Unit 1- radiation biology

atom is ionized=

biological effects begin here

ionization

photon hits an electron, electron is loose

Radiation interacts at the ___ level

atomic

Atoms combine to form ___

molecules (which make the cells & organs of the body)

X-ray energy deposited in the atom & ionization can affect…

the bonds holding atoms together (causing the molecule to break apart)

radiation is more likely to… (in medicine)

kill a cell, rather than cause cancer

When do early effects of radiation occur?

minutes, hours, days, or weeks after exposure

Examples of early tissue interactions

• nausea/ fatigue

• erythema

• hair loss (epilation)

• blood disorders

Why do early effect of radiation occur

typically from high doses given acutely

Acute radiation syndrome

radiation sickness

Whole body exposure examples: early effects of radiation

• hemopoietic

• GI

• CNS

Local tissue damage examples: early effects of radiation

• skin, gonads

**most common in radiation therapy

when do late tissue interactions typically occur?

months or years after exposure

examples of late tissue interactions

• cataracts

• fibrosis

• organ atrophy

• reduction in fertility/ sterility

• cancers

• local tissue damage (skin, cataracts)

why do late effects of radiation occur?

lower doses that are given over long periods of time, but can also occur from higher acute exposure

fetal effects on radiation

• embryo/fetus exposed in utero to low or high levels of radiation

examples of fetal effects of radiation

• prenatal death

• neonatal death

• congenital malformation

• childhood malignancy

• diminished growth & development

What unit is used to measure the amount of radiation exiting the tube? (OUtput)

cOUlomb

__ can be described as the amount of radiation produced in air when ionizing radiation is present

air kerma

EXCAGES

• exposure- coulomb

• absorbed dose/ air kerma- gray

• equivalent/ effective dose- sievert

Coulomb/kg

• exposure to ionizing radiation in air; electrical charge

• measures OUTPUT of machines

• only applies to x-rays & gamma rays

Air kerma (gy)- acronym

Kinetic energy released in matter

Air kerma metric unit

joules/kg

1gy= 1j/kg

___ is preferred over coulomb/kg

air kerma

Air kerma (gy)

• Kinetic energy transferred from photons to electrons during ionization/ excitation

• expresses how energy transfers from beam to air

if air kerma is shown ‘per minute’ it is showing air kerma from__

fluoro

Absorbed dose in air=

to be delivered to patient (air kerma)

DAP meter (dose area product)

• measures amt of energy delivered to pt by x-ray beam

• total sum of air kerma over exposed area of patient’s surface

where is DAP meter located?

beyond collimator (between collimator & patient)

DAP equation

absorbed dose x collimated area

(most accurate measurement for pt dose)

Measurement for DAP

mgy-cm²

absorbed dose is measured in

gray

Absorbed dose

• ionizing radiation that passes through the patient or stays there (absorbed)

  • some gets absorbed due to density (bone) & higher atomic number

what is responsible for biologic damage to the tissue that is exposed?

absorbed dose

what unit is used to measure the biologic effects of radiation (effective/ equivalent dose)

sievert

What is the radiation weighting factor?

• takes into account the radiation type & energy range that may cause biologic damage

equivalent dose

• Average dose in a tissue or organ in the human body and its associated radiation weighting factor

• compares biologic damage to different types of radiation

equivalent dose equation

•EqD = D  x  W_R

_{D= absorbed dose}

W_{R= weight factor}

1 mGy= __mSv

1

what is the quantity of radiation received by radiation workers? (badge reports)

equivalent dose

 The concept of tissue weighting factor is used to do what?

• Takes into account the radiosensitivity of the organ or tissue irradiated

effective dose

sum of the type of radiation used(WR) and the tissue irradiated (WT)

effective dose equation

•EfD = Dose  x  W_R  x  W_T

what is the best measure to overall risk of exposure to humans from ionizing radiation

effective dose

radiation weighting factors: x-rays, gamma rays, alpha particles

x-rays= 1

gamma rays=1

alpha particles= 20

radiation in tissue

absorbed dose (D)- patient

• gray

• joules/kg

effects in tissue (biologically)

equivalent dose (EqD) (radiation quality/harm)

• Sv

• D x Wr

effective dose (EfD) (patient overall risk)

• Sv

• D x Wr x Wt

Conversion help:

• 1 Gy= 1 Sv

• 1000 mGy= 1 Gy

example for conversions

• 1000 mGy = 1 Gy

  • Divide mGy by 1000 or move decimal to left 3

    • Example: 150mGy = 0.15

• 1 Gy = 1000 mGy

  • Multiply Gy by 1000 or move decimal to right 3

    • Example: 0.5Gy = 500mGy

slide 29

know how to convert, & the yellow highlighted box

from report 116

Cumulative occupational dose limit

10 x age

• 10 mSv or .01 Sv

Annual occupational dose limit

50 msv or .05 Sv

Lens of eye occupational dose limit

150 msv or .15 Sv

skin/ extremities occupational dose limit

500 mSv or 0.5 Sv

embryo/fetus dose limit- 1 month

0.5 mSv or .0005 Sv

embryo/fetus dose limit entire gestation period

5 mSv or .005 Sv

General public annual dose limit- continuous

1 mSv or .001 Sv

general public annual limit- infrequent

5 mSv or .005 Sv

lens of eye dose limit- for public

50 mSv or .05 Sv

skin, extremities dose limit for public

50 mSv or .05 Sv

what is within the nucleus

protons & neutrons

what is outside of the nucleus

electrons

closer an e-shell is to the nucleus, the ___ the binding energy

higher

max # of electrons in a shell increases with..

the distance of the shell from the nucleus

outer shell can have a max # of ___ electrons

8

electron shell equation

2n²

shell orders

K, L, M, N, O, P

K= highest binding energy (requires most to get rid of)

P= lowest binding energy

in a neutral/ balanced atom, the total # of electrons in shells is equal to what

#of protons in the nucleus

the larger the atom, the more __ needed to ionize

energy

compton interaction ionizes an ___ electron

outer shell

photoelectric interaction ionizes an ___ electron

inner shell

how much keV to ionize the inner shell of tungsten?

70 keV or higher

what is the first step in how x-rays create images or damage cells

ion pairs

steps of ionization- ion pair

1. atom is neutral

2. an x-ray photon strikes the atom w/ enough energy to knock an electron out of its orbit

3. results in ion pair

• negative electron (anion)- sometimes called photoelectron

• positive ion (cation)- the rest of the atom, which lost a negative electron

what is made of 2 or more atoms bonded together

molecules

molecules are formed by __ and __ bonding

ionic & covalent

valence electrons are what?

• electrons in the outmost shell of an atom

• atoms tend to gain, lose, or share valence electrons to achieve filled outer shell

ionic binding

• attraction between POSITIVELY charged ions & NEGATIVELY charged ions that forms AFTER electrons are TRANSFERRED from 1 atom to another

• GIVING AN ELECTRON AWAY

an atom of sodium + an atom of chlorine=

sodium chloride (Na + Cl= NaCl)

example of ionic bond (sodium & chloride)

• Sodium has one e- in outermost shell and
    chlorine has space for one more e-

• Sodium is now (+) because it gave an e- and
     chlorine is now (-) because it gained an e-

covalent bonding

• when two atoms share one or more pairs of electrons so that both atoms can fill their outer (valence) shells.

• SHARING OF ELECTRONS

example of covalent bonding with oxygen & hdyrogen

•Oxygen has 6 electrons in outermost shell and hydrogen has 1 and there are 2 hydrogen atoms

• So in water, two hydrogen atoms each share an electron with the oxygen to form a molecule

mass number (A number) is

#of protons AND # of neutrons in a nucleus

Atomic number (Z number) is

#of protons in a nucleus (determines element we are looking at)

isotopes

• Atoms with the same number of protons and electrons, but a different number of neutrons
 (which does NOT change the element just the mass#)

barium atomic (Z) number is__ and mass number is ___

56 (protons) & 138 MASS

Barium atomic mass is

138

coherent (classical) scattering

•X-ray interacts with an atom and excites it

• change in direction WITHOUT energy loss

• seen with low energy (less than 10 keV)

• do nothing for the image at all

isotopes are atoms of an element that differ in:

number of neutrons (mass #)

this is an example of?

coherent (classical)

compton scattering

•Ionization of outer shell e-

•Incident photon will scatter in a different direction

**adds unwanted exposure & reduces contrast

what type of scatter is this?

compton

what scatter attributes most dose to techs

compton

the process of photoelectric absorption is an interaction between

x-ray photon & inner-shell electron

photoelectric absorption

• Ionization of inner shell e-

• Inner shell e- ejected = X-ray photon absorbed,
      becoming ‘photoelectron’

• Atom is unstable because inner shell e- is missing

• bone absorbs this the most!!

• Inner shell vacancy filled by an outer shell e-

  • Characteristic Cascade

what process results in the major part of image production/ contrast?

photoelectric absorption

what happens to the energy of the x-ray photon during pair production?

 Energy of the photon is absorbed and transformed into matter composed of two particles:

• negatron

• positron.

pair production

• A very high‑energy X‑ray passes close to the nucleus.

• The photon disappears and becomes:

     One electron  (−)  and One positron (+)

what process is this?

photoelectric absorption

what process is this?

pair production