TEDE: Summing External and Internal Dose

Total effective dose equivalent (TEDE) is the sum of the external effective dose equivalent and the internal committed effective dose equivalent, and it is the quantity the NRC's 5-rem annual occupational limit is written against. For most medical workers the external term, read from a whole-body dosimeter, dominates — but when a worker is likely to take in radioactive material, the internal term must be calculated and added before compliance can be demonstrated.¹²³

Getting this right is a core radiation-safety responsibility: it determines who needs bioassay or air monitoring, how a dosimeter reading and an intake are combined, and how a program documents that each worker stayed under the limit.³⁷

Introduction

The occupational dose limit most people quote — 5 rem (0.05 Sv) per year — is often pictured as a badge reading. In the regulations it is something more complete. Under 10 CFR Part 20, the primary adult occupational limit is 5 rem total effective dose equivalent, and TEDE deliberately combines two different pathways of exposure: radiation delivered from sources outside the body and dose committed by radioactive material taken into the body.²

This structure exists because the two pathways are biologically additive. A worker who receives 2 rem from external gamma exposure and 2 rem of committed effective dose from an inhaled radionuclide has received 4 rem of stochastic risk-weighted dose, and the limit is meant to cap that total.¹¹¹ The regulatory machinery — definitions in 10 CFR 20.1003, the summation rule in 10 CFR 20.1202, the internal-dose method in 10 CFR 20.1204, and the monitoring triggers in 10 CFR 20.1502 — all serve to make that addition explicit and auditable.¹³⁴⁵

This guide defines TEDE and its components, explains when summation is required, shows how to convert an intake or DAC-hours into committed dose with a worked example, places the limits in context, and covers the practical and regulatory steps a medical radiation-safety program follows.

Topic Explanation

The components of TEDE

TEDE = effective dose equivalent (external) + committed effective dose equivalent (internal). Each component is a defined quantity in 10 CFR 20.1003:¹

• Effective dose equivalent (external). The external component of TEDE. Because it cannot be measured directly, the deep-dose equivalent (DDE) — the dose equivalent at a tissue depth of 1 cm (1000 mg/cm²), obtained from a whole-body dosimeter — is used as its practical estimator, and it is generally a reasonable and conservative one.
• Committed effective dose equivalent (CEDE). The internal component. After an intake, radioactive material irradiates organs and tissues over time; the committed dose equivalent is the dose to an organ over the 50 years following the intake, and the CEDE is the tissue-weighted sum of those organ doses, expressing the internal exposure as a single whole-body-equivalent value.

A few supporting terms recur:

• Annual limit on intake (ALI). The intake of a radionuclide that would result in either 5 rem CEDE (the stochastic ALI) or 50 rem committed dose equivalent to a limiting organ (the non-stochastic ALI), whichever is smaller. ALIs are tabulated in 10 CFR Part 20, Appendix B.⁶
• Derived air concentration (DAC). The airborne concentration that, breathed for a 2,000-hour working year, results in an intake of one ALI.¹⁶
• DAC-hour. The product of airborne concentration (in DAC) and time (in hours); the NRC allows 2,000 DAC-hours to represent one ALI, equivalent to 5 rem CEDE for a stochastic-limited radionuclide.¹

Why TEDE, and not just a badge reading

The historical reason is the shift to effective-dose thinking in radiation protection: rather than limiting each organ separately, the system weights organ doses by their contribution to total stochastic risk and sums them, so that disparate exposures can be compared and added on one risk-relevant scale.¹¹ TEDE operationalizes that idea for occupational dose by letting an external effective dose equivalent and an internal committed effective dose equivalent be placed on the same footing and added. Without this common quantity, there would be no defensible way to combine a dosimeter reading with an inhaled intake.

What TEDE does not include

TEDE is a whole-body, stochastic-risk quantity. The lens dose equivalent limit (15 rem) and the shallow-dose equivalent limit for skin and extremities (50 rem) are separate localized-dose limits and are not added into TEDE.² They are checked independently, typically from a lens or extremity dosimeter. Confusing a shallow-dose or lens reading with the TEDE term is a common error that a well-designed dose-record review catches.

Key Technical Principles

The summation equation

The fundamental relationship is simply additive:¹³

where $H_{E,\text{ext}}$ is the external effective dose equivalent (estimated by the deep-dose equivalent) and CEDE is the committed effective dose equivalent from all intakes during the period. Compliance with the adult limit is then:

Converting an intake to committed dose

The internal term can be computed two equivalent ways. From the intake of each radionuclide relative to its stochastic ALI:⁴⁶

or, when exposure is assessed from air sampling, from DAC-hours:¹

Both express the same physical quantity; the choice depends on whether intake is estimated from bioassay (body or excreta measurements) or from workplace air concentrations. For non-stochastic (organ-limited) radionuclides the same 2,000 DAC-hours corresponds instead to 50 rem committed dose equivalent to the limiting organ, or 25 mrem per DAC-hour — a distinction that matters for radionuclides such as radioiodine, where the thyrocommitted organ dose, not the stochastic effective dose, is limiting.¹

A worked summation example

Consider a radiopharmacy technologist over a monitoring year:

• External. The whole-body dosimeter records a deep-dose equivalent of 350 mrem.
• Internal. Air sampling and bioassay indicate the worker accrued 300 DAC-hours of a soluble, stochastic-limited radionuclide.

The committed effective dose equivalent is:

The total effective dose equivalent is therefore:

Expressed as a fraction of the 5-rem limit, this is $1100/5000=0.22$, or 22% of the annual limit — compliant, with margin. The same result can be written as a sum of fractions, which is the form a licensee uses to demonstrate compliance across mixed external and internal exposures:¹³

This worker is clearly controlled by the internal term — a reminder that, for staff handling unsealed material, the dosimeter reading alone can understate the regulated dose by a wide margin.

The occupational and related dose limits

How the two components are actually measured

For the external side, our discussion of OSL and TLD personnel dosimetry covers how the deep-dose equivalent is recorded; for the internal side, the intake-to-dose machinery sits alongside the ALI/DAC internal dose limits.

Clinical Impact

For a medical radiation-safety program, TEDE is the quantity that decides who needs internal monitoring and how two very different measurements are combined into one compliance number. The practical consequence is a monitoring design: the program must identify which workers are likely to exceed 10% of an applicable ALI — the trigger for internal monitoring under 10 CFR 20.1502 — and ensure those workers have bioassay or air-sampling data that can be converted to CEDE and added to their external dose.³⁵

In most diagnostic and interventional settings, workers are externally monitored only, because credible intakes are negligible; their TEDE is effectively their deep-dose equivalent. The picture changes in nuclear medicine and radiopharmacy, where staff draw, dispense, and administer unsealed radionuclides, and in radionuclide therapy, where handling I-131 or similar agents makes an intake credible. There, a thyroid bioassay or urinalysis result is not a stand-alone check — it feeds the CEDE that must be summed with the badge reading. A program that measures intakes but never combines them with external dose has not actually demonstrated compliance with the TEDE limit. Related monitoring obligations are summarized in our overview of occupational exposure monitoring.

TEDE also anchors the facility's ALARA program. Investigational levels, dose-trend reviews, and corrective actions are most meaningful when they are applied to the combined dose that the limit actually regulates, rather than to the external term alone.

Practical Optimization Tips

Build the monitoring program around the summation trigger

• Assess likely intake against 10% of the ALI. The decision to perform internal monitoring follows from whether a worker is likely to receive an intake exceeding 10% of the applicable annual limit on intake, so this assessment should be documented for each class of worker.⁵
• Choose the right internal-dose tool. Match the bioassay or air-sampling method to the radionuclide and its chemical form — thyroid counting for radioiodine, urinalysis or whole-body counting for other agents — so the intake estimate is defensible.
• Record the components separately, then sum. Keep the external deep-dose equivalent and the internal CEDE identifiable in the dose record, and report the TEDE as their sum, consistent with the NRC's recording and reporting guidance.⁷⁸

Avoid the common errors

• Do not treat the badge reading as the whole dose for workers with credible intakes; the internal term can dominate, as the worked example shows.
• Do not add lens or shallow-dose equivalent into TEDE. Those are separate localized limits.²
• Do not confuse the stochastic and non-stochastic ALI. For organ-limited radionuclides such as radioiodine, the organ (non-stochastic) limit governs, and the DAC-hour-to-dose conversion differs.¹
• Use consistent units and assumptions. Mixing rem and mrem, or stochastic and non-stochastic ALIs, is a frequent source of dose-record errors.

Document the basis

Every CEDE value should trace back to a measured intake and a stated model — the ALI or DAC used, the chemical form, and the method of measurement — so the calculation can be reconstructed during an inspection. The NRC's guidance on monitoring criteria and on recording and reporting occupational dose describes the expected documentation.⁷⁸

Regulatory Considerations

TEDE is a regulatory construct, defined and required by 10 CFR Part 20, and its summation rule is enforced against the medical-use license.

• Definitions — 10 CFR 20.1003. TEDE, deep-dose equivalent, committed effective dose equivalent, ALI, DAC, and the DAC-hour relationship are all defined here.¹
• Limits — 10 CFR 20.1201. The adult occupational limit is the more limiting of 5 rem TEDE or 50 rem DDE-plus-committed-dose to any individual organ, with separate 15-rem lens and 50-rem shallow-dose limits.²
• Summation — 10 CFR 20.1202. When both external and internal monitoring are required, the deep-dose equivalent and the committed effective dose equivalent must be summed to demonstrate compliance.³
• Internal exposure — 10 CFR 20.1204. Specifies acceptable methods — air sampling, bioassay — for determining intake and committed dose, and the conditions for disregarding minor radionuclides in a mixture.⁴
• Monitoring triggers — 10 CFR 20.1502. Individual external monitoring is required for workers likely to exceed 10% of the external limit, and internal monitoring for those likely to exceed 10% of the applicable ALI.⁵
• Guidance. NRC Regulatory Guides 8.34, 8.7, and 8.9 describe how to calculate occupational doses, record and report them, and design a bioassay program, and NCRP Report No. 116 provides the radiation-protection framework behind the effective-dose approach.⁷⁸⁹¹¹

These requirements apply under the NRC in direct-NRC jurisdictions — including Washington DC and Delaware for radioactive material — and under equivalent Agreement State programs elsewhere. DRPS serves Florida, Maryland, Virginia, Washington DC, California, Nevada, Pennsylvania, New York, New Jersey, and Delaware; the Agreement States administer parallel Part 20-equivalent rules. Always confirm requirements with the authority having jurisdiction.

Frequently Asked Questions (FAQs)

What is total effective dose equivalent (TEDE)?

TEDE is the sum of the effective dose equivalent received from external exposure and the committed effective dose equivalent received from internal exposure (an intake of radioactive material). It is the quantity the NRC's primary 5-rem annual occupational dose limit is written against, so compliance is demonstrated on the combined external-plus-internal dose, not on a dosimeter reading alone.¹²

When must external and internal dose be summed?

Under 10 CFR 20.1202, when a licensee is required to monitor both external and internal occupational exposure, the deep-dose equivalent and the committed effective dose equivalent must be added to show compliance with the dose limits. Monitoring of internal exposure becomes necessary when a worker is likely to receive an intake exceeding 10 percent of the applicable annual limit on intake.³⁵

How is committed effective dose equivalent calculated from an intake?

CEDE is determined from the intake relative to the stochastic annual limit on intake (ALI) for the radionuclide, scaled to 5 rem, or equivalently from DAC-hours. The NRC allows 2,000 DAC-hours to represent one ALI, which corresponds to 5 rem CEDE, so each DAC-hour corresponds to about 2.5 mrem of committed effective dose equivalent for a stochastic-limited radionuclide.¹⁴

Are the lens, skin, and extremity limits part of TEDE?

No. The 15-rem lens dose equivalent limit and the 50-rem shallow-dose equivalent limit for skin and extremities are separate limits on localized external dose, and they are not added into TEDE. TEDE combines whole-body external effective dose equivalent with internal committed effective dose equivalent; the localized limits are checked independently.²

Do most medical radiation workers need internal dose monitoring?

For many diagnostic and interventional staff, external dose dominates and the likely intake stays well under 10 percent of the applicable ALI, so routine internal monitoring is not required. Internal monitoring and TEDE summation become relevant for workers handling significant quantities of unsealed radioactive material — radiopharmacy, therapy with I-131 or other radionuclides, and certain research uses — where an intake is credible.⁵

What is the difference between deep-dose equivalent and effective dose equivalent in TEDE?

The external part of TEDE is formally the effective dose equivalent, but because effective dose equivalent cannot be measured directly, the deep-dose equivalent — the dose equivalent at a 1-cm tissue depth from a whole-body dosimeter — is used as its practical, generally conservative estimator. In routine personnel monitoring the recorded deep-dose equivalent serves as the external term that is summed with the committed effective dose equivalent.¹

Key Takeaways

• TEDE is the sum of external effective dose equivalent and internal committed effective dose equivalent, and the 5-rem adult occupational limit is a TEDE limit.¹²
• The deep-dose equivalent from a whole-body dosimeter is the practical, conservative estimator of the external term.¹
• Internal dose must be summed with external dose when both are monitored; internal monitoring is triggered at a likely intake above 10% of the applicable ALI.³⁵
• CEDE is computed from intake/ALI or from DAC-hours, with 2,000 DAC-hours = 1 ALI = 5 rem CEDE (about 2.5 mrem per DAC-hour, stochastic).¹⁴
• Lens (15 rem) and shallow/skin/extremity (50 rem) limits are separate and are not part of TEDE.²
• For unsealed-source workers the internal term can dominate, so a program that never sums the two has not demonstrated compliance.³

Conclusion

The 5-rem number is familiar, but its meaning is precise: it caps the total effective dose equivalent, the deliberate sum of what a worker receives from outside the body and what they commit by taking radioactive material in. For most of medical imaging the external term carries the day, and TEDE and the badge reading are nearly the same thing. For radiopharmacy and radionuclide therapy they are not — and the discipline of identifying credible intakes, converting them to committed effective dose, and adding them to the external dose is what turns a collection of measurements into a defensible demonstration of compliance. A radiation-safety program built around TEDE, rather than around the dosimeter alone, protects workers and withstands inspection.¹²³

How DRPS Can Help

Diagnostic Radiation Physics Services (DRPS) supports medical facilities across Florida, Maryland, Virginia, Washington DC, California, Nevada, Pennsylvania, New York, New Jersey, and Delaware with radiation safety officer services, dose-monitoring program design, internal-dosimetry and bioassay program setup, and radiation safety training — all delivered by board-certified medical physicists. We help licensees decide which workers need internal monitoring, implement defensible intake-to-CEDE calculations, and document TEDE in the form inspectors expect, so that external and internal dose are combined correctly and the program stands up to review.

Related Resources

• NRC occupational dose limits (Part 20)
• ALI/DAC internal dose limits
• Operational dose quantities for radiation monitoring
• OSL and TLD personnel dosimetry
• Occupational exposure monitoring
• Radiation safety officer services

References

1. U.S. Nuclear Regulatory Commission. 10 CFR 20.1003, Definitions (total effective dose equivalent, deep-dose equivalent, committed effective dose equivalent, ALI, DAC, DAC-hour). nrc.gov
2. U.S. Nuclear Regulatory Commission. 10 CFR 20.1201, Occupational dose limits for adults. nrc.gov
3. U.S. Nuclear Regulatory Commission. 10 CFR 20.1202, Compliance with requirements for summation of external and internal doses. nrc.gov
4. U.S. Nuclear Regulatory Commission. 10 CFR 20.1204, Determination of internal exposure. nrc.gov
5. U.S. Nuclear Regulatory Commission. 10 CFR 20.1502, Conditions requiring individual monitoring of external and internal occupational dose. nrc.gov
6. U.S. Nuclear Regulatory Commission. 10 CFR Part 20, Appendix B, Annual Limits on Intake (ALIs) and Derived Air Concentrations (DACs) of Radionuclides for Occupational Exposure. nrc.gov
7. U.S. Nuclear Regulatory Commission. Monitoring Criteria and Methods to Calculate Occupational Radiation Doses. Regulatory Guide 8.34, Revision 1. Washington, DC: NRC; 2022. nrc.gov
8. U.S. Nuclear Regulatory Commission. Instructions for Recording and Reporting Occupational Radiation Dose Data. Regulatory Guide 8.7. Washington, DC: NRC. nrc.gov
9. U.S. Nuclear Regulatory Commission. Acceptable Concepts, Models, Equations, and Assumptions for a Bioassay Program. Regulatory Guide 8.9. Washington, DC: NRC. nrc.gov
10. International Commission on Radiological Protection. Limits for Intakes of Radionuclides by Workers. ICRP Publication 30. Oxford: Pergamon Press; 1979. icrp.org
11. National Council on Radiation Protection and Measurements. Limitation of Exposure to Ionizing Radiation. NCRP Report No. 116. Bethesda, MD: NCRP; 1993. ncrponline.org