1. Ch 36 Radiation Protection Design
RTMR 284 Winter 2013

2. Ch 36-Designing for Protection…….Features:
Protective X-Ray tube housing
Protective housing to reduce leakage radiation
Must be less than 100 mR/hr at a distance of 1m from protective housing.
Control Panel
Must show exp. Conditions and when
tube is energized
Beam ON must be clear to techs.
SID Indicator
Indicator must be present (tape measure or readout)
Must be accurate within 2% of the indicated SID

3. Protection Features cont.
Collimation
Light field, variable aperture
X-ray beam and light filed must coincide w/in 2% of SID
PBL-Positive Beam Limitation
Auto collimation circa
Must be accurate w/in 2% of SID
Beam Alignment
How do we know the tube is aligned with the image receptor ???

4. Protection Features cont.
Filtration
Inherent plus added
Total must be at least 2.5 mm above 70 kVp
Reproducibility
Constant output radiation intensity
Should not exceed 5% through same technique
Linearity
Constant output for varied mA settings while time is adjusted to keep mAs the same.
Max variation is 10% from one mA to adj. mA station

5. Portable / Fluoro Protection
Operator Shield
It must not be possible to expose in a room outside of the operator booth
Portable x-ray must have >2m tether for exposure
Fluoroscopic Protection
SSD-source to skin distance
Divergence of x-ray beam means the ESE or entrance skin exp. is lessened for the required exit exposure as SSD is increased
SSD must be not less than 38cm on stationary fluoroscopes and not less than 30cm on mobile fluoroscopes.

6. Portable / Fluoro Protection

7. Fluoro Protection cont.
Additional Fluoro Protection
Primary Protective Barrier
IR assembly must be 2 mm Pb eq. w/ interlock
Filtration
Total filtration at least 2.5 mm Al eq.
Collimation
Visible unexposed boarder w/ II 35 cm above TT
Exposure Control
Dead man…
Bucky Slot Cover / Protection Curtain
At least 0.25 mm Pb eq.
Cumulative Timer
Audible signal if time > 5 min.
Intensity
At tabletop must not exceed 2.1 R/min for ea. 80kVp

8. DAP
Dose Area Product
The intensity of the x-ray beam at the tabletop of a fluoroscope should not exceed 2.1 R/min per 80kVp. If there is no optional high-level control, the intensity must not exceed 10R/min (20 R/min with high level control)
Quantity that reflects not only the dose, but also the volume of tissue irradiated.
R-cm^2 units
DAP increases with increase field size
Used for monitoring equipment

9. Protective Barriers
3 types of radiation to consider when designing barriers
primary radiation
the useful beam
secondary radiation
scatter radiation
the patient is the most important scattering object
Intensity of SR 1m from the pt. ~0.1% of intensity of the useful beam at the pt.
leakage radiation
limit of 100mR/hour (not recommended)

10. Protective Barriers Primary Protective Barrier
protects against the primary beam
floor
wall behind an upright bucky
Secondary Barriers
protects against secondary radiation
control booth
walls without upright bucky

11. Factors Affecting Barriers
Distance
distance between source of radiation and barrier
Use
what is the area used for?
Controlled area
Uncontrolled area
Use factor
Workload
the greater the # of exams/week the thicker the shielding

12. Definitions Controlled area
area occupied mostly by Radiology Personnel and patients.
Exposure rate must be less than 100 mR/week
Uncontrolled area
occupied by anyone
maximum exposure rate is 2 mR/weekUse Factor
Use Factor
The percentage of time that the x-ray beam is on and directed toward a particular wall

13. Radiation Detection & Measurement
Instruments are Designed to:
Detect radiation
Measure radiation
Both detect and measure radiation

14. 4 Types of Radiation Detection Devices
Gas-filled
ionization chambers
proportional counters
Geiger-Muller detectors
Thermoluminescence dosimeters (TLD)
Scintillation detectors
Optically Stimulated Luminescence (OSL)

15. Gas-filled 3 types of gas-filled radiation detectors
ionization chambers
proportional counters
Geiger-Muller detectors

16. Gas Filled
All 3 types of Gas filled Radiation Detection Devices are based on the same principle
Radiation passes through gas and ionizes atoms of gas
Electrons released in ionization are detected as an electrical signal
Electrical signal is proportional to radiation intensity
Usually, the larger the chamber, the more sensitive the instrument
Because there are more gas molecules for ionization
A pressurized chamber has more molecules available as well

17. Scintillation detectors
Some materials emit a flash of light in response to the absorption of ionizing radiation
The light emitted is proportional to amount of energy absorbed
most often used to indicate individual ionizing events
used in fixed or portable radiation detection devices
Used in detector arrays of many CT scanners
Basis for the gamma camera in Nuclear Med

18. Thermoluminescence dosimeters (TLD)
Some materials glow when heated
After this material is exposed to ionizing radiation, it is heated
The light let off is proportional to the ionizing radiation it was exposed to

19. Optically Stimulated Luminescence (OSL)
Developed in the late 1990s
Uses aluminum oxide to detect radiation
Irradiation of aluminum oxide stimulates electrons into an excited state
During processing, laser light stimulates these electrons returning them to normal state with the emission of visible light.
The intensity of visible light emission is proportional to the radiation dose received.

20. Optically Stimulated Luminescence (OSL)
The OSL process is similar to the TLD
Both are based on stimulated luminescence.
Advantages of OSL over TLD are:
More sensitive than TLD
More precise
Reanalysis for confirmation of dose is available
Qualitative information about exposure conditions
A wide dynamic range
Excellent long-term stability

21. The End
Projects Due in Class next week….