Week 6 Flashcards
What is the target theory as it applies to irradiated cells?
Target theory suggests that cell death or damage occurs if radiation inactivates a vital master molecule (likely DNA). Thus, hit probability is crucial in assessing radiation effects.
What is radiation biology and why is it relevant to radiation protection?
Radiation biology is the study of the effects of ionizing radiation on living systems. It is relevant to radiation protection because it helps understand how ionizing radiation causes damage and the measures needed to mitigate its effects on biological tissues.
What are the implications of radiation damage to somatic and germ cells?
Somatic cell damage can lead to tissue or organ dysfunction, while germ cell damage may cause heritable genetic mutations affecting future generations.
How do the laws of Bergonie and Tribondeau explain radiosensitivity?
These laws state that radiosensitivity is directly proportional to a cells reproductive activity and inversely proportional to its degree of differentiation, meaning rapidly dividing, undifferentiated cells are more sensitive to radiation.
How does radiation affect the genetic information passed during meiosis?
Radiation can cause mutations by altering DNA bases, potentially transmitting incorrect genetic information during cell division and affecting offspring.
Explain what happens during the protraction of a radiation dose.
Protraction involves delivering a radiation dose continuously at a low rate over a long period, minimizing damage by allowing cellular repair mechanisms to act.
Identify and describe chromosomal aberrations caused by ionizing radiation.
Aberrations include chromosomal fragments, chromosome and chromatid anomalies, leading to genetic material loss or mutation and impaired cell function.
How does linear energy transfer (LET) influence the effects of ionizing radiation?
LET describes the average energy deposited per unit track length by ionizing radiation. It influences biologic damage as higher LET radiation causes more damage due to the high energy deposition within a short distance.
What types of radiation can produce biologic damage through ionization?
Types include X-rays, gamma rays, alpha particles, beta particles, and protons.
What factors influence the survival curves for mammalian cells exposed to radiation?
Key factors include the radiosensitivity of cell types, dose rate, radiation type, and the presence of oxygen, which can alter the cell’s ability to repair damage.
What are the primary effects of ionizing radiation on DNA?
Primary effects include single and double-strand breaks in DNA, mutations due to changes in nitrogenous bases, and covalent cross-links that alter DNA structure and function.
What types of experiments and observations contribute to our understanding of radiation biology?
Experiments on animals and plants, as well as observations of humans exposed to radiation (e.g., radiologists, nuclear workers, survivors of atomic bombs), provide valuable insights.
How does cell maturity and specialization affect radiosensitivity?
Cells that are immature and undifferentiated, like stem cells, are more radiosensitive because they divide frequently, unlike mature, specialized cells which are more radioresistant.
What effect does oxygen have on radiosensitivity during radiation exposure?
Oxygen increases radiosensitivity as it enhances free radical formation, thereby amplifying radiation damage, a principle used in hyperbaric oxygen therapy to boost radiotherapy effectiveness.
What is relative biologic effectiveness (RBE) and how is it calculated?
RBE is the ratio of the dose of a reference radiation to the dose of a different type of radiation needed to produce the same biological effect. It is calculated by comparing the effectiveness of various radiations to a standard, typically 250-kVp x-rays.
How do LET and RBE vary between different types of radiation?
High LET radiation (e.g., alpha particles) is more damaging, leading to higher RBE, compared to low LET radiation (e.g., X-rays) that causes damage over a longer range.
Describe the process of radiolysis of water and its biological implications.
Radiolysis of water is the ionization of water molecules by radiation, leading to free radical formation. These radicals can cause biological damage by interacting with critical cellular components like DNA.
How does the target theory explain cell death following radiation exposure?
Target theory posits that cell death occurs if radiation inactivates a vital master molecule, usually DNA, crucial for cell survival and function.
How does ionizing radiation cause damage to the molecular structure of living systems?
Ionizing radiation damages molecular structures by ionizing atoms, leading to incorrect molecular bonding and impacting cellular functions.
How does the restitution process affect chromosomal structure after radiation?
Restitution refers to the repair and return of chromatid or chromosome to its original configuration, minimizing visible damage and preserving genetic information.
Discuss the single-strand and double-strand breaks in DNA caused by radiation.
Single-strand breaks involve rupture of chemical bonds, usually repairable, while double-strand breaks are more severe, potentially leading to cell death if not properly repaired.
Describe the consequences of radiation-induced molecular damage at the cell and organic levels.
Molecular damage can impair cell function, leading to potentially visible damage at cellular and organic levels, resulting in disrupted body processes or organ failure.
How does broken-end rearrangement occur, and what are its effects?
Broken-end rearrangement occurs when chromosomal ends rejoin incorrectly, forming misshapen chromosomes, which may lead to defective cells unable to function or reproduce.
Define oxygen enhancement ratio (OER) and explain its significance in radiation biology.
OER is the ratio of radiation doses required to achieve a specific biological response under anoxic vs. oxygenated conditions. It is significant because oxygen presence enhances radiation effects, increasing tissue radiosensitivity.
What is the outcome of chromosomal deletion in radiation-damaged cells?
Deletion results in loss of genetic material, possibly creating acentric fragments, which can severely impact cell function and viability during subsequent cell division.
What are covalent cross-links and how do they affect DNA following irradiation?
Covalent cross-links are chemical unions between DNA strands, forming structural changes that can hinder DNA replication and repair, possibly leading to mutations or cell death.
Why does indirect action of low-LET radiation primarily occur in the human body?
The body is mostly water, and low-LET radiation often interacts with water molecules, causing indirect damage by producing free radicals that affect critical molecules like DNA.
How do the age and gender of a patient influence radiosensitivity?
Younger individuals are more radiosensitive, and men may be slightly more sensitive due to X chromosome susceptibility, influencing risk assessments and treatment planning.
What protective and sensitizing effects can chemical agents have in radiation biology?
Protective agents, like antioxidants, reduce damage, while sensitizers, such as some drugs, increase tissue susceptibility, affecting radiation therapy outcomes.
Differentiate between direct and indirect actions of radiation on tissues.
Direct action occurs when radiation directly ionizes DNA, while indirect action involves radiation ionizing water molecules, producing free radicals that in turn damage DNA and other molecular structures.
List and define the different classes of cell death due to radiation exposure.
Classes include instant death, reproductive death, apoptosis (programmed cell death), mitotic death, mitotic delay, and interference with function.
How might the OER change with different doses of radiation?
OER is higher at greater radiation doses (approximately 3 for high doses), as oxygen significantly enhances radiation damage, and is lower (around 2) at doses below 2 Gy.
Define main-chain scission, cross-linking, and point lesions as types of molecular damage.
Main-chain scission is the breakage of the molecular chain, cross-linking refers to abnormal attachments within or between molecules, and point lesions are small damage sites.
What role does fractionation play in radiation therapy?
Fractionation involves delivering radiation doses in multiple small fractions, allowing normal cells to repair and reducing side effects while maintaining tumor control.
