RADİATİON PHYSİCS, X-RAY SAFETY AND PROTECTİON

Başar Sarikaya, M.D.Associate Professor of Radiology

Yeditepe University

What is Radiation? Radiation: is the transfer of energy in

the form of particles or waves.

What is Energy? Energy: the ability to do work

(Force·Distance)

What is Energy?

Energy: the ability to do work (Force·Distance)

Electromagnetic Radiation Electromagnetic radiation (EM

radiation or EMR) is one of the fundamental phenomena of electromagnetism, behaving as waves propagating through space, and also as photon particles traveling through space, carrying radiant energy.

Electromagnetic Spectrum The types of electromagnetic radiation are

broadly classified into the following classes:I. Gamma radiationII. X-ray radiationIII. Ultraviolet radiationIV. Visible radiationV. Infrared radiationVI. Terahertz radiationVII. Microwave radiationVIII. Radio waves

Electromagnetic Spectrum

Ionizing radiation Radiation with sufficiently

high energy can ionize atoms. This occurs when an electron is stripped (or "knocked out") from an electron shell of the atom, which leaves the atom with a net positive charge. Because living cells and, more importantly, the DNA in those cells can be damaged by this ionization, it can result in an increased chance of cancer. 

photons and particles with energies above about 10 electron volts (eV) are ionizing.

Ionizing radiation Alpha particles, beta particles, cosmic

rays, gamma rays, and X-ray radiation, all carry enough energy to ionize atoms. In addition, free neutrons are also ionizing since their interactions with matter are inevitably more energetic than this threshold.

What is X-Rays? X-radiation (composed of X-rays) is a

form of electromagnetic radiation. Most X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 100 eV to 100 keV.

Wilhelm Conrad Roentgen(27 March 1845 – 10 February 1923)Nobel Prize in Physics 1901

December 22, 1895

Nouvelle Iconographie de la Salpetrière", a medical journal. (1896)

1874-1901

1897

X-Ray Production X-rays are produced when high velocity

electrons are decelerated (slowed or stopped) or by a nucleus of an atom especially by high atomic number material, such as the tungsten target (anode) in a X-ray tube.

X-Ray Production An electrically heated filament (cathode) within the X-

ray tube generates electrons that are accelerated from the filament to the tungsten target by the application of a high voltage to the tube. 

The energy gained by the electron is equal to the potential difference (voltage) between the anode and cathode.   This electron energy is typically expressed in kilovolts (kV). 

The accelerated electron interacts with the target (anode) nucleus.  As the electric field of the electron interacts with nucleus, the electron releases energy in the form of X-rays.  This method of of x-ray production is called bremsstrahlung or braking radiation

X-Ray Production

X-Ray Machine Parameters The quantity  of electron flow (current)

in the X-ray tube is described in units of milliamperes (mA). The rate of X-ray production is directly proportional to the X-ray tube current. Higher mA values indicate more electrons are striking the tungsten target, thereby producing more X-rays.

The voltage (kVp) primarily determines the maximum X-ray energy produced but also influences the number of X-rays produced.

X-ray Interaction with Matter

No interaction: X-ray passes completely through tissue and into the image recording device. Producing an image

Complete absorption: X-ray energy is completely absorbed by the tissue. This produces radiation dose to the patient. 

Partial absorption with scatter: Scattering involves a partial transfer of energy to tissue, with the resulting scattered X-ray having less energy and a different trajectory. This interaction does not provide any useful information (degrades image quality) and is the primary source of radiation exposure to staff.

X-ray Interaction with Matter

The probability of X-ray interaction is a function of tissue electron density, tissue thickness, and X-ray energy (kVp). Electron dense material like bone and contrast dye attenuates more X-rays from the X-ray beam than less dense material (muscle, fat, air). The differential rate of interaction provides the contrast that forms the image. 

X-ray Interaction with Matter

As electron density increases, the interaction with X-rays substantially increases. Higher atomic number materials have increased electron density. 

Bone, which is substantially comprised of calcium, produces more attenuation, than tissue, which is comprised of carbon, hydrogen and oxygen (all of which have a lower electron density or atomic number than calcium).  Thus, the image of bone and soft tissue has contrast, or difference, between bone and soft tissue.

X-ray Interaction with Matter

Photoelectric absorption

Compton scattering the predominant interaction between X-

rays and soft tissue in medical imaging

Rayleigh scattering

Where do we use X-Rays in Radiology?

All plain X-ray films Fluoroscopic Imaging Mammography Computed Tomography Angiograms (including DSA)

Where do we use X-Rays in Radiology?

No X-rays, therefore no ionizing radiation

Ultrasonography Magnetic Resonance Imaging

X-Ray Protection Everyone on the planet is exposed

to background radiation, including from internal body sources, with a worldwide average annual effective dose of 2.4 mSv. Airline crews on long flights experience a higher level of cosmic radiation and can receive doses of 4-5 μSv each hour, for instance, so that one flight may result in the equivalent of a number of chest X-rays for them and their passengers. The annual effective doses for aircrew are typically on average 1–2 mSv for those employed on short-haul flights and 3–5 mSv for those on long-haul flights

X-Ray ProtectionFor this procedure: * Approximate effective

radiation dose is:Comparable to natural background radiation for:

** Additional lifetime risk of fatal cancer from examination:

ABDOMINAL REGION:Computed Tomography (CT)-Abdomen and Pelvis

10 mSv 3 years Low

Computed Tomography (CT)-Abdomen and Pelvis, repeated with and without contrast material

20 mSv 7 years Moderate

Intravenous Pyelogram (IVP) 3 mSv 1 year LowBONE:Radiography (X-ray)-Spine 1.5 mSv 6 months Very LowRadiography (X-ray)-Extremity 0.001 mSv 3 hours NegligibleCENTRAL NERVOUS SYSTEM:Computed Tomography (CT)-Head 2 mSv 8 months Very LowComputed Tomography (CT)-Head, repeated with and without contrast material

4 mSv 16 months Low

Computed Tomography (CT)-Spine 6 mSv 2 years LowCHEST:Computed Tomography (CT)-Chest 7 mSv 2 years LowComputed Tomography (CT)-Chest Low Dose 1.5 mSv 6 months Very Low

Radiography-Chest 0.1 mSv 10 days MinimalDENTAL:Intraoral X-ray 0.005 mSv 1 day NegligibleHEART:Coronary Computed Tomography Angiography (CTA)

12 mSv 4 years Low

Cardiac CT for Calcium Scoring 3 mSv 1 year LowMEN'S IMAGING:Bone Densitometry (DEXA) 0.001 mSv 3 hours NegligibleNUCLEAR MEDICINE:Positron Emission Tomography – Computed Tomography (PET/CT)

25 mSv 8 years Moderate

WOMEN'S IMAGING:Bone Densitometry (DEXA) 0.001 mSv 3 hours NegligibleMammography 0.4 mSv 7 weeks Very Low

X-Ray Protection Dose limits for staff: annual effective dose limits of 20 mSv for occupationally-

exposed people (averaged over 5 years, with an annual limit of 50 mSv in any single year) and of 1 mSv for the public are recommended by the ICRP - along with additional limits for the skin, the hands and feet, and the lens of the eye and for pregnant workers.

Personal dose monitors are therefore worn by radiation workers to ensure that doses are below the annual limits and to assess their radiation safety practices. Annual staff doses are of the order of 0.25 mSv for radiographers, 0.75 mSv for radiologists and 2.5 mSv for interventionists. It is important to realize that the dose limits should not be considered as acceptable levels, but rather as maximum values which should not be exceeded.

X-Ray Protection Three fundamental principles

for radiation protection have been developed by the ICRP for any exposure to ionizing radiation:

Justification of exposure; Optimization of protection; Application of Dose Limits.

X-Ray Protection An implication of the principle of

optimization is that all exposures should be kept as low as reasonably achievable (ALARA). This should be applied with both economic and societal factors taken into account which implies that the level of protection should be the best available given the circumstances.

X-Ray ProtectionTime scaleFractions of

seconds

Seconds

Minutes

HoursDays

WeeksMonths

Years

Decades

Generations

EffectsEnergy absorption

Changes in biomolecules(DNA, membranes)

Biological repair

Change of information in cell

EffectsEnergy absorption

Changes in biomolecules(DNA, membranes)

Biological repair

Change of information in cell

Mutations in a

Germ cell Somatic cell

Leukaemia

or Cancer

Hereditary effects

Radiation EffectsEarly

(deterministic only)

LocalRadiation injury ofindividual organs:functional and/or

morphologicalchanges withinhrs-days-weeks

CommonAcute radiation disease

Acute radiation syndrome

Late

DeterministicRadiation dermatitisRadiation cataractaTeratogenic effects

StochasticTumours LeukaemiaGenetic effects

Radiation Effects Deterministic effects develop due to

cell killing by high dose radiation, appear above a given threshold dose, which is considerably higher than doses from natural radiation or from occupational exposure at normal operation, the severity of the effect depends on the dose, at a given high dose the effect is observed in severe form in all exposed cells, at higher doses the effect cannot increase.

Radiation Effects Stochastic effects develop due to

mutation effect of low dose radiation, the threshold dose is not known accurately; it is observed that cancer of different location appears above different dose ranges, the severity of the effect does not depend on the dose, but the frequency of the appearance of the (probabilistic) effect in the exposed population group is dose dependent, (in most cases) linearly increasing with the dose.

Radiation Effects Carcinogenic effects have been known practically

since the discovery of radioactivity and since the first case of radiation-induced cancer was described in 1902.

The epidemiological assessment was made from over 575 cancers and leukaemias for the 80,000 survivors irradiated at Hiroshima and Nagasaki, and about 2,000 cancers of the thyroid in children in the Chernobyl region.

The actual data does not enable us to show a risk of cancer at greater than 0,1 Gy by acute irradiation. Nevertheless, it is considered that risk of cancer and the relationship dose/risk remains linear for doses below 0,1 Gy.

Radiation EffectsLatency period of cancers after exposure

Thank you for your attention!