Module 4 (Radiosensitivity) Flashcards
Which body systems have high radiosensitivity?
Hematopoietic system (lymphoid organs, bone marrow, blood, spleen)
Which body systems have fairly high radiosensitivity?
Gastrointestinal (GI) system (esophagus, bladder, rectum, intestines)
Which body systems have moderate radiosensitivity?
Epidermal tissues (skin, epithelial tissues), Eyes (cornea, optic lens), Growing cartilage, fine vasculature, and growing bone
Which body systems have fairly low radiosensitivity?
Mature bone and cartilage, Salivary glands, Respiratory organs, Kidneys, Liver, Pancreas, Thyroid, Adrenals, Pituitary glands
Which body systems have low radiosensitivity?
Muscle, Brain, Spinal cord
Why is understanding radiosensitivity important for radiographers?
It helps in recognizing which tissues are more vulnerable to radiation damage and understanding how sensitivity changes throughout a person’s lifespan.
What are the two main compartments of tissues and organs?
Parenchymal compartment: Contains specialized cells specific to the tissue or organ.
Stromal compartment: Contains connective tissue and vasculature that provide structural support.
Which tissue compartment is more affected by radiation exposure?
The parenchymal compartment, because its cells are highly differentiated and specialized.
What is the function of parenchymal cells?
Parenchymal cells perform functions specific to their tissue or organ (e.g., renal cells support kidney function, liver cells support liver function).
Example: Renal cells support kidney function, liver cells support liver function.
What is the function of stromal cells?
Stromal cells provide structural support without specialized function.
How does cellular differentiation affect radiosensitivity?
Immature cells: Less differentiated, rapidly dividing, more radiosensitive.
Mature cells: Fully differentiated, less radiosensitive.
What is an example of radiosensitivity in cell development?
Sperm cell maturation: Immature sperm cells are highly radiosensitive due to rapid division, while mature sperm cells are more resistant.
Example: Immature sperm cells are highly radiosensitive due to rapid division.
What biological factors influence inherent radiosensitivity?
Mitotic rate (higher rate = more radiosensitive)
Degree of differentiation (less differentiated = more radiosensitive)
Stage in the cell cycle (cells in mitosis are most radiosensitive).
Why does high mitotic activity increase radiosensitivity?
During mitosis, there is an increased probability of direct radiation effects on DNA, making rapidly dividing cells more vulnerable.
What is an example of an organ with high mitotic activity?
The liver, which contains about 60% hepatocytes that make up 80% of its volume and has a strong regenerative capacity.
What is the Law of Bergonie and Tribondeau?
It states that radiosensitivity is the relative susceptibility of cells, tissues, organs, and organisms to the injurious effects of radiation.
What determines a cell’s radiosensitivity according to Bergonie and Tribondeau?
Directly proportional to reproductive activity (mitotic rate) and inversely proportional to the degree of differentiation.
What type of cells were used in Bergonie and Tribondeau’s experiments?
Rodent testicle cells, which contain both immature and mature specialized cells.
What were the key conclusions from Bergonie and Tribondeau’s research?
Immature cells are damaged at lower doses than mature cells. Stem cells that actively divide are radiosensitive. Higher metabolic activity = higher radiosensitivity. Younger tissues and organs are more radiosensitive. Faster cell mitotic rate and tissue growth rate = higher radiosensitivity.
How is the Law of Bergonie and Tribondeau relevant to radiation therapy?
It helps target rapidly dividing cancer cells, as they are more radiosensitive.
How does the Law of Bergonie and Tribondeau apply to diagnostic radiology?
It highlights that fetuses are significantly more radiosensitive than children or adults, reinforcing the need for radiation protection.
Why are fetuses and children highly radiosensitive?
High ratio of immature cells, increased proportion of stem cells, high mitotic rate, and young tissue age.
How does the Law of Bergonie and Tribondeau relate to fetal and pediatric radiosensitivity?
It states that cells that divide rapidly and are less differentiated are more radiosensitive, making fetuses and children highly susceptible to radiation effects.
Why is the first trimester the most radiosensitive period?
The embryo is rapidly dividing and undifferentiated. Organ and system formation occurs. Radiation exposure can cause embryonic death or congenital abnormalities.
What factors influence radiation effects on an embryo?
The stage of development determines the severity of radiation effects, with the first trimester being the most critical.
Why are children more affected by radiation than adults?
Smaller body size increases internal dose absorption. Longer life expectancy allows more time for long-term radiation effects to develop.
How does radiosensitivity change with age?
Radiosensitivity decreases as age progresses, meaning infants and young children are more sensitive than adults.
What is the Oxygen Enhancement Ratio (OER)?
The OER describes the relationship between tissue oxygenation and radiation damage, showing that oxygenated tissues are more radiosensitive than hypoxic tissues.
What is the oxygen effect?
The oxygen effect refers to the increased radiosensitivity of highly oxygenated tissues compared to hypoxic tissues.
How does the OER express the oxygen effect numerically?
OER is the ratio of the radiation dose required to produce the same biological response in hypoxic vs. oxygenated environments.
How does OER vary between high-LET and low-LET radiation?
High-LET radiation: OER ≈ 1 (less oxygen effect)
Low-LET radiation (e.g., X-rays): OER ≈ 2.5-3.0 (strong oxygen effect)
Why does low-LET radiation have a higher OER?
Low-LET radiation causes indirect damage via free radical formation, which is amplified by oxygen, increasing biological effects.
How does oxygen affect DNA damage from radiation?
Oxygen reduces the ability for cells to repair DNA damage caused by free radicals, increasing radiation sensitivity.
How does OER impact radiation therapy?
Tumors with low oxygen levels (hypoxic) are more resistant to radiation, whereas oxygenated tissues are more sensitive to treatment.
What is an example of highly oxygenated tissues with increased radiosensitivity?
The lungs, where biological impacts from low-LET radiation can be 2.5-3x higher due to oxygen presence.
What radiation factors affect cell radiosensitivity?
Linear Energy Transfer (LET), Relative Biological Effectiveness (RBE), Oxygen Enhancement Ratio (OER)
What is Linear Energy Transfer (LET)?
LET is the rate at which energy is transferred from ionizing radiation to soft tissue, measured in keV/µm.
What is the LET of diagnostic X-rays?
About 3 keV/µm.
How does LET affect biological damage?
Higher LET radiation causes more biological damage because it transfers more energy per unit length of tissue.
What is Relative Biological Effectiveness (RBE)?
RBE measures the effectiveness of radiation in causing biological damage compared to a reference radiation (usually X-rays, RBE = 1).
How does LET relate to RBE?
As LET increases, RBE also increases, meaning high-LET radiation causes more severe biological effects.
What is the Oxygen Enhancement Ratio (OER)?
OER describes the increased radiosensitivity of oxygenated tissues compared to hypoxic tissues.
How does OER differ for high-LET vs. low-LET radiation?
High-LET radiation: OER ≈ 1 (little oxygen effect)
Why does oxygen increase radiation effects in low-LET radiation?
Oxygen enhances free radical formation, which increases biological damage.
