Unit 1- radiation biology

atom is ionized=

deposit of energy in tissue (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 syndrome

• GI syndrome

• CNS syndrome

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?

coulomb

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

air kerma

EXCAGES

• exposure- coulomb

• absorbed dose- 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

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

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

The sum of the weighted equivalent doses for all irradiated tissues or organs

• Takes into account the effect of the type of radiation used (WR) and the radiosensitivity of the organ or 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:

1gy= 1 sv

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