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.
Define
Annual Limit of Intake (ALI)
The activity of a radioactive material, in becquerels or microcuries, that would have to be taken into a human body in order to exactly deliver 0.05 Sv (5 rems) of committed effective dose equivalent to the body or a committed dose equivalent of 50 rem to any individual organ or tissue.
Draw the ICRP Biological Model
When is a total organ dose equivalent calculated?
- When the CEDE > 1.2 rems
- The preferred method is to use the organ-specific committed dose equivalent converion factors tabulated in FGR#11
Why do you need to take two measurements when measuring the thyroid?
- A correction for the thyroid gland depth must be made.
- This is accomplished by measuring the count rate from the radioiodine (e.g., 125I, 131I) directly over the gland and then taking a second reading at 90 degrees from the first reading (i.e., along the side of the neck).
- The ratio of these two counts can be used to locate the gland depth.
Radionuclide intakes by a pregnant worker must be monitored if they are likely to exceed _____ of the ALI values during the pregnancy.
Radionuclide intakes by a pregnant worker must be monitored if they are likely to exceed 1% of the ALI values during the pregnancy.
What are three major factors to define the committed effective dose equivalent received by a patient who has been injected with a radiopharmaceutical?
- Activity injected (I, intake)
- Total effective removal rate constant (k) which can be used to determine mean residence time in the body
- Specific effective energy, SEE(WB←WB), which is the energy absorbed per gram of the whole body (WB) per transformation within the WB.
What is the difference between intake and uptake?
- Intake – Total activity taken into the body
- Uptake – Percentage of intake that enters systemic circulation
List
In-Vivo Analysis
Advantages & Disadvantages
Advantages
- Repetitive thyroid measurement (q) can only be directly related to the accumulated thyroid activity and dose.
- The total intake can be simply estimated by the equation Σq/ΣIRF
Disadvantages
- Requires presence of working during thyroid count
- Care must be used to assure the measurement reflects only the organ burden and not external contamination, nor the burden of the radionuclide in other organs in the body
List
In-Vitro Analysis
Advantages & Disadvantages
Advantages
- The exposed person need not be present during the analysis of the 24 hour samples
- The total activity (Σq) of consecutive 24 hour urine samples over the first several days is 75% of body deposition
Disadvantages
- Requires cooperation of the worker to submit all urine during each 24 hour period
- Represents only excretion and not necessarily the organ burden, especially if a blocking agent had been used to block the uptake
A worker’s hand is severely lacerated by a grossly contaminated saw blade while cutting a drain line containing 239Pu.
State and justify the preferred bioassay technique.
Urinalysis for Pu-239
- Direct uptake into the blood from the wound
- Lack of significant photons associated with decay of 239Pu to perform to whole body counting
A diver is pulled from a spent fuel pool after a leak in the dive suit is detected. The pool water is heavily contaminated with tritium (3H).
State and justify the preferred bioassay technique.
Urinalysis for H-3
- Direct uptake into the blood from contact with the skin
- Lack of significant photons associated with the decay of 3H to detect through whole body counting
A worker is grossly contaminated upon the face, hair, neck, and upper torso with 137Cs following work in a highly contaminated area.
State and justify the preferred bioassay technique.
Whole body count for high yield 0.662 MeV gammas
- All inhaled 137Cs is assumed to be in the relatively transportable class “D”
- All 137Cs ingested is essentially taken directly into the blood and rapidly distributed throughout all the soft tissue in the body
- Should be performed following successful whole body decontamination.
A researcher swallows a quantity of 35S during a pipetting operation.
State and justify the preferred bioassay technique.
Urinalysis for S-35
- Direct uptake into the blood from small intestine
- Lack of significant photons associated with the decay of S-35 to detect from external whole body counting
A worker’s respiratory protective equipment fails during work in a high 131I airborne area.
State and justify the preferred bioassay technique.
Thyroid counting for I-131 gammas
- All inhaled 131I is assumed to be in the relatively transportable class “D.”
- Rapidly taken into the blood and distributed to the thyroid gland.
List 4 categories of medical intervention techniques used to minimize internal dose following an intake/uptake
- Removal of contamination to prevent internal contamination ⇒ Washing skin, excision of contaminated tissue.
- Diuretics ⇒ Enhance excretion of contaminated body fluids to reduce deposition of radionuclides in systemic tissue.
- Blocking agents ⇒ KI prevent deposition of 131I in the thyroid.
- Chelating (chemical) agents ⇒ Ca/Zn DTPA forms a complex with Pu-239 before it can deposit in the liver.
A worker’s hand is severely lacerated by a grossly contaminated saw blade while cutting a drain line containing 239Pu.
What is the best medical intervention technique?
What is a concern and precaution for thsi method?
Washing of Pu-239 contaminated wound and excision of contaminated tissue.
- Concern ⇒ Disfigurement from tissue excision at wound site.
- Precaution ⇒ Collection of all excised tissue and cleaning water for further analysis.
A diver is pulled from a spent fuel pool after a leak in the dive suit is detected. The pool water is heavily contaminated with tritium (3H).
What is the best medical intervention technique?
What is a concern and precaution for thsi method?
Increased fluid intake and physical activity to enhance excretion of tritiated water
- Concern ⇒ High fluid intake could cause an electrolyte imbalance
- Precaution ⇒ Daily sampling and analysis of urine samples to monitor effectiveness of procedure
A worker is grossly contaminated upon the face, hair, neck, and upper torso with 137Cs following work in a highly contaminated area.
What is the best medical intervention technique?
What is a concern and precaution for thsi method?
Use of blocking agent (e.g., Prussian Blue) to limit uptake of 137Cs by the small intestine.
- Concern ⇒ Toxic effect of the blocking agent
- Precaution ⇒ Limiting amount of agent to limit the toxic effect
A research swallows a quantity of 35S during a pipetting operation.
What is the best medical intervention technique?
What is a concern and precaution for thsi method?
Induce vomiting
- Concern – Need for early implementation to limit uptake into blood from small intestine
- Precaution – Collection and analysis of vomit and urine samples to determine its effectiveness and estimate internal dose for future guidance
A worker’s respiratory protective equipment fails during work in a high 131I airborne area.
What is the best medical intervention technique?
What is a concern and precaution for thsi method?
Use a blocking agent (e.g., KI)
- Concern ⇒ Early administration required to be effective
- Precaution ⇒ Limit the amount of agent to amounts not likely to cause toxic effect
Name three changes to the lung model that occurred from ICRP 30 to ICRP 66.
- An increase in the default AMAD from 1 μm to 5 μm for deriving intake to dose conversion factors (e.g., ALIs, DACs).
- Extension of the model’s application from occupationally exposed adults vs. children, smokers vs. nonsmokers, and mouth vs. nose breathers.
- Changed inhalation chemical compound classes from D, W, Y (day, week, year) to F, M, S (fast, medium, slow) clearance. This change treats mechanical and dissolution clearance pathways specifically.
When can a nuclear medicine patient be released from the hospital?
Release is allowed if it is not likely that any individual coming into contact with the patient will receive a dose greater than 0.5 rem.
What are four precautions you should give a nuclear medicine patient upon discharge from the hospital?
- Do not nurse an infant until sufficient clearance of radionuclide has taken place.
- Do not hold an infant or child for an extended period of time.
- Maintain distance between self and other persons and limit contact with any persons.
- Notify supervisor of patient if occupational radiation worker. ⇒ An accidentally exposed TLD from a non-occupational source would cause compounding problems.
What are four advantages of a whole body count when measuring for 137Cs and 60Co?
- Both radionuclides emit high intensity gamma-rays associated with their decay
- Whole body counting provides a rapid evaluation of whether significant intakes took place. Urine bioassay requires a longer collection time of 24 hour samples and separate chemical processing and counting of the samples
- Whole body counting provides a direct result of the body burden, which can directly relate to internal dose. Urine samples require a biokinetic model to reverse to the time of intake
- Repetitive whole body counts provide a measure of the clearance rate and the cumulated activity. These can be directly related to the internal dose over the time of the measurement. Urine bioassay only indicates what has been excreted by the urine.
