(Midterms) Cellular Radiobiology

Question 1

Characteristics of Ionizing Radn

Answer 1

Charge, mass, and energy

Question 2

Determine the extent to which diff radn modalities transfer energy to biological tissue

Answer 2

Charge, mass, and energy

Question 3

Amount of ionization produced in an irradiated object that would correspond to the amount of energy it absorbs

Answer 3

Linear Energy Transfer (LET)

Question 4

When passing through a medium, IR may interact with it

Answer 4

LET

Question 5

During its passage, and as a result, it will deposit energy along its path (“track”)

Answer 5

LET

Question 6

Assessing potential tissue and organ damage from exposure to irradiation

Answer 6

LET

Question 7

LET and chance of biological response relationship

Answer 7

Direct; LET increases chance of producing a significant biological response (DNA)

Question 8

LET Unit

Answer 8

keV per kilogram (μm)

Question 9

LET of diagnostic XR

Answer 9

3kev/μm (Low LET)

Question 10

Another method of expressng radiation quality and is used in determining Wr

Answer 10

LET

Question 11

External EM radn such as xrays and gamma rays

Answer 11

Low LET

Question 12

Causes damage primarily through indirect action that involves the production of free radicals

Answer 12

Low LET

Question 13

Unpaired hydrogen atoms; most often a combination of atoms that are chemically reactive as a result of an unpaired electron

Answer 13

Free radicals

Question 14

Single strand breaks/ main chain scission with one rail severed

Answer 14

Low LET

Question 15

Sublethal damage to DNA, repair enzymes can usually reverse the cellular damage

Answer 15

Low LET

Question 16

LET reaction that is less likely to happen as it happens by chance/ probability

Answer 16

Low LET

Question 17

Dense ionization

Answer 17

High LET

Question 18

Examples of High LET radn

Answer 18

1. Alpha particles
2. Ions of heavy nuclei
3. Charged particles released from interaction bn neutrons and atoms
4. Low-energy neutrons

Question 19

Loses energy more rapidly as it produces more ionization per unit distance

Answer 19

High LET

Question 20

Parameter that describes the average energy deposited over small distances in the material

Answer 20

High LET

Question 21

Electron must be a Compton scattered electron or a photoelectron

Answer 21

High LET

Question 22

LET of alpha is — the LET of electrons

Answer 22

1000x

Question 23

Relative capability of radiation with different LETs to produce a particular damage

Answer 23

Relative Biological Effectiveness (RBE)

Question 24

Ratio of the dose of a reference radiation quality that is necessary to produce the same biologic reaction in a given treatment

Answer 24

RBE

Question 25

RBE Formula

Answer 25

Do (XR) to produce an effect / Do (Test radn) to produce the same effect

Question 26

LET and RBE relationships

Answer 26

Direct

Question 27

Standard radn

Answer 27

Ortho voltage radn (200-250kvp)

Question 28

RBE of diagnostic xr

Answer 28

<1

Question 29

Has been used in the calculation of the dose equivalent to determine ability to age

Answer 29

Quality Factor (Qf)/ Wr

Question 30

Measure of RBE

Answer 30

Quality Factor (Qf)/ Wr

Question 31

In general, a large --- is associated with a large value of RBE

Answer 31

Quality Factor (Qf)/ Wr

Question 32

Dose delivered continuously but at lower dose rate

Answer 32

Protracted

Question 33

Reduces effect because it undergoes repair and recovery between doses

Answer 33

Fractionated

Question 34

Used in radiation oncology

Answer 34

Fractionated

Question 35

Tiss­e is more sensitive to radiation when irradiated in the oxygenated state than when irradiated ­nder anoxic or hypoxic conditions

Answer 35

Oxygen Effect

Question 36

Oxygen effect is described numerically by ---

Answer 36

Oxygen Enhancement Ratio (OER)

Question 37

Ratio of radn dose required to cause a particular biological response in an oxygen-deprived environment

Answer 37

Oxygen Enhancement Ratio (OER)

Question 38

OER - diagnostic XR imaging is performed under conditions of ---

Answer 38

full oxygenation

Question 39

OER is highest when there is (1) LET radn, with max value of (2) that decreases to approximately (3) for high LET radn

Answer 39

1. low 2. 3 3. 1

Question 40

OER Formula

Answer 40

OER= (Dose necessary required to cause biologic response WITHOUT O2)/ (Dose required to cause biologic response WITH O2)

Question 41

Target molecule

Answer 41

DNA (w/in cell's nucleus)

Question 42

Inactivation of target inside an organism by radiation that results to its death

Answer 42

Target theory

Question 43

T or F It is not possible to distinguish between a direct and an indirect hit

Answer 43

True

Question 44

Difference when molecules of cells are over abundant vs not abundant

Answer 44

Overabundant: Damage is not noticeable (ex. ribosome and mitochondria) Not abundant: Necessary for normal cell function; dame could affect cell severely (ex. nucleus)

Question 45

Serves as the basis for the target theory

Answer 45

Sensitive key molecule

Question 46

A concept that describe the interaction of ionizing radn w/ a key molecule (target) or within a short distance around one of these molecule

Answer 46

Target Theory

Question 47

Dose required to kill a cell when nucleus is irradiated

Answer 47

approx 100 rad

Question 48

Dose required to kill a cell when cytoplasm is irradiated

Answer 48

approx 1,000 rad

Question 49

In the absence of oxygen, the probability of a hit in a target molecule is low because of the relatively large distances bn ionizing events

Answer 49

Low LET radn

Question 50

Distance vn ionization is so close that the probability by a direct effect is high

Answer 50

High LET Radn

Question 51

As the number of raindrops increases, however, it becomes more probable that a given square will be hit by two or more drops

Answer 51

Single-Target, Single-Hit Model

Question 52

When the number of raindrops is equal to the number of squares (100 in this case), 63% of the squares will be wet and 37% of the squares will be dry. If the raindrops had fallen uniformly, all 100 squares would become wet with 100 raindrops.

Answer 52

Poission Distribution

Question 53

When the radiation dose reaches a level sufficient to kill 63% of the cells (37% survival)

Answer 53

D37

Question 54

A measure of the cell's radiosensitivity

Answer 54

D37

Question 55

Low D37 vs High D37

Answer 55

Low D37: Highly radiosensitive High D37: Radioresistant

Question 56

Model that represents a threshold

Answer 56

Multi-Target, Single-Hit Model

Question 57

2 or more hits requires for cell death to occur

Answer 57

Multi-Target, Single-Hit Model

Question 58

Thought to have more than one target

Answer 58

Human cellls

Question 59

What model is high and low LET under?

Answer 59

High LET radn: Single-Target, Single-Hit Model Low LET radn: Multi-Target, Single-Hit Model

Question 60

Average time fron one mitosis to another

Answer 60

Cell Cycle Time/ Cell Generation Time

Question 61

Cell Generation time (normal proliferation)

Answer 61

24hrs

Question 62

Longer generation times primary result from lengthening of what phase?

Answer 62

G1

Question 63

Human cells are most radioresistant in what phase?

Answer 63

M phase

Question 64

Human cells are most radiosensitive in what phase?

Answer 64

Late S Phase