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Medical Event Reporting & 10 CFR 37 Category 1/2 Source Security
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
Medical Event Reporting & 10 CFR 37 Category 1/2 Source Security
Key Takeaways Explain This Topic AI
Except for permanent implants, a medical event under 10 CFR 35.3045(a)(1) needs a dose difference above 0.05 Sv EDE, 0.5 Sv to an organ or tissue, or 0.5 Sv to the skin together with a 20% total-dose or dosage error or a 50% single-fraction error; a wrong drug, route, individual, mode, or leaking source above those doses; or a wrong-site dose exceeding expectations by both 0.5 Sv and 50%.
Permanent implant brachytherapy uses source-strength criteria (10 CFR 35.3045(a)(2)): a 20% difference in total source strength, more than 20% implanted outside the treatment site, wrong radionuclide or individual, or sources placed in a discontiguous location.
The licensee telephones the NRC Operations Center no later than the next calendar day after discovery, sends a written report within 15 days that may not identify the patient, and notifies the referring physician and the patient within 24 hours unless the referring physician takes on that task or judges that telling the patient would be harmful.
Under 10 CFR Part 37, unescorted access to Category 1 and 2 quantities requires a trustworthiness and reliability determination by a licensee-named reviewing official, based on fingerprinting and an FBI criminal history check, identity, 7-year employment history, education, and character references.
Part 37 requires security zones, continuous monitoring and detection of unauthorized entry with immediate assessment, removal detection (immediate for Category 1, weekly verification for Category 2), and LLEA coordination at least every 12 months.
Last updated: October 2026
Medical Event Criteria under 10 CFR 35.3045
A Medical Event is an unintended radiation exposure during a medical administration of byproduct material or radiation from byproduct material that meets specific dose divergence and delivery failure criteria codified in 10 CFR 35.3045.
Structure of the Medical Event Criteria (10 CFR 35.3045(a))
All administrations except permanent implant brachytherapy, (a)(1). Unless the event results from patient intervention, a medical event occurs when any of three conditions is met:
Dose or dosage error, (a)(1)(i): the dose differs from the prescribed dose (or from the dose the prescribed dosage would have given) by more than 0.05 Sv (5 rem) effective dose equivalent, 0.5 Sv (50 rem) to an organ or tissue, or 0.5 Sv (50 rem) shallow dose equivalent to the skin , and one of the following is true:
the total dose delivered differs from the prescribed dose by 20% or more ;
the total dosage delivered differs from the prescribed dosage by 20% or more , or falls outside the prescribed dosage range; or
the fractionated dose delivered differs from the prescribed dose for a single fraction by 50% or more .
Wrong administration, (a)(1)(ii): a dose that exceeds 0.05 Sv EDE, 0.5 Sv to an organ or tissue, or 0.5 Sv shallow dose from a wrong radioactive drug (or wrong brachytherapy radionuclide), the wrong route, the wrong individual or research subject, the wrong mode of treatment, or a leaking sealed source.
Wrong site, (a)(1)(iii): a dose to the skin or an organ or tissue other than the treatment site that exceeds the expected dose by both 0.5 Sv (50 rem) and 50% .
Permanent implant brachytherapy, (a)(2). These criteria use source strength rather than dose, and seeds implanted in the correct site that later migrate are excluded:
total source strength administered differs by 20% or more from the post-implantation portion of the written directive;
total source strength administered outside the treatment site exceeds 20% of the documented total; or
the wrong radionuclide, the wrong individual, sources implanted directly into a location discontiguous from the treatment site, or a leaking source that gives more than 0.5 Sv to an organ or tissue.
Regulatory Nuances & Exclusions
No dose, no event: A diagnostic dosage given to the wrong patient (for example, 740 MBq 740\text{ MBq} 740 MBq of 99 m Tc ^{99\text{m}}\text{Tc} 99 m Tc -MDP, well under 0.05 Sv EDE and 0.5 Sv to any organ) does not reach the (a)(1)(ii) dose threshold; it is handled as an internal quality event.
Patient intervention: Events that result from patient intervention (such as a patient removing an applicator or vomiting a capsule) are excluded from (a). Under 35.3045(b), however, the licensee must still report a patient-intervention event that results, or will result, in unintended permanent functional damage to an organ or physiological system, as determined by a physician.
Leaking sources: A sealed source counts as leaking at 185 Bq 185\text{ Bq} 185 Bq ( 0.005 μ Ci 0.005\ \mu\text{Ci} 0.005 μ Ci ) of removable contamination (35.67); it becomes a medical event only if the dose criteria above are met.
Embryo/fetus and nursing child (10 CFR 35.3047): An unintended dose greater than 50 mSv 50\text{ mSv} 50 mSv ( 5 rem 5\text{ rem} 5 rem ) to an embryo/fetus from an administration to a pregnant individual (unless the AU approved it in advance), or to a nursing child (or any dose causing unintended permanent functional damage), is reported under 35.3047 rather than 35.3045.
Notification Timelines & Reporting Protocols
When a Medical Event is discovered, federal regulations enforce strict notification deadlines tied to the date and time of discovery :
24-Hour Telephone Notification (10 CFR 35.3045(c)): The licensee must notify the NRC Operations Center by telephone no later than the next calendar day (within 24 hours) after discovery .
Referring Physician and Patient Notification (10 CFR 35.3045(e)): The licensee must notify the referring physician and the patient (or responsible relative/guardian) no later than 24 hours after discovery . The licensee need not notify the individual without first consulting the referring physician, and it does not notify the individual if the referring physician personally informs the licensee that he or she will tell the individual, or that, based on medical judgment, telling the individual would be harmful. Appropriate medical care may not be delayed because of notification.
15-Day Written Report (10 CFR 35.3045(d)): The licensee must submit a comprehensive written report to the NRC Regional Office within 15 days of discovery . The report details the event description, root cause, estimated patient impact, and corrective actions.
Caution
Patient Privacy Rule: Under 10 CFR 35.3045(d)(2), the written report to the NRC may not contain the individual's name or any other information that could identify the individual. Under 35.3045(g), the licensee annotates a copy of that report with the individual's name and identification number and sends it to the referring physician (if other than the licensee) within 15 days of discovery. If the individual is notified verbally, the licensee must tell the individual that a written description of the event is available on request, and provide it if asked.
10 CFR Part 37: Category 1 & Category 2 Security Thresholds
Title 10 CFR Part 37 establishes mandatory physical protection standards for facilities possessing Category 1 and Category 2 quantities of radioactive material to safeguard against radiological dispersal devices ("dirty bombs").
Radionuclide Activity Thresholds (10 CFR Part 37, Appendix A, Table 1; the TBq values govern)
Radionuclide Primary Medical / Clinical Use Category 1 (TBq) Category 1 (Ci) Category 2 (TBq) Category 2 (Ci)
Cobalt-60 ( 60 Co ^{60}\text{Co} 60 Co ) Teletherapy, Gamma Knife 30 TBq 30\text{ TBq} 30 TBq 810 Ci 810\text{ Ci} 810 Ci 0.3 TBq 0.3\text{ TBq} 0.3 TBq 8.1 Ci 8.1\text{ Ci} 8.1 Ci
Cesium-137 ( 137 Cs ^{137}\text{Cs} 137 Cs ) Blood irradiators, calibration 100 TBq 100\text{ TBq} 100 TBq 2,700 Ci 2{,}700\text{ Ci} 2 , 700 Ci 1.0 TBq 1.0\text{ TBq} 1.0 TBq 27 Ci 27\text{ Ci} 27 Ci
Iridium-192 ( 192 Ir ^{192}\text{Ir} 192 Ir ) HDR remote afterloaders 80 TBq 80\text{ TBq} 80 TBq 2,160 Ci 2{,}160\text{ Ci} 2 , 160 Ci 0.8 TBq 0.8\text{ TBq} 0.8 TBq 21.6 Ci 21.6\text{ Ci} 21.6 Ci
Radium-226 ( 226 Ra ^{226}\text{Ra} 226 Ra ) Historical brachytherapy 40 TBq 40\text{ TBq} 40 TBq 1,080 Ci 1{,}080\text{ Ci} 1 , 080 Ci 0.4 TBq 0.4\text{ TBq} 0.4 TBq 10.8 Ci 10.8\text{ Ci} 10.8 Ci
Sum-of-Fractions Aggregation Rule
Under 10 CFR Part 37, Appendix A, when sources are aggregated (accessible by breaching a single physical barrier), the licensee calculates the sum of fractions :
∑ i = 1 n A i T i = A 1 T 1 + A 2 T 2 + ⋯ + A n T n ≥ 1.0 \sum_{i=1}^{n} \frac{A_i}{T_i} = \frac{A_1}{T_1} + \frac{A_2}{T_2} + \cdots + \frac{A_n}{T_n} \ge 1.0 ∑ i = 1 n T i A i = T 1 A 1 + T 2 A 2 + ⋯ + T n A n ≥ 1.0
where A i A_i A i is source activity and T i T_i T i is the threshold. If the ratio ≥ 1.0 \ge 1.0 ≥ 1.0 , the aggregation triggers Part 37 security controls.
- Access Authorization & Physical Security Controls
- Subpart B: Trustworthiness & Reliability (T&R) Program
Unescorted access to Category 1 or 2 material requires a trustworthiness and reliability (T&R) determination, which only a reviewing official (RO) may make. The licensee names its ROs and certifies each RO's trustworthiness to the NRC under oath, with the RO's fingerprints submitted for an FBI check (37.23(b)). The background investigation (37.25) covers at least the 7 years before the investigation (or since age 18) and includes:
Fingerprinting and an FBI identification and criminal history records check .
Verification of true identity against official documents.
Employment history verification for the most recent 7 years , including military history.
Verification of education.
Character and reputation determination through reference checks (not with close family members unless no other references exist).
Reinvestigation (fingerprinting and FBI check) is required every 10 years (37.25(c)), and the access authorization program itself must be reviewed at least annually (37.33).
Subpart C: Physical Security Zones & LLEA Coordination
Security Zones: Radioactive materials must be isolated behind continuous physical barriers (vault walls, locked steel doors) with access restricted to T&R-approved individuals or escorted personnel.
Monitoring, Detection, and Assessment (37.49): For both categories the licensee must continuously monitor and detect unauthorized entry into the security zone (a monitored intrusion detection system, alarms that alert nearby staff, monitored video, or direct surveillance) and immediately assess each actual or attempted entry. To detect unauthorized removal , Category 1 quantities need immediate detection (alarmed sensors, monitored video, or direct visual surveillance), while Category 2 quantities need weekly verification that the material is still present (physical check, tamper-indicating device, or use).
Local Law Enforcement Agency (LLEA) Coordination (37.45): Licensees coordinate with the LLEA at least every 12 months (and whenever changes increase vulnerability), describing the facility, the Category 1 and 2 material, and the security measures, and notifying the LLEA that the licensee will request a timely armed response to any actual or attempted theft, sabotage, or diversion. If the LLEA does not respond within 60 days or declines to participate, the licensee notifies the NRC regional office within 3 business days; coordination records are kept for 3 years.
- Worked Numerical Examples & Clinical Calculations
- Example 1: Medical Event Determination (Catheter Displacement)
An HDR 192 Ir ^{192}\text{Ir} 192 Ir plan prescribes 5.0 Gy to the vaginal cuff in 1 fraction. An unrecognized 4.0 cm catheter shift delivers only 0.5 Gy to the target while normal rectum receives 8.5 Gy 8.5\text{ Gy} 8.5 Gy (planned rectal dose was 1.2 Gy 1.2\text{ Gy} 1.2 Gy ).
Target, (a)(1)(i): The target received 0.5 Gy 0.5\text{ Gy} 0.5 Gy instead of 5.0 Gy 5.0\text{ Gy} 5.0 Gy , a difference of 4.5 Gy 4.5\text{ Gy} 4.5 Gy (far above 0.5 Sv 0.5\text{ Sv} 0.5 Sv to an organ or tissue) and a single-fraction error of ∣ ( 0.5 − 5.0 ) / 5.0 ∣ × 100 % = 90 % |(0.5 - 5.0)/5.0| \times 100\% = 90\% ∣ ( 0.5 − 5.0 ) /5.0∣ × 100% = 90% ( ≥ 50 % \ge 50\% ≥ 50% ). This criterion is met.
Rectum, (a)(1)(iii): The rectum, a site other than the treatment site, received 8.5 Gy 8.5\text{ Gy} 8.5 Gy against an expected 1.2 Gy 1.2\text{ Gy} 1.2 Gy : an excess of 7.3 Gy 7.3\text{ Gy} 7.3 Gy (more than 0.5 Sv 0.5\text{ Sv} 0.5 Sv ) and of about 608 % 608\% 608% (more than 50 % 50\% 50% ). This criterion is also met.
Conclusion: This is a medical event under 10 CFR 35.3045 , requiring a telephone report to the NRC Operations Center by the next calendar day after discovery and a written report within 15 days.
Example 2: Category 2 Source Aggregation During HDR Exchange
An HDR suite contains a spent 192 Ir ^{192}\text{Ir} 192 Ir source ( A old = 388.5 GBq = 10.5 Ci A_{\text{old}} = 388.5\text{ GBq} = 10.5\text{ Ci} A old = 388.5 GBq = 10.5 Ci ) and a newly delivered replacement source ( A new = 444.0 GBq = 12.0 Ci A_{\text{new}} = 444.0\text{ GBq} = 12.0\text{ Ci} A new = 444.0 GBq = 12.0 Ci ) temporarily co-located during exchange. ( T 192 Ir = 800 GBq = 21.6 Ci T_{^{192}\text{Ir}} = 800\text{ GBq} = 21.6\text{ Ci} T 192 Ir = 800 GBq = 21.6 Ci ).
∑ A i T i = 10.5 Ci 21.6 Ci + 12.0 Ci 21.6 Ci = 0.486 + 0.556 = 1.042 \sum \frac{A_i}{T_i} = \frac{10.5\text{ Ci}}{21.6\text{ Ci}} + \frac{12.0\text{ Ci}}{21.6\text{ Ci}} = 0.486 + 0.556 = 1.042 ∑ T i A i = 21.6 Ci 10.5 Ci + 21.6 Ci 12.0 Ci = 0.486 + 0.556 = 1.042
Because the sum of fractions 1.042 ≥ 1.0 1.042 \ge 1.0 1.042 ≥ 1.0 , the co-located sources trigger 10 CFR Part 37 Category 2 security mandates .
Comparison Table & Clinical Pitfalls
Regulatory Metric Medical Event Reporting (10 CFR 35.3045) Physical Security Program (10 CFR Part 37)
Primary Metric Dose divergence ( > 0.05 Sv >0.05\text{ Sv} > 0.05 Sv TEDE, > 0.5 Sv >0.5\text{ Sv} > 0.5 Sv organ) + delivery error Source activity exceeding Cat 1 or Cat 2 thresholds
Immediate Notification NRC Operations Center call within 24 hours of discovery LLEA emergency response dispatch upon alarm trigger
Written Filing NRC Regional Office within 15 days of discovery Security plans and T&R files retained for 3 years
Patient Involvement Patient and referring physician notified within 24 hours N/A (Facility access and physical security)
Privacy Protection Absolute ban on patient identifiers in 15-day NRC report Strict protection of FBI criminal history records
Clinical Practice Pitfalls
Discovery Clock vs Event Occurrence: The 24-hour NRC notification clock begins at the time of discovery , not when the event occurred.
Patient Privacy Violation: Attaching clinical sheets containing patient names to the 15-day NRC report violates 10 CFR 35.3045(d)(2).
HDR Source Aggregation Oversight: Failing to implement Category 2 security during source exchanges when two co-located sources exceed 21.6 Ci constitutes a security infraction.
Patient-Intervention Misclassification: Events caused by patient intervention are excluded from 35.3045(a), but 35.3045(b) still requires a report if a physician determines that unintended permanent functional damage results.