Safety - Radiation Protection (Pt.2)

What is the Primary Beam?

X-ray Beam between Tube and Patient, aka: Useful beam

What is the Secondary beam?

The x-ray beam that remains after interaction with the patient and exits to expose the image receptor; aka: Remnant

What comprises the Secondary Beam?

Stray Radiation = Leakage + Scattered Radiation

What is leakage radiation?

radiation that emerges from the leaded tube housing in directions other than that of the useful beam

What is scatter radiation?

radiation that has been deflected from its path by interaction with matter

What is the primary cause for occupational exposure?

Comptom Scatter

What is the primary cause for patient exposure?

Photoelectric Absorption

Scatter becomes ____ of the roginal intenstiy at a distance of 1 meter

0.1% 1/1000th

______ Is the greatest source of scatter

Patient

What are the principles of protection?

• Time
• Distance
• Shielding

What is the relationship between time and exposure?

Proportional

What is the relationship between distance and exposure?

Inverse Square relationship

What is the relationship between Shielding and exposure?

Inverse exponental

What is the tenth-value layer (TVL)?

It is the thickness of absorber that reduces the radiation intensity to 1/10 it's original value. 1 TVL = 3.3 half value layers

What is the half value layer?

amount of material required to reduce the intensity of an x-ray to half

What is considered a controlled area?

Areas for workers and under the control of a radiation safety officer

Controlled Areas are limited to an exposure rate of _____

1 mSv/week

What is considered an uncontrolled area?

Anywhere where the general population can be; Ex: hallway, office, waiting room

Uncontrolled Areas are limited to an exposure rate of _____

0.1 mSv/week

What is a barrier used for?

Lead-lined: walls, floors, ceilings to protect outside

What is considered a primary barrier?

Barrier perpendicular to the line of travel of the primary beam

Primary Barriers are required to have protection of ____ when tube is 5-7 ft from barrier

1.5 mm Pb Equivalent

What is considered a secondary barrier?

Barrier protecting against stray radiation; Ex: Booth, Ceilings, Tube housing

Secondary Barriers are required to have protection of ____ when tube is 5-7 ft from barrier

0.75 mm Pb Equivalent

What are Factors of Barrier Thickness?

• Distance from source
• Occupancy Factor, time behind barrier
• Workload, exposure + radiation output
• Use Factor, time beam is on and directed at barrier
• max kVp

When is protective apparel worn?

Exposure rate exceeds 0.05 mGya/hr

What kind of material is use for protective material?

• Lead-impregnated vinyl/rubber
• Composite of Lead and tungsten or barium

Minimum Apron shield thickness

0.25 mm Pb Equivalent

Minimum Glove shield thickness

0.25 mm Pb Equivalent

Minimum Thyroid Shield thickness

0.5 mm Pb Equivalent

Minimum Eye Glasses Shield thickness

0.35 mm Pb Equivalent

Exposure cord on mobile X-ray units must be at least ____ long

1.8 m (6 ft)

SSD of stationary units should be at least

38 cm (15")

SSD of mobile units shall not be less than

30 cm (12")

Minimum thickness of the protective Drapes of Fluorscopic units _____

0.25 mm Pb Equivalent

Protective Bucky slot cover should have at least _____ of shielding material

1 TVL, 0.5 mm Pb Equivalent

What is the cumulative timer?

Sounds audible alarm after 5 minutes; reminds fluoroscopist of exposure time

Fluoroscopic Exposure rate w/ AERC should not exceed _____

10 R/min or 100 mGya/min

Fluoroscopic Exposure rate w/o AERC should not exceed _____

5 R/min or 50 mGya/min

What is the deadman switch?

Button requiring continuous pressure for activation

What are dosimeters?

Instruments used to measure radiation exposure

Who wears Dosimeters?

Anyone at risk of 1/10 of the annual dose limit, 5 mSv

What are some tpyes of dosimeters

• Electric Charge
• luminescence
• physical/chemical change

What are type of Electric charge dosimeters

• Gas Filled Chamber: Ion Chamber, Geiger
• Pocket Dosimeter
• Solid State Conductor
• Spark gap detector

What are types of Physical or chemcial change dosimeters?

• Photographic Film
• Chemical Dyes
• Cloud Chamber

What are the types of luminescence dosimeters

• TLD
• OSL
• Scintillation Detectors

How do Luminecence dosimeters work?

Detection of radiation based on light emission

How Do Thermoluminescent Dosimeters (TLD) work?

Under heat, crystals emit light proportional to radiation exposure

What is the material used for TLD?

Calcium Fluoride crystals

How Do Optically stimulated Dosimeters (TLD) work?

Under a laser light, crystals emit light proportional to radiation exposure

What is the material used for OSL?

Aluminum Oxide

Which kind of dosimeter has material the most similar to human tissue

TLD

Where are dosimeters worn?

collar level outside the lead apron, as the greatest dosages are directed to the face and shield

Where are fetal dosimeters worn?

Under lead at waist level

What are secondary dosimeters?

Used to record fetal dose of pregnant workers

How does recorded fetal dose readings compare to the actual dose

25-30%

NCRP #116

defines annual exposure limits; makes recommendations

What is Entrance Skin Dose (ESD)?

entry dose of skin, recorded with TLD and OSL

What is Entrance Skin Exposure (ESE)?

Specific amount of radiation received by patients skin

What is Entrance Skin Air KERMA?

Specifies Exposure just above patients skin

What is depth dose?

Percentage measurement of skin dose a certain depth

What is Effective Dose?

Estimate of total risk of whole body exposure based on radiation and tissue type

What is air KERMA?

Amount of radiation absorbed in a quantity of air

Occupational worker limits include?

Workers exposed to radiation and over 18 yo

Annual Occupational Whole Body Dose Limit:

50 mSv

Annual Occupational Lens Dose Equivalent Limit:

150 mSv

Annual Occupational Body Part Limit:

500 mSv

How is Lifetime Total Effective Dose calculated

Age in years x 10 mSv

Average annual Dose Equivalent received by workers in the US ____

0.2 mSv

What is the annual dose limit for infrequent exposure?

5 mSv

What is the annual dose limit for frequent exposure?

1 mSv

Annual Public Lens Dose Equivalent Limit:

15 mSv

Annual Public Body Part Limit:

50 mSv

What is the Monthly fetal effective dose limit?

0.5 mSv

What is the fetal effective dose limit for the entire gestation?

5 mSv