External Monitoring
External occupational exposures from certain radionuclides and/or types of radiation are primarily monitored with the use of personnel dosimetry. The need for dosimetry is based on the nature and frequency of usage, among other factors. Dosimetry is for all uses of radiation and radioactive materials at NIH.
Dosimetry Eligibility
All users of radiation and radioactive materials at NIH are required to be evaluated for dosimetry. To complete the registration/training process, all users must submit a completed Dosimetry Evaluation Form. 
The form contains a radionuclide usage worksheet where you should indicate the estimated types and quantities of radiation and radioactive materials that you intend to use. Filling this worksheet out completely will ensure that that your need for dosimetry can be evaluated appropriately. If you are unsure of the radionuclides, amounts or types of radiation you will be using, consult your Authorized User or Area Health Physicist for guidance.
A new Dosimeter Evaluation Form be submitted to DRS whenever an individual's usage pattern changes signifcantly!
Due to the very low energy of emission, dosimetry is required for use of the following radionuclides:
However, dosimetry be required for use of the following radionuclides:
Other areas where the use of radiation and radioactive material require a dosimetry evaluation by DRS:
- Patient care
- Animal use
- Nuclear Medicine / PET
- X-ray machines
- Fluoroscopy
- Linear Accelerators
Dosimetry should be worn properly and at all times when working with or around radiation and radioactive materials.
When not in use, dosimetry should be stored away from (or shielded from) sources of radiation.
Dosimetry should not be left in closed cars (due to sun or heat stress), and should not be subjected to wet environments or chemicals.
Dosimetry is used to monitor occupational radiation exposure only, so it should not be worn outside of work, taken home, or otherwise removed from the facility.
Dosimetry is not intended to monitor radiation exposure from non-occupational medical procedures.
Interpretation of Dosimetry Results
Dosimetry results are received from the dosimetry contractor and reviewed by DRS on a monthly basis for most monitored individuals.
DRS may conduct an investigation of elevated exposures, based on predetermined action levels and the nature of the work performed during the period in question.
Exposure investigations are not cause for alarm, as they are most often conducted for exposures that are well within regulatory limits. Investigations help determine the cause of an elevated exposure, identify corrective actions, and ensure that future radiation exposures are kept ALARA.
Internal Monitoring
Internal monitoring activities are conducted to assess the potential intake (ingestion, inhalation, or absorption) of radioactive material into the body. Bioassays (direct measurement of radioactive material in the body) and personnel air sampling are the accepted methods of internal monitoring at NIH. Internal monitoring requirements depend on a number of factors including the experimental procedure, activity used, and the chemical form (volatility) of the compound in question.
Thyroid Bioassay
Thyroid bioassays are used to assess the intake of radionuclide compounds that tend to concentrate in the thyroid gland (e.g., radioiodines). As such, thyroid bioassays are sometimes required after the use of volatile I-125 and I-131.
A baseline thyroid bioassay is required prior to handling or observing work with volatile radioiodine for the first time.
Thyroid bioassays are a requirement of radiation safety protocols that involve the use of potentially volatile radionuclides. Depending on the activity and frequency or usage, a protocol user may be required to undergo thyroid bioassay on a regular basis.
Thyroid bioassays may also be requested by DRS after spills, personnel contamination, or other abnormal occurrences.
Thyroid bioassays are conducted in Building 21, and may be scheduled through the DRS Technical Services Section (6-4803).
Urine Bioassay
Urine bioassays are used to assess the intake of radionuclides that don't exhibit uptake within a particular organ. These compounds are typically cleared from the blood via the kidneys, and can be measured in the urine for a finite period following the intake.
A baseline urine bioassay is required prior to participation in most radiation safety protocol activities. If urine bioassay is required by the protocol, a second urine bioassay will be requested after the initial experiment.
Urine bioassays may also be requested by DRS after spills, personnel contamination, or other abnormal occurrences.
Urine bioassay kits are available from the DRS Technical Services Section (6-4803).
Personnel Air Monitoring
Along with bioassay, personnel air monitoring is a requirement of radiation safety protocols that involve the use of potentially volatile radionuclides.
A personnel air monitoring (breathing zone) apparatus is typically installed by DRS, after which the research staff must collect air samples during each experiment involving volatile radionuclides.
Based on air monitoring results, DRS may request a bioassay or initiate an intake investigation.
Limits and Action Levels
Occupational radiation exposures are subject to regulatory limits, based on the type of radiation or radioactive material involved. However, the NIH Radiation Safety Program works to maintain compliance with regulatory limits and minimize occupational exposures through an ALARA Program.
Regulatory Limits
Whole Body |
5 rem/year |
1.25 rem/quarter |
|---|
Lens of Eye |
15 rem/year |
1.25 rem/quarter |
|---|
Skin |
50 rem/year |
7.5 rem/quarter |
|---|
Extremities |
50 rem/year |
18.75 rem/quarter |
|---|
Embryo/fetus |
500 mrem/gestation |
N/A |
|---|
Minor |
10% of adult |
10% of adult<5(N-18) rem lifetime |
|---|
General Public |
100 mrem/year2 mrem/hour |
N/A |
|---|
Action Guidelines
To ensure compliance with regulatory limits, investigations are performed when an occupational exposure exceeds pre-established trigger levels:
| Level I |
10% |
10% |
|---|
| Level II |
30% |
30% |
|---|
| Level III |
N/A |
50% |
|---|
Investigations may be formal or informal, depending on the circumstances of the exposure in question.
DRS will determine when an investigation is warranted, based on the external and/or internal monitoring results available for a given individual.
NIH Policy on Breast-feeding Radiation Workers
A breast-feeding radiation worker is capable of transmitting radioactive material to her child if she receives an internal uptake herself.
Not all radioactive material is a concern to breast-feeding women; the potential for uptake and subsequent transmission to a child via breast milk is greatest for volatile forms of radioiodine, and some potentially volatile forms of H-3, S-35, Br 76, and At-211.
A breast-feeding woman may choose to declare her breast-feeding status to the Division of Radiation Safety, similar to the "Declaration of Pregnancy" policy, above. The declaration form may be obtained from her Area Health Physicist.
A declared breast-feeding radiation worker will have her potential for internal uptake assessed and precautions agreed upon so that the child's dose will be ALARA, below the general public dose limit of 100 millirem per year.
The declared breast-feeding worker may rescind her breast-feeding declaration at her discretion.
Fetal Exposure Monitoring Declared Pregnancy Policy
The NIH Fetal Protection Program has been established to minimize occupational exposures to the embryo/fetus of a woman who has formally declared her pregnancy to DRS.
Dose Limit
Participation in the Fetal Protection Program establishes a special dose limit for the embryo/fetus of a declared pregnant woman (DPW).
The special dose limit (500 mrem) applies to the entire gestation period (nine months).
This limit includes both internal and external doses received due to occupation exposure to radiation and radioactive material.
Declaration
Participation in the Fetal Protection Program is entirely voluntary, and is established through a formal declaration of pregnancy to DRS.
Declaration of pregnancy is completely confidential. However, a DPW must notify her Authorized User or supervisor, who is then responsible for enforcing any radiation safety restrictions or precautions.
Declaration of pregnancy may be made at any time during the pregnancy. However, it is recommended that a declaration be made as soon as possible to allow timely assessment of occupational exposure risk.
To participate in the Fetal Protection Program, a Declaration of Pregnancy form may be submitted in confidence to DRS. Mailing instructions are included on the form.
Medical documentation of pregnancy is not required unless modification of work assignment is necessary. If necessary, confirmation of pregnancy may be obtained free of charge from the NIH Occupational Medical Service(OMS).
If a woman chooses not to declare her pregnancy, DRS will not take steps to evaluate or limit the dose to the embryo/fetus. However, the pregnant woman will still be subject to the standard regulatory limits for occupational radiation exposure, and will be required to maintain her dose as low as reasonably achievable (ALARA).
Consultation
Following written declaration of pregnancy, a health physicist will meet with the DPW and her Authorized User (or supervisor) to:
- review information on the bioeffects of ionizing radiation
- assess the woman's exposure potential
- discuss any restrictions and/or precautions that may be necessary
- establish an appropriate exposure monitoring program
The special dose limit is not expected to affect the scope of work for the majority of women at NIH. Restrictions are only necessary if there is a realistic potential for the embryo/fetus to receive a dose in excess of 500 mrem during the pregnancy.
Regulatory Guidance
For more information on radiation health effects and prenatal radiation exposure, feel free to consult the following sources:
NRC Regulatory Guide 8.13, Instruction Concerning Prenatal Radiation Exposure
NRC Regulatory Guide 8.29, Instruction Concerning Risks from Occupational Radiation Exposure
Monitoring Records
All results of exposure monitoring are maintained electronically or on file at DRS, and are available to individuals upon written request.
Instructions for Requesting Records
Submit a written request to the Chief, Technical Services Branch, DRS (Building 21).
Include your name, social security number, and dates of employment.
All requests for monitoring records are confidential. Therefore, all written requests must be signed by the requesting individual.
ALARA
The NIH Radiation Safety Program has been designed to ensure that occupational doses and doses to members of the general public are As Low As Reasonably Achievable (ALARA), and not just in compliance with regulatory dose limits.
ALARA Principles
- A concept to reduce unnecessary radiation exposure in the workplace
- Applies even if the maximum permissible dose is not exceeded
- A regulatory requirement [10CFR20.1003, 10CFR20.1101(b), and 10CFR35.20]
- A requirement of the NRC Type A Broad Scope license granted to NIH
Methods of ALARA Compliance at NIH
- Administrative Controls
- Engineering Measures
- Surveillance
- Enforcement
- Training