Linear Energy Transfer (LET)

How are mass, charge, velocity, chemical related? 

Weightless packages of pure energy
No electric charge
Travel in waves
Travel with a specific frequency
at the speed of light

range of wavelengths:   
0.1A to 0.5 A (1 A = 1/10 nm)

Bremsstrahlung:
                Electron to nucleus interaction

X rays are produced when high velocity electrons are suddenly decelerated when they pass close to the nuclei of high Z # absorbing material = tungsten 

Bremsstrahlung 70%

Characteristic 30% 

Electron Source (Cathode) -

Suitable Target to stop electrons (Anode) +

both are tungsten 

effective focal size needs to be small in order for good focus

EFS smaller than AFS 

#protons goes up

mean E of beam goes up

max E of beam is increased 

The intensity of radiation varies inversely as the square of the source film distance

Intensity = I / D2
 

Scattered - no absorption 

Low energy photon passes near an outer electron
Causes electron to vibrate
Incident photon ceases to exist
The vibration of the electron causes it to radiate energy in the form of another x-ray photon
Only 8% of total interactions

Completely absorbed 

Incident photon gives up all its energy to an inner electron ejected from an atom
An electron from higher energy level fills the vacancy
Characteristic radiation is emitted
The recoil electron travels a short distance before giving up all its energy..
30% of all interactions

Partial absorption 

Photon interacts with an outer orbital electron
A scattered photon of lower energy is produced
And a recoil electron is ejected from the target atom
62% of all interactions
Scattered photon travels in all directions
30% of the scattered photons exit the patient’s head

Ionization is directly proportional to charge 

Ionization is directly proportional to particulate energy
Greater cell killing potential

Cells from different organs react differently 

Number of cells in active proliferation
Degree of cellular differentiation
Number of future divisions
The larger effect there will be

Vegetative Intermitotic Cells
Differentiating Intermitotic Cells
Multipotential Connective Tissue Cells
Reverting Postmitotic Cells
Fixed Postmitotic Cells

Which are affected most by radiation? 

NOT DOSE DEPENDENT- ALL OR NOTHING

DENTAL RADIOGRAPHY FALLS INTO THIS CATEGORY 

Effects where the risk is proportional to the dose
Implies that there is no threshold
e.g. cancer,
    mutations (genetic effects)
Severity of the effect is independent of the dose

( deterministic effects)
Effects where the severity is proportional to the dose
Implies a threshold
e.g. sunburn, in utero birth defects,cataracts,
    radiation burns

Oral Mucous membrane
        -Desqamation
        -Inflammation…pain
        -white/yellow pseudomembrane
        -Secondary Fungal Infections
        -Long term…atrophic, thin, avascular mucosa
        -healing –2months after
Taste buds
-    decreased Taste acquity
- recovery to almost normal – 60-120 days post irradiation
Teeth
prior to calcification- tooth bud destroyed
Post calcification- malformations, arrested growth
Severity == dose (non stochastic)
Eruption…radioresistant

Salivary Glands (Radiation caries)
  Reduced secretion
Xerostomia
pH altered…decalcification of enamel
Radiation caries
Bone
OSTEORADIONECROSIS
 

Can be both

Stochastic
Childhood cancer
mutation

Non stochastic
Birth defects

Occupational exposure and dose  

MPD (Maximum Permissible Dose)

MAD (Maximum Accumulated Dose)

 

MPD (Maximum Permissible Dose)
50 mSv (5.0 rem) for whole body radiation per year

MAD (Maximum Accumulated Dose)
10 mSv x age (1 rem x age)
 

Film Badges
 Special type of sensitive film in a special holder with metallic filters
Attached to external area
Permanent record
Inexpensive
Reasonably accurate (~20 mR)
over response at low energies
not for periods of longer than 1 month

TLD (Thermoluminescent Dosimeter)
Lithium fluoride crystal
Absorb energy which will be read by a special reader
Heating  method result in visible light
Can be re-used over and over
More sensitive and accurate (~5 mR)
More useful for quarterly period
 

when these things are increased they have the following results 

Anatomy being imaged
         (Thickness
         Density (g/cm3)
         Atomic Number)-all cause lighter film
2. Beam Energy / Quality
        (KVp
        Filtration)-both cause darker film

 3. Beam Intensity / Quantity
        (MA
        Exposure time)-both cause darker film        (Filtration

        Collimation
        Distance (inverse square law)) -cause lighter film

   4. Film Speed
        Faster Film greater Density and vice versa 

5.  Processing
         (Time
         Temperature
         Concentration)- cause darker film

6. Artifacts (lead aprons, film reversal, earrings, thyroid collars)….. lighter areas in the film
 
 

due to Compton or coherent interactions
Photons are in different directions from the primary beam
Produces fog (overall darkening reducing the contrast)

Reduces contrast! 

Radiographic features :
Radiolucent lesion
Loss of the lamina dura
Margins
Ill-defined / well-defined
Corticated / non-corticated
Size : varies

“Halo” Sign-Maxillary posterior teeth
Elevation of the floor of maxillary sinus 

Differential Diagnosis :
Periapical cemento-osseous dysplasia
Other benign fibroosseous lesions
Periapical scar
Surgical defects
 

Radiographic features :
Increasing in radiopacity
Around apical periodontitis or apical rarefying osteitis
Margins :
Well defined / Diffused
Extents : varies

Differential Diagnosis :
Osteosclerosis
Periapical cemento-osseous dysplasia
Hypercementosis
Projected radiopacity :
Osteoma
Odontoma
Exostosis / Enostosis
 

Inflammation of bone marrow
Predisposing conditions :
Malnutrition
Diabetes
Leukemia
Anemia
Alcoholism
 

Beam Geometry- angle

of PA and Bite Wing 

PA- 25

BW- 5 

(Early-onset Periodontitis)

Occurs in healthy individuals between puberty and age 25
Amount of bone loss is not consistent with local factors and oral Hygiene habits. Rate of bone loss is 3-4 times faster than in typical periodontitis
Typically affects crestal bone of first molars and incisors. Eventually affects greater # of teeth.
Bone loss is progressive and frequently bilaterally symmetrical. Many teeth show vertical bone loss
Host neutrophil dysfunction has been demonstrated by several investigators

(Langerhans’ Cell Histiocytosis)

Complex of three diseases:
Eosinophilic granuloma (usually solitary)
Hand-Schuller-Christian disease
Letterer-Siwe disease
Due to abnormal proliferation of Langerhans’ cells or their precursors

Arise from structures located on the opposite side of the center of rotation away from the image layer
Produced when the object is located between the x-ray source and the rotational center.

Characteristics
Same general shape
Appears on the opposite side
Positioned higher than real structure
More blurred than the real structure
Vertical component is more blurry
Vertical component is highly magnified

forward = small teeth because they are closer to the film

backward = large teeth because they are closer to the center of rotaion and further from the film

Computed Tomography (CT)

Pros v Cons 

(Gorlin Cyst)
*only jaw cyst that may have radiopaque foci

*    cyst-like radiolucency with variable margin
*    unilocular or multilocular
*    may be associated with unerupted tooth
*    possible root resorption may contain foci of calcification

Benign Non- Odontogenic Cyst

∗    radiolucent lesion
∗    moderately to well-defined borders
∗    may create scalloping between roots of
involved teeth
∗    does not resorb or displace tooth roots
 

Benign Odontogenic Tumor

∗    radiolucent
∗    unilocular or multilocular
∗    well-circumscribed
∗    expands and thins cortices (may erode)
∗    may arise in wall of cyst (Mural ameloblastoma) 
∗    may displace teeth/resorb roots
 

benign odontogenic tumor

Radiographic findings
∗    central radiolucency
∗    unilocular or multilocular
∗    well-defined border
∗    may have opaque foci
∗    may be associated with unerupted tooth
∗    may expand cortex
∗    may resorb roots