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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levillm 9 U.S. NUCLEAR REGULATORY COMMISSION 81PSeptaiff 1979 o ..AuIn&..i

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REGULATORY GUIDE

ease, OFFICE OF STANDARDS DEVELOPMENT

REGULATORY GUIDE 8.20

APPLICATIONS OF BIOASSAY FOR 1-125 AND 1-131

A. INTRODUCTION

vitro of materials excreted or removed from the body..

Section 20. 108, "Orders Requiring Furnish ing of Bioassay Services," of 10 CFR Part 20, Intake-The total quantity of radioactive

"Standards for Protection Against Radiation,' material entering the body.

indicates that the Nuclear Regulatory Commis sion (NRC) may incorporate into a license pro In vivo measurements-Measurement of gamma visions requiring a specific program of or x-radiation emitted from radioactive material bioassay measurements as necessary or located within the body for the purpose of desirable to aid in determining the extent of an detecting or estimating the quantity of radio individual's exposure to concentrations of active material present.

radioactive material. In certain cases, the requirement of bioassay may also be included in In vitro measurements-Measurement of radio the license by reference to procedures specify activity in samples of material excreted from ing in vivo measurements, measurements of the human body.

radioactive material in excreta, or both.

C. REGULATORY POSITION

This guide provides criteria acceptable to the NRC staff for the development and implementa 1. Conditions Under Which Bioassay Is Necessary tion of a bioassay program for any licensee handling or processing 1-125 or 1-131. It a. Routine' bioassay is necessary when an further provides guidance to such licensees individual handles in open form unsealed 2 regarding the selection of workers who should quantities of radioactive iodine that exceed participate in a program to detect and measure those shown in Table 1 of this guide. The possible internal radiation exposure. The guide quantities shown in Table 1 apply to both the is programmatic in nature and does not deal quantity handled at any one time or integrated with measurement techniques and procedures.

as the total amount of activity introduced into a process by an employee over any 3-month

B. DISCUSSION

period.

The topics treated in this guide include de b. When quantities handled in unsealed terminations of (1) whether bioassay should be form are greater than 10% of Table 1 values, performed, (2) frequencies of bioassay, (3)

who should participate, (4) the actions to take *Lines indicate substantive changes from previous issue.

based on bioassay results, and (5) the partic ular results that should initiate such actions. IRoutine means here that an individual is assigned on a sche u**-edand repeatable basis to submit specimens for bioassay or to report for in vivo measurements. Either radiochemical For the user's convenience, the following bioassay of urine or in vivo counting is acceptable to the NRC

terms are presented with their definitions as staff for estimating internal radioactivity burdens or intakes.

In some cases, however, a licensee may wish to corroborate used in this guide: 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 Bioassay-The determination of the kind, recommended analytical procedures. Each installation should quantity or concentration, and location of adopt. procedures or obtain services best suited to its own radioactive material in the human body by needs..

direct (in vivo) measurement or by analysis in ;See discussion in the footnote to Table 1 of this guide.

USNRC REGULATORY GUIDES Comments should be sent to the Secretary of the Comm.ison, U.S.

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public methods acceptable to the NRC staff of implementing specific arts oh te Comrmision's regulations, to delineate techniques used The guides are lised in the following ten broad divsons:

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routine bioassay may still be necessary under 3. Types of Bioasays That Should Be Performed certain circumstances. A written justification for not performing such measurements should a. Baseline (preemployment or preopera be prepared and recorded for subsequent re tional). Prior to beginning work with radio view during NRC inspections whenever bio active iodine in sufficient quantity that bio assay is not performed and the quantities assay is specified in regulatory position 1.

handled exceed 10% of the levels in Table 1.

b. Routine. At the frequency specified in c. Except as stated in regulatory posi regulatory position 4.

tion 1.e, bioassay is not required when pro cess quantities handled by a worker are less c. Emergency. As soon as possible after any than 10% of those in Table 1. incident that might cause thyroid uptakes toi exceed burdens given in regulatory posi-i e d. In nuclear reactor installations, employ tion 5.a(2), so that actions recommended inI

ees should be bioassayed by an in vivo count regulatory position 5.a(2)(b) can be most within 30 days after the end of exposure in effective.

work locations where concentrations exceeded, or might have exceeded, 9 x 10-1Q pCi/ml d. Postoperational and with Separation Phys averaged over any 40-hour period. Table 1 and ical. A bioassay should be performed within 2 regulatory position 4 regarding frequency of weeks of the last possible exposure to 1-125 or bioassays are not applicable to reactor 1-131 when operations are being discontinued I licensees. or when the worker is terminating activities with potential exposure to these radionuclides.

e. Special bioassay measurements should e. Diagnostic. Followup bioassay should be be performed to verify the effectiveness of performed within 2 weeks of any measurements respiratory protection devices and protective exceeding levels given as action points in clothing. If an individual wearing a respiratory regulatory position 5 in order to confirm the protective device or protective clothing is sub initial results and, in the case of a single jected to a concentration of 1-125 or 1-131 (in intake, to allow an estimate of the effective any form) in air such that his or her intake half-life of radioiodine in the thyroid.

with no protection would have exceeded the limits specified in paragraph 20.103(a)(1) of

4. Frequency

10 CFR Part 20,3 bioassays should be per formed to determine the resulting actual 1-125 a. Initial Routine. Except in situations or 1-131 intake. These special bioassay proce where thyroid burdens may exceed quantities dures should also be conducted for personnel specified in regulatory position 5.a(2), a bio wearing respirators if for any reason the 1-125 assay sample or measurement should be or 1-131 concentration in air and the duration 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 -1

'of exposure are unknowvn or cannot be conser individual into an area where bioassay is I vatively estimated by calculation. 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

2. Participation frequently thereafter as long as the conditions;

described in regulatory positions 1 and 21 AUl workers handling radioactive iodine or exist. When work with radioactive iodine is on sufficiently close to the process so that intake an infrequent basis (less frequently than every is possible (e.g., within a few meters and in 2 weeks), bioassay should be performed within the same room as. the worker handling the 10 days of the end of the work period during material) should participate in bioassay pro which radioactive iodine was handled (but not grams described in regulatory position 1. 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

3 blocking treatment are appropriate4).

Muitfplying the concentrations riven in Appendix B to

10 CFR Part 20, Table r, column i, 5 x 10-9 wCi/ml for 1-125 b. After 3 Months. When a periodic meas (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 urement frequency has been selected in iodines by inhalation. These quarterly intakes would be about accordance with regulatory position 4.a, it may

3.2 pCi for 1-125 and 5.7 pCi for 1-131, which would give a be changed to quarterly if, after 3 months, all thyroid dose commitment of about 7. rems to a 20-gram thyroid integrated over all future time using effective half-lives of 41.8 the following conditions sre met:

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 (1) The average thyroid burden for case of 1-125. (This QF of 1.7 ie used for conservatism, even each individual working in a given area was though the International Commission on Radiological Protection

(1969) and the National Council on Radiation Protection (1971) 4 have published a QF of 1, because some calculations in more NC*RP Report No. 55, "Protection of the Thyroid Gland in recent scientific Literature have suggested the use of QF values the Event of Releases of Radlioodine," National Council on higher than I for electron or beta energies of 0.03 MeV or Radiation Protection and Measurements, Washington, D C.,

less.) August 1, 1977, p. 21.

8.20-2

less than 0.12 pCi of 1-125, less than 0.04 pCi § 20.103 of 10 CFR Part 20 to be exceeded, the of 1-131, and less than the corresponding pro licensee should restrict the worker from portionate amounts of a mixture of these further exposure until the source of exposure nuclides during the initial 3-month period; is discovered and corrected.

(c) Corrective actions that will elim

(2) The quarterly average radioiodine concentration (pCi/ml) in air breathed by any inate or lower the potential for further expo worker (as obtained when measurements of sures should be implemented.

radioiodine concentrations in air are required)

does not exceed 25% of the concentration values (d) A repeat bioassay should be for "soluble"(s) iodine given in Appendix B to taken within 2 weeks of the previous measure

10 CFR Part 20, Table I, Column 1, (5 x 10-9 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 /> pCi/ml for 1-125 and 9 x 10-9 pCi/ml for 1-131), after measurement in order to confirm the i.e., 25% of these concentrations multiplied by presence of internal radioiodine and to obtain the total air breathed by an employee at work an estimate of its effective half-life for use in during one calendar quarter, 6.3 x 108 ml, estimating dose commitment.

does not exceed 0.8 pCi of 1-125 or 1.4 pCi of

1-131. The appropriate proportionate amounts (e) Reports or notification must be of a mixture of these nuclides should be used provided as required by §§ 20.405,20-408, as a guide when both 1-125 and 1-131 are and 20.409 of 10 CFR Part 20 or as required present; and by conditions of the license pursuant to

§ 20.108 of 10 CFR Part 20.

(3) The working corditions during the

3-month period with respect to the potential for (2) If the thyroid burden at any time exposure are representative of working condi exceeds 0.5 pCi of 1-125 or 0.14 pCi of 1-131, tions during the period in which the quarterly the following actions should be taken:

bioassay frequency will be employed, and there is no reasonable'expectation that the criteria in (a) Carry out all steps described in regulatory positions 4.b(1) and 4.b(2) above regulatory position 5.a(1).

will be exceeded.

(b) As soon as possible, refer the c. After Use of Respiratory Protection De case to appropriate medical consultation for 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 recommendations regarding therapeutic proce protective devices, suits, hoods, or gloves are dures that may be carried out to accelerate used to limit exposure as stated in regulatory removal of radioactive iodine from the body.

position 1. e. This should be done within 2-3 hours after exposure when the time of exposure is known For individuals placed on a quarterly so that any prescribed thyroid blocking agent schedule, sampling should be randomly distri would be effe,-rive. 4 buted over the quarter but should be done within one week after a procedure involving (c) Carry out repeated measurements the handling of 1-125 or 1-131. This will pro at approximately 1-week intervals at least until vide a more representative assessment of expo the thyroid burden is less than 0.12 pCi of 1-125 sure conditions or 0.04 pCi of 1-131. If there is a possibility of longer-term compartments containing 1-125 or

5. Action Points and Corresponding Actions 1-131 that require evaluation, continue meas a. Biweekly or More Frequent Measurements urements as long as necessary to ensure that appreciable exposures to these other compart

(1) Whenever the thyroid burden at the ments do not go undetected.

time of measurement exceeds 0.12 pCi of 1-125 or 0.04 pCi of 1-131, the following actions b. Quarterly Measurements. Carry out should be taken: actions at levels as indicated under regulatory position 5.a(1) and (2). If measurements and (a) An investigation of the opera surveys indicate an appreciable likelihood that tions involved, including air and other in-plant a worker will receive further exposures surveys, should be carried out to determine exceeding the criteria of regulatory posi the causes of exposure and to evaluate the tions 4.b(1) and 4.b(2), reinstitute biweekly potential for further exposures. or more frequent bioassays.

(b) If the investigation indicates that further work in the area might result in exposure of a worker to concentrations that

D. IMPLEMENTATION

would cause the limiting intakes established in The purpose of this section is to provide in ssee Appendix B to this guide for a description and example of using this condition for mixtures formation to applicants and licensees regarding

8.20-3

the NRC staff's plans for using this regulatory incorporated in their licenses in accordance guide. with § 20.108 of 10 CFR Part 20.

Except in those cases in which the applicant or licensee proposes an acceptable alternative If an applicant or licensee wishes to use the method described in this regulatory guide on 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 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

ActivityHandled in Unsealed Form Making Bioassay Necessary$

Volatile Bound to or Nonvolatile Types of Operation Dispersible* Agent*

Processes in open room or bench, with possible escape

1 mCi 10 mCi of iodine from process vessels Processes with possible escape of iodine carried out 10 mCi 100 mCi within a fume hood of adequate design, face velocity, and performance reliability Processes carried out within gloveboxes, ordinarily 100 mCi 1000 mCi closed, but with possible release of iodine from process and occasional exposure to contaminated box and box leakage

'Quantities may be considered the cumulative amount in process handled by a worker during a 3-month period;

total quantity introduced into a chemical or physical process over a 3-month e.g. , the 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.

1. American National Standard, ANSI N44.3-1973, Radiological Protection, Pergamon Press,

"Thyroid Radioiodine Uptake Measurements Oxford, p. 17, 1968.

Using a Neck Phantom," American National Standards Institute, Inc., 1430 Broadway, 9. ICRP Publication 10A, "The Assessment of New York, N.Y. 10018, approved Internal Contamination Resulting from August 24, 1973. Recurrent or Prolonged Uptakes," Recom mendations of the International Commission

2. R. C. Brown, "1211 Ingestions in Research on Radiological Protection, Pergamon Personnel," Operational Health Physics, Press, Oxford, 1969.

pp. 276-278, 1976, proceedings of the Ninth Midyear Topical Symposium of the 10. A. L. Orvis, "What Is a 'Reportable' Thy Health Physics Society, Denver, Colorado, roid Burden?" op. cit., Ref. 2., pp. 268 February 1976 (P. L. Carson, W. R. 271.

Hendee, and D C. Hunt, Eds., Central Rocky Mountain Chapter, Health Physics 11. P. Plato, A. P. Jacobson, and S. Homan, Society, P.O. Box 3229, Boulder, Colorado "In Vivo Thyroid Monitoring for Iodine-131

80303, $15). in the Environment," Int. J. A lied Radiat. and Isotopes, vol. 27, pp 539

3. E. J. Browning, K. Banerjee, and W. E. 545, 1976.

Reisinger, Jr., "Airborne Concentration of

1-131 in a Nuclear Medicine Laboratory," J. 12. Radiological Protection Bulletin 25, "Safe Nucl. Med., vol. 19, pp. 1078-1081, 1978. Working with Iodine-125," National Radio logical Protection Board, Harwell, Didcot,

4. J. G. Dare and A. H. Deutchman, "The Oxon, England, pp. 19-20, 1978.

Decay Scheme of Iodine-125 and Its Rela tionship to Iodine Bioassay," op. cit., 13. R. P. Rossi, J. Ovadia, K. Renk, A. S.

Ref. 2, pp. 250-254. Johnston, and S. Pinsky, "Radiation Safety Considerations in the Management of

5. B. C. Fasiska, "Radiation Safety Proce Patients Receiving Therapeutic Doses of dur,. and Contamination Control Practices i13I," op. cit., Ref. 2, pp. 279-286.

Involved in High Level 1-131 Thyroid Thera py Cases," op. cit., Ref. 2, pp. 287-291. 14. C. T. Schmidt, "Thyroid Dosimetry of 1251 and an Instrumental Bioassay Procedure,"

6. A. Gavron and Y. Feige, "Dose Distribu Program and Abstracts: Twenty-Third An tion and Maximum Permissible Burden of 1 bioassay, Environmental

1251 in the Thyroid Gland," Health and Analytical

1977. CL- y I

Physics, vol. 23, pp. 491-499, 1972. Sept. 15, 16,

7. B. Y. Howard, "Safe Handling of Radio 15. A. Taylor, J. W. Verba, N. P. Alazraki, iodinated Solutions," op. cit., Ref. 2, pp. and W. C. McCutchen, "Monitoring of 1-125

247-249. Contamination Using a Portable Scintillation Camera," J. Nucl. Med., vol. 19, pp. 431

8. ICRP Publication 10, "Report of Commit 432, 1978.

tee IV on Evaluation of Radiation Doses to Body Tissues from Internal Contamination 16. Technical Reports Series No. 148, "Control Due to Occupational Exposure," Recommen of Iodine in the Nuclear Industry," Inter dations of the International Commission on national Atomic Energy Agency, Vienna, 1973.

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APPENDIX B

CALCULATION OF ACTION LEVELS FOR MIXTURES OF 1-125 AND 1-131

-1 B.I Controlling Instantaneous Thyroid Burdens period when air concentration data are avail Regulatory position 4.b(1) is based on con able to assess the potential exposure of the worker either to random single intakes or to trolling the instantaneous amount in the thy variable or constant continuous exposures. The roid and is taken as 25% of the maximum per quantities of 0.8 pCi of 1-125 and 1.4 pCi of I

missible organ burden (MPOB) of 1-125 or 1-131 131 were obtained by calculating 25% of the that would give a dose rate of 0.6 rem/week if total quarterly intakes of 3.2 pCi of 1-125 or continuously present in the thyroid. If a mix 5.7 pCi of 1-131 (see footnote 3) that would be ture of both nuclides is present in the thyroid inhaled when breathing a total of 6.3 x 108 ml and X is the fractional activity that is 1-125, a per quarter working at the standard man

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

0.12X + 0.04(1 - X) Example Example If the average quarterly concentrations esti mated from air sampled in a worker's breathing If the measurements of 1-125 and 1-131 in a zone are 3 x 10-9 pCi/ml for 1-125 and 5 x 10-f worker's thyroid are 0.10 pCi of 1-125 and 0.05 pCi/ml for 1-131, the total quarterly intakes pCi of 1-131, the fractional 1-125 activity is are:

X = 0.10/(0.10 + 0.05) 3 x 10-9 x 6.3 x 108 = 1.89 pCi 1-125

= 0.667

5 x 10-9 x 6.3 x 108 = 3.15 pCi 1-131 Then Total = 5.04 pCi

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

0.0932 Also, X, the proportion of 1-125, is 1.89/5.04

0.375 Total= 0.10 + 0.05= 0.15 I.Ci Thus the control level for maintaining Thus, in this case, the worker involved biweekly or more frequent bioassay checks is: 1, should remain on the biweekly (or more fre quent) schedule and should not be put on the 0.8X + 1.4(1 - X) = 0.8(0.375) + 1.4(1 - 0.375)

quarterly frequency. Total = 1. 18 pCi for this mixture.

B.2 Controlling Total Intakes Since the intake of 5.04 pCi is greater than Regulatory position 4.b(2) is based on con 1.18, this employee should stay on the more frequent bioassay schedule.

trolling total intakes 6 during a quarterly

$The limiting total quarterly intakes are in different propor Note: The numbers of significant digits carried tions for 1-125 and 1-131 than are the MPOBs. This difference in the above calculations do not imply is a result of the fact that permissible concentrations are any given degree of accuracy of mea inversely proportional to effective half-liver where" an MPOB

is calculated aasuning a constant burden in the organ of con surement. Enough digits are carried to cern that is miuntained by continuous intAke of activity allow following the arithmetic for pur balanced by an equal rate of elimiation from the organ poses of the examples.

8.20-6 I