Biological Effects of Ionizing Radiation & Commonly Used Radiation Units

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1 INAYA MEDICAL COLLEGE (IMC) RAD LECTURE 3, 4 & 5 Biological Effects of Ionizing Radiation & Commonly Used Radiation Units DR. MOHAMMED MOSTAFA EMAM

2 How does radiation injure people? - High energy radiation breaks chemical bonds or DNA molecules. + This creates free radicals, like those produced by other insults as well as by normal cellular processes in the body. The free radicals can change chemicals in the body. These changes can disrupt cell function and may kill cells.

3 DNA is the most important molecule that can be changed by radiation Effects of DNA Damage Gene Expression A gene may respond to the radiation by changing its signal to produce protein. This may be protective or damaging. Gene Mutation Sometimes a specific gene is changed so that it is unable to make its corresponding protein properly Chromosome Aberrations Sometimes the damage effects the entire chromosome, causing it to break or recombine in an abnormal way. Sometimes parts of two different chromosomes may be combined Genomic Instability Sometimes DNA damage produces later changes which may contribute to cancer. Cell Killing Damaged DNA may trigger apoptosis, or programmed cell death. If only a few cells are affected, this prevents reproduction of damaged DNA and protects the tissue. Studies have shown that most radiation-induced DNA damage is normally repaired by the body

4 How does this damage from ionizing radiation effect our bodies? Sufficient Cell Killing Sufficient Genetic Alterations Radiation Sickness Cancer

5 Radiation Dose

6 Radiation Dose One of the most confusing things about understanding radiation effects is visualizing how much radiation is involved. It is very difficult to keep the units which measure radiation straight. A number describing the amount of radiation means nothing without evaluating the units, but this is not easy. For example...

7 ...try to match the letter with the amount of radiation involved in each example Amount of potassium 40 in the body Dose to Atomic bomb survivors You can safety hold this amount of alpha radiation One coast to coast flight A diagnostic X-ray A. Billions of becquerels B. About 250 picocuries C millirem D. 0-5 Gy E. 2 millirads

8 Commonly Used Radiation Units Each of these units has a different technical meaning. All are used by experts to talk about radiation. With so many terms, you can see why it is important to know what the unit means when you are evaluating radiation information. RAD Sievert Becquerel Absorbed dose (Gray or rad) Average dose Organ dose Dose commitment Collective dose Effective dose (Sievert or rem) Committed effective dose Equivalent dose Collective equivalent dose Committed equivalent dose Uniform equivalent dose Dose equivalent Collective dose equivalent Ambient dose equivalent Directional dose equivalent Individual dose equivalent Individual dose equivalent, penetrating Individual dose equivalent, superficial Dose and dose-rate effectiveness factor Man-gray Man-sievert Tissue weighting factor Relative biological effectiveness (RBE) Quality factor (Q) Fatality probability coefficient Nominal fatality probability coefficient Radiation weighting factor (w R ) Linear energy transfer (LET) Radioactivity (Becquerel or curie)

9 Understanding Radiation Units Activity The number of times, each second, a radioactive material decays and releases radiation. Exposure Amount of ionization per mass of air due to x and gamma rays. Dose (Absorbed) The amount of radiation energy absorbed into a given mass of tissue. Dose (Equivalent) H & Effective dose equivalent (HE ) Measures the energy per unit mass times adjustments for the type of radiation; Involved Radiation (quality factor) and the biological response in the tissue (a weighting factor). * Equivalent dose converts dose into a measure of risk.

10 Understanding Radiation Units Activity Disintegration/sec=1 Becquerel (Bq) 37 billion Bq = 1 curie Exposure Roentgen Dose (Absorbed) 1 joule/kg=1 Gray(Gy) 1Gray=100 rad =100,000 mrad Dose (Equivalent) Gray x quality factors= Sievert (Sv) 1 Sievert =100 rem =100,000 mrem Standard Units S.I. Units

11 ACTIVITY What is the meaning of activity? This is the expectation rate of spontaneous nuclear transitions in a source. Becquerel = 1 disintegration/second. This is the SI unit for measuring radioactivity. Curie. Defined as 3.7 x disintegrations per second= 3.7 x Bq. This is the activity of 1 gram of radium in equilibrium with its decay products The Rutherford. 1 Rd = 10 6 Bq.

12 ACTIVITY How much is a Becquerel (Bq)? The natural 40 K activity in the body of an adult human of normal weight is Bq. There is an average of about 50 Bq per cubic meter of air inside a home from radon. Even though a 60 Co source of strong gamma radiation containing billions of Bq can kill you if you are standing 5 meters from it, it is harmless at a distance of 100 meters. A Bq has 27 times more disintegrations than a pci, but is still a very small amount of radiation.

13 ACTIVITY How much is a picocurie (pci)? Many times the media reports excess radiation in picocuries. It takes 1,000,000,000,000 pci to make 1 Curie. A Becquerel is 1 disintegration/second. It takes 27 pci to make one Bq, so a pci represents less radioactivity that a Bq and results in very, very little dose.

14 Exposure What is the meaning of exposure? The quantity of X- or gamma-radiation to which an object is exposed. This electromagnetic radiation produces ionization within the object. Amount of ionization per mass of air due to x and gamma rays. This is the amount of ionization produced by photons in air. Since it is impossible to directly measure the absorbed dose in tissue, the measurement of radiation is performed in air. It is measured in roentgen (R) and Sieverts (Sv).

15 Exposure What is the meaning of exposure? Roentgen. Röntgen or Roentgen may refer to: Roentgen (unit), unit of measurement for ionizing radiation, named after Wilhelm Röntgen Wilhelm Röntgen ( ), German physicist, discoverer of X-rays

16 Exposure What is the meaning of exposure? Roentgen. This is defined as the amount of gamma radiation that produces 1 cm 3 of air ionization equal to 1 electrostatic unit (esu). 1 esu = 3.3 x coulombs = 2 x 10 9 ion pairs/cm 3 of air. Equivalent to 2.58 x 10-4 C/kg air ( J/kg of air). 1R is approximately 10-2 Sv.

17 ROENTGEN Roentgen was defined as 1R=1 electrostatic unit (esu)/cm 3 air at standard temp and pressure(stp) = Δ Q by Δ m; Where: Δ Q is the absolute value of total charge of ions of one sign produced in air when all the electrons liberated by photons in air of mass (Δ m). X = Δ Q/ Δ m Conventional units is Roentgen SI unit : c/kg 1R=2.58*10-4 c/kg

18 ABSORBED DOSE What is the meaning of absorbed dose? This is the energy imparted/ given to matter by charged or uncharged ionizing particles.

19 ABSORBED DOSE What is the meaning of absorbed dose? Gray 1Gy = 1 J/kg. This is the SI unit for absorbed dose of ionizing radiation. The Rad. 1 rad = 10-2 Gy (= 10-2 J/kg). This is defined as the amount of radiation that deposits 100 ergs (10-5 J) in each gram of tissue it traverses. Two different types of radiation may, however, produce different degrees of biological damage even though they are both rated as 1 rad.

20 ABSORBED DOSE How much radiation is an X-ray? 1Gray=100 rad =100,000 mrad So, the average chest X-ray may give a dose; 10 millirads = 0.01 rads = Gray. A millirad is comparatively small. Average normal background level of radiation is 370 mrad/year. One Gray is a relatively large amount of radiation. If 3-4 Gray are delivered over a short time to the whole body, they can be deadly.

21 EQUIVALENT DOSE What is the meaning of equivalent dose? This is the quantity used to express on a common scale the risk to exposed persons from all ionizing radiations.

22 Dose Equivalent Since different radiations have different harmful effects on human tissues. It is measured in Sieverts (Sv). H = D Q.F. H = equivalent dose (Sv) D = dose (Gy) Q.F. = radiation quality factor of radiation (no unit) 1 Sv = 1 J/kg = 100 rem Biological effects of ionizing radiation 22

23 EQUIVALENT DOSE What is the meaning of equivalent dose? Sievert 1 Sv = 1 J/kg. The Sievert is equal to the absorbed dose in tissue (Gy) multiplied by the 'quality factor' for the particular type of ionizing radiation. The quality factor is a dimensionless number representing the relative effect produced by the same absorbed doses of different types of radiation. In older terminology the quality factor was referred to as the Relative Biological Effectiveness (next slides) rem (roentgen equivalent man): 1 rem = 10-2 Sv (= 10-2 J/kg). This is defined as the amount of radiation which when absorbed by a person, will produce the same biological effects as the absorption of 1 roentgen of x- ray or gamma-ray radiation.

24 Dose Equivalent Conventional unit is Roentgen equivalent in man(rem) SI unit is Sivert 1rem=10 Sivert RADIATION Q.F. X-rays & gamma rays 1.0 Electron (incld. β-rays) of energy >30kv Thermal ( slow) neutron Fast neutrons 20

25 EQUIVALENT DOSE Radiation Q. Factors Illustration Type and Energy Range X and γ rays, electrons, positrons and muons 1 Neutrons <10 kev 5 Neutrons 10 kev to 100 kev 10 Neutrons >10 kev to 2 MeV 20 Neutrons > 2 MeV to 20 MeV 10 Neutrons >20 MeV 5 Protons, other than recoil protons and energy 2 >2 MeV Alpha particles, fission fragments, nonrelativistic heavy nuclei Q. Factor 20

26 EQUIVALENT DOSE What is Radiation Quality Factor? Different types of radiation behave in different ways. In order to compare the amount of risk or biological change that occurs, quality factors are introduced. Biologic effects of radiation depend not only on dose but also on the type of radiation.

27 EQUIVALENT DOSE What is Radiation Quality factor? For example: The damage produced by 1 Gy of x-radiation is equal to that produced by 1 Gy of gamma radiation. Thus, gamma radiation has a quality factor of 1 or 1 Gy gramma rays x 1 =1 Sv. The damage produced by 20 Gy of x-radiation is equal to that from 1 Gy of alpha radiation. Alpha radiation has a quality factor of 20 or 1 Gy of alpha radiation x 20 = 20 Sv. Quality factors for other types of radiation are between 1 & 20.

28 EQUIVALENT DOSE What is the meaning of equivalent dose? To define the rem quantitively, a relative biological effectiveness (RBE) has been established (number of rem) = (number of rad) x RBE. The following table gives RBE for the usual types of radiation. RELATIVE BIOLOGICAL EFFECTIVENESS Type of radiation rad x RBE = rem x-rays and gamma-rays Beta radiation Protons Alpha particles Fast Neutrons Slow Neutrons

29 EQUIVAENT DOSE How much is a Sievert (Sv)? Radiation induced cancers have been seen in the atomic bomb survivors exposed to as low as 0.2 Sieverts. A Sievert is a relatively large amount of radiation. The annual background radiation exposure for a typical American is Sv, 3.7 msv or 370 millirem. 1 Sv = 100 rem 1000 msv = 100,000 mrem

30 EQUIVAENT DOSE How much is a millirem (mrem)? The annual background radiation exposure for a typical American 370 mrems. The average dose from watching color TV is 2 mrem each year. The granite from Grand Central Station exposes its employees to 120 mrem of radiation each year People in Denver receive 50 mrem more each year than those in LA because of the altitude. The nuclear industry contributes to less than 1 mrem/year to an individual s background radiation. A millimrem is a small unit of measure.

31 EQUIVALENT DOSE EFFECTIVE (H E ) Whole body exposures are rarely uniform. Tissues vary in sensitivity to radiation induced effects Effective dose is a measure of radiation and organ system specific damage in man The effective dose equivalent H E =Sum of H t x W t H t = mean dose equivalent received by the tissue t W t =weighing factor of tissue t

32 EQUIVALENT DOSE EFFECTIVE (H E ) Tissue Weighting Factors Illustration Bone surface Bladder Bone Marrow Gonads Skin Breast Colon Liver Lung Esophagus Stomach Thyroid Remainder

33 Dose-rate The effectiveness of the dose is dependent on the dose-rate Dose 1 bottle of Aspirin or 250,000 mrem of Radiation Dose -Rate Over 50 seconds?? Or over 50 years?? Over 50 seconds?? Or over 50 years?? Death Minimal health risk Death Minimal health risk