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RADIATION BIOLOGY

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					RADIATION BIOLOGY

 Prof. Janet Gruber, RDH, MS
           DEN 106
         Oral Radiology
Two Effects of Ionizing
Radiation
 Excitation – x-ray photon interacts with an
  atom’s electron causing it to vibrate and
  possibly break apart, but it returns to a
  stable state.
 Ionization – orbital electron removed from a
  shell causing it to be ionized.
Two Types of Biological
Damage
 Direct hit effect – x-ray collides with cell
  causing no damage or breaking them apart
  causing critical damage. Cell repairs or
  dies.
 Indirect hit – Based on the poison H20
  theory. H2O is poison for the cells and
  potential exists for a cell to turn malignant.
Classification of Damage
 Somatic damage – damage to tissues not
  inherited from one generation to the next.
  75% of somatic cells repair within 24 hours
  after damage.
 Genetic damage – damage to reproductive
  cells. They never repair themselves.
Latent Period
   Time b/w irradiation and clinical
    appearance of symptoms. Latent period can
    be from a few hours to days. ie. sunburn
Effects
 Acute effects from excessive radiation:
   Nausea, hemorrhage, diarrhea, erythema,

    malaise, fever and death 400-500 RADS.
 Chronic effects – long term:
   Cancers, cataracts (not caused by dental

    radiation) genetic defects, nail splitting,
    alopecia, shortened life span.
Determinants of Biological
Effects
1.   Dose
2.   Frequency
3.   Area or volume exposed
4.   Patient’s age
5.   Individual sensitivity
6.   Cell nutrition
7.   Rate of cell division
8.   Oxygen concentration
9.   Cell sensitivity
Hierarchy of Tissue Sensitivity
   Small lymphocyte
   Reproductive tissue
   Bone marrow
   Skin
   Lens of the eye
   Oral mucosa
   Small blood vessels
   Mature bone
   Thyroid gland
   Kidney
   Muscle
   Nerve
Non-Threshold & Threshold
Dose
 Threshold Dose:
  Small exposures produce no observable
  changes. When threshold is reached we see
  observable changes. ie. sunburn
 Non Threshold Dose:
  No threshold needed – small dose causes
  changes. Genetic tissues fall into this
  category.
Stochastic vs. Nonstochastic
Effects
 Stochastic effects:
  Similar to non-threshold – occurrence
  increases with absorbed dose. Genetic
  mutations and cancer are examples.
 Nonstochastic effects:
  Somatic effects that have a threshold.
  Below that dose, no damage noted.
Critical Organs in Dentistry
 Skin
 Thyroid
 Lens of eye
 Bone marrow
Radiation Measurement and
Units
   Limits set by NCRP based on info gathered…
   Maximum Permissible Dose (MPD)
      It is the MAXIMUM dose a person may receive
       in a stated period of time.
      Upper threshold of a permissible dose.
       Anything less is not harmful anything more
       could result in biological injury if repeated
       often enough.
MPD
 MPD for radiation workers:
5 REMS = .05Sv (50mSv) / calendar year

 MPD for 13 week period for radiation workers:
3 REMS = .03 Sv / 13 weeks

 MPD for general public and pregnant workers:
.1REMS = .001Sv (1mSv) / calendar year
Values
 20 film FMS = .002REMS…10 sets = .02
  REMS and 100 sets = .2 REMS
 Lethal Dose = ~4.5 Grays or 450 RADS
 GI Series = .01Sv or 1 REM
 FMS = ~3 days in the sun
 4BWX = ~8 hours in the sun
Radiation Measurement Terms
   Exposure is the measurement of ionization in the
    air. It is measured in units called
    Roentgen/Coulomb per kilogram.
   Absorbed Dose is the unit for measuring the
    energy absorbed by the tissues from all types of
    ionizing radiation…RADS/GRAY.
   Dose Equivalent is a unit used to measure the
    biological effect of radiation…REMS/SIEVERTS.
CONVERSIONS
 100 RADS = 1Gy
 100 REMS = 1 Sievert


 .001RADS = 1 mRAD
 .001 REMS = 1mREM
Effects of Oral Radiation in
Cancer TX Patients
1.   Healed and repaired tissue has fewer and smaller
     blood vessels = reduced repair potential.
2.   Osteoradionucrosis – bone loses blood supply
     and susceptible to infection.
3.   Xerostomia – dry mouth & increase in caries
     rate.
4.   Rampant caries – decease saliva = plaque =
     cervical caries.
Overexposure to Certain Organs
 Skin = cancer
 Lens of the eye = cataract
 Blood forming organs = leukemia
 Thyroid gland = cancer
 Reproductive organs = genetic mutations
 Fetus = birth defects
 Breast (female) = cancer
RADIATION HYGIENE
 Radiation Control for Health and Safety Act
  1968, regulation of x-ray machines.
 Consumer Patient Radiation Health and
  Safety Act 1981, Developed min. standards
  for operators of dental equipment.
 NY Sanitary code requirements…
 ADA recommendations…
Personal Monitoring
 Film Badges
 Geiger Counter
 Home made film badge
 Pocket dosimeter
 Thermoluminescent dosimeter
     ALARA CONCEPT
AS
L OW
AS
R EASONABLY
A CHIEVABLE
METHOD OF EXPOSURE
AND DOSE REDUCTION
   Patient selection
   Conduct of the examination
      Choice of equipment

      Operation of equipment

   Personnel protection
      Establishment of radiation safety procedures
       (90-135 angle from primary beam)
      Quality assurance

      Continuing education
CHOICE OF EQUIPMENT
 Collimators (rectangular reduces dose 2/3)
 Filter
 Lead aprons and collars
 Receptor selection (fast film E / F or digital)
 Focal spot to film distance (long PID)

				
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