Chapter 7: Molecular & Cellular Radiation Biology (RADIATION PROTECTION)

Branch of biology concerned with the effects of ionzing radiation on living systems is called

radiation biology

radiation biology includes:

-Sequence of events occurring after the absorption of energy from ionizing radiation

- The action of the living system to make up for the consequences of this energy assimilation

-The injury to the living system that may be

produced

ionizing radiation damages living systems by ________ the atoms comprising the molecular structure of these systems

ionizing (removing electrons from)

Biologic damage begins with the ionization produced by various types of radiation such as:

•X-rays

• Gamma rays

• Alpha particles

• Beta particles

• Protons

Ionized atoms will not bond properly in ________.

molecules

Radiation Energy Transfer Determinants

To understand the way ionizing radiation causes injury or changes the severity of injury to biologic tissue, 3 concepts must be studied:

•1. Linear Energy Transfer (LET)

•2. Relative Biological Effectiveness (RBE)

•3. Oxygen Enhancement Ratio (OER)

Linear Energy Transfer (LET)

average energy deposited per unit of path length

LET is an important factor in assessing _________ and ______ from exposure to ionizing radiation

potential tissue and organ damage

xrays are _______ ionizing over a longer path

sparsely

(wr of 1)

alpha particles are ______ ionizing in a short path

densely

(wr of 20)

xrays have a _______ LET

low

***dont cause much damage**

alpha particles have a _______ LET

high

*cause a lot of damage if they are ingested*

higher charge=

higher LET

alpha particles

lower charge=

lower LET

xrays and gamma rays

high energy=

lower LET

low energy=

High LET

LET and RBE have a ______ proportional relationship

directly

increased LET=

increased RBE

RBE of 5 example:

5x more biological damage than a 250 kev xray beam (reference radiation/ test radiation)

higher weighting factor=

more biological harm

weighting factor of 1

weighting factor of 5

weighting factor of 10

weighting factor of 20

an increase in LET, RBE, and Wr=

increased risk of biological harm

cells are way more sensitive to radiation when they are in an _______ state

oxygenated

normal oxygenation:

aerobic

decreased oxygenation:

hypoxic

no oxygenation:

anoxic

xrays + oxygen=

increased radiosensitivity

alphas + oxygen=

no effect on radiosensitivity because they are already damaging

the OER for xrays is

3

(3x more damaging in an oxygenated cell vs a non oxygenated cell)

the OER for alpha particles is

1

(1x more damaging in an oxygenated cell vs a non oxygenated cell)

aerobic

less radio resistant

hypoxic

more radio resistant

cells that have oxygen

they survive at a lower doe because they are more radiosensitive

cells that have no oxygen

they survive at a higher dose because they are radioresistant

when there is O2 present in a cell=

more sensitive to radiation

when there is NO O2 present in a cell=

they are less sensitive to radiation

can undergo more dose of radiation

fractionation

a treatment radiation dose is broken down into multiple exposures over several weeks to minimize side effects, cannot receive it all at once.

hyperbaric chamber is used to

increase tissue sensitivity

cells are more sensitive to radiation when they are in an

oxygenated state

the higher the tissue weighting factor are

more sensitive to radiation

ex: bone marrow, breasts, lungs, colon, and stomach (0.12)

what has the lowest moderate radiosensitivity:

gonads (0.08) , liver, and thyroid (0.04)

what has the lowest radiosensitivity:

brain (0.01), kidneys, and muscle tissue

blood cells are very

radiosensitivity

most sensitive to radiation

bone marrow, breasts, lungs, colon, and stomach

what blood cell is most radiosensitive

leukocytes, white blood cells

Law of Bergonie and Tribondeau states that the most radiosensitive cells are

immature (at the early stages of its life cycle)

unspecialized (has not yet formed into a certain tissue type)

high reproductive activity (rate at which the cell is dividing and multiplying)

cells that are immature and still developing refers to the word

blast

cells that are mature and fully developed refer to the word

cyte

higher effective dose=

more biologic damage

bone marrow is super

radiosensitive

indirect is more common because it

interacts with water first which makes sense because the cell is 80-85% water

direct action involves

high LET and directly with DNA helix

95% of the time the chromosome will be

repaired (recitation occurs)

restitution

where chromosomes can be repaired, the break rejoins in their original shape with no visible damage (95% of the time)

deletion

part of the chromosome is lost at the time of the next cell division

broken end rearrangement

grossly misshapen chromosomes produced

(two broken ends)

dont happen often

translocation

chromosomes genetic material has been rearranged even though it appears normal

deletion, broken end rearrangement, and translocation cause an

alter of cell function

what is the target for target theory

DNA molecule

"master molecule"

the cell will die if it is struck by a photon that interacts with the DNA in the nucleus

3 Principle Observable Effects Resulting from Irradiation of DNA:

•Cell Death

•Malignant Dz (diseases)

•Genetic Damage

low LET survival curves is called a

shoulder (means some cells were repaired)

the higher the dose (high LET) little to no repair, mostly death

radioinsensitive cells

brain cells

muscle cells

nerve cells

mature, highly specialized, divide slowly if at all

radiosensitice cells

most radiosensitive blood cell

lymphocytes (white blood cells)

=