Internal Radiation Monitoring
Reviewed 1/23/25
When handling unsealed sources of radioactive material, the potential always exists for introduction of the materials into the body. Internal deposition can result from inhalation, ingestion or absorption.
Bioassay is required of individuals working with quantities and types of radioactive materials where significant internal deposition may occur. Bioassay is defined as the determination of the kind, quantity or concentration and location of radioactive material in the human body. The determinations are either by direct measurement (in vivo) or by analysis of materials excreted or removed from the body (in vitro).
When a potential authorized user is being evaluated for permission to use radioactive materials, the need for bioassay will be reviewed by the Radiation Safety Officer during his or her initial review of the application.
When established authorized users wish to change a research protocol, or increase significantly the quantity of radioactive material used in a procedure, etc., the possible need for bioassay should be discussed with the Radiation Safety Officer.
Bioassays are required under specific conditions as listed below when using Hydrogen-3 (Tritium) and any of the radioisotopes of Iodine.
Hydrogen-3 Compounds
Conditions under which bioassay is necessary:
a) Handling on a bench top a quantity of Hydrogen-3 which equals or exceeds 10 millicuries.
b) Handling in a properly functioning chemical (fume) hood a quantity of Hydrogen-3 which equals or exceeds 100 millicuries.
c) When an individual processes at any one time, or enters into process during any one month time period, quantities which exceed 10% of the values show in Table I.
d) When surveys or calculations indicate an individual has been exposed to concentrations in air or water in excess of the Annual Limit on Intake (ALI), Part 16, Chapter 1, N.Y. State Sanitary Code.
e) The Radiation Safety Officer has reason to suspect an individual may be internally contaminated.
f) As required by any other applicable state or federal guidelines.
TABLE I
ACTIVITY LEVELS OR CONCENTRATIONS ABOVE WHICH TRITIUM BIOASSAY IS NECESSARY
|
Types of Operation (a) |
HTO(b) and Other Tritiated Compounds (Including Nucleotide Precursors) |
Tritium (HT or T2)(c) Gas in Sealed Process Vessels |
HTO Mixed with More Than 10 kg of Inert H20 (e.g., in Reactor Coolant)(d)(e) |
|
Processes in open room or bench with possible escape of tritium from process vessels |
0.1 Ci |
100 Ci |
0.01 Ci/kg |
|
Processes with possible escape of tritium carried out within a fume hood of adequate design, face velocity, and performance reliability |
1 Ci |
1000 Ci |
0.1 Ci/kg |
|
Processes carried out within gloveboxes that are ordinarily closed but with possible release of tritium from process vessels and occasional exposure to contaminated box and leakage |
10 Ci |
10,000 Ci |
1 Ci/kg |
|
(a) |
Quantities (< 10 kg) of substances containing tritium that are present during operations may be considered to be either the amount processed by an individual at any one time (when accidental intake is more likely) or the amount of activity that entered into the process (throughout) during any one month (when routine handling of repeated batches is the more likely source of exposure). |
|
(b) |
HTO is a symbol for a water molecule in which a tritium atom (T) is present in place of a normal hydrogen atom (H). |
|
(c) |
A molecule of hydrogen gas contains two hydrogen atoms. Either one of these atoms may be replaced with T to form HT, or two T atoms may combine to form T2 gas. |
|
(d) |
This assumes that adequate air monitoring has established that there is no tritium leakage or that no significant amount of tritium gas can be converted to HTO before intake. |
|
(e) |
This column is applicable in place of the previous two columns in cases where tritium can be identified at measurable concentrations in large amounts of water or other substances, such as at nuclear power plants. |
Radioiodine Compounds
Conditions Under Which Bioassay is Necessary:
a) Use on a bench top of a quantity of Iodine-125 or Iodine-131 at any time which equals or exceeds 100 microcuries.
b) Use in an adequately functioning fume hood, a quantity of Iodine-125 or Iodine-131 at any time which equals or exceeds 1 millicurie.
c) When an individual handles in an open form, unsealed quantities of radioactive Iodine that exceeds 10% of those shown in Table II. Table II quantities apply to quantities handled at any one time or integrated as the total amount of activity introduced into a process by an employee over any three month period.
d) Surveys or calculations indicate an individual has been exposed to concentrations in air or water in excess of maximum permissible concentrations listed in Part 16, Chapter 1, N.Y. State Sanitary Code.
e) The Radiation Safety Officer has reason to suspect an individual has been internally contaminated.
f) As required by state or federal regulations.
TABLE II
ACTIVITY LEVELS ABOVE WHICH BIOASSAY FOR I-125 OR I-131 IS NECESSARY
|
Types of Operation (a) |
Volatile or Dispersible(a) |
Bound to Nonvolatile Agent |
|
Processes in open room or bench with possible escape of iodine from process vessels |
1 mCi |
10 mCi |
|
Processes with possible escape of iodine carried out within a fume hood of adequate design, face velocity, and performance reliability |
10 mCi |
100 mCi |
|
Processes carried out within gloveboxes, ordinarily closed, but with possible release of iodine from process and occasional exposure to contaminated box and box leakage |
100 mCi |
1000 mCi |
(a) Quantities may be considered the cumulative amount in process handled by a worker during a 3-month period; e.g., the total quantity introduced into a chemical or physical process over a 3-month period, or on one or more occasions in that period, by opening stock reagent containers from which radioactive iodine may escape. Quantities in the right hand column may be used when it can be shown that activity in process is always chemically bound and processed in such a manner that 125I or 131I will remain in nonvolatile form and diluted to concentrations less than 0.2 mCi/mg of nonvolatile agent. Capsules (such as gelatin capsules given to patients for diagnostic tests) may be considered to contain the radioiodine in a contained form, and bioassay would not be necessary unless a capsule were inadvertently opened (e.g., dropped and crushed). However, certain compounds where radioiodine is normally bound are known to release radioiodine when the material is in process, and the left-hand column may then be applicable. In those laboratories working with only 125I in radioimmunassay (RIA) kits, the quantities of 125I are very small and in less volatile forms; thus, bioassay requirements may be judged from the right-hand column. In field operations, where reagent containers are opened outdoors for simple operations such as pouring liquid solutions, the above table does not apply; bioassay should be performed whenever an individual employee handles in open form (e.g., an open bottle or container) more than 50 mCi at any one time.
Operations involving the routine use of 125I or 131I in an open room or bench are discouraged. Whenever practicable, sealed bottles or containers holding more than 0.1 mCi of 125I or 131I should be opened at least initially within fume hoods having adequate face velocities of 100 feet/min or more.
Scheduling Bioassay Tests
Please contact the Radiation Safety Office for scheduling bioassay tests before handling of the radioactive material occurs.
In any event, appropriate testing must be carried out according to the following schedule:
a) Hydrogen-3. Urine samples within 24-48 hours of exposure.
b) Iodine-125 and Iodine 131. In vivo thyroid assay within 24-72 hours of exposure.