Radiobiology COPY COPY Flashcards
Which of the DNA bases are single-ring (pyrimidine) and which are double-ring (purine)?
Pyrimidine = thymine & cytosine Purine = adenine & guanine
What is the D0 dose?
The dose of radiation that induces an average of one lethal event per cell, leaving 37% still viable
What is the comet assay?
single-cell electrophoresis (for apoptosis)
Why is DNA in cells more resistant to radiation damage than free DNA?
- presence of molecular scavengers
- physical protection via protein (histone) packaging
What is gamma-H2AX?
phosphorylated form of histone protein H2AXm which is rapidly phosphorylated in response to DNA damage
What do nuclear foci of phosphorylated 53BP1 indicate?
DNA DSB
What is the extrapolation number, n? What type of curve results if n is large?
n is a measure of shoulder width
if n is large, the survival curve has a broad shoulder
Which genes appear to be responsible for induction of senescence?
Rb, p53
Following radiation, one cell line shows clear DNA laddering on electrophoresis, while another shows little evidence of DNA laddering. Which of these is more likely radiosensitive?
cell line with laddering –> indicates apoptosis
this is likely the more radiosensitive cell line
What is the OER for protons?
2.5-3.0
equivalent to x-rays
What is the average LET during the entrance plateau for protons? during the Bragg peak?
entrance: 0.5keV/um
Bragg peak: 100keV/um
The probability of which type of effect increases with radiation dose: deterministic or stochastic?
Both
What type of effect has a practical threshold dose and increases in severity with dose: deterministic or stochastic?
Deterministic
Which type of effect is best described as “random”, with no threshold observed and no change in severity with dose: What type of effect has a practical threshold dose and increases in severity with dose: deterministic or stochastic?
Stochastic
Which radiation-induced malignancy has the shortest latent period?
Leukemia
Peak incidence at 5-7 years
T/F: Radiation-induced solid tumors occur in younger patients than spontaneous tumors.
FALSE
Radiation-induced solid tumors tend to be expressed later in life, at the same time as spontaneous tumors of the same type
Which of the following risk models for malignancy following radiation exposure is favored by the BEIR committee:
absolute risk model
relative risk model
time-dependent risk model
Time-dependent risk model
Name the two international committees on radiation protection.
UNSCEAR - United Nations Scientific Committee on the Effects of Atomic Radiation (scholarly)
ICRP - Int’l Council on Radiological Protection
Name the two US committees on radiation protection.
BEIR - Biological Effects of Ionizing Radiation (US Nat’l Academy of Sciences)
NCRP - Nat’l Council on Radiological Protection and measurement
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T/F: The incidence of CLL increases following radiation.
False - AML/CML account for most of the increase
The incidence of which types of leukemia increases most after radiation of a human population?
AML and CML
Which populations are most susceptible to increased incidence of ALL and stem cell leukemia following radiation?
Children
Which type of cancer has the highest relative risk of any malignancy following radiation of a population?
Leukemia (specifically AML, CML)
The risk of leukemia rises in a dose-dependent manner up to what dose?
3 Sv
Risk per unit dose at 1 Sv is about 3X greater than 0.1 Sv
Which population is most sensitive to induction of thyroid carcinoma following radiation?
Children
What is the threshold dose to the developing fetus for radiation-induced mental retardation?
0.3Gy
What is the unit for absorbed dose (J/kg)?
Gy
1 Gy = 100 rad
What dose rate defines high dose rate brachytherapy?
HDR is >12Gy/h
What dose rate defines low dose rate brachytherapy?
LDR brachytherapy is ~2Gy/hr
