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SECTION 12: Internal Dose Control
and Bioassays
Control (top)
As a matter of policy and practical necessity, the "Authorized
User" must be the individual responsible for controlling the dose
received by personnel under his or her supervision and/or using "Sources
of Radiation" under his or her authorization so that no person
receives a total dose in excess of the maximum permissible limits specified
in Appendix D. The total dose includes both that due to exposure to
internally deposited radioisotopes and exposure to external "Sources
of Radiation." The monitoring of radiation dose provides information
essential to the control process. The program under which the internal
dose is monitored is described below. The program under which the external
dose is monitored is described in Section
11.
Exposure investigations, regulatory notifications and physician referrals
all depend on the outcome of bioassays performed as required by this
section. The University is legally required to initiate these actions
via license conditions and the regulations in "10
CFR Part 20". The
cooperation
of the "Principal
Investigator" and the individual is essential
to ensure compliance with this section of the Radiation Safety Guide.
Internal Monitoring Requirement
(top)
The "Authorized User" is responsible for ensuring that persons
under his or her supervision or using radioisotopes under his or her
authorization are provided with bioassay services. Arrangements for
bioassays are made by contacting the Office of Environmental Health
and Safety when the criteria given below are met.
Bioassays commonly involve urinalysis, external counting of the thyroid,
breath analysis, or whole body counting.
Special Bioassays
Bioassay analyses may be required of any person or persons who:
- Are likely to receive an annual intake in excess of 10 percent
of the Annual Limits of Intake specified in Table 1, Columns 1 and
2,
of Appendix B
- Are minors or declared pregnant women likely to receive an annual
committed effective dose equivalent in excess of 50 mrem
- Have been involved in a spill, an incident, or other occurrence
during which radioactive material may have been taken into the body
either by inhalation, ingestion, or by absorption through the skin
or a wound.
Routine Bioassays
The use of any radioisotope may require that routine bioassays be required
upon the determination of the "Health
Physicist." Such a determination
has been made for certain uses of tritium and radioiodine; the criteria
for bioassay for these radioisotopes are described below:
Tritium
Routine bioassays are required for those persons who handle tritium
under the following conditions:
1. Use in an open room or on a bench top with possible release*
| Form |
Minimum Amount Requiring Routine Bioassay** |
| H-3 gas in a sealed vessel |
100 Ci |
| HTO and other forms, including nucleotide precursors |
100 mCi |
2. Use in a fume hood with possible release*
| Form |
Minimum Amount Requiring Routine Bioassay** |
| H-3 gas in a sealed vessel |
1000 Ci |
| HTO and other forms, including nucleotide precursors |
1 Ci |
*Possible release means that the possibility of a significant airborne
release of radioactive material exists because 1) the techniques
used to process the material may create an aerosol, 2) the material
is inherently volatile, or 3) the techniques used to process the
material may increase its volatility.
**The amount requiring routine bioassay is considered to be either
1) the amount handled at any one time by an individual who uses
tritium on an infrequent basis, or 2) the cumulative amount of activity
handled during any one month when small amounts of tritium are used
on a frequent basis.
3. The "Health
Physicist" may determine, depending on
handling procedures and other conditions, that bioassays are required
for the use of smaller amounts of tritium.
4. Frequency of Routine Bioassays
Routine bioassays samples should be submitted within 48 hours of
the initial exposure to tritium and then once a month while routine
use of tritium continues. When work with tritium is on an infrequent
basis (less frequently than every two weeks) bioassays should be
performed within 72 hours of the end of the work period during which
tritium is handled.
5. Types of Required Bioassays
The tritium bioassay program for each individual should consist
of the following bioassays:
- Baseline (within one month prior to the beginning of any tritium
use requiring bioassay)
- Routine
- Post operational (within one month following last tritium use)
- Follow up (to follow the course of a significant uptake of
tritium)
Radioiodine
Routine bioassays are required for those persons who
handle I-125 or I-131 under the following
conditions:
1. Use in an open room or bench top with possible release*
| Form |
Minimum Amount Requiring Routine Bioassay** |
| Volatile |
1 mCi |
| Bound to non-volatile agent |
10 mCi |
2. Use in an adequate fume hood with possible release*
| Form |
Minimum Amount Requiring Routine Bioassay** |
| Volatile |
10 mCi |
| Bound to non-volatile agent |
100 mCi |
*Possible release means that the possibility of a significant airborne
release of radioactive material exists because 1) the techniques
used to process the material may create an aerosol, 2) the material
is inherently volatile, or 3) the techniques used to process the
material may increase its volatility.
**The amount requiring routine bioassay is considered as the cumulative
quantity handled by an individual during a 3-month period or on
one or more occasions in that period by opening stock reagent containers
from which radioiodine may escape.
3. The "Health Physicist" may determine, depending on
handling procedures and other conditions, that bioassays are required
for the use of smaller amounts of radioiodine.
4. Frequency of Routine Bioassay
Routine bioassay for I-125 should be performed within 6 to 72 hours
after the initial exposure to radioiodine and then once every three
months provided the results of the initial routine bioassay are
negative and routine use continues. When work with I-125 is on an
infrequent basis (less frequently than every two weeks), bioassays
should be performed within 10 days of the end of the work period
in which the I-125 is handled.
Routine bioassays for I-131 shall be performed within 6 to 72 hours
after initial exposure and then once a month provided the results
of the initial routine are negative and routine use continues. When
work with I-131 is on an infrequent basis (less frequently than
every two weeks) bioassays shall be performed within 6 to 72 hours
of the end of the work period in which I-131 is handled.
5. Types of Bioassays Required
The bioassay program for each individual should consist of the
following bioassays:
- Baseline (within one month prior to the beginning of any use
of radioiodine requiring bioassay)
- Routine
- Post iodination (within 6 to 72 hours of the end of a procedure
in which 5 mCi or more of free iodine is used)
- Post-operational (within one month following the last possible
exposure to radioiodine, when work is being discontinued)
- Follow-up (to follow the course of a significant uptake of
radioiodine)
6. Depending on the nature of the work and if a significant uptake
of radioiodine is found for one individual, other persons who frequent
the laboratory may be required by the "Health Physicist"
to obtain bioassays.
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