principles of radiobiology

Question 1

the harmful effects of radiation primarily affect at what level

Answer 1

cellular

Question 2

what are the generalizations of interactions (3)

Answer 2

a probability
damage may/not occur
90% of interactions are harmless

Question 3

what are the generalizations about visible damage (3)

Answer 3

indistinguishable from other causes
damage may occur after latent period
latent duration dec as dose inc

Question 4

why is the ionization of atoms in a living system bad?

Answer 4

ionized atoms will not bond properly

Question 5

what are the 3 radiation energy transfer determinants

Answer 5

charge, mass, energy

Question 6

what 3 concepts help understand how rad causes injury and how effects may vary in biologic tissue

Answer 6

linear energy transfer (LET)
relative biologic effectiveness (RBE)
oxygenated enhancement ratio (OER)

Question 7

what is LET

Answer 7

linear energy transfer
average energy deposited as ionizing radiation passes through a medium (per unit length of track)

Question 8

LET is measured in what

Answer 8

keV/μm

Question 9

increased LET increases…

Answer 9

the chances of producing a significant biological response

Question 10

what are the 2 radiation categories according to LET

Answer 10

low-linear energy transfer radiation
high-linear energy transfer radiation

Question 11

EMR has high or low LET

Answer 11

low mass, - charge
so LOW LET

Question 12

particulate radiation has high or low LET

Answer 12

can b high mass, high charge
higher LET

Question 13

Is low LET more or less penetrating?

Answer 13

more penetrating

Question 14

how does low LET interect

Answer 14

random interactions along the track, few and sparse

Question 15

is high LET more or less penetrating

Answer 15

less

Question 16

how does high LET ionize

Answer 16

transfers a large amount of energy to a small area

Question 17

what is RBE

Answer 17

relative biologic effectiveness
the relative capabilities of radiation with different LETs to produce a particular biologic reaction

Question 18

what is the conventional dose of reference radiation for RBE

Answer 18

250-kVp xrays

Question 19

what is the Wr of xrays

Answer 19

1

Question 20

what is the Wr of alpha

Answer 20

20

Question 21

what is OER

Answer 21

oxygen enhancement ratio
ratio of dose req to cause a particular biologic response in any oxygen-deprived enviro, to the dose req to do same in oxygenated

Question 22

OER = ?

Answer 22

OER = dose for reaction no O2 / dose for SAME reaction with O2

Question 23

what makes a cell less radiosensitive

Answer 23

more mature, more specialized

Question 24

what is the Law of bergonie and tribondeau

Answer 24

radiosensitivity of cells is directly proportional ato their reproductive activity and inversely peoportional to their degree of differentiation

Question 25

spermatogonia mature into what

Answer 25

spermatozoa

Question 26

eryhtroblasts mature into what

Answer 26

red blood cells

Question 27

stem cells mature into what

Answer 27

differentiated cells

Question 28

Can LET influence radiosensitivity?

Answer 28

yes!

Question 29

what does oxygen do to radiosensititvyt

Answer 29

increases it thfr enhances the effects of ionizing radiation on biologic tissue

Question 30

how is oxygen used in radiotherapy

Answer 30

hyperbaric oxygen is used to increase radiosensitivity of the tumour

Question 31

what is the master/key/molecule

Answer 31

one part in every cell that maintains normal cell function

Question 32

what is target theory

Answer 32

the concept that a master, key, or target is necessary for the survival of the cell

Question 33

what are the 2 classifications of ionizing radiation interaction on a cell

Answer 33

direct action indirect action

Question 34

what type of action do the majority of irradiation effects result from

Answer 34

indirect - because the body is mostly water

Question 35

what is the radiolysis of water

Answer 35

dissociation of water due to ionization

Question 36

what things can ionization of water produce? (4)

Answer 36

free radicals undesireable chem reactions, bio damage cell-damaging substances organic free radical formation

Question 37

what does the radiolysis of water do to target size?

Answer 37

increases it

Question 38

what 2 ion pairs can be created by water radiolysis

Answer 38

HOH+ and e- HOH+ and unstable ion

Question 39

why is HOH+ and e- a better ion pairs?

Answer 39

because they can recombine into stable H2O

Question 40

what happens if HOH+ does not recombine?

Answer 40

it will break apart into smaller molecules

Question 41

what does HOH+ decompose into?

Answer 41

H+ (hydrogen ion) OH* (hydroxyl radical)

Question 42

Why is the decomposition producing OH* bad?

Answer 42

OH* hydroxyl radical is a VERY reactive free radical

Question 43

what results if free e- combines with another water molecule?

Answer 43

H2O + e- = HOH-

Question 44

why is HOH- bad?

Answer 44

decomposes into OH- (hydroxyl ion) and H* (hydrogen radical)

Question 45

why is H* (hydrogen radical) bad

Answer 45

free radical that is VERY unstable

Question 46

why are H* and OH* so bad?

Answer 46

excess energy that can be transferred to other molecules break chemical bonds, cause point lesions

Question 47

what happens if OH* and OH* bind?

Answer 47

H2O2 - hydrogen peroxide poisonous to the cell

Question 48

what happens if a H* and O2 bond?

Answer 48

HO2* hydroperoxyl radical

Question 49

what are believed to be the two most damaging resultants of water radiolysis

Answer 49

H2O2 hydrogen peroxide HO2* hydroperoxyl radical