Rad Bio-Chapter 6
Rationale for Radiation Protections
1. Purpose of radiation protection
2. Early Effects of Radiation
3. Late Effects of Radiation
Purpose of radiation protection
lesson likelihood of occurences
Early Effects of radiation
when human cells respond to high doses of radiation within minutes, days, or weeks post exposure
What do early effects of radiation include?
hematologic depression
erythema
chromosomal damage
gonadal damage
death
Late Effects of radiation
if damage to cells is not detected for months or years after radiation exposure
Dosimetry
measurement of ionizing doses to personnel
When is monitoring of personnel mandatory?
when they are likely to receive 10% of the annual effective dose-equivalent limit
Types of Dosimeters:
1. Film Badges
2. Thermoluminescent Dosimeters (TLDS)
3. Optically Stimulated Luminescence Dosimeter (OSL)
4. Pocket Dosimeters
What are the advantages of Film Badges?
-Inexpensive
-Simple to use
-Readily processed by
commercial labs
-Provide permanent record by lab and radiology department
What are the disadvantages of Film Badges?
-Are not reusable
-Accuracy limited to +/-
10-20%
-Susceptible to heat, humidity, and light leaks
What is the purpose of Film Badges?
-measures occupational radiation exposure
How often are film badges checked?
Monthly
What are the advantages of Thermoluminescent Dosimeters?
-Can be made very small
-Sealed in Teflon, reducing
damage
-Low exposure limit, to 5 mrem
-Response to x-rays
proportional up to 400 R
-Accuracy to about +/- 5%
-Response
to similar tissues
-Less heat sensitive to film badge
-Can
be worn for three months (reusable)
What are the disadvantages of Thermoluminescent Dosimeters?
-Cannot be stored as a permanent record
-More expensive than a
film badge
What is the purpose of Thermoluminescent Dosimeters?
-measures personnel exposure usually Nuc Med techs
What are Thermoluminescent Dosimeters made of?
Calcium fluoride crystals
As crystals in TLDs heat what do they emit?
Light
How can TLDs be worn?
At collar level or worn as a ring
What are the advantages of Pocket Dosimeters?
-Provides an immediate exposure reading
-Sensitive up to 200
mR
-Can be reset to record individual exposure readings
What are the disadvantages of Pocket Dosimeters?
-Does not provide a permanent legal record of exposure
-Bumping
or shock to unit can cause false high readings
-Predetermined
range, any measure that exceeds range cannot be documented
How often should Pocket Dosimeters be recalibrated?
Daily
What are the advantages of Optically Stimulated
-Dose measurement range very wide: 1 mrem-1,000 mrem
-Accuracy
+/-15% for shallow and deep exposure
-Precision within +/- 1
mrem
-Energy range 5 keV to over 40 keV
-Not affected by
heat, moisture, or pressure
-Bi-monthly readings
What are the disadvantages of Optically Stimulated Luminescence Dosimeters?
-More expensive that film badges and TLD
What is the purpose of OSLs?
Calculates personnel exposure by using aluminum oxide crystals
Radiation Safety Officer duties:
1. receiving, using, and disposal of radioactive material
2. conducting radiation surveys
3. monitoring personnel and areas
4. testing for leakage radiation
5. designing protective shielding
6. responding to radiation-related emergencies
7. Radioactive spill decontamination
What are Geiger-Muller Detectors used for?
to detect alpha and beta readings
What is another name for ionization chamber?
Cutie Pie
What is the purpose of ionization Chambers?
measures exposures for x-ray, gamma, alpha, and beta radiation
What is the definition for Effective Dose Limit?
Lowest dose of radiation that will maintain health with no ill effects
What does DEL stand for?
Dose Equivalent Limits
What MPD stand for?
Maximum Permissible Dose
Lifeline Limit= ?
Age
Implied Yearly limit is
100 mrem (1 mSv)
Prospective Yearly Limit is `
5 rem (50 mSv)
Embryo/Fetus/Month is
.05 rem (.5 mSv)
Students under 18 yearly limit is
.1 rem (1 mSv)
Emergency-1 Event per Lifetime is
50 rem (.5 Sv)
DELs are based on what type of relationship?
linear, non threshold dose response
Whole Body Dose Limit
5 rem (50 mSv)
Lens of eye Dose Limit
15 rem (150 mSv)
Skin/Extremities Dose Limit
50 rem (500 mSv)
Whole body cumulative (life time) Dose Limit
Age x 1 rem (AGe 10 mSv)
Fetus (10 month/280 days) Dose Limit
0.5 rem (5 mSv)
Fetus (one month/ 28 days) Dose Limit
0.05 rem (0.5 mSv)
Infrequent Public Exposure
0.5 rem (5 mSv)
Frequent Public Exposure
0.1 rem (1 mSv)
Occupational Partial Body DEL for
Red Bone Marrow
Breast
Lungs
Gonads
Skin
Hand
Forearms
50 rem
Radiology personnel= ?
5 rem (50 mSv/yr) whole body
Exposure= ?
Exposure rate x Time
Effective Dose= ?
Wr x Wt x Absorbed Dose (mSv)
The Dose Limit established for non-occupational exposed person is ________ of that for the radiation worker.
1/10
Cumulative whole-body effective dose limit equation
Age x 1 rem
Output intensity
K(mAs) kVp2
D2
Entrance skin exposure equation
Dosimeter exposure
(mR)= SSD2
ESE (mR) SDD2
Primary barrier lead equivalent
1/16"
Primary barrier height is
7 feet
Primary barrier located
perpendicular to line of travel of primary x-ray beam
Secondary barrier lead equivalent
1/32" Pb
Secondary barrier located
parallel to line of travel
Control booths are considered
secondary barriers
Tube housing for x-ray tube's lead equivalent
1.5 mm (1/16") Pb
Leakage radiation should not exceed:
100 mR/hr @ 3" (1 meter)
X-ray tube housing purpose
reduces leakage radiation
Factors that determine protective barrier thickness:
Time of Occupancy (T)
Workload (W)
Use (U)
Time of occupancy (T)
amount of time a hospital area is occupied by people
Workload (W)
amount of activity of the x-ray machinery
Use (U)
the % of time the x-ray beam is energized and directed to a particular wall
Controlled areas
an area occupied by radiation personnel
Uncontrolled areas
an area occupied by non-radiation personnel
Controlled areas are designed to reduce exposure less than
100 mrem/week
Uncontrolled areas are designed to reduce exposure less than
10 rem/week (Forshier)
2 rem/week (Bushong)
Protective apparel protection lead equivalent
.25 mm Pb
Lead aprons lead equivalent
.5 mm
Lead aprons lead equivalency must provide how much attenuation at how much kVp?
90% attenuation at 75 kVp
Lead gloves lead equivalent is
minimum .25 mm
The source to-table top distance in fluoro is
minimum 15 inches (38 cm)
Mobile unit distance must not be less than
minimum 12 inches (30 cm)
Filtration requirements for Fluoroscopic Exam
total 2.5 mm Al
Image Intensifier acts as ______ and should be at least ______ Pb.
protective barrer; 2 mm Pb
Inverse Square Law definition
the intensity of radiation at a given distance is inversely proportional to the square of the distance of the object from the source
workload equation
patients/day x day/week= patients/week
patients/week x films/patient= films/week
films/week x mAs/film= mAs/week
mAs/week x 1 min/60 seconds= mA-min/week
Useful beam
primary x-ray beam
ALARA agreement states
those states that have agrees with the Nuclear Regulatory Commission to take responsibility to enforce radiation protection guidelines through the states' department of health