dose reduction mechanisms Flashcards
Goals for Oral and Maxillofacial
Radiology
- Reduce radiation exposure
- Maintain a high degree of diagnostic
efficiency
juggling act of oral radiology
●reduce a patient’s radiation exposure
●maintain a high degree of diagnostic efficiency
Dose Reduction Mechanisms
X-ray Tube Head
Patient Protection
Operator Safety
Et cetera
ALARA:
As Low As Reasonably Achievable
Guiding Principle ofRadiation Protection
Since the probability or severity of biological damage increases as the radiation dose increases, it is desirable to avoid receiving even the smallest dose of radiation unnecessarily.
ALADA:
As Low As Diagnostically Acceptable
Guiding Principle of Radiation Protection
* ALADA lowers exposure to patients
* ALADA lowers exposure of all office personnel
mandated dose reduction mechanisms of tube head
- Filtration
- Collimation
purpose of the filter
removal of low E (large wavelenght) photons
* Selectively removes a greater proportion of low keV x-ray photons
* Increases mean energy of the beam
based on? Al filtration needed?
Mandated Minimum Total Filtration
for X-ray Tubes
majority of machines in the 50-70/ 1.5mm range
tube head collumination
mandated on tube side
can be circular or rectangular
* Maximum 2.75” diameter
* (Rectangular preferred)
optional dose reduction mechanisms xray tube options
- Rectangular collimator
- High kV generator/ transformer
- Constant potential (DC) fully rectified
- Increased focal length
rectangular collimination
decreases beam size to size of receptor= decrease in dose
no compromise to diagmostic info if done correctly (alignment)
must learn to have precise placement of both source and receptor
area exposed and beam size
directly related
what can help with rectangular collimnator alignment
ring assemblies like in clinic (XDR?)
can depend on?
_________ dose is reflective
of the specific technique
effective dose is reflective of the specific technique
can depend on receptor and collination
higher kV and dose
will actually reduce the dose, may be due to increased filtration measures (distance and actual filter)
higher kV units are?
larger and heavier
constant potential of xray tube and dose
reduced dosage with constant production of xrays (no intermittment periods of low E production= less low E photons)
increased focal length (distance) and dosage
based on TRD, TOD, BID
due to the inverse square law
although increasing the distance means that exposure must be increased as well, overall will usually decrease dosage
Increased of Long BID Benefits
- 27% less head volume
- reduced effective dose
- sharper image (smaller pneumbra)
how can the xray tube be modified to increase focal length and increase sharpness?
recessed tube, away from the window
also helps to increase image sharpness
practice options to decrease dosage
- Film speed
- Lead (Pb) thyroid collar
- Film-holding devices with beam alignment capability
- Time-temperature quality control processing
film speed and dosage
decreased with solid state sensors
CCD with lowest dosage (most sensitive)
film has much higher doses but better resolution (negligable)
lead apron and thyroid collar
usually only a concern with larger beams/ very little beam exposure in these areas with rec collimination
helps to protect the pt
should pt hold receptors?
Avoid holding the receptor, would increase dose (hand exposed)
can also cause receptor to move and decrease image quality
Film-holding devices with beam alignment capability
Rinn ORA XCP (clinic)
help align sensor to source
During an exposure taken with a wall-mounted x-ray unit, the operator shall stand:
stand behind a protective barrier.
If a barrier is not present, the operator shall stand:
at least six feet from the patient and at an angle between 90° - 135° to the direction of the useful beam.
where should you never stand
in the primary beam
when standing behind barrier what shluld we be able to see?
pt
can you hold the receptor in pts mouth?
no, will expose yourself
radiation mnitoring devices
optional to wear but can detect leakages from machines
operators should wear what when generating xrays
Dosimeter badges will be worn by all full-time operators of radiographic equipment while x-ray exposures are being made.
Annual occupational whole body exposure will
not exceed ______ mSv
Annual occupational whole body exposure will
not exceed 50 mSv
Operators who have declared a pregnancy will not receive more than ____ mSv to the embryo or fetus during the term of the pregnancy.
5mSv
The NOMAD and NOMAD Pro
The NOMAD and NOMAD Pro are
self-contained, hand-held, portable
dental X-ray units.
why would hand held units be popular?
conveinent, actually more expensive than wall unit
risk of handheld units
operator exposure
do possess a backscatter sheild but not very effective given operator positions
must wear a dosimeter
NOMAD Use Violations of current
radiology statutes
- “During each exposure, the operator
shall stand at least 6 feet from the
patient or behind a protective barrier.” - “Neither the tube housing nor the
position indicating device (cone, cylinder) shall be hand-held during exposure.
requirements of all handheld units
- A backscatter shield (provided by the
manufacturer) must be permanently mounted to the cone and used at all times during radiographic exposure. - Operators must wear a personnel monitor device that is evaluated monthly.
- All personnel must receive training in the safe use of these X-ray systems, and records of the training kept for review.
maximizing Area of Protection Provided by the Backscatter Shield of handheld
Maximize the operator’s area of protection by doing the following:
* Place the backscatter shield at the end of the PID (closest to the patient).
* Align the PID close to the patient.
* Keep all body parts within the area of the shield’s protection.
