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NRC Form 313 Authorizations, RSO Responsibilities & Written Directives
ABMP Medical Health Physics Exam
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1 Radiation Detection Instrumentation
Ionization Chambers & Geiger-Mueller Counters Scintillation Detectors, Photomultipliers & Gamma Spectroscopy Liquid Scintillation & Gamma Counting Systems: Well Counters & Thyroid Probes Personnel Dosimeters & Electronic Radiation Monitors Neutron Detection & Emergency Field Instrumentation
2 Laboratory Design & Contamination Control
Radiopharmaceutical Laboratory Design & USP <825> Standards Ventilation Systems, Fume Hoods & Contamination Engineering
3 Radiation Protection Standards & Dose Limits
Federal Regulatory Framework & Advisory Authorities Federal Guidance Documents: NRC Regulatory Guides, NUREGs, EPA & FDA Guidance Occupational & Public Dose Limits and ALARA Principles Radiobiological Basis of Limits & Risk Communication
4 Medical Licensing, Written Directives & Security
NRC Form 313 Authorizations, RSO Responsibilities & Written Directives Medical Event Reporting & 10 CFR 37 Category 1/2 Source Security
5 Diagnostic Radiology Structural Shielding
Diagnostic Shielding Methodology: NCRP Report 147 Modality Shielding: Radiography, Fluoroscopy & CT Facilities
6 Megavoltage Therapy Vault & Facility Shielding
Megavoltage Vault Primary & Secondary Barriers: NCRP Report 151 Therapy Maze Design, Photoneutrons & Shielded Doors PET/CT & Nuclear Medicine Facility Shielding (AAPM TG-108)
7 Radiation Oncology Quality Management & Safety
External Beam QA & Dosimetry Calibration Protocols Brachytherapy Safety, Inventory Control & Leak Testing
8 Radiation Oncology Emergency Procedures & TPS QA
Treatment Planning System (TPS) QA & Patient Verification Radiation Oncology Emergency Procedures: HDR Stuck Sources & Linac Failures Medical Events, Incident Investigation & Joint Commission Requirements in Radiation Oncology
9 Diagnostic Imaging Safety & Fluoroscopy Management
Diagnostic X-ray & Fluoroscopy Safety Interventional Fluoroscopy Dose Management & NCRP Report 168
10 CT Optimization, MQSA & Diagnostic Accreditation
Computed Tomography Dosimetry & Protocol Optimization Mammography Quality Standards Act (MQSA) & Mammography Physics Diagnostic Imaging Quality Management, Accreditation & Regulatory Oversight
11 Nuclear Medicine Radiopharmacy & Unsealed Therapy
Radiopharmaceutical QC & Radionuclide Calibrators Unsealed Source Therapy: I-131 Protocols & Patient Release Criteria
12 Targeted Radionuclide Therapy, Decontamination & RAM Transport
Targeted Radionuclide Therapies: Lu-177, Ra-223, Y-90 & Radioimmunotherapy Contamination Surveys, Spill Response & Personnel Decontamination Radioactive Waste Disposal & US DOT Transport Regulations
13 Radiobiology & Radiation Risk Assessment
Cellular Radiobiology, DNA Damage & Dose-Response Models Prenatal Radiation Risks & Population Exposures
14 Non-Ionizing Radiation Safety: Lasers & MRI
Healthcare Laser Safety: ANSI Z136.1 & Z136.3 MRI Safety, Facility Design & Bioeffects
NRC Form 313 Authorizations, RSO Responsibilities & Written Directives
Key Takeaways Explain This Topic AI
Medical byproduct authorizations are organized under 10 CFR Part 35 Subparts D through K, either on a specific medical use license that names each AU, AMP, ANP, and RSO or on a Type A broad scope license (10 CFR Part 33) whose Radiation Safety Committee approves users internally.
Under 10 CFR 35.50, an RSO qualifies through a recognized specialty board (such as ABHP or ABMP Medical Health Physics) plus training for the uses on the license, the 200-hour classroom and one-year supervised experience pathway with a preceptor attestation, or as a board-certified medical physicist or listed AU, AMP, or ANP with relevant radiation safety experience.
A written directive is required under 10 CFR 35.40 before any administration of I-131 sodium iodide above 1.11 MBq (30 µCi), any therapeutic dosage of unsealed byproduct material, and any therapeutic dose of radiation from byproduct material.
Oral directives (35.40(a)(1)) and oral revisions (35.40(c)(2)) are allowed only when a delay would jeopardize the patient; they are documented as soon as possible and followed by a written directive or signed revision within 48 hours.
10 CFR 35.41 procedures must address patient identity, conformance with the plan and directive, manual and computer dose-calculation checks, transfer of computer calculations to treatment consoles, determining whether a medical event occurred, and the 60-day source-strength check for permanent implants.
Last updated: October 2026
NRC Form 313 & Medical Byproduct Licensing Categories
The acquisition, clinical administration, and disposal of byproduct material in medical facilities are licensed by the US Nuclear Regulatory Commission (NRC) or Agreement States under Title 10 of the Code of Federal Regulations (10 CFR). Licensees apply for new authorizations or amendments using NRC Form 313 ( Application for Materials License ), supported by the NRC Form 313A series documenting clinical training and preceptor attestations for Radiation Safety Officers (313A[RSO]), Authorized Medical Physicists (313A[AMP]), Authorized Users (313A[AU]), and Authorized Nuclear Pharmacists (313A[ANP]).
Under 10 CFR Part 35 ( Medical Use of Byproduct Material ), authorizations are categorized into specific clinical modalities:
Subpart D (10 CFR 35.100 and 35.200): Unsealed byproduct material, written directive not required. Uptake, dilution, and excretion studies (35.100), such as diagnostic 131 I ^{131}\text{I} 131 I thyroid uptake measurements at or below 1.11 MBq 1.11\text{ MBq} 1.11 MBq ( 30 μ Ci 30\ \mu\text{Ci} 30 μ Ci ), and imaging and localization studies (35.200) with 99 m Tc ^{99\text{m}}\text{Tc} 99 m Tc , 111 In ^{111}\text{In} 111 In , 201 Tl ^{201}\text{Tl} 201 Tl , 18 F ^{18}\text{F} 18 F , 68 Ga ^{68}\text{Ga} 68 Ga , and 82 Rb ^{82}\text{Rb} 82 Rb .
Subpart E (10 CFR 35.300): Unsealed byproduct material, written directive required. Therapeutic radiopharmaceuticals, including 131 I ^{131}\text{I} 131 I sodium iodide for hyperthyroidism and thyroid cancer, 177 Lu ^{177}\text{Lu} 177 Lu dotatate and PSMA agents, and 223 Ra ^{223}\text{Ra} 223 Ra dichloride.
Subpart F (10 CFR 35.400): Manual brachytherapy. Interstitial, intracavitary, and topical sealed sources such as 125 I ^{125}\text{I} 125 I , 103 Pd ^{103}\text{Pd} 103 Pd , and 131 Cs ^{131}\text{Cs} 131 Cs seeds and 137 Cs ^{137}\text{Cs} 137 Cs tubes.
Subpart G (10 CFR 35.500): Sealed sources for diagnosis , for example 153 Gd ^{153}\text{Gd} 153 Gd transmission sources.
Subpart H (10 CFR 35.600): Photon-emitting remote afterloader units, teletherapy units, and gamma stereotactic radiosurgery units , including HDR 192 Ir ^{192}\text{Ir} 192 Ir afterloaders, 60 Co ^{60}\text{Co} 60 Co teletherapy, and Gamma Knife units.
Subpart K (10 CFR 35.1000): Other medical uses , emerging technologies licensed case by case under NRC licensing guidance, such as 90 Y ^{90}\text{Y} 90 Y microspheres (SIR-Spheres and TheraSphere).
Specific Medical Use vs. Broad Scope Type A Licenses
Healthcare institutions operate under one of two primary licensing frameworks:
Specific Medical Use License of Limited Scope (10 CFR Part 35): The NRC or Agreement State directly names every AU, AMP, ANP, and RSO on the license document. Any operational modification—such as adding a physician, introducing a new modality, altering treatment vaults, or adjusting possession limits—requires a formal regulatory license amendment prior to clinical implementation.
Type A Specific License of Broad Scope (10 CFR Part 33): Large medical institutions and universities establish an internal oversight structure under 10 CFR 33.13. The institution's executive Radiation Safety Committee (RSC) possesses legal authority to evaluate and internally approve AUs, AMPs, ANPs, research protocols, and clinical facilities without submitting individual license amendments to the regulator.
Radiation Safety Committee (RSC) Mandates
Under 10 CFR 35.24(f), a licensee authorized for two or more different types of use under Subparts E, F, and H (or two or more types of units under Subpart H) must establish an RSC that includes:
The Radiation Safety Officer (RSO) .
An Authorized User (AU) for each medical use authorized by the license.
A representative of the Nursing Service .
A representative of Executive Management who is neither an AU nor an RSO.
Part 35 no longer prescribes a meeting frequency or quorum (the pre-2002 rule required meetings at least every six months with a quorum that included the RSO and management); licensees set these in their procedures and license commitments. Typical RSC work includes reviewing ALARA and dosimetry trends, incidents, and the annual radiation protection program review required by 10 CFR 20.1101(c). A broad scope licensee has its own RSC requirement under 10 CFR 33.13, with membership that includes the RSO, a management representative, and persons trained and experienced in the safe use of radioactive material.
- Regulatory Parameter Specific Medical License (10 CFR Part 35) Broad Scope Type A License (10 CFR Part 33)
- AU / AMP Approval Direct NRC/State license amendment Internal review and approval by institutional RSC
- Facility Additions Regulatory amendment required before use Internal RSC safety evaluation and authorization
- Possession Limits Radionuclide-specific curie limits Multi-curie broad limits (atomic numbers 1–83)
RSC Requirement Required for two or more types of use under Subparts E, F, and H (or two or more Subpart H unit types) Required by 10 CFR 33.13
Primary Oversight Regulatory agency inspects named authorizations Regulatory agency audits RSC governance and quality
Radiation Safety Officer (RSO) Mandates & Qualifications (10 CFR 35.50)
Under 10 CFR 35.24(b), licensee management appoints an RSO who agrees in writing to be responsible for implementing the radiation protection program. Management may also appoint Associate RSOs; the RSO may delegate duties and tasks to them but not the authority or responsibility for the program. Under 35.24(e) and (g), the RSO's authority, duties, and responsibilities are set out in writing, and management must provide sufficient authority, organizational freedom, time, resources, and management prerogative to:
Identify radiation safety problems and initiate, recommend, or provide corrective actions.
Stop unsafe operations , and verify that corrective actions are implemented.
NRC licensing guidance offers a model delegation-of-authority memo for documenting this.
Qualification Pathways under 10 CFR 35.50
Specialty board certification (35.50(a)): Certification by a board whose certification process the NRC or an Agreement State has recognized (the list is posted on the NRC Medical Uses Licensee Toolkit and includes, for example, the American Board of Health Physics and ABMP certification in Medical Health Physics), plus the 35.50(d) training in radiation safety, regulatory issues, and emergency procedures for the types of use on the license.
Structured training and experience (35.50(b)): 200 hours of classroom and laboratory training in radiation physics and instrumentation, radiation protection, mathematics of radioactivity measurement, radiation biology, and radiation dosimetry; one year of full-time radiation safety experience under the RSO (or an Associate RSO) of a license authorizing similar uses; and a written preceptor attestation , documented on NRC Form 313A(RSO).
Board-certified medical physicists and listed authorized individuals (35.50(c)): A medical physicist certified by a board recognized under 35.51(a), or an AU, AMP, or ANP already identified on the license, who has experience with the radiation safety aspects of similar types of use.
ABMP states that its Medical Health Physics certification is recognized by the NRC for RSO eligibility, and candidates who meet the standard receive that recognition on the diploma.
Under 10 CFR 35.59 , all required training and experience must have been obtained within the 7 years preceding the application , or the candidate must document related continuing professional education.
Written Directive Requirements (10 CFR 35.40)
A Written Directive (WD) is an Authorized User's dated and signed medical prescription for administering byproduct material or radiation to a specific patient.
Clinical Triggers Mandating a Written Directive
Under 10 CFR 35.40(a), a Written Directive is legally mandatory prior to:
Any administration of iodine-131 sodium iodide > 1.11 MBq > 1.11\text{ MBq} > 1.11 MBq ( 30 μ Ci 30\ \mu\text{Ci} 30 μ Ci ) .
Any therapeutic dosage of unsealed byproduct material (e.g., 177 Lu ^{177}\text{Lu} 177 Lu , 223 Ra ^{223}\text{Ra} 223 Ra , 90 Y ^{90}\text{Y} 90 Y , 89 Sr ^{89}\text{Sr} 89 Sr , 131 I ^{131}\text{I} 131 I MIBG).
Any therapeutic dose of radiation from byproduct material, including manual brachytherapy , HDR remote afterloading , teletherapy , and gamma stereotactic radiosurgery .
Required Contents (10 CFR 35.40(b))
Every written directive contains the patient's name plus:
I-131 sodium iodide above 1.11 MBq (30 µCi): the dosage.
Other therapeutic unsealed byproduct material: the radioactive drug, dosage, and route of administration.
Gamma stereotactic radiosurgery: total dose, treatment site, and target coordinate settings per treatment for each anatomically distinct site.
Teletherapy: total dose, dose per fraction, number of fractions, and treatment site.
HDR remote afterloading: radionuclide, treatment site, dose per fraction, number of fractions, and total dose.
Permanent implant brachytherapy: before implantation, the treatment site, radionuclide, and total source strength; after implantation but before the patient leaves the post-treatment recovery area, the treatment site, number of sources implanted, total source strength implanted, and date.
All other brachytherapy (including LDR, MDR, and PDR afterloaders): before implantation, the treatment site, radionuclide, and dose; after implantation but before completion, the radionuclide, treatment site, number of sources, total source strength and exposure time (or total dose), and date.
Emergency Directives and Written Revisions
Emergency oral directives (10 CFR 35.40(a)(1)): If the emergent nature of the patient's condition means a delay would jeopardize the patient's health, an oral directive is acceptable. Its content is documented in writing in the patient's record as soon as possible, and a written directive must be prepared within 48 hours .
Revisions (10 CFR 35.40(c)): A written revision must be dated and signed by an AU before the dosage, the brachytherapy dose, the GSR or teletherapy dose, or the next fractional dose is given (c)(1). If a delay would jeopardize the patient, an oral revision is acceptable; it is documented as soon as possible, and the revised written directive must be signed by the AU within 48 hours (c)(2).
Procedures for Administrations Requiring a Written Directive (10 CFR 35.41)
Under 10 CFR 35.41, licensees must maintain written procedures ensuring high confidence that:
Verifying the patient's identity before each administration (NRC guidance expects more than one method, such as name and date of birth checked against a wristband; never a room number alone).
Verifying that the administration follows the treatment plan, if applicable, and the written directive.
Checking both manual and computer-generated dose calculations.
Verifying that computer-generated dose calculations are correctly transferred into the consoles of 35.600 and 35.1000 units (for example, HDR or GSR consoles).
Determining whether a medical event (10 CFR 35.3045) has occurred.
For permanent implant brachytherapy, determining within 60 calendar days the total source strength administered outside the treatment site compared with the post-implantation portion of the directive, unless patient unavailability is documented.
Reviewing a sample of administrations during the annual program review is good practice, although 35.41 itself does not set an audit frequency.
- Worked Verification Scenario & Clinical Pitfalls
- Worked Verification: HDR Ir-192 Cylinder Administration
An AU prescribes 3 fractions of 6.0 Gy ( 18.0 Gy 18.0\text{ Gy} 18.0 Gy total) to vaginal mucosa at 0.5 cm depth using an HDR 192 Ir ^{192}\text{Ir} 192 Ir cylinder. Initial source calibration was A 0 = 370.0 GBq A_0 = 370.0\text{ GBq} A 0 = 370.0 GBq ( 10.0 Ci 10.0\text{ Ci} 10.0 Ci ) 28 days prior ( T 1 / 2 = 73.83 d T_{1/2} = 73.83\text{ d} T 1/2 = 73.83 d , decay constant λ = 0.009388 d − 1 \lambda = 0.009388\text{ d}^{-1} λ = 0.009388 d − 1 ).
Calculate current source activity: A ( 28 d ) = 370.0 GBq × e − ( 0.009388 × 28 ) = 370.0 × 0.76885 = 284.5 GBq ( 7.69 Ci ) A(28\text{ d}) = 370.0\text{ GBq} \times e^{-(0.009388 \times 28)} = 370.0 \times 0.76885 = 284.5\text{ GBq}\quad (7.69\text{ Ci}) A ( 28 d ) = 370.0 GBq × e − ( 0.009388 × 28 ) = 370.0 × 0.76885 = 284.5 GBq ( 7.69 Ci )
The Authorized Medical Physicist verifies that the TPS and console source tables match 284.5 GBq 284.5\text{ GBq} 284.5 GBq within ± 1.0 % \pm 1.0\% ± 1.0% .
The AMP checks total dwell time ( 214.6 s 214.6\text{ s} 214.6 s ) against an independent nomogram ( 215 s ± 2 % 215\text{ s} \pm 2\% 215 s ± 2% ) and confirms dual patient identifiers prior to beam-on.
Clinical Practice Pitfalls
Diagnostic I-131 Written Directive Trap: Diagnostic 131 I ^{131}\text{I} 131 I whole-body scans administering > 1.11 MBq >1.11\text{ MBq} > 1.11 MBq ( 30 μ Ci 30\ \mu\text{Ci} 30 μ Ci , e.g., 100 μ Ci 100\ \mu\text{Ci} 100 μ Ci ) legally mandate a signed Written Directive under 10 CFR 35.40, whereas a 5 μ Ci 5\ \mu\text{Ci} 5 μ Ci uptake test does not.
Broad Scope Portability Trap: AU approval granted under an institution's Broad Scope Type A license does not transfer to a facility with a Specific Medical Use License without a formal regulatory amendment.
Single Patient Identifier Error: Using room numbers or leading prompts ("Are you Mr. Davis?") does not give the "high confidence" that 35.41 procedures require; ask the patient to state identifiers and check them against the record.