Dose Response, Fractionation, LET and RBE

Question 1

LET

Answer 1

energy transferred per unit length of track (keV/𝝁m). Can be track or E average

Question 2

fol sparsely ionizing radiation

Answer 2

track and E averages are similar

Question 3

Correlates better with biological responses

Answer 3

E average

Question 4

The higher the E

Answer 4

the lower the LET for a given particle

Question 5

Relative Biological Effectiveness - RBE

Answer 5

of some test radiation (r) is the ratio Dx/Dr, where Dx and Dr
are the doses of 250 kV x-rays and the test radiation, respectively,
required to produce equal biological effects

Question 6

The RBE generally increases

Answer 6

as the dose decreases

Question 7

RBE is greater for many low dose fractions than for a single dose

Answer 7

true

Question 8

RBE lower

Answer 8

for curves with little or no shoulder (X vs neutron)

Question 9

Peak RBE reached at E

Answer 9

100keV/𝝁m. Same for many cells

Question 10

The probability of causing DSBs of x-rays

Answer 10

is low, low RBE

Question 11

LET > 100keV

Answer 11

waste of E, overkill- inefficient as deposits more E than needed for DSB

Question 12

Factors that determine RBE

Answer 12

LET, D, Number of fractions, D rate, Biosystem

Question 13

OER decreases

Answer 13

as LET increases

Question 14

radiation weighting factor WR

Answer 14

the dimensionless multiplier used to place biological effects from exposure to different types of radiation on a common scale.

Question 15

Equivalent Dose

Answer 15

Absorbed Dose x WR [Sv]

Question 16

Tissue Weighting Factor WT

Answer 16

the relative contribution of each tissue or organ to the total detriment resulting from uniform irradiation of the whole body

Question 17

Effective Dose

Answer 17

𝚺 Absorbed Dose x WR x WT

Question 18

Prolonging overall time within the normal radiotherapy range

Answer 18

has a little sparing effect on late reactions, but a large sparing effect on early reactions

Question 19

The dose-response relationship for late-responding tissues is

Answer 19

more curved than for early-responding tissues

Question 20

𝛂/𝛃 ratio for early effects

Answer 20

larger than for late effects as 𝛂 dominates. at low doses.

Question 21

Late-responding tissues are

Answer 21

more sensitive to changes in fractionation

patterns than early-responding tissues

Question 22

biological effect formula

Answer 22

E=𝜶d+𝜷d^2=𝜶(nd)(1+d/𝜶/𝜷)

Question 23

for early responding tissues 𝜶/𝜷

Answer 23

10Gy

Question 24

for late responding tissues 𝜶/𝜷

Answer 24

3Gy

Question 25

example

Answer 25

30 fractions of 2 Gy for 6 weeks (5 days a week): E/𝜶=nd(1+d/𝜶/𝜷)=60(1+2/10)=72Gy for early responding and 60(1+2/3)=100 for late

Question 26

Committed Effective Dose

Answer 26

Committed equivalent dose to individual organs or tissue resulting from the
intake of a radionuclide, multiplied by the appropriate WT and then summed.

Question 27

Committed Equivalent Dose

Answer 27

In the case of irradiation from internally deposited radionuclides: the integral
over 50 years of the Equivalent Dose in a given tissue (Sv). (equal to annual equivalent dose for short-lived and greater for long-lived isotopes)

Question 28

Somatic Effects

Answer 28

related to body health of an irradiated person

Question 29

Acute effect

Answer 29

Radiation sickness (nausea, vomiting, secondary infections due to depletion of
white blood cells)
• Death that occurs

within minutes or up to several months

Question 30

LD50(30) for human

Answer 30

3.5-4.5 Sv. Can be raised to 7 with antibiotics

Question 31

Tolerance dose

Answer 31

an estimated dose that might cause injury over a certain period of time

Question 32

TD5/5

Answer 32

5% chance of injury occurring over the next 5 years

Question 33

Prodromal syndrome

Answer 33

nausea, vomiting, etc

Question 34

Latent period

Answer 34

few hours to a few weeks. People report feeling better

Question 35

Manifest illness

Answer 35

The patient feels worse after the latent period.

Question 36

Recovery or death

Answer 36

may last for years. If a death hasn’t occurred in a few months then it is likely that the subject will recover

Question 37

At very high doses (> 20 Gy)

Answer 37

the collapse of the central
nervous system and the cardiovascular system that leads to shock
and prompt death

Question 38

~100 Gy of gamma-rays results

Answer 38

in death in 24 to 48 hours

Question 39

at dose 10 Gy

Answer 39

Gastrointestinal Syndrome, leads to death in 3-10 days. Cells responsible for the absorption of water and electrolytes from the gastrointestinal tract are being killed.nausea, vomiting, loss of appetite, diarrhea, inanition

Question 40

Hematopoietic Syndrome (Bone Marrow Syndrome) – 2.5-5 Gy

Answer 40

Signs: bleeding, infections, and anemia

• Death 30-60 days

Question 41

Radionecrosis, deep ulceration

Answer 41

> 50 Gy

Question 42

Erythema; distinguishable from thermal burn; minutes to weeks postexposure,
depending on dose

Answer 42

6 Gy:

Question 43

Cataract

Answer 43

deterministic effect with a threshold may be linear - no threshold. An annual limit of 15 rem (0.15 Sv) to the eye

Question 44

Deterministic Effects

Answer 44

Always has threshold dose
below which effects not
observed, above which severity is proportional to the dose.

Question 45

Stochastic Effects

Answer 45

The severity of stochastic effects

is independent of dose