Internal Dosimetry Techniques Flashcards
What are the steps in calculating an internal dose?
1. Determine the body (or organ) burden // from bioassay or whole body (or partial body) count 2. Compute the intial intake at time = 0 or intake history 3. Chose a dose model 4. Calculate the internal committed effective dose equivalent
What are examples of useful body products for bioassay?
- Urine
- Sweat
- Saliva
- Hair
- Feces
- Nail Clippings
What are routes of entry into the body for radioactive materials?
- Inhalation - Through the nose
- Ingestion - Through the mouth
- Percutaneous - Absorption directly through the skin
- Wounds (impingement) - Injection through the skin
Classifiy the different internally deposited contaminants.
What is ICRP 23?
Report of the Task Group on Reference Man
ICRP 23
What is the total body water content for the reference adult male and female?
- Male ⇒ 42 kg
- Female ⇒ 29 kg
What is the biological clearance from the thyroid gland?
- 70 days
- ICRP recommends 120 days for radiation protection calculations
In a normal adult, how much iodine circulating in the blood will be removed and stored in the thyroid gland tissue?
25 - 30%
What are biological half-lives for various bone seekers?
- Pu ⇒ 200 years
- Radium ⇒ 45 years
- Calcium ⇒ 49 years
What information is required on a bioassay (in vitro) sample?
- Sample Date
- Victim’s Name
- Sampling Person’s Name
- Time Collected
- Victim’s Identification #
- Unusual circumstances
Rule of Thumb
Action level for alpha inhalation
200 disintegrations per minute of alpha contamination from the swabs of both nostrils counted together on a portable alpha survey meter.
Rule of Thumb
Converting nasal swabs to predicted inhalation
10% of the intake is on the nasal swabs taken within one hour of exposure.
// from Radiation Emergency Assistance Center/Training Site, REAC/TS
If someone exceeds an inhalation action level, what should you do?
Persons should be immediately referred to a physcian for analysis and should be put in a urine sampling program.
If an accident involving radionuclide intake is less than 1 hour old at the time of the sample collection, how should the victim be instructed to provide a urine sample?
- The preson should be instructed to empty his bladder without providing a urine sample.
- Otherwise, the urine present from before the accidental intake will dilute the contamination, and the sample will show a deceptively low concentration.
What are urine samples normally provided in?
- Waxed containers or polyethylene bottles
- Glass for tritium (so it does not diffuse rapidly through the sample container).
Rule of Thumb
It takes about _____ hours before the maximum urine concentration is reached following an acute uptake.
It takes about 4 hours before the maximum urine concentration is reached following an acute uptake.
When should urine samples be collected?
- After the decontamination shower.
- Reduces the chance of contaminating the collected sample from external body radioactivity which may transfer into the container during collection.
- Such external contamination could easily lead to a false diagnosis of an extremely large body burden.
Define
“In Vivo” counting
- Placement of an external radiation detector near the body to measure radiations emitted from internally deposited radionuclides.
- Also known as “whole body counting.”
In vivo counting gives the burden at what time?
The time of measurement
What are advantages and disadvantages of using NaI(Tl) for in vivo counting?
Advantage
- Energy resultion ⇒ With NaI(Tl), gamma rays can differ by only about 50 keV in energy (1 MeV for liquid scintillation).
Disadvantage
- Low counting efficiency (10%)
- Need for shielded rooms which are very expensive
When performing whole body counting (in vivo), what two factors much be taken into account before a reasonable body burden or organ burden estimate can be arrived at?
- Depth of organ ⇒ Shielding effect of the body tissues between the radioactive material and the detector (close to surface will measure more radiation).
- Body size ⇒ Correction factors for unusually small or large persons which do not approximate the reference man/woman.
Equation
How do you calculate the amount of an intake at time = 0?
I = A / IRF
- I ⇒ Intake (Ci)
- A ⇒ Measure of current activity at a specified time (Ci)
- IRF ⇒ Intake Retention Factor at a specified time
Define
Critical organ
- The body organ which receives the greatest damage as a result of radioactive intake.
- Normally the organ having the highest concentration of radioactivity.
The internal dose of a person is _____ to the effective half life.
The internal dose of a person is directly proportional to the effective half life.