranges from ______Rads. Or
_____ G
- Total radiation doses to treat malignant
tumors ranges from 6,000 - 8,000 Rads. Or
60 -80 G
fractionation of radiation doses for cancer tx
- Fractionation of the total dose into multiplesmall doses provides greater tumor destructionthan a single large dose
- Fractionation also increases cellular repair of the normal tissues
RADIATION EFFECTS ON THE ORAL CAVITY
* Mucosa
* Taste Buds:
* Salivary Glands:
* Teeth:
* Bone:
* Muscle:
RADIATION EFFECTS ON THE ORAL CAVITY
* Mucosa: - mucosits (2 infections)
* Taste Buds: - loss of taste
* Salivary Glands: - xerostomia
* Teeth: - lack of or retarded development
- radiation caries with stronger adhered plaque
* Bone: - osteoradionecrosis (decreased angiogenesis)
* Muscle: - fibrosis
what can casue this? when is onset? recovery?
hypoguesia of radiation
- Epithelial atrophy, xerostomia and
mucositis all result in loss of taste
(hypoguesia) by the 2nd- 3rd week of treatment - recovery of taste sensitivity will occur in 2 - 4 months followingtreatment
adult teeth and radiation
- Adult teeth are very resistant to the directeffects of radiation exposure
- There is no discernible effect on the crystallinestructure of enamel, dentin, or cementum
- Radiation does not increase the solubility ofteeth
developing teeth and radiation
- When teeth are irradiated during the
developmental stage, their growth may beseverely retarded - If the radiation precedes calcification, thetooth bud may be destroyed
- Irradiation after initiation of calcification,teeth may demonstrate malformations and arresting general growth
xerostomia and radiation
if a portion spared?
can it persist?
- Generally, if some portion of the salivary gland has been spared, the dryness of the mouth subsides in 6 month to 1 year
- However, xerostomia may persist without any significant return of salivation
when could these be exposed? what makes this tissue so susceptiable?
major salivary glands exposed
- Major salivary glands are often exposed unavoidably to radiation during treatment for carcinoma of the oral cavity or oropharynx
- Parenchymal cells (especially of the parotid glands) are very sensitive to X-rays and are replaced by fibrosis and adiposis with parenchymal degeneration and loss of fine vasculature
makes mouth? pH? buffering capacity?
scanty saliva with radiation
- The scanty saliva makes the mouth dry (xerostomia) and tender. Swallowing is difficult and painful
- The residual saliva has a lowered pH (from 6.5 to 5.5), which is acidic enough to initiate decalcification of enamel
- The buffering capacity of saliva is reduced 40 -45%
A dose as low as ____ R at the age of 5 monthshas been reported to cause hypoplasia of the enamel
A dose as low as 200 R at the age of 5 months has been reported to cause hypoplasia of the enamel
radiation and tooth eruption
- Although irradiation may retard or abort toothformation, the eruptive mechanism is much more radiation resistant
- Irradiated teeth with altered root formation will still erupt
radiation caries
- A rampant form of decay that may affect individuals who received a course of radiation therapy that include exposure of the salivary glands
osteoradinecrosis
- The primary damage to bone is from
irradiation to
– fine vasculature
– marrow – affecting vascular and hemopoieticelements.
radiation effect on oral masculature
- Inflammation and fibrosis – results in contracture and trismus in the muscles
where can ionizing radiation be encountered
everywhere
mrem, rem, mSv
Maximum Permissible Doses
medical and dental exposure make up what fraction of exposure to ionizing rad
1/6
why was there a scare with radiation expsoure not long ago
too many CT scans given and nuclear med
avg was above 5mSv for everyone
cancers associated with dental xrays
- Leukemia and thyroid cancer have the highest risk from dental radiographic exposure
Artificial/Manmade Radiation Sources
– %?
– 2%
* Consumer products
– Televisions, wristwatches, computers
* Airport scanners
* Nuclear fuel cycle
* Weapons production
* Fall-out from atomic weapons
how to airport scanners work
use of compton scatter to find metal objects
compared to PAs? whole body?
Radiation Erythema dosage levels
- 250 Rads – Threshold radiation Erythema Dose (TED)
- 500 Rads – Average radiation Erythema Dose
- 750 Rads – Maximum radiation Erythema Dose
- all of these much more than normal PA
- not a whole body exposure (would be fatal)
current imaging and TED
At a 16” focal distance 1/3 of the TED is delivered with ~473 intraoral dental exposures
risk for congenital defects in pregnant women with imaging
- Studies show risk for congenital defects is negligible at 50 mSv or less
absorbed doses of 50mSv/mGy and risk of deterministic effects on fetus
virtually none, almost all intraorla techniques are considerably less than 50mSv (CBCT can be more)
what dosage can increase risk of childhood cancer? by how much?
stoichastic risks to the fetus
absorbed doses >25mSv doubles the childhood cancer rate, cn occur with film, pano, CBCT
radiographs of a new pt who is pregnant
- Radiographs of pregnant patients as part of any new patient or recall exam must be postponed until post-partum.
when should pregnant pts be imaged
- If urgent care dental treatment is required during pregnancy, radiographs may be necessary as the standard of care to treat and diagnose a condition that threatens the health of the mother and the unborn child. The clinician must assure that the primary beam is not directed toward the child-bearing area.
any infection/condition that threatens the mother or child
why take radiogrpahs if there is a risk
for diagnostic benefit
R to Gy conversion
100R=1Gy
x rays believed to have what dose response curve?
linear non-threshold
photoelectric vs compton scatter effect
In the photoelectric effect, all of the photon energy is absorbed in the ionization process as this usually involves an inner shell electron.. In the Compton effect, the ionization is with an outer shell electron with low binding energy. So with respect to the original x-ray photon, it loses some kinetic energy, but there is still enough energy to ionize other atoms especially if the ionization is with peripheral electrons.
metric and standard units conversions
One metric unit = 100 standard units
1 Gy = 100 Rads; 1 Rad = 0.01 Gy
1 Sv = 100 Rems; 1Rem = 0.01 Sv
stochastic vs deterministic effects
deterministic – dose dependent
stochastic risks - incident dependent -each incident of exposure to ionizing radiation
examples?
stochastic effects?
sublethal DNA damage
