Veterinary Radiation Safety

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Veterinary Radiation Safety

• X-Ray (Diagnostic)
• Nuclear Medicine
• Other

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Changes in Diagnosis Treatment Options
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Things to look for

• Radiation safety of veterinary personnel during
• handling of animals
• Dealing with excretia and bodily fluids
• Types of radiation generating machines and
  radionuclides utilized
• Calibration equipment
• Detection equipment

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General Radiology

• The image, or a x-ray film, is produced when a
  small amount of radiation passes through the body
  to expose sensitive film on the other side. The
  ability of x-rays to penetrate tissues and bones
  depends on the tissue's composition and mass. The
  difference between these two elements creates the
  images.
• The chest x-ray is the most common radiological
  examination.
• Contrast agents, such as barium, can be swallowed
  to highlight the esophagus, stomach, and
  intestine and are used to help visualize an organ
  or film.

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Explanation - X-ray Production

• Accelerated electrons bombard the anode
• X-rays emerge with a scattering angle profile
• Beam collimation is inserted to reduce angle of
  divergence

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X-Ray Beam Spectrum - 100 kVp

• A. Hypothetical total Bremsstrahlung beam
• B. - Spectrum from tungsten target without
  filtration
• C. Spectrum with filtration equivalent to 2.4 mm
  Al (inherent added)

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Explanation of X-ray Terms

• mAs (milli-amp second)
• governs the quantity (e.g. intensity) of X-rays
  produced.
• directly proportional to patient dose. Double
  mAs, double dose.
• kVp (kilovolt peak)
• governs quality of the X-ray beam
• Relates to energy of the beam
• influences image quality.
• effects image contrast (ability to distinguish
  regions).
• higher kVp radiographs show greater density and
  longer scale of contrast.
• For radiographs, setting the kVp as high as
  possible, without a loss of contrast, will give
  the lowest patient dose because a greater
  fraction will penetrate through the body to the
  imaging medium.

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Nuclear Medicine

• Also referred to as scintigraphy, is a sensitive
  diagnostic procedure.
• It often can detect abnormalities before they
  become apparent on other imaging studies.
• To perform a nuclear medicine procedure, a small
  quantity of a radioactive tracer is administered
  to the animal.

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Nuclear Medicine

• The most common radioisotope used is
  Technetium-99m (99mTc)
• Technetium-99m has a short half-life (6 hours)
  and 94 of it will decay within 24 hours.
• A gamma camera is used to record the distribution
  of the radiotracer within the body.
• The radiotracer can be attached to a variety of
  biologically active chemicals to localize in
  certain areas of the body. Above is an example of
  a bone scan in a normal dog. The study was
  performed by injecting 99mTc-MDP. The 99mTc-MDP
  will localize in bone proportional to the
  metabolic activity of the bone.

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Scintagraphy

• One of the most common uses of bone scintigraphy
  is to detect bone metastasis
• Below is an example of a dog with multiple sites
  of bone metastases seen as multiple areas of high
  intensity uptake.

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Feline hyperthyroidism

• Recently been recognized as the most common
  endocrine disorder of the cat.
• Elevated circulating levels of the thyroid
  hormones thyroxine (T4) and triiodothyronine (T3)
  that occur in hyperthyroidism result in a
  multisystemic disease.

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Feline hyperthyroidism

• Radiation safety precautions require that cats
  remain hospitalized following their 131I therapy
  until they have eliminated a majority of the
  radioactive iodine from their bodies.
• This typically requires a hospitalization of 3 to
  7 days. Radioactive iodine therapy is considered
  the optimum treatment for feline hyperthyroidism.
  
• Involves a single nonstressful procedure that is
  without associated morbidity or mortality.

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Feline hyperthyroidism

• Significant side effects have not been observed.
  Unlike surgery, anesthesia is not necessary.
• A single dose of radioactive iodine will result
  in a return to persistent normal thyroid function
  in a majority (gt95) of cats with
  hyperthyroidism.
• Since the cats's thyroid function returns to
  normal following 131I therapy, no ongoing thyroid
  medications are needed following this form of
  treatment.

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CT

• A computed tomography (CT) scan uses X-rays to
  produce detailed pictures of structures inside
  the body. A CT scan is also called a computerized
  axial tomography (CAT) scan.
• A CT scanner directs a series of X-ray pulses
  through the body. Each X-ray pulse lasts only a
  fraction of a second and represents a slice of
  the organ or area being studied. The slices or
  pictures are recorded on a computer and can be
  saved for further study or printed out as
  photographs

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Interventional Radiography

• Patient EDE
• typical fluoroscopy doses tens to thousands of
  millirem
• typical interventional fatal cancer risk 0.001
• Dose to Radiologist
• tens of millirad to head or extremities per
  procedure

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The Interventional Fluoroscopic Suite

• C-arm fluoroscopic unit
• Arrows point to the X-ray tube beneath the table
  and the Image Intensifier above the table

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Interventional Fluoroscopic Suite

• Note the low level of the X-ray tube beneath the
  table and the close proximity of the Image
  Intensifier above the table.
• Monitors as seen by the clinical team are in the
  background.

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Interventional Fluoroscopic Suite

• A 23 cm. Phantom is positioned beneath the Image
  Intensifier.
• An ion chamber is located at the base of the
  phantom to measure Entrance Skin Dose

PHANTOM
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RADIATION ONCOLOGY
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RADIATION ONCOLOGY- Bracytherapy Implant of
nasal tumor, lateral view. Iridium-192 treatment
of canine nasal tumor, lateral view.
                                                  
                                                  
                                                  
                                                  
        . Implant of nasal tumor, dorsoventral
view. Iridium-192 treatment of canine nasal
tumor, dorsoventral view.                        
                                                  
        
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Large Animal Operations

• The equine and food animal sectors of the
  veterinary profession rarely have the luxury of
  transporting the patient to the x-ray machine, so
  they must take the machine to the patient.
• Fortunately, technology has made the modern
  veterinary portable x-ray machine safer than it
  ever has been, but it is far from risk-free.
• In some respects, portable x-ray machines may be
  more hazardous than the fixed versions, even
  though they are usually less powerful.

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Large Animal Diagnostic Room  
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Large Animal Diagnostic Equipment
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Equine Bone Scans   
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Computed Tomography

• Computed tomography or CT, shows organs of
  interest at selected levels of the body. They are
  visual equivalent of bloodless slices of anatomy,
  with each scan being a single slice.
• CT examinations produce detailed organ studies by
  stacking individual image slices. CT can image
  the internal portion of organs and separate
  overlapping structures precisely.
• The scans are produced by having the source of
  the x-ray beam encircle or rotate around the
  patient. X-rays passing through the body are
  detected by an array of sensors. Information from
  the sensors is computer processed and then
  displayed as an image on a video screen.
• Doses are not low!

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Typical dynamic image of a heart
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Nuclear Imaging Scans

• Brain Scans These investigate blood circulation
  and diseases of the brain such as infection,
  stroke or tumor. Technetium is injected into the
  blood so the image is that of blood patterns.
• Thyroid Uptakes and Scans These are used to
  diagnose disorders of the thyroid gland. Iodine
  131 is given orally , usually as sodium iodide
  solution. It is absorbed into the blood through
  the digestive system and collected in the
  thyroid.
• Lung Scans These are used to detect blood clots
  in the lungs. Albumen, which is part of human
  plasma, can be coagulated, suspended in saline
  and tagged with technetium.

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Nuclear Imaging Scans

• Cardiac Scans These are used to study blood flow
  to the heart and can indicate conditions that
  could lead to a heart attack. Imaging of the
  heart can be synchronised with the patient's ECG
  allowing assessment of wall motion and cardiac
  function.
• Bone Scans These are used to detect areas of bone
  growth, fractures, tumors, infection of the bone
  etc. A complex phosphate molecule is labeled with
  technetium. If cancer has produced secondary
  deposits in the bone, these show up as increased
  uptake or hot spots.

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Radioisotopes Used in Nuclear Medicine

• For imaging Technetium is used extensively, as it
  has a short physical half life of 6 hours.
  However, as the body is continually eliminating
  products the biological half life may be shorter.
  Thus the amount of radioactive exposure is
  limited.
• Technetium is a gamma emitter. This is important
  as the rays need to penetrate the body so the
  camera can detect them.
• Because it has such a short half life, it cannot
  be stored for very long because it will have
  decayed. It is generated by a molybdenum source
  (parent host) which has a much greater half life
  and the Tc extracted on the day it is required.
  The molybdenum is obtained from a nuclear reactor
  and imported. For treatment of therapy, beta
  emitters are often used because they are absorbed
  locally.

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HOW IS TECHETIUM USED FOR A HEART SCAN

• The isotope is injected into a vein and absorbed
  by healthy tissue at a known rate during a
  certain time period. The radionuclide detector,
  in this case a gamma scintillation camera, picks
  up the gamma rays emitted by the isotope.
• The technetium heart scan uses technetium Tc-99m
  stannous pyrophosphate (usually called
  technetium), a mildly radioactive isotope which
  binds to calcium. After a heart attack, tiny
  calcium deposits appear on diseased heart valves
  and damaged heart tissue. These deposits appear
  within 12 hours of the heart attack. They are
  generally seen two to three days after the heart
  attack and are usually gone within one to two
  weeks. In some patients, they can be seen for
  several months.
• The technetium heart scan is not dangerous. The
  technetium is completely gone from the body
  within a few days of the test. The scan itself
  exposures the patient to about the same amount of
  radiation as a chest x ray. The patient can
  resume normal activities immediately after the
  test.

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The Gamma CameraWhat is about ?
The modern gamma camera consists of- multihole
collimator - large area (e.g 5 cm ) NaI(Tl)
(Sodium Iodide - Thallium activated)
scintillation crystal - light guide for optical
coupling array (commonly hexagonal) of
photo-multiplier tubes - lead shield to minimize
background radiation
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A crucial component of the modern gamma camera is
the collimator. The collimator selects the
direction of incident photons. For instance a
parallel hole collimator selects photons incident
OS the normal. Other types of collimators include
pinhole collimator often used in the imaging of
small superficial organs and structures (e.g
thyroid,skeletal joints) as it provides image
magnification. Fan beam (diverging) and cone
beam (converging) collimators are often used for
whole body or medium sized organ imaging. Such
collimators are useful because they increase the
detection efficiency because of the increased
solid angle of photon acceptance.
The action of a parallel hole collimator
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Detail of the pin-hole collimator
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Features and parameters

• The following are the typical features of the
  scintialltion crystal used in modern gamma
  cameras
• most gamma cameras use thallium-activated NaI
  (NaI(Tl))
• NaI(Tl) emits blue-green light at about 415 nm
• the spectral output of such a scintillation
  crystal matches well the response of standard
  bialkali photomultipliers (e.g SbK2Cs )
• the linear attenuation coefficient of NaI(Tl) at
  150 KeV is about 2.2 1/cm . Therefore about 90
  of all photons are absorbed within about 10 mm
• NaI(Tl) is hyrdoscopic and therefore requires
  hermetic encapsulation

• NaI(Tl) has a high refractive index ( 1.85 )
  and
  thus a light guide is used to couple the
  scintillation crystal to the photomultiplier tube
  
• the scintillation crystal and associated
  electronics are surrounded by a lead shield to
  minimize the detection of unwanted radiation
• digital and/or analog methods are used for
  image capture

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Things to Look for

• Radiation safety of veterinary personnel during
• handling of animals
• Dealing with excretia and bodily fluids
• Types of radiation generating machines and
  radionuclides utilized
• Calibration equipment
• Detection equipment
• Dosimetry
• Other?