The Associate Radiation Safety Officer (ARSO)

Introduction

The Associate Radiation Safety Officer, or ARSO, is a named individual who shares the Radiation Safety Officer's workload but never the RSO's ultimate accountability. Formalized in 10 CFR 35.24, the ARSO can be appointed in writing and listed on a medical-use license to carry specific delegated duties for particular types of use — while one RSO remains responsible for the whole radiation protection program. ¹

As medical-use programs grow — more modalities, more sites, higher therapy volumes, new PET or radiopharmaceutical-therapy services — a single RSO can become a bottleneck and a single point of failure. The ARSO role gives the NRC and Agreement States a structured way to distribute radiation-safety oversight without diluting the clear line of responsibility that regulators expect. ^{1, 5}

This article explains what an ARSO is, what the role can and cannot do, how an ARSO qualifies and is appointed, and when a facility should add one. DRPS helps facilities build and document these structures through its radiation safety officer consulting and radioactive material license support services across Florida, Maryland, Virginia, Washington DC, California, and Nevada.

Topic Explanation

What the ARSO role is

An Associate Radiation Safety Officer is an individual appointed in writing by licensee management to support the Radiation Safety Officer, listed on the license for specified types of use, and assigned specific radiation-safety duties and tasks under 10 CFR 35.24. ¹

The structure has three defining features:

• It is tied to specific types of use. An ARSO is qualified and listed for particular medical uses — for example unsealed byproduct material for imaging and localization, or a therapy modality — not for the program in the abstract.
• It is a written, documented appointment. Licensee management appoints the ARSO in writing, and the RSO, with management's written agreement, assigns the specific duties and tasks. ¹
• It does not transfer ultimate responsibility. The RSO may delegate duties and tasks but may not delegate the authority or responsibility for implementing the radiation protection program. ¹

For the broader program these roles serve, see building an ALARA program and the function of the radiation safety committee.

Why the role exists

Before the role was formalized, large programs often relied on informal assistants who did real radiation-safety work without a clear regulatory status. That created two problems: the work was not always tied to a qualified, accountable, named individual, and inspectors had no clean way to confirm who was authorized to do what. The ARSO role resolves that by putting qualified support on the license, in writing, for defined uses, while preserving one accountable RSO. ^{1, 5}

Key Technical Principles

Authority versus duties: the central distinction

The most important principle in 10 CFR 35.24 is the separation of duties and tasks (which can be delegated) from authority and responsibility for the program (which cannot). An ARSO can run surveys, review records, supervise training, oversee a modality's day-to-day radiation safety, and investigate incidents — but the obligation to implement and answer for the radiation protection program stays with the RSO. ¹

The table below contrasts the common named roles in a medical-use program.

The roles can overlap in one person, but the regulatory bases and the scope of each remain distinct. ^{1, 2}

Qualification: matching training to the use

An ARSO must satisfy the training and experience requirements of 10 CFR 35.50 for the types of use they will support. In practice there are two routes: ²

• Board certification by a certifying body whose program the NRC or Agreement State recognizes for the relevant category; or
• The alternate pathway — a defined amount of classroom and laboratory training in radiation safety plus supervised work experience, capped by a written attestation from a preceptor (a qualified RSO or ARSO) that the individual is competent to function in the role for the relevant uses.

The recurring theme is scope matching: an individual qualified for the radiation-safety aspects of unsealed imaging material is not automatically qualified to serve as ARSO for a therapy or sealed-source modality. The qualification has to line up with the duties. ^{2, 5}

A worked oversight example: verifying occupational dose

A core ARSO duty is reviewing occupational dose and confirming it stays within limits and the facility's ALARA goals. Occupational dose is tracked as the total effective dose equivalent (TEDE), the sum of the external and internal contributions defined in 10 CFR Part 20:

where DDE is the deep-dose equivalent from external exposure (for example from a personnel dosimeter) and CEDE is the committed effective dose equivalent from any intake of radioactive material (for example estimated from a thyroid bioassay after I-131 work). ³

Suppose a nuclear-medicine technologist's annual records show a deep-dose equivalent of 4.2 mSv from the whole-body dosimeter and a committed effective dose equivalent of 0.8 mSv from a measured intake:

The ARSO compares that 5.0 mSv against the occupational limit of 50 mSv in a year in 10 CFR 20.1201 and, just as important, against the facility's ALARA investigational levels, which are typically set well below the regulatory limit. A result that is legally compliant but above an ALARA action level still triggers investigation and follow-up — and documenting that review is exactly the kind of delegated duty an ARSO performs under the RSO's program. ³

For how those thresholds are set and trended, see building an ALARA program and the radiation protection program under 20.1101.

A second quantitative check: decay-in-storage

Another common delegated task is confirming that short-lived waste held for decay-in-storage has decayed to background before disposal as ordinary waste. The regulatory rule of thumb is to hold material for at least ten half-lives and then survey it to confirm it is indistinguishable from background with detectors set on their most sensitive scale:

For fluorine-18, with a half-life of about 110 minutes, that is roughly 18 hours of hold time before the survey; for technetium-99m, with a 6-hour half-life, about 60 hours. The ARSO or a technologist under the ARSO's oversight performs and documents the confirmatory survey. The arithmetic is simple, but the documentation and the survey technique are what an inspector checks. ³

Clinical Impact

Distributing oversight without diluting accountability

In a busy department, the practical value of an ARSO is reach. The RSO can concentrate on program-level responsibilities — the radiation protection program, the committee, regulatory interface — while a qualified ARSO owns the day-to-day radiation safety of a specific modality or site. The work gets done by someone qualified and named, and the accountability still lands in one place. ^{1, 5}

Multi-site and multi-modality programs

Health systems increasingly run byproduct material use across several buildings or campuses on one license. An ARSO listed for the relevant uses at a given site provides on-the-ground oversight that a single central RSO cannot physically maintain everywhere at once. This is a common and appropriate use of the role, provided each ARSO's qualifications match the uses at their location. ⁵

Succession and resilience

An ARSO is also a documented, qualified backup. If the RSO is unavailable, on leave, or leaves the organization, a qualified ARSO already listed on the license provides continuity and a natural succession path — far better than scrambling to qualify and appoint a new RSO under time pressure. Building that depth deliberately is a risk-management decision as much as a staffing one.

Practical Optimization Tips

1. Match qualifications to the exact use types

Before appointing an ARSO, map each type of use on the license to the qualification the individual actually holds. Do not assume general radiation-safety experience covers a specialized therapy or PET use. ²

2. Put the appointment and duties in writing

Have licensee management sign the written appointment, and have the RSO — with management's written agreement — assign the specific duties and tasks. Keep both documents current and retrievable. ¹

3. Amend the license correctly

Adding or removing an ARSO generally requires a license amendment, because the ARSO is a named individual on the license. Plan the amendment timing so oversight is never left to someone who is not yet listed. Coordinate with radioactive material license support and see NRC medical license amendments for the process.

4. Keep the records for the required period

Retain the written appointment document for five years after the ARSO is removed from the license, consistent with the Part 35 recordkeeping requirements. See NRC Part 35 recordkeeping requirements. ⁴

5. Define the RSO–ARSO interface explicitly

Write down who does what, how the ARSO reports to the RSO, and how the RSO maintains oversight of delegated work. An inspector will expect the division of labor to be clear and the RSO to remain genuinely in control. ⁵

Common pitfalls to avoid

• Treating the ARSO as a co-RSO. There is one accountable RSO; the ARSO supports, with delegated duties only.
• Mismatched qualifications. Appointing an ARSO for uses they are not trained and experienced for.
• Skipping the written appointment or the license amendment. Informal help is exactly what the role was created to replace.
• Delegating authority, not just tasks. The RSO cannot hand off responsibility for implementing the program.
• Letting records lapse. Appointment documents must be retained for the required period after removal.

Regulatory Considerations

The ARSO role is defined in the NRC's medical-use rules and administered equivalently by Agreement States; a facility must base its structure on the regulation and the program-specific guidance, and document it so it is defensible at inspection. ^{1, 2, 5}

Key frameworks to reference:

• 10 CFR 35.24 — the core provision on the RSO and ARSO: management's written appointment of one or more ARSOs, the RSO's assignment of specific duties and tasks with management's written agreement, and the prohibition on delegating authority and responsibility for the program. ¹
• 10 CFR 35.50 — training and experience for the RSO and ARSO, through recognized board certification or the alternate training, experience, and preceptor-attestation pathway, matched to the relevant types of use. ²
• 10 CFR 35.2024 — recordkeeping for the appointment, including retaining the written ARSO appointment document for five years after removal from the license. ⁴
• 10 CFR Part 20 — Standards for Protection Against Radiation, including the occupational dose limits and ALARA framework an ARSO helps enforce. ³
• NRC NUREG-1556, Volume 9 — program-specific guidance for medical-use licenses, with expectations for RSO and ARSO qualifications, appointment, and program structure. ⁵

Agreement States administer their own equivalent programs. Of the states DRPS serves, Florida, Maryland, Virginia, California, Nevada, Pennsylvania, New York, and New Jersey are NRC Agreement States that license medical use under their own radiation-control rules, while Washington, DC and Delaware are regulated directly by the NRC. A facility must confirm which authority issues its license and apply that authority's version of the Part 35 requirements before appointing an ARSO. Coordinate the structure with radiation safety officer consulting, radiation safety training, and medical physics consulting, and prepare the supporting documentation the way you would for any inspection — see preparing for an NRC inspection.

Frequently Asked Questions (FAQs)

What is an Associate Radiation Safety Officer (ARSO)?

An Associate Radiation Safety Officer is an individual appointed in writing by licensee management to support the Radiation Safety Officer under 10 CFR 35.24. The ARSO is listed on the medical-use license for specified types of use and can be assigned specific radiation-safety duties and tasks. The role was formalized by the NRC to let larger or multi-modality programs distribute the radiation-safety workload while keeping one accountable RSO.

Can an ARSO replace the Radiation Safety Officer?

No. Every medical-use licensee must still have one Radiation Safety Officer who holds overall responsibility for the radiation protection program. The RSO may delegate specific duties and tasks to an ARSO, but 10 CFR 35.24 prohibits delegating the authority and responsibility for implementing the program. The ARSO supports and extends the RSO's reach; it does not substitute for the RSO's accountability.

What training and experience does an ARSO need?

An ARSO must be qualified under 10 CFR 35.50 for the specific types of use for which they are assigned duties, typically through board certification recognized by the NRC or an Agreement State, or through the alternate pathway of classroom and laboratory training plus supervised work experience and a written attestation by a qualified preceptor. The key point is that the qualification must match the use types the ARSO oversees.

Does the ARSO have to be listed on the license?

Yes. The ARSO is a named individual on the medical-use license for the specified types of use, which usually requires a license amendment to add or remove. Licensee management must appoint the ARSO in writing, and the licensee must retain the written appointment document for five years after the ARSO is removed from the license.

Who can serve as an ARSO?

An individual who meets the 10 CFR 35.50 training and experience requirements for the relevant types of use. In practice an ARSO is often a qualified medical physicist, an authorized medical physicist, an authorized nuclear pharmacist, or an authorized user who has the specific radiation-safety training and experience for the uses they will support, appointed in writing and listed on the license.

When should a facility add an ARSO?

Consider an ARSO when the program spans multiple modalities or sites, when patient and procedure volume outgrows a single RSO's capacity, when a specialized use such as a new therapy or PET program needs focused oversight, or when succession planning calls for building and documenting a qualified backup. An ARSO formalizes distributed oversight rather than leaving it to informal, undocumented help.

Is an ARSO the same as an authorized medical physicist?

No. An authorized medical physicist (AMP) is an individual qualified and named for specific physics responsibilities such as certain therapy device calibrations and surveys. An ARSO is a radiation-safety oversight role under 10 CFR 35.24. The same person may hold both designations if they meet both sets of requirements, but the roles and their regulatory bases are distinct.

Key Takeaways

• The ARSO supports the RSO; it does not replace the RSO. One accountable RSO remains per license.
• Duties can be delegated; authority cannot. 10 CFR 35.24 lets the RSO assign tasks but not the responsibility for implementing the program.
• Qualification must match the use types. An ARSO is trained, experienced, and listed for specific medical uses under 10 CFR 35.50.
• The appointment is written and on the license. Management appoints in writing, the RSO assigns duties, and adding or removing an ARSO generally needs a license amendment.
• Records are retained for five years after removal, consistent with Part 35 recordkeeping.
• The role adds reach, resilience, and succession depth for multi-site and multi-modality programs.

Conclusion

The Associate Radiation Safety Officer is a deceptively simple idea with real organizational value: it lets a growing medical-use program put qualified, named, accountable support behind the RSO without blurring who is ultimately responsible. The regulation draws a bright line — duties and tasks can be shared, but the authority and responsibility for the radiation protection program cannot — and a well-run program keeps that line visible in its appointments, its records, and its day-to-day practice.

For facilities weighing whether to add an ARSO, the question is rarely whether the help is needed; it is whether the help is qualified, documented, and properly on the license. Done right, the ARSO role turns informal assistance into defensible structure.

How DRPS Can Help

Diagnostic Radiation Physics Services helps medical-use licensees design and document radiation-safety oversight that holds up at inspection. That can include RSO and ARSO program structure, qualification and scope-matching reviews, written appointment and duty documentation, license amendment support, recordkeeping systems, radiation safety officer consulting, radioactive material license support, and radiation safety training aligned with NRC and Agreement State requirements.

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

Strong radiation-safety oversight is not about adding titles. It is about making sure the right qualified person is accountable for the right work — and that the paperwork proves it.

Related Resources

• Building an ALARA program
• The radiation safety committee
• The radiation protection program under 20.1101
• NRC Part 35 recordkeeping requirements
• Preparing for an NRC inspection
• Radiation Safety Officer consulting
• Radioactive material license support

References

1. U.S. Nuclear Regulatory Commission. 10 CFR 35.24: Radiation Safety Officer and Associate Radiation Safety Officer. ecfr.gov
2. U.S. Nuclear Regulatory Commission. 10 CFR 35.50: Training for Radiation Safety Officer and Associate Radiation Safety Officer. ecfr.gov
3. U.S. Nuclear Regulatory Commission. 10 CFR Part 20: Standards for Protection Against Radiation. ecfr.gov
4. U.S. Nuclear Regulatory Commission. 10 CFR 35.2024: Records of authority and responsibilities for radiation protection programs. ecfr.gov
5. U.S. Nuclear Regulatory Commission. NUREG-1556, Volume 9, Revision 3: Consolidated Guidance About Materials Licenses — Program-Specific Guidance About Medical Use Licenses. 2019. nrc.gov
6. U.S. Nuclear Regulatory Commission. Medical Uses of Nuclear Materials — Authorized Individuals (Medical Use Toolkit). nrc.gov
7. U.S. Nuclear Regulatory Commission. 10 CFR 35.51: Training for an Authorized Medical Physicist. ecfr.gov