Registry Review

1
Registry Review

• Remember to draw the
• Dang PICTURE!!!

2
Law of Bergonie Tribondeau - French scientists
that experimented with rabbit testis-Theory that
radiosensitivity was a function of the metabolic
state of the tissue being irradiated
3
Sensitivity

• Stem cells are radiosensitive. The more MATURE,
  the MORE radioresistant!
• The younger the tissue/organ, the MORE
  radiosensitive!
• As metabolic activity increases, so does
  RADIOSENITIVITY

4
Linear Energy Transfer (LET)

• Rate of energy transfer of ionizing radiation to
  soft tissue
• As LET increases, biologic damage also INCREASES

5
Relative Biological Effectiveness(RBE)

• Linked to what is being irradiated (man vs. a
  rabbit, etc.) and the damaging factor (type) of
  radiation.
• X-rays have an RBE of 1
• Alpha particles have an RBE of 3!

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Oxygen Enhancement Ratio (OER)

• Anoxic cells tend to be LESS radiosensitive than
  hypoxic cells
• OER is the ratio of oxygen enhanced tissue damage
  verses that of anoxic tissue damage (an example
  of anoxic tumor is tonsil) - increased oxygen
  INCREASES the radiation effect on the tumor when
  irradiated

7
Radiosensitizers

• Enhance the effect of radiation
• Examples are halogenated pyrimidines,
  methotrexate m, actinomycin D, hydroxurea and
  vitamin K

8
Radioprotectors

• Help to protect from ionizing radiation
• Molecules containing a sulfydral group component
  are examples

9
Radioresponse rates

• Linear dose response damage is directly
  proportional to the dose
• Non-linear simply means the dose is NOT
  directly proportional to the amount of radiation
  (ALARA no safe threshold dose)

10
DNA is the MOST radiosensitive macromolecule

• In G-1 there is HALF as much DNA as in G-2
• Types of DNA damage include one rail severed
  both side rails severed cross linking rails
  rung breakage

11
Radiolysis of water

• The body is about 80 water. When water is
  irradiated, it dissociates into other molecular
  products creating highly charged free radicals
  (free radicals are uncharged molecules containing
  a single UNPAIRED electron in the valence outer
  most shell and are VERY unstable usually last
  less than one ms)
• Often produce TOXIC agents to the body (hydrogen
  peroxide)

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Damage

• Only about 10 of body damage is DIRECT (direct
  hits)
• 90 is indirect damage caused by free radical
  related toxins!

13
D Q is called threshold dose

• Measure of the capacity to accumulate sub-lethal
  dose AND measure the ability of the cell to
  recover from sub-lethal damage
• Human cells are MOST radiosensitive in the M
  phase and most RADIORESISTANT in the late S phase

14
Periods of RADIATION SYNDROME Lethality

• Prodromal Less than100 rads nausea, vomiting,
  diarrhea (the immediate response of RADIATION
  sickness)
• Latent 100-10,000 RADS no outward signs of
  sickness

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Manifest (dose related periods)

• Hematologic 200-1000 RADS 10-60 days survival
  nausea, vomiting, diarrhea, leukopenia,
  hemmorage, fever, infection
• GI 1000-5000 RADS 4-10 days survival same as
  Hematologic PLUS electrolytic imbalance,
  lethargy, fatigue and shock
• CNS 5,000 RADS less than 3 days survival same
  as GI plus ataxia, edema, vasculitis and
  meningitis

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Most Radiosensitive

• The lymphocytes and the sperm CELLS are the MOST
  radiosensitive CELLS in the body

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3 Cardinal Principles of RAD protection

• Time
• Distance
• Shielding

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Problems

• Inverse square law
• Old mAs/New mAs
• Direct proportion/ratios

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Tolerances/values

• HVL half value layer
• TVL tenth value layer
• Protective tube housing less than 100 mR/hr at
  1 m
• Collimation within -2 of the SID
• Filtration inherent .5 mm al added 2.0mm al
  for 70-80 kVp
• Reproducibility same x-ray exposure factors
  cannot exceed 5 diff. exposure to exposure

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Tolerances/values, cont

• Linearity using the SAME mAs, but differing mA
  stations should give the same exposure within
  10
• Primary protective barrier 2mm lead equivalent
  (any direction the useful beam may be directed
  toward)
• Factors affecting distance, occupancy, control
  (controlled area/hallway/office), workload (how
  many studies per unit of time)

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Dose

• RAD (Gy) radiation ABSORBED dose
• REM (Sv) roentgen equiv. man
• Dose limit to radiographers is 50 mSv/yr (5000
  mrem)
• General Population is less than 1 mSv/yr
  (100mrem/yr)
• many sources state the gen. population as well
  as pregnant radiation workers maximum dose be
  1/10th that of a radiation worker

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Dose cont

• Many types of dose
• ESE (entrance skin dose) sometimes call patient
  dose
• Marrow dose
• Genetically Significant Dose (GSD)
• Somatic Dose
• Glandular Dose (most frequently in mammo)

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Personnel Monitoring

• Required when there is any probability that dose
  will exceed 1/10th of the recommended dose limit
  (if not probable to exceed, then need NOT be
  badged)

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Four MAJOR Types of Badges

• Film badge inexpensive, easy to handle, easy to
  process, cannot be reused, cannot be worn for
  long periods of time due to fog potential
  (sensitive to all like x-ray film)
• TLD (lithium fluoride) more sensitive and
  accurate than film badge can be worn longer, can
  be used at high temps and humidity, can be read
  and reused BIGGEST advantage is lower cost

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Badges, cont

• Pocket ionization chambers (size of a pen) can be
  read immediately and continuously
• Optically Stimulated Luminescence Device (OSL)
  more sensitive than the others and can be used
  for a longer time (aluminum oxide)
• Badge should be warn OUTSIDE the lead apron and
  at collar level

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Protective barriers

• Bucky slot curtain .25 mm pb.
• Bucky slot hinge .25 mm pb.
• Lead aprons 2005/6 - .5 mm pb.
• Lead gloves .25 mm pb. And are SECONDARY barriers
  not primary

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Patient shielding

• Contact (right on the body lead apron, etc over
  the patient)
• Can be flat or formed (testicle cup shield),
  butterfly shield for ovaries
• Shadow shields (not as good as direct contact as
  scatter radiation can be diffused around the
  shield)