Radiobiology COPY COPY

Question 1

Which of the DNA bases are single-ring (pyrimidine) and which are double-ring (purine)?

Answer 1

Pyrimidine = thymine & cytosine
Purine = adenine & guanine

Question 2

What is the D0 dose?

Answer 2

The dose of radiation that induces an average of one lethal event per cell, leaving 37% still viable

Question 3

What is the comet assay?

Answer 3

single-cell electrophoresis (for apoptosis)

Question 4

Why is DNA in cells more resistant to radiation damage than free DNA?

Answer 4

• presence of molecular scavengers

- physical protection via protein (histone) packaging

Question 5

What is gamma-H2AX?

Answer 5

phosphorylated form of histone protein H2AXm which is rapidly phosphorylated in response to DNA damage

Question 6

What do nuclear foci of phosphorylated 53BP1 indicate?

Answer 6

DNA DSB

Question 7

What is the extrapolation number, n? What type of curve results if n is large?

Answer 7

n is a measure of shoulder width

if n is large, the survival curve has a broad shoulder

Question 8

Which genes appear to be responsible for induction of senescence?

Answer 8

Rb, p53

Question 9

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?

Answer 9

cell line with laddering –> indicates apoptosis

this is likely the more radiosensitive cell line

Question 10

What is the OER for protons?

Answer 10

2.5-3.0

equivalent to x-rays

Question 11

What is the average LET during the entrance plateau for protons? during the Bragg peak?

Answer 11

entrance: 0.5keV/um

Bragg peak: 100keV/um

Question 12

The probability of which type of effect increases with radiation dose: deterministic or stochastic?

Answer 12

Both

Question 13

What type of effect has a practical threshold dose and increases in severity with dose: deterministic or stochastic?

Answer 13

Deterministic

Question 14

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?

Answer 14

Stochastic

Question 15

Which radiation-induced malignancy has the shortest latent period?

Answer 15

Leukemia

Peak incidence at 5-7 years

Question 16

T/F: Radiation-induced solid tumors occur in younger patients than spontaneous tumors.

Answer 16

FALSE
Radiation-induced solid tumors tend to be expressed later in life, at the same time as spontaneous tumors of the same type

Question 17

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

Answer 17

Time-dependent risk model

Question 18

Name the two international committees on radiation protection.

Answer 18

UNSCEAR - United Nations Scientific Committee on the Effects of Atomic Radiation (scholarly)
ICRP - Int’l Council on Radiological Protection

Question 19

Name the two US committees on radiation protection.

Answer 19

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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Question 20

T/F: The incidence of CLL increases following radiation.

Answer 20

False - AML/CML account for most of the increase

Question 21

The incidence of which types of leukemia increases most after radiation of a human population?

Answer 21

AML and CML

Question 22

Which populations are most susceptible to increased incidence of ALL and stem cell leukemia following radiation?

Answer 22

Children

Question 23

Which type of cancer has the highest relative risk of any malignancy following radiation of a population?

Answer 23

Leukemia (specifically AML, CML)

Question 24

The risk of leukemia rises in a dose-dependent manner up to what dose?

Answer 24

3 Sv

Risk per unit dose at 1 Sv is about 3X greater than 0.1 Sv

Question 25

Which population is most sensitive to induction of thyroid carcinoma following radiation?

Answer 25

Children

Question 26

What is the threshold dose to the developing fetus for radiation-induced mental retardation?

Answer 26

0.3Gy

Question 27

What is the unit for absorbed dose (J/kg)?

Answer 27

Gy

1 Gy = 100 rad

Question 28

What dose rate defines high dose rate brachytherapy?

Answer 28

HDR is >12Gy/h

Question 29

What dose rate defines low dose rate brachytherapy?

Answer 29

LDR brachytherapy is ~2Gy/hr