Authorized User Training & Experience (10 CFR 35)

Before a physician can administer radiopharmaceutical therapy or a physicist can calibrate a therapy unit, they must be named on the radioactive material license as an authorized user or authorized medical physicist — and 10 CFR Part 35 Subpart J defines exactly how they qualify. There are two routes: certification by an NRC-recognized specialty board, or a documented training-and-experience pathway with specific hour and case requirements plus a preceptor attestation. ^{1, 2}

Getting this right is not paperwork for its own sake. An individual practicing a use for which they are not authorized is a license violation, a potential medical-event contributor, and a common inspection finding. Understanding the categories, the hour thresholds, and the attestation requirements is core radiation-safety-program knowledge for any radioactive material licensee. ^{1, 7}

Introduction

The medical use of byproduct material in the United States is authorized person-by-person and use-by-use. A radioactive material license does not simply permit "nuclear medicine"; it names specific authorized users (AUs) for specific categories of use, and specific authorized medical physicists (AMPs) for the therapy modalities that require physics support. This structure is what allows the NRC and Agreement States to tie competency to authority. ^{1, 2}

The requirements live in 10 CFR Part 35, Subpart J — Training and Experience Requirements, together with the definitional and administrative sections in Subpart B. Every category of use has its own training-and-experience (T&E) threshold, and each threshold can be satisfied one of two ways: the board-certification pathway or the alternate T&E pathway with a preceptor attestation. ^{1, 2}

This guide explains what an authorized user and authorized medical physicist are, walks through the T&E requirements by category, shows how the hours are counted, and places the framework in its current regulatory context — including the 2018 final rule that revised these requirements and the NRC's more recent decisions to maintain the two-pathway structure. DRPS supports licensees with this analysis as part of its radioactive material license support, radiation safety officer, and medical physicist consulting services across Florida, Maryland, Virginia, Washington DC, California, and Nevada.

Topic Explanation

What is an authorized user?

An authorized user is a physician named on the license who may use, or supervise the use of, byproduct material for a specific category of medical use. The word "specific" is essential: authorization is granted per use category, not globally. A physician authorized for diagnostic imaging under 10 CFR 35.290 is not thereby authorized to administer I-131 therapy under 35.390 — that requires separately meeting the 35.390 requirements. ¹

The use categories map to the Subpart of Part 35 that governs them:

35.100 / 35.190 — uptake, dilution, and excretion studies (non-imaging diagnostic use).
35.200 / 35.290 — imaging and localization studies (diagnostic nuclear medicine).
35.300 / 35.390 — unsealed byproduct material for which a written directive is required (radiopharmaceutical therapy).
35.392 / 35.394 — oral sodium iodide I-131 therapy, below and above 1.22 GBq (33 mCi). ⁹
35.396 — parenteral administration requiring a written directive (for example, Lu-177, Ra-223, and Y-90 agents).
35.400 / 35.490 — manual brachytherapy sources. ¹⁰
35.600 / 35.690 — sealed sources in remote afterloaders, teletherapy, and gamma stereotactic units.

For the therapy categories, authorized-user status is inseparable from the written-directive process that governs each administration; see our guide to written directives in nuclear medicine and, for a concrete therapy example, I-131 thyroid cancer therapy.

What is an authorized medical physicist?

An authorized medical physicist is named on the license to perform the calibration, quality assurance, and safety functions for therapeutic modalities — full calibrations of remote afterloaders, teletherapy units, and gamma stereotactic radiosurgery units, and the associated spot checks and safety reviews. The AMP role is defined and its qualifications set in 10 CFR 35.51. ³

The AU and AMP roles are distinct from, but coordinated with, the Radiation Safety Officer (RSO), who runs the overall radiation safety program. A single individual may hold more than one of these roles if they meet each set of requirements. For the RSO's scope, see the radiation safety officer role.

Key Technical Principles

The two pathways

Every AU and AMP category can be satisfied by either of two pathways: ^{1, 2, 3}

Board-certification pathway. An individual certified by a specialty board whose certification process the NRC (or an Agreement State) has recognized is deemed to meet the requirements for the corresponding category. The NRC publishes the list of recognized boards and the categories each certification covers. ⁸
Alternate training-and-experience (T&E) pathway. The individual documents the required classroom and laboratory training, the required supervised work experience, and (for therapy) the required clinical cases, and obtains a written preceptor attestation from an AU or AMP qualified for that use. ^{1, 2}

Both pathways require a preceptor attestation of competency, documented on the applicable NRC Form 313A (or Agreement State equivalent). ⁸

T&E requirements by category

The hour and case thresholds are set in the individual Subpart J sections. The table below summarizes the alternate-pathway requirements for the most common categories; in every case, board certification by a recognized board is the alternative route. ^{1, 3, 4, 5, 6, 9, 10}

Category (10 CFR)	Representative use	Classroom & lab minimum	Total training & experience	Clinical cases
35.190 — uptake, dilution, excretion	Non-imaging diagnostics (e.g., I-131 uptake)	8 hours	60 hours total	—
35.290 — imaging & localization	Diagnostic nuclear medicine (Tc-99m agents)	80 hours	700 hours total	—
35.390 — unsealed, written directive	Radiopharmaceutical therapy	200 hours	700 hours total	3 per category
35.392 — oral I-131 ≤ 1.22 GBq	Hyperthyroidism therapy	80 hours	(within 80-hour framework)	3 cases
35.490 — manual brachytherapy	Sealed-source implants	200 hours	500 hours supervised work	3 cases
35.51 — authorized medical physicist	Therapy unit calibration & QA	Graduate degree	1 yr training + 1 yr work experience	—

For the AMP, 35.51 requires a master's or doctoral degree in physics, medical physics, another physical science, engineering, or applied mathematics from an accredited institution, plus one year of full-time training in medical physics and one additional year of full-time supervised work experience under a qualified AMP, in clinical facilities that provide high-energy external-beam therapy (photons or electrons ≥ 1 MeV) and brachytherapy — or board certification by a recognized board. ³

Worked example: counting 35.290 hours

The alternate pathway is satisfied only when the documented hours meet both the total and the classroom-and-laboratory minimum. For imaging and localization under 35.290, that means:

H_{total} = H_{classroom} + i \sum H_{work, i} \geq 700 h, H_{classroom} \geq 80 h

Consider a nuclear medicine resident whose logged experience is 120 hours of classroom and laboratory training plus four supervised clinical rotations of 200, 180, 150, and 90 hours:

i \sum H_{work, i} = 200 + 180 + 150 + 90 = 620 h

H_{total} = 120 + 620 = 740 h

Both conditions are satisfied: $H_{total} = 740 \geq 700$ and $H_{classroom} = 120 \geq 80$ . If the same candidate had logged only 60 classroom hours, the total might still exceed 700, but the application would fail the 80-hour classroom minimum — a subtle but common documentation gap. The lesson is that the two thresholds are independent constraints; meeting the total does not excuse a shortfall in the classroom-and-laboratory component. ⁴

Clinical Impact

Authorized-user and authorized-medical-physicist status is the gate between a license and clinical practice. A therapy program cannot administer Lu-177 DOTATATE or I-131 without a physician who is an AU for that use, and cannot operate a remote afterloader without an AMP to calibrate it. When a program adds a new service line — a first radiopharmaceutical therapy, a new theranostic agent, a gamma stereotactic unit — the credentialing timeline often controls the launch date, not the equipment. ^{1, 3}

The clinical risk of getting this wrong is concrete. Practicing a use for which one is not authorized is a license violation and a frequent inspection finding, and gaps in authorized-user coverage contribute to medical events when administrations proceed without the required oversight. For how these failures are reported and analyzed, see medical event reporting under 10 CFR 35.3045.

The practical impact also lands on succession planning. When the sole AU for a therapy leaves, the program's authority to perform that therapy can lapse until a replacement is added to the license. A program that tracks its authorized-user coverage as a managed risk — rather than discovering a gap during an inspection — protects both patients and continuity of service.

Practical Optimization Tips

Building and maintaining authorized-user coverage is an ongoing program function, not a one-time application. ^{1, 7}

1. Map coverage to your use categories

Maintain a matrix of every use category on your license against the AUs (and AMPs) who cover it. This makes coverage gaps and single-point dependencies visible before they become compliance problems.

2. Document hours and cases contemporaneously

The alternate pathway stands or falls on documentation. Log classroom, laboratory, and supervised-work hours as they occur, and record therapy cases with dates and categories. Reconstructing hours years later is the most common cause of a stalled application.

3. Secure preceptor attestations early

A preceptor must be an AU or AMP for the relevant use and must attest to competency, not merely to attendance. Identify the preceptor at the start of training, not at the end, and confirm they hold the correct authorization for every category being attested.

4. Use the board-certification pathway where it fits

For candidates certified by an NRC-recognized board in the relevant category, the board-certification pathway is usually the cleaner route. Confirm that the specific certification covers the specific use — some certifications cover diagnostic categories but not therapy.

5. Submit the right form and amendment

Adding an AU or AMP is a license amendment (NRC Form 313, with the individual's Form 313A). Build the amendment lead time into any new-service timeline. For the broader licensing process, see the NRC medical use license guide.

Common pitfalls to avoid

Assuming authorization is global. It is granted per use category; imaging authorization does not cover therapy.
Meeting the total but missing the classroom minimum. The two thresholds are independent.
A preceptor without the right authorization. The preceptor must be qualified for the exact use being attested.
No succession plan. Losing the sole AU for a use can suspend that service.
Reconstructing hours after the fact. Contemporaneous logs are far more defensible.

Regulatory Considerations

Authorized-user and authorized-medical-physicist requirements are set in 10 CFR Part 35 and administered by the NRC or the Agreement State that issued the license. The framework has been stable in structure but actively reviewed. ^{1, 2}

10 CFR Part 35, Subpart J — the training-and-experience requirements for AUs, AMPs, RSOs, and nuclear pharmacists, category by category. ¹
10 CFR 35.51, 35.190, 35.290, 35.390 — the specific AMP and AU requirements summarized above. ^{3, 4, 5, 6}
NRC Final Rule, 83 FR 33046 (July 16, 2018), effective January 14, 2019 — revised the medical-event definitions, the training-and-experience requirements, and associated clarifying amendments that shape the current thresholds and attestation process. ²
NUREG-1556, Volume 9 — the consolidated program-specific guidance for medical-use licenses, including how the NRC evaluates T&E and preceptor attestations. ⁷
NRC Forms 313A — the training, experience, and preceptor-attestation forms for each role, including Form 313A(AMP). ⁸

The two-pathway structure has been affirmed rather than narrowed. In 2022, the Commission decided to maintain the status quo — retaining both the board-certification pathway and the alternate T&E pathway, including the 700-hour requirement for therapy — rather than requiring board certification alone. The NRC subsequently issued interim staff guidance in 2024 to clarify how T&E requirements are implemented, keeping the underlying thresholds intact. ^{2, 7, 11}

Agreement States administer compatible programs. Of the states DRPS serves, Florida, Maryland, Virginia, California, Nevada, Pennsylvania, New York, and New Jersey are NRC Agreement States whose medical-use requirements must be compatible with Part 35, while Washington, DC and Delaware are regulated directly by the NRC. The hour and case thresholds are generally equivalent across jurisdictions, but the forms, submission process, and board recognition should always be confirmed with the authority that issued the license. Getting authorized-user documentation right is also one of the surest ways to avoid findings; see preparing for an NRC inspection.

Frequently Asked Questions (FAQs)

What is an authorized user under 10 CFR Part 35?

An authorized user (AU) is a physician named on a radioactive material license who is permitted to use, or supervise the use of, byproduct material for a specific category of medical use. Each category — such as imaging studies or radiopharmaceutical therapy — has its own training and experience requirements, and an individual is only an AU for the uses for which they qualify.

What is the difference between the board-certification and training-and-experience pathways?

Part 35 offers two routes to authorized status. Under the board-certification pathway, an individual certified by an NRC-recognized specialty board is deemed to meet the requirements. Under the alternate training-and-experience (T&E) pathway, the individual documents a specified number of classroom, laboratory, and supervised work hours (and, for therapy, a number of clinical cases) and obtains a preceptor attestation.

How many hours are required to become an authorized user?

The requirement depends on the use category. Uptake, dilution, and excretion studies under 35.190 require 60 hours of training and experience including 8 hours of classroom and laboratory training. Imaging and localization studies under 35.290 require 700 hours including at least 80 classroom and laboratory hours. Unsealed therapy requiring a written directive under 35.390 requires 700 hours including at least 200 classroom and laboratory hours, plus supervised clinical cases.

What is an authorized medical physicist?

An authorized medical physicist (AMP) is named on the license to perform calibration, quality assurance, and safety functions for therapeutic modalities such as remote afterloaders, gamma stereotactic units, and teletherapy. Under 35.51, an AMP holds a graduate degree in a physical science, completes structured training and work experience under a qualified AMP, and obtains a preceptor attestation — or is certified by an NRC-recognized specialty board.

Is a preceptor attestation required?

Yes. For the training-and-experience pathway, a preceptor who is an authorized user or authorized medical physicist for the relevant use must provide a written attestation that the individual has satisfactorily completed the requirements and is competent to function independently. The attestation is documented on the applicable NRC Form 313A or an Agreement State equivalent.

Do Agreement States use the same requirements?

Agreement States administer their own radiation-control programs, but their medical-use requirements must be compatible with 10 CFR Part 35. The hour and case thresholds are generally equivalent, and board-certification recognition is coordinated, but the exact forms, submission process, and any additional state requirements should always be confirmed with the specific state authority.

Key Takeaways

Authorization is per use category. An AU qualifies for specific uses; imaging authorization does not cover therapy, and each therapy category has its own requirements.
Two pathways exist. Board certification by an NRC-recognized board, or the alternate training-and-experience pathway with documented hours, cases, and a preceptor attestation.
The hour thresholds are category-specific. 60 hours (8 classroom) for 35.190; 700 hours (80 classroom) for 35.290; 700 hours (200 classroom) plus 3 cases per category for 35.390.
The AMP route runs through 35.51. A graduate degree plus structured training and supervised work experience, or board certification.
Preceptor attestation and Form 313A are mandatory for the alternate pathway, attesting to competency, not just attendance.
The structure is stable but managed. The 2018 rule set the current requirements; the NRC affirmed the two-pathway model in 2022 and clarified implementation with 2024 interim staff guidance.

Conclusion

Authorized-user and authorized-medical-physicist status is where regulatory competency meets clinical authority. A radioactive material license names who may do what, and 10 CFR Part 35 Subpart J defines how each person earns that name — through board certification or through a documented training-and-experience pathway with a preceptor attestation. The categories are specific, the hour and case thresholds are precise, and the two constraints on the alternate pathway (total hours and classroom minimum) must both be met.

For a licensee, the practical work is coverage management: mapping every use category to a qualified individual, documenting hours and cases contemporaneously, securing the right preceptor attestations, and building amendment lead time into every new service. Programs that treat authorized-user coverage as a managed risk — rather than discovering a gap during an inspection or a staffing change — protect both their patients and their authority to practice.

How DRPS Can Help

Diagnostic Radiation Physics Services helps medical-use licensees build and maintain defensible authorized-user and authorized-medical-physicist coverage. This may include mapping license use categories to qualified individuals, reviewing training-and-experience documentation against the Subpart J thresholds, supporting preceptor attestations and NRC Form 313A submissions, serving as the authorized medical physicist for therapy programs, and preparing license amendments through our radioactive material license support, radiation safety officer, and medical physicist consulting services.

DRPS supports facilities across our service locations, including Florida, Maryland, Virginia, Washington DC, California, Nevada, New York, Pennsylvania, New Jersey, and Delaware.

A strong credentialing program is not just about passing an inspection. It is about ensuring that every use on the license is covered by a qualified, documented, and attested individual — so the program can practice with authority and continuity.

Related Resources

References

U.S. Nuclear Regulatory Commission. 10 CFR Part 35: Medical Use of Byproduct Material (Subpart J — Training and Experience Requirements). ecfr.gov
U.S. Nuclear Regulatory Commission. Medical Use of Byproduct Material — Medical Event Definitions, Training and Experience, and Clarifying Amendments. Final Rule, 83 FR 33046 (July 16, 2018; effective January 14, 2019). federalregister.gov
U.S. Nuclear Regulatory Commission. 10 CFR 35.51: Training for an Authorized Medical Physicist. ecfr.gov
U.S. Nuclear Regulatory Commission. 10 CFR 35.290: Training for Imaging and Localization Studies. ecfr.gov
U.S. Nuclear Regulatory Commission. 10 CFR 35.390: Training for Use of Unsealed Byproduct Material for Which a Written Directive Is Required. ecfr.gov
U.S. Nuclear Regulatory Commission. 10 CFR 35.190: Training for Uptake, Dilution, and Excretion Studies. ecfr.gov
U.S. Nuclear Regulatory Commission. NUREG-1556, Volume 9, Revision 3: Consolidated Guidance About Materials Licenses — Program-Specific Guidance About Medical Use Licenses. nrc.gov
U.S. Nuclear Regulatory Commission. Training and Experience (T&E) Evaluation and Medical Uses Licensee Toolkit (NRC Forms 313A and recognized specialty boards). nrc.gov
U.S. Nuclear Regulatory Commission. 10 CFR 35.392: Training for the Oral Administration of Sodium Iodide I-131 Requiring a Written Directive in Quantities Less Than or Equal to 1.22 Gigabecquerels (33 Millicuries). ecfr.gov
U.S. Nuclear Regulatory Commission. 10 CFR 35.490: Training for Use of Manual Brachytherapy Sources. ecfr.gov
U.S. Nuclear Regulatory Commission. Frequently Asked Questions About Licensing Medical Uses of Byproduct Material Under Revised 10 CFR Part 35. nrc.gov