Regulatory Guide 8.20

Applications of Bioassay for I-125 and I-131

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Issue date:	09/30/1979
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RG-8.020, Rev. 1
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U.S. NUCLEAR REGULATORY COMMISSION

REGULATORY GUIDE

OFFICE OF STANDARDS DEVELOPMENT

REGULATORY GUIDE 8.20

APPLICATIONS OF BIOASSAY FOR 1-125 AND 1-131

A. INTRODUCTION

Section 20. 108,

"Orders Requiring Furnish ing of Bioassay Services," of 10 CFR Part 20,

"Standards for Protection Against Radiation,'

indicates that the Nuclear Regulatory Commis sion (NRC) may incorporate into a license pro visions requiring a

specific program of bioassay measurements as necessary or desirable to aid in determining the extent of an individual's exposure to concentrations of radioactive material.

In certain cases, the requirement of bioassay may also be included in the license by reference to procedures specify ing in vivo measurements, measurements of radioactive material in excreta, or both.

This guide provides criteria acceptable to the NRC staff for the development and implementa tion of a bioassay program for any licensee handling or processing

1-125 or

1-131.

It further provides guidance to such licensees regarding the selection of workers who should participate in a program to detect and measure possible internal radiation exposure. The guide is programmatic in nature and does not deal with measurement techniques and procedures.

B. DISCUSSION

The topics treated in this guide include de terminations of (1) whether bioassay should be performed,

(2)

frequencies of bioassay,

(3)

who should participate, (4) the actions to take based on bioassay results, and (5)

the partic ular results that should initiate such actions.

For the user's convenience, the following terms are presented with their definitions as used in this guide:

Bioassay-The determination of the kind, quantity or concentration, and location of radioactive material in the human body by direct (in vivo) measurement or by analysis in vitro of materials excreted or removed from the body..

Intake-The total quantity of radioactive material entering the body.

In vivo measurements-Measurement of gamma or x-radiation emitted from radioactive material located within the body for the purpose of detecting or estimating the quantity of radio active material present.

In vitro measurements-Measurement of radio activity in samples of material excreted from the human body.

C. REGULATORY POSITION

1. Conditions Under Which Bioassay Is Necessary a. Routine' bioassay is necessary when an individual handles in open form unsealed 2 quantities of radioactive iodine that exceed those shown in Table 1 of this guide. The quantities shown in Table 1 apply to both the quantity handled at any one time or integrated as the total amount of activity introduced into a process by an employee over any 3-month period.

b. When quantities handled in unsealed form are greater than 10% of Table 1 values,

• Lines indicate substantive changes from previous issue.

I Routine means here that an individual is assigned on a sche u**-ed and repeatable basis to submit specimens for bioassay or to report for in vivo measurements.

Either radiochemical bioassay of urine or in vivo counting is acceptable to the NRC

staff for estimating internal radioactivity burdens or intakes.

In some cases, however, a licensee may wish to corroborate estimates from urinalysis data with in vivo determinations.

Since there are adequate references in the literature to hellp devise bioassay measurements, thia guide does not include recommended analytical procedures.

Each installation should adopt. procedures or obtain services best suited to its own needs..

See discussion in the footnote to Table 1 of this guide.

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81PSeptaiff 1979

routine bioassay may still be necessary under certain circumstances.

A written justification for not performing such measurements should be prepared and recorded for subsequent re view during NRC inspections whenever bio assay is not performed and the quantities handled exceed 10% of the levels in Table 1.

c. Except as stated in regulatory posi tion 1.e, bioassay is not required when pro cess quantities handled by a worker are less than 10% of those in Table 1.

e d. In nuclear reactor installations, employ ees should be bioassayed by an in vivo count within 30 days after the end of exposure in work locations where concentrations exceeded, or might have exceeded,

9 x 10-1Q pCi/ml averaged over any 40-hour period. Table 1 and regulatory position 4 regarding frequency of bioassays are not applicable to reactor I licensees.

e. Special bioassay measurements should be performed to verify the effectiveness of respiratory protection devices and protective clothing. If an individual wearing a respiratory protective device or protective clothing is sub jected to a concentration of 1-125 or 1-131 (in any form) in air such that his or her intake with no protection would have exceeded the limits specified in paragraph 20.103(a)(1)

of

10 CFR

Part 20,3 bioassays should be per formed to determine the resulting actual 1-125 or 1-131 intake. These special bioassay proce dures should also be conducted for personnel wearing respirators if for any reason the 1-125 or 1-131 concentration in air and the duration

'of exposure are unknowvn or cannot be conser I vatively estimated by calculation.

2. Participation AUl workers handling radioactive iodine or sufficiently close to the process so that intake is possible (e.g., within a few meters and in the same room as. the worker handling the material)

should participate in bioassay pro grams described in regulatory position 1.

3Muitfplying the concentrations riven in Appendix B

to

10 CFR Part 20,

Table r, column i, 5 x 10-9 wCi/ml for 1-125 (soluble) and 9 x 10-9 *Ci/ml for 1-131 (Soluble), by 6 3 x 108 m= gives the corresponding quarterly intake of the respective iodines by inhalation. These quarterly intakes would be about

3.2 pCi for 1-125 and 5.7 pCi for 1-131, which would give a thyroid dose commitment of about 7.

rems to a 20-gram thyroid integrated over all future time using effective half-lives of 41.8 days for I-I25 and 7.6 days for 1-131 and using a quality factor (QF)

of 1.7 to calculate effective disintegration energy in the case of 1-125. (This QF of 1.7 ie used for conservatism, even though the International Commission on Radiological Protection

(1969)

and the National Council on Radiation Protection (1971)

have published a QF of 1, because some calculations in more recent scientific Literature have suggested the use of QF values higher than I for electron or beta energies of 0.03 MeV or less.)

3. Types of Bioasays That Should Be Performed a. Baseline (preemployment or preopera tional). Prior to beginning work with radio active iodine in sufficient quantity that bio assay is specified in regulatory position 1.

b. Routine.

At the frequency specified in regulatory position 4.

c. Emergency. As soon as possible after any incident that might cause thyroid uptakes toi exceed burdens given in regulatory posi-i tion 5.a(2),

so that actions recommended inI

regulatory position 5.a(2)(b)

can be most effective.

d. Postoperational and with Separation Phys ical. A bioassay should be performed within 2 weeks of the last possible exposure to 1-125 or

1-131 when operations are being discontinued or when the worker is terminating activities with potential exposure to these radionuclides.

e. Diagnostic. Followup bioassay should be performed within 2 weeks of any measurements exceeding levels given as action points in regulatory position 5 in order to confirm the initial results and, in the case of a single intake, to allow an estimate of the effective half-life of radioiodine in the thyroid.

4. Frequency a.

Initial Routine.

Except in situations where thyroid burdens may exceed quantities specified in regulatory position 5.a(2), a bio assay sample or measurement should be obtained within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> following entry of an individual into an area where bioassay is performed in accordance with regulatory posi tions 1 and 2 (but waiting at least 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> for distribution of a major part of the iodine to the thyroid')

and every

2 weeks or more frequently thereafter as long as the conditions;

described in regulatory positions 1 and

21 exist. When work with radioactive iodine is on an infrequent basis (less frequently than every

2 weeks), bioassay should be performed within

10 days of the end of the work period during which radioactive iodine was handled (but not sooner than 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> unless emergency actions to obtain an early prognosis and thyroid blocking treatment are appropriate4).

b. After 3 Months. When a periodic meas urement frequency has been selected in accordance with regulatory position 4.a, it may be changed to quarterly if, after 3 months, all the following conditions sre met:

(1)

The average thyroid burden for each individual working in a given area was

4NC*RP Report No. 55,

"Protection of the Thyroid Gland in the Event of Releases of Radlioodine,"

National Council on Radiation Protection and Measurements, Washington, D C.,

August 1, 1977, p. 21.

8.20-2

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less than 0.12 pCi of 1-125, less than 0.04 pCi of 1-131, and less than the corresponding pro portionate amounts of a

mixture of these nuclides during the initial 3-month period;

(2)

The quarterly average radioiodine concentration (pCi/ml)

in air breathed by any worker (as obtained when measurements of radioiodine concentrations in air are required)

does not exceed 25% of the concentration values for "soluble"(s) iodine given in Appendix B to

10 CFR Part 20,

Table I,

Column 1,

(5 x 10-9 pCi/ml for 1-125 and 9 x 10-9 pCi/ml for 1-131),

i.e.,

25% of these concentrations multiplied by the total air breathed by an employee at work during one calendar quarter,

6.3 x 108 ml, does not exceed 0.8 pCi of 1-125 or 1.4 pCi of

1-131.

The appropriate proportionate amounts of a mixture of these nuclides should be used as a guide when both

1-125 and

1-131 are present; and

(3)

The working corditions during the

3-month period with respect to the potential for exposure are representative of working condi tions during the period in which the quarterly bioassay frequency will be employed, and there is no reasonable'expectation that the criteria in regulatory positions 4.b(1) and 4.b(2) above will be exceeded.

c.

After Use of Respiratory Protection De vices. Between 6 and 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> after respiratory protective devices, suits, hoods, or gloves are used to limit exposure as stated in regulatory position 1

. e.

For individuals placed on a quarterly schedule, sampling should be randomly distri buted over the quarter but should be done within one week after a procedure involving the handling of 1-125 or 1-131. This will pro vide a more representative assessment of expo sure conditions

5. Action Points and Corresponding Actions a. Biweekly or More Frequent Measurements

(1) Whenever the thyroid burden at the time of measurement exceeds 0.12 pCi of 1-125 or 0.04 pCi of 1-131, the following actions should be taken:

(a)

An investigation of the opera tions involved, including air and other in-plant surveys, should 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 that would cause the limiting intakes established in ssee Appendix B to this guide for a description and example of using this condition for mixtures

§ 20.103 of 10 CFR Part 20 to be exceeded, the licensee should restrict the worker from further exposure until the source of exposure is discovered and corrected.

(c)

Corrective actions that will elim inate or lower the potential for further expo sures should be implemented.

(d)

A

repeat bioassay should be taken within 2 weeks of the previous measure ment and should be evaluated within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> 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)

Reports or notification must be provided as required by

§§ 20.405,20-408, and 20.409 of 10 CFR Part 20 or as required by conditions of the license pursuant to

§ 20.108 of 10 CFR Part 20.

(2)

If the thyroid burden at any time exceeds 0.5 pCi of 1-125 or 0.14 pCi of 1-131, the following actions should be taken:

(a) Carry out all steps described in regulatory position 5.a(1).

(b)

As soon as possible, refer the case to appropriate medical consultation for recommendations regarding therapeutic proce dures 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 effe,-rive. 4 (c)

Carry out repeated measurements at approximately 1-week intervals at least until the thyroid burden is less than 0.12 pCi of 1-125 or 0.04 pCi of 1-131. If there is a possibility of longer-term compartments containing 1-125 or

1-131 that require evaluation, continue meas urements as long as necessary to ensure that appreciable exposures to these other compart ments do not go undetected.

b.

Quarterly Measurements.

Carry out actions at levels as indicated under regulatory position 5.a(1) and (2).

If measurements and surveys indicate an appreciable likelihood that a

worker will receive further exposures exceeding the criteria of regulatory posi tions 4.b(1)

and 4.b(2), reinstitute biweekly or more frequent bioassays.

D. IMPLEMENTATION

The purpose of this section is to provide in formation to applicants and licensees regarding

8.20-3

the NRC staff's plans for using this regulatory guide.

Except in those cases in which the applicant or licensee proposes an acceptable alternative method, the staff will use the methods

[described herein after December 15,

1979, in evaluating the radiation protection programs of licenseer who have bioassay requirements incorporated in their licenses in accordance with § 20.108 of 10 CFR Part 20.

If an applicant or licensee wishes to use the method described in this regulatory guide on or before December 15,

1979, the pertinent portions of the application or the licensee's performance will be evaluated on the basis of this guide.

L

Table I

ACTIVITY LEVELS ABOVE WHICH BIOASSAY FOR 1-125 OR 1-131 IS NECESSARY

Types of Operation Processes in open room or bench, with possible escape of iodine from process vessels Processes with possible escape of iodine carried out within a fume hood of adequate design, face velocity, and performance reliability Processes carried out within gloveboxes, ordinarily closed, but with possible release of iodine from process and occasional exposure to contaminated box and box leakage ActivityHandled in Unsealed Form Making Bioassay Necessary$

Volatile Bound to or Nonvolatile Dispersible*

Agent*

1 mCi

10 mCi

100 mCi

10 mCi

100 mCi

1000 mCi

'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 1-125 or 1-131 will remain in nonvolatile form and diluted to concentrations less than 0.I mCi/mg of nonvolatile agent. Capsules (such as gelatin capsules given to patients for diagnostic tests) may be considered to contain the radloiodine in nonfre6 form, and bioassay would not be necessary unless a capsule were inadvertently opened (e.g.,

dr*pped and crushed). However, certain compounds where radiolodine is normaly 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 only with I~-1 in radioimmunasaay (RIA)

kits, the quantities of [-125 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 mCt at any one time.

Operations involving the routine use of 1-125 or 1-131 in an open room or bench should be discouraged.

Whenever practýicsble, sealed bottles or containers holding more than 0.1 mCi of 1-125 or 1-131 should be opened at least initially within hoods having adequate face velocities of 0.5 m/sec or more.

8.20-4 L

APPENDIX A

SUGGESTED REFERENCES TO ASSIST IN ESTABLISHING A BIOASSAY PROGRAM

In response to public comments, this list of publications is provided to assist the licensee in estab lishing measurements and administrative procedures for a bioassay program appropriate to his opera tions. This list is not intended to be exhaustive and does not replace the need for professional assis

!tance in establishing analytical procedures or services.

Radiological Protection, Pergamon Press, Oxford, p. 17, 1968.

1. American National Standard, ANSI N44.3-1973,

"Thyroid Radioiodine Uptake Measurements Using a Neck Phantom," American National Standards Institute, Inc.,

1430 Broadway, New York, N.Y.

10018, approved August 24, 1973.

2.

R. C. Brown, "1211 Ingestions in Research Personnel,"

Operational Health Physics, pp. 276-278,

1976, proceedings of the Ninth Midyear Topical Symposium of the Health Physics Society, Denver, Colorado, February

1976 (P.

L.

Carson, W.

R.

Hendee, and D

C.

Hunt, Eds.,

Central Rocky Mountain Chapter, Health Physics Society, P.O. Box 3229, Boulder, Colorado

80303, $15).

3. E. J. Browning, K. Banerjee, and W. E.

Reisinger, Jr., "Airborne Concentration of

1-131 in a Nuclear Medicine Laboratory," J.

Nucl. Med., vol. 19, pp. 1078-1081, 1978.

4. J.

G.

Dare and A.

H.

Deutchman, "The Decay Scheme of Iodine-125 and Its Rela tionship to Iodine Bioassay,"

op.

cit.,

Ref. 2, pp. 250-254.

5. B.

C.

Fasiska,

"Radiation Safety Proce dur,.

and Contamination Control Practices Involved in High Level 1-131 Thyroid Thera py Cases," op. cit., Ref. 2, pp. 287-291.

6.

A.

Gavron and Y.

Feige, "Dose Distribu tion and Maximum Permissible Burden of

1251 in the Thyroid Gland,"

Health Physics, vol. 23, pp. 491-499, 1972.

7. B.

Y.

Howard,

"Safe Handling of Radio iodinated Solutions," op. cit., Ref. 2, pp.

247-249.

8. ICRP Publication

10,

"Report of Commit tee IV on Evaluation of Radiation Doses to Body Tissues from Internal Contamination Due to Occupational Exposure," Recommen dations of the International Commission on

8,20-5

9. ICRP Publication 10A, "The Assessment of Internal Contamination Resulting from Recurrent or Prolonged Uptakes," Recom mendations of the International Commission on Radiological Protection, Pergamon Press, Oxford, 1969.

10. A. L. Orvis, "What Is a 'Reportable' Thy roid Burden?" op. cit., Ref. 2., pp. 268

271.

11.

P. Plato, A. P. Jacobson, and S. Homan,

"In Vivo Thyroid Monitoring for Iodine-131 in the Environment,"

Int.

J.

A

lied Radiat.

and Isotopes, vol. 27, pp

539

545, 1976.

12. Radiological Protection Bulletin 25,

"Safe Working with Iodine-125," National Radio logical Protection Board, Harwell, Didcot, Oxon, England, pp. 19-20, 1978.

13. R. P. Rossi, J.

Ovadia, K. Renk, A.

S.

Johnston, and S.

Pinsky,

"Radiation Safety Considerations in the Management of Patients Receiving Therapeutic Doses of i13I," op. cit., Ref. 2, pp. 279-286.

14. C. T. Schmidt, "Thyroid Dosimetry of 1251 and an Instrumental Bioassay Procedure,"

Program and Abstracts: Twenty-Third An

1 bioassay, Environmental and Analytical CL-

y I

Sept. 15, 16, 1977.

15.

A. Taylor, J. W. Verba, N. P. Alazraki, and W. C. McCutchen, "Monitoring of 1-125 Contamination Using a Portable Scintillation Camera," J. Nucl. Med., vol. 19, pp. 431

432, 1978.

16. Technical Reports Series No. 148, "Control of Iodine in the Nuclear Industry," Inter national Atomic Energy Agency, Vienna, 1973.

APPENDIX B

CALCULATION OF ACTION LEVELS FOR MIXTURES OF 1-125 AND 1-131 B.I Controlling Instantaneous Thyroid Burdens Regulatory position 4.b(1) is based on con trolling the instantaneous amount in the thy roid and is taken as 25% of the maximum per missible organ burden (MPOB)

of 1-125 or 1-131 that would give a dose rate of 0.6 rem/week if continuously present in the thyroid. If a mix ture of both nuclides is present in the thyroid and X is the fractional activity that is 1-125, a

3-month interval may be resumed when the total activity of 1-125 and 1-131 is below

0.12X + 0.04(1 - X)

Example If the measurements of 1-125 and 1-131 in a worker's thyroid are 0.10 pCi of 1-125 and 0.05 pCi of 1-131, the fractional 1-125 activity is X = 0.10/(0.10 + 0.05)

= 0.667 Then

0.12X + 0.04(1 - X) = 0.12(0.667) + 0.04(0.33)

= 0.0932 Total= 0.10 + 0.05= 0.15 I.Ci Thus, in this case, the worker involved should remain on the biweekly (or more fre quent) schedule and should not be put on the quarterly frequency.

B.2 Controlling Total Intakes Regulatory position 4.b(2) is based on con trolling total intakes 6 during a quarterly

$The limiting total quarterly intakes are in different propor tions for 1-125 and 1-131 than are the MPOBs. This difference is a result of the fact that permissible concentrations are inversely proportional to effective half-liver where"

an MPOB

is calculated aasuning a constant burden in the organ of con cern that is miuntained by continuous intAke of activity balanced by an equal rate of elimiation from the organ period when air concentration data are avail able to assess the potential exposure of the worker either to random single intakes or to variable or constant continuous exposures. The quantities of 0.8 pCi of 1-125 and 1.4 pCi of I

131 were obtained by calculating 25% of the total quarterly intakes of 3.2 pCi of 1-125 or

5.7 pCi of 1-131 (see footnote 3) that would be inhaled when breathing a total of 6.3 x 108 ml per quarter working at the standard man breathing rate for 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> per week for 13 weeks.

Example If the average quarterly concentrations esti mated from air sampled in a worker's breathing zone are 3 x 10-9 pCi/ml for 1-125 and 5 x 10-f pCi/ml for 1-131, the total quarterly intakes are:

3 x 10-9 x 6.3 x 108 = 1.89 pCi 1-125

5 x 10-9 x 6.3 x 108 = 3.15 pCi 1-131 Total = 5.04 pCi Also, X, the proportion of 1-125, is 1.89/5.04 =

0.375 Thus the control level for maintaining biweekly or more frequent bioassay checks is:

0.8X + 1.4(1 - X) = 0.8(0.375) + 1.4(1 - 0.375)

Total = 1. 18 pCi for this mixture.

Since the intake of 5.04 pCi is greater than

1.18, this employee should stay on the more frequent bioassay schedule.

Note: The numbers of significant digits carried in the above calculations do not imply any given degree of accuracy of mea surement.

Enough digits are carried to allow following the arithmetic for pur poses of the examples.

8.20-6 I

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1,