Overview
Learn what to do if you may have been exposed to certain kinds of radioactivity
Bioassays are performed on persons who use unsealed quantities of radioactive materials to determine whether any activity has entered the body. The results are used to:
1. Estimate internal organ doses.
2. Determine the presence of airborne radioactive materials.
3. Evaluate work habits, experimental and facility design. Bioassays are performed either by:
a. Analyzing samples of blood, urine, or tissue. OR
b. Monitoring the organ of interest to determine the presence and quantity of radioisotopes. The method chosen depends upon the type of radioisotope involved (e.g. urine analysis for 3H or thyroid scanning for 125I).
BIOASSAY PROGRAM FOR 3H, 14C, 32P AND 35S, and other radioactive materials except radio-iodine.
1. Criteria
Bioassays should ideally be performed:
a. After each procedure where there is a potential for airborne activity, or personnel exposure.
b. When there is a suspicion that internal contamination might have occurred. The University of California, San Francisco (UCSF) bioassay policy requires that each individual handling greater than 100 millicuries of potentially volatile 3H, or greater than 50 millicuries of potentially volatile 14C, 35S, 32P MUST perform a bioassay after such uses and document the results in a logbook. However, it is strongly recommended that all individuals using millicurie quantities of any volatile radioisotope per experiment perform a urine assay after such uses.
Notes:
- The quantity HANDLING refers to the activity of the stock solution from which it is drawn. This will be obtained from the Single Purchase Amount listed on the Radiation Use Authorization (RUA).
- The Radiation Safety Program (RSP) will determine the need for bioassays; this will be indicated in the RUA approval.
2. Procedure
Urine is analyzed to estimate any uptake of radioactive materials other than radioiodine.
a. Place 1.0 cc of urine in a scintillation counting vial.
b. Add 9 cc of liquid scintillation cocktail.
c. Set the counter for the appropriate radioisotope.
d. Count the sample for 1 minute.
e. Count a 10 cc LS cocktail for 1 minute as a background count (Cb).
3. Analysis
a. Obtain net count (Cn). Cn = Cs - Cb
b. Divide the net count by counter efficiency to obtain dpm. (dpm = Cn / efficiency)
c. Convert dpm to activity (uCi).
d. Log the results in the appropriate radioisotope bioassay record sheet. The results of the calculations on the record sheet should be compared with those given below.
4. Maximum Values
Reference Annual Limit of Intake (ALI) 10 CFR 20 Appendix B. The activity should not exceed the following values:
5. Action Levels
If the calculated body burdens exceed 10% of ALI values, inform the Radiation Safety Officer (RSO) so that an investigation can be conducted to determine the causes of the uptake and recommendations for remedial can action be made.
BIOASSAY PROGRAM FOR 123I, 125I, AND 131I
1. Criteria
The bioassay program is developed for persons working with radioiodine to aid in determining the extent, if any, of an individual's exposure to concentrations of airborne radioiodine. Bioassays are performed by measuring the emissions from radioiodine within the thyroid. Routine bioassays are performed for those quantities listed below:
For 125I:
| (A=) Single Purchase Authorization (mCi) | Frequency | |
| 1.0 < A < 15.0 | Volatile | Quarterly |
| 15.0 < A < 20.0 | Volatile | Monthly |
| 20.0 < A | Volatile | Within 14 Days |
| 5.0 < A | Non-Volatile | Quarterly |
Notes:
- The bioassay frequency is based on the activity in the vial of the 125I stock handled to perform the iodination.
- Single Purchase Authorization is the maximum activity the laboratory can receive in each vial. This determines the frequency.
- The bioassay frequency will be communicated to the Principal Investigator (PI) in the RUA conditions. The usage quantity is not the determinant factor but "A" quantity is!
- Bioassays must be performed by those individuals who have used radioiodine in the laboratory during the period (e.g. month, quarter etc.).
- The bioassay frequency is based on the activity in the vial of the 125I stock handled to perform the iodination.
- Single Purchase Authorization is the maximum activity the laboratory can receive in each vial. This determines the frequency.
- The bioassay frequency will be communicated to the Principal Investigator (PI) in the RUA conditions. The usage quantity is not the determinant factor but "A" quantity is!
- Bioassays must be performed by those individuals who have used radioiodine in the laboratory during the period (e.g. month, quarter etc.).
For 123I and 131I:
- 123I users must obtain a bioassay within 24 hours if the iodination utilizes more than 5.0 mCi.
- 131I users must obtain a bioassay within 2 weeks of any iodination utilizing more than 1.0 mCi.
- Individuals administering volatile quantities of 131I for therapeutic purposes, in excess of five (5) millicurie must obtain a bioassay within two weeks of administration. This does not include other personnel in the room at the time of the administration or subsequent patient care. However, it is strongly recommended that all persons in the room during such an administration should obtain a bioassay within two weeks. If capsules are used no bioassays are required, unless an unusual event takes place.
2. Location of Bioassays
- Thyroid monitoring will be performed at the locations listed below:
- All 125I users
- Radiation Safety Office at L-235 Parnassus Campus or Building 1, Room 3 (floor below Gallo Foundation) at San Francisco General Hospital (SFGH).
- All persons using 123I and 131I will have their bioassays performed in the Nuclear Medicine Department at ZSFGH or University of California Medical Center (Long Hospital Third Floor) or Mt. Zion Nuclear Medicine Section.
3. Occupation Ali
The annual limits on intakes are as follows: Isotope to be Monitored ALI 123I 3000 µCi 125I 40 µCi 131I 30 µCi
4. Action Level
The action levels set are 10% of the ALIs. When action levels are exceeded the following steps should be taken:
a. An investigation of the operation involved, including air sampling, will be carried out to determine the causes of exposure and to evaluate the potential for further exposures.
b. If the investigation indicates that further work in the area might result in exposure of a worker to concentrations exceeding the Derived Air Concentrations (DAC) the worker will be restricted from further exposure until the cause of exposure is discovered and corrected.
c. Corrective actions that will eliminate or lower the potential for further exposures will be implemented.
d. A repeat bioassay will be taken within 2 weeks of the previous measurement and should be evaluated within 24 hours after measurement in order to confirm the presence of internal radioiodine, and to obtain an estimate of its effective half-life for use in estimating dose commitment.
e. If the thyroid burden exceeds 50% of ALI, refer the case to appropriate medical consultation as soon as possible for recommendations regarding therapeutic procedures that may be carried out to accelerate removal of radioactive iodine from the body. This should be done within 2-3 hours after exposure when the time of exposure is known so that any prescribed thyroid blocking agent would be effective.
NOTE: All exposures exceeding the ALI will be reported to the State of California immediately by telephone and followed by additional reports and actions prescribed by the State of California.
5. Incidents or Unusual Events
Contact the RSO if an incident or unusual event occurs involving any radioisotope other than radioiodine. The RSO will request that a urine sample be submitted for examination to determine if an exposure occurred.