RAB: ch.20 Radiation Biology Flashcards
Adverse biological effects from ionizing radiation were observed shortly after __________’s discovery of x-rays in year ____ and _________’s discovery of __________ in ____.
Wilhelm Conrad Roentgen, 1895
Becquerel, 1896
The study of the action of ionizing radiation on healthy and diseased tissue is the scientific discipline known as _________?
radiation biology
[Determinants of biologic effects of radiation]
What are the 3 radiation-related factors?
- absorbed dose (quantity)
- dose rate
- type and energy (quality) of radiation
The radiosensitivity of a complex biologic system is determined by a num
How do you classify the Biologic Effects of radiation exposure?
- Stochastic effect
- Deterministic effect
One in which the probability of the effect occurring, (rather than its severity), increases with dose.
Stochastic effect
Radiation-induced cancer and hereditary effects are stochastic in nature. For example, the probability of radiation-induced leukemia is substantially greater after an exposure to 1 Gy than to 10 mGy, but there will be no difference in the severity of the disease if it occurs
Regarded as the principal health risk from low-dose radiation, including exposures of patients and staff to radiation from diagnostic imaging procedures?
Stochastic effect
T or F?
Stochastic effects are believed not to have a dose threshold, because damage to a few cells or even a single cell could theoretically result in production of the disease.
True
It is this basic, but unproven, assumption that risk increases with dose and there is no threshold dose below which the magnitude of the risk goes to zero, that is the basis of modern radiation protection programs, the goal of which is to keep exposures as low as reasonably achievable
If a radiation exposure is very high, the predominant biologic effect is _____, which presents clinically as degenerative changes in the exposed tissue.
cell killing
The severity of the injury, (rather than its probability of occurrence), increases with dose.
Deterministic effect
T or F:
Deterministic effects (also referred to as tissue reactions) differ from stochastic effects in that they require much higher doses to produce a clinically observable effect and there is a threshold dose below which the effect does not occur or is subclinical.
True
What are examples of deterministic effects that can result from large radiation exposures?
- Skin erythema
- fibrosis
- hematopoietic damage
___ effects can be caused by severe radiation accidents and can be observed in healthy tissue that is unavoidably irradiated during radiation therapy.
Deterministic
T or F:
In the context of diagnostic x-ray exposure, cell death does not mean the acute physical destruction of the cell by radiation but rather a radiation-induced loss of mitotic capacity (i.e., reproductive death) or premature activation of apoptotic pathways (i.e., programmed cell death). There is considerable evidence that damage to DNA is the primary cause of radiation-induced cell death.
True
Spectrum of DNA Damage The deposition of energy (directly or indirectly) by ionizing radiation induces chemical changes in large molecules that may then undergo a variety of structural changes. These structural changes include ___?
- hydrogen bond breakage
- molecular degradation or breakage
- intermolecular and intramolecular cross-linking.
True or False:
Molecular breakages also may involve the sugar-phosphate polymers that comprise the backbones of the two helical DNA strands. They may occur as single-strand breaks (SSBs), double-strand breaks (DSBs) (in which both strands of the double helix break simultaneously at approximately the same nucleotide pair), base loss, base changes, or cross-links between DNA strands or between DNA and proteins.
True
A type of molecular breakage where the sugar and phosphate can rejoin, provided there is no opportunity for the broken portion of strands to separate.
SSB (single-strand breaks)
___ can occur if two SSBs are juxtaposed or when a single, densely ionizing particle (e.g., an alpha particle) produces a break in both strands. DNA DSBs are very genotoxic lesions that can result in chromosome aberrations.
Double strand breaks (DSB)
Regardless of its severity or consequences, the loss or change of a base is considered a type of ____
mutation
chromosome breaks produced by radiation do occur and can be observed microscopically during ___and ___, when chromosomes are condensed.
anaphase, metaphase
In DNA repair, the cell may activate _ checkpoint (which arrests cell cycle progression), to allow for repair of damaged or incompletely replicated chromosomes.
G1/S checkpoint
___ is a form of cell death that is characteristically different from cell necrosis in morphology and biochemistry, leading to the elimination of cells without releasing inflammatory substances into the surrounding area. Apoptosis results in cell shrinkage via nuclear condensation and extensive membrane blebbing ultimately resulting in the fragmentation of the cell into membrane bound apoptotic bodies composed of cytoplasm and tightly packed organelles that are eliminated by phagocytosis.
Apoptosis (programmed cell death)
What are the types of DNA reparie mechanisms
- direct repair of a damaged nucleotide
- short and long patch base excision repair (SP BER, LP BER)
- nucleotide excision repair (NER)
- SSB and DSB repair
- cross-link repair
Most DNA base damage and SSBs are repaired by the ___?
base excision repair pathway
___ is the major pathway for the repair of bulky, helix-distorting lesions such as thymine dimers produced by exposure to ultraviolet radiation.
nucleotide excision repair (NER)