MOD 3 - Radiation Biology

low energy radiations…

do not have sufficient energy to penetrate bio tissues and ionize atoms

eg. of low energy radiations

• UV light

• microwaves

ionizing radiations have..

sufficient energy and penetrate tissues and interact with the orbiting electrons of atoms

eg. ionizing radiations

• x-rays

• gamma rays

radiobiology

study of the effects of ionizing radiation on the human body

low LET ionizing radiation

photons without mass or charge that cause sparse ionization

eg. low LET ionizing radiation

• x-rays

• gamma rays

low let indirect action

= do not effect critical cell structures directly but the free radicals produced can impact DNA and cause cell death

low let indirect action PROCESS

1. low let photons usually interact with water molecules

2. photon and water interaction leads to radiolysis (water molecule dissociation)

3. this dissociation either doesn’t affect cell damage = water molecule reforms

OR

3. does affect cell damage and forms ions and free radicals

which free radical causes 2/3 of all radiation damage

hydroxyl radical

low let direct action

ionizing radiation interacts with essential cellular structures

low let direct action damage

low LET radiation is typically capable of only single strand DNA breaks (point lesions) which are very repairable, but even the probability of this interaction is very low

high let ionization

includes radiation that has both mass and charge

high let interaction causes

destruction to biologic matter by causing multistrand breaks and double-strand breaks

Types of DNA damage caused by radiation

• single strand break = typically repaired

• base damage = cause mutation

• double strand break = cell death

• cross linking = cause lesions (area of abnormal or damaged tissue)

• rung breakage = cause molecular lesions

chromosome abberation

breaks in the chromosomes due to radiation exposure

target theory

indicates cell death only occurs when DNA is inactivated due to ionizing radiation exposure

targets

• DNA

• RNA

• proteins

• enzymes

Five trends of Radiation Interaction with Biological Materials

1. radiation and cell interaction is random, damage may not occur even if interaction did occur

2. initial deposit of energy into cell is very rapid (10-17s)

3. the area radiation interacts with is random

4. radiation damage on cells, tissue, and organs are indistinguishable from other types of trauma.

5. latent period exists for biological changes to manifest, length of time is dependent on initial dose (min-years)