Occupational & Public Dose Limits and ALARA Principles

ABMP Medical Health Physics Exam

Track your progress as you read

Finished sections get a check mark.

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

Occupational & Public Dose Limits and ALARA Principles

Key Takeaways Explain This Topic AI

The 10 CFR Part 20 occupational dose limit for adult radiation workers is a Total Effective Dose Equivalent (TEDE) of 50 mSv 50\text{ mSv} 50 mSv ( 5 rem 5\text{ rem} 5 rem ) per calendar year, calculated as TEDE = DDE + CEDE \text{TEDE} = \text{DDE} + \text{CEDE} TEDE = DDE + CEDE .

Organ-specific annual occupational limits under 10 CFR 20.1201 restrict Lens Dose Equivalent (LDE) to 150 mSv 150\text{ mSv} 150 mSv ( 15 rem 15\text{ rem} 15 rem ), Shallow-Dose Equivalent (SDE) to skin or extremities to 500 mSv 500\text{ mSv} 500 mSv ( 50 rem 50\text{ rem} 50 rem ), and Total Organ Dose Equivalent (TODE) to 500 mSv 500\text{ mSv} 500 mSv ( 50 rem 50\text{ rem} 50 rem ).

For a declared pregnant worker under 10 CFR 20.1208, the embryo/fetus dose limit is 5 mSv 5\text{ mSv} 5 mSv ( 0.5 rem 0.5\text{ rem} 0.5 rem ) for the entire gestation, with a requirement to make efforts to avoid substantial variation above a uniform monthly rate (NCRP Report 116 recommends no more than 0.5 mSv 0.5\text{ mSv} 0.5 mSv in any month); declaration is strictly voluntary and revocable in writing at any time.

Public dose limits under 10 CFR 20.1301 restrict annual TEDE to 1 mSv 1\text{ mSv} 1 mSv ( 0.1 rem 0.1\text{ rem} 0.1 rem ) from licensed operations, with an external dose rate ceiling in unrestricted areas of 0.02 mSv 0.02\text{ mSv} 0.02 mSv ( 2 mrem 2\text{ mrem} 2 mrem ) in any one hour.

Last updated: October 2026

10 CFR Part 20 Occupational Limits: Whole Body & Dosimetric Summation

Title 10 of the Code of Federal Regulations, Part 20 (10 CFR Part 20), establishes legally binding radiation protection standards. Under 10 CFR 20.1201(a)(1)(i), the annual occupational limit for adult radiation workers is a Total Effective Dose Equivalent (TEDE) of: TEDE = 50 mSv ( 5 rem or 5000 mrem ) \text{TEDE} = 50\text{ mSv}\quad (5\text{ rem}\text{ or }5000\text{ mrem}) TEDE = 50 mSv ( 5 rem or 5000 mrem )

per calendar year. TEDE sums external deep-dose and internal committed stochastic radiation exposures: TEDE = DDE + CEDE \text{TEDE} = \text{DDE} + \text{CEDE} TEDE = DDE + CEDE

where:

Deep-Dose Equivalent (DDE): Applies to external whole-body radiation exposure, measured at a tissue depth of 1 cm 1\text{ cm} 1 cm ( 1000 mg/cm 2 1000\text{ mg/cm}^2 1000 mg/cm 2 ).

Committed Effective Dose Equivalent (CEDE): Quantifies stochastic risk from internal intakes of radioactive material over a 50-year commitment period: CEDE = ∑ T w T H 50 , T \text{CEDE} = \sum_{T} w_T H_{50,T} CEDE = T ∑ ​ w T ​ H 50 , T ​

where w T w_T w T ​ is the tissue weighting factor (10 CFR 20.1003, derived from ICRP Publication 26/60) and H 50 , T H_{50,T} H 50 , T ​ is the committed equivalent dose delivered to organ or tissue T T T over 50 years.

Since the 2008 amendment of the TEDE definition in 10 CFR 20.1003, licensees may use the effective dose equivalent (EDE) for external exposure in place of the DDE when it is determined by an acceptable method. For staff wearing lead aprons, Regulatory Guide 8.40 describes two-dosimeter methods such as the NCRP Report 122 formula H E = 0.5 H W + 0.025 H N H_E = 0.5\,H_W + 0.025\,H_N H E ​ = 0.5 H W ​ + 0.025 H N ​ and the Webster formula H E = 1.5 H W + 0.04 H N H_E = 1.5\,H_W + 0.04\,H_N H E ​ = 1.5 H W ​ + 0.04 H N ​ , where H W H_W H W ​ is the under-apron waist reading and H N H_N H N ​ the over-apron collar reading.

Organ-Specific Limits: Lens, Extremities, and Total Organ Dose Equivalent

To prevent deterministic tissue reactions, 10 CFR 20.1201 codifies specific annual non-stochastic occupational limits:

Lens Dose Equivalent (LDE): LDE = 150 mSv ( 15 rem ) per calendar year \text{LDE} = 150\text{ mSv}\quad (15\text{ rem})\quad\text{per calendar year} LDE = 150 mSv ( 15 rem ) per calendar year

evaluated at a tissue depth of 0.3 cm 0.3\text{ cm} 0.3 cm ( 300 mg/cm 2 300\text{ mg/cm}^2 300 mg/cm 2 ). This limit prevents radiation-induced cataractogenesis. Candidates must note an essential regulatory divergence: ICRP Publication 118 (2012) recommended reducing the occupational lens limit to 20 mSv/yr 20\text{ mSv/yr} 20 mSv/yr (averaged over 5 years, no year > 50 mSv >50\text{ mSv} > 50 mSv ) based on subcapsular cataract thresholds at ≈ 0.5 Gy \approx 0.5\text{ Gy} ≈ 0.5 Gy . While adopted internationally, the US NRC standard in 10 CFR 20.1201 remains legally codified at 150 mSv/yr 150\text{ mSv/yr} 150 mSv/yr .

Shallow-Dose Equivalent (SDE): SDE = 500 mSv ( 50 rem ) per calendar year \text{SDE} = 500\text{ mSv}\quad (50\text{ rem})\quad\text{per calendar year} SDE = 500 mSv ( 50 rem ) per calendar year

applicable to the skin of the whole body or skin of an extremity (hands, forearms, feet, ankles), evaluated at a tissue depth of 0.007 cm 0.007\text{ cm} 0.007 cm ( 7 mg/cm 2 7\text{ mg/cm}^2 7 mg/cm 2 ) averaged over 10 cm 2 10\text{ cm}^2 10 cm 2 of the most highly irradiated area.

Total Organ Dose Equivalent (TODE): TODE = 500 mSv ( 50 rem ) per calendar year \text{TODE} = 500\text{ mSv}\quad (50\text{ rem})\quad\text{per calendar year} TODE = 500 mSv ( 50 rem ) per calendar year

to any individual organ or tissue other than the lens of the eye (10 CFR 20.1201(a)(1)(ii)). TODE prevents deterministic organ dysfunction and is defined as: TODE = DDE + CDE \text{TODE} = \text{DDE} + \text{CDE} TODE = DDE + CDE

where CDE \text{CDE} CDE ( H 50 , T H_{50,T} H 50 , T ​ ) is the committed dose equivalent to the specific organ over 50 years. In medical health physics, TODE commonly governs personnel handling unsealed 131 I ^{131}\text{I} 131 I , where thyroid dose limits may be approached before the TEDE whole-body limit.

Minors (< 18 yrs): Annual limits are exactly 10% of adult limits (10 CFR 20.1207): TEDE = 5 mSv \text{TEDE} = 5\text{ mSv} TEDE = 5 mSv , LDE = 15 mSv \text{LDE} = 15\text{ mSv} LDE = 15 mSv , and SDE/TODE = 50 mSv \text{SDE/TODE} = 50\text{ mSv} SDE/TODE = 50 mSv .

Embryo/Fetus Dose Limits & Declared Pregnant Worker Management

Protection of the embryo/fetus of an occupationally exposed worker is governed by 10 CFR 20.1208:

Voluntary Written Declaration: Declaration is strictly voluntary. An employer cannot compel a worker to declare pregnancy or alter job assignments without consent. The declaration must be in writing, dated, and state the estimated month and year of conception. The worker retains the unconditional right to revoke the declaration in writing at any time without explanation.

Dose Limit: The dose equivalent to the embryo/fetus during the entire gestation period, due to occupational exposure of a declared pregnant woman, shall not exceed: Embryo/Fetus Limit = 5 mSv ( 0.5 rem or 500 mrem ) \text{Embryo/Fetus Limit} = 5\text{ mSv}\quad (0.5\text{ rem}\text{ or }500\text{ mrem}) Embryo/Fetus Limit = 5 mSv ( 0.5 rem or 500 mrem )

Monthly Dose Uniformity: Under 10 CFR 20.1208(b) the licensee must make efforts to avoid substantial variation above a uniform monthly exposure rate. NCRP Report 116 recommends a monthly equivalent-dose limit of: Monthly Rate ≤ 0.5 mSv/month ( 50 mrem/month ) \text{Monthly Rate} \le 0.5\text{ mSv/month}\quad (50\text{ mrem/month}) Monthly Rate ≤ 0.5 mSv/month ( 50 mrem/month )

Remedial Provision (10 CFR 20.1208(d)): If the embryo/fetus dose has reached or exceeded 5 mSv 5\text{ mSv} 5 mSv (or is within 0.5 mSv 0.5\text{ mSv} 0.5 mSv of this limit) by the declaration date, the licensee is compliant if additional dose during the remainder of pregnancy does not exceed: Additional Allowance = 0.5 mSv ( 50 mrem ) \text{Additional Allowance} = 0.5\text{ mSv}\quad (50\text{ mrem}) Additional Allowance = 0.5 mSv ( 50 mrem )

Dosimetric Monitoring: A dedicated fetal badge must be worn at the waist under any lead protective garments to measure dose to the conceptus.

Public Dose Limits & Unrestricted Area Dose Rate Constraints

Under 10 CFR 20.1301, licensed operations must satisfy two independent public radiation protection criteria:

Annual TEDE Limit: Total effective dose equivalent to individual members of the public shall not exceed: Public TEDE = 1 mSv ( 0.1 rem or 100 mrem ) per calendar year \text{Public TEDE} = 1\text{ mSv}\quad (0.1\text{ rem}\text{ or }100\text{ mrem})\quad\text{per calendar year} Public TEDE = 1 mSv ( 0.1 rem or 100 mrem ) per calendar year

Excludes natural background radiation, medical administrations to the individual, voluntary medical research, and licensed sanitary sewer disposals.

2. Unrestricted Area Hourly Rate Limit: The external radiation dose rate in any unrestricted area shall not exceed: Hourly Rate ≤ 0.02 mSv ( 2 mrem ) in any one hour \text{Hourly Rate} \le 0.02\text{ mSv}\quad (2\text{ mrem})\quad\text{in any one hour} Hourly Rate ≤ 0.02 mSv ( 2 mrem ) in any one hour

This hourly ceiling prevents localized radiation hot spots in corridors, waiting rooms, and perimeter areas.

Medical Patient Release (10 CFR 35.75)

A major statutory exception permits releasing patients administered radiopharmaceuticals (e.g., 131 I ^{131}\text{I} 131 I ) or permanent brachytherapy implants (e.g., 125 I ^{125}\text{I} 125 I seeds) if the TEDE to any other individual from exposure to the patient is not likely to exceed: Patient Release Threshold = 5 mSv ( 0.5 rem ) \text{Patient Release Threshold} = 5\text{ mSv}\quad (0.5\text{ rem}) Patient Release Threshold = 5 mSv ( 0.5 rem )

If the dose to any individual is likely to exceed 1 mSv 1\text{ mSv} 1 mSv ( 0.1 rem 0.1\text{ rem} 0.1 rem ), the licensee must provide written safety instructions to maintain family and public doses ALARA, including specific breastfeeding cessation guidance.

Operational ALARA Programs, Action Levels, and RSO Investigations

Under 10 CFR 20.1101, licensees must maintain an active ALARA program. Regulatory Guide 8.10 states the ALARA operating philosophy; in practice, RSOs screen dosimetry reports with the two-tier investigational levels of the NRC's long-standing model ALARA program (historically Regulatory Guide 10.8, Appendix G), which many medical licensees still adopt:

Investigational Level I (10% of the annual limit, prorated per quarter):

TEDE = 1.25 mSv \text{TEDE} = 1.25\text{ mSv} TEDE = 1.25 mSv ( 125 mrem 125\text{ mrem} 125 mrem ); LDE = 3.75 mSv \text{LDE} = 3.75\text{ mSv} LDE = 3.75 mSv ( 375 mrem 375\text{ mrem} 375 mrem ); SDE/TODE = 12.5 mSv \text{SDE/TODE} = 12.5\text{ mSv} SDE/TODE = 12.5 mSv ( 1250 mrem 1250\text{ mrem} 1250 mrem ).

Action: RSO reviews dosimeter reading against worker history and files documentation. No formal operational change required unless an adverse trend appears.

Investigational Level II (30% of the annual limit, prorated per quarter):

TEDE = 3.75 mSv \text{TEDE} = 3.75\text{ mSv} TEDE = 3.75 mSv ( 375 mrem 375\text{ mrem} 375 mrem ); LDE = 11.25 mSv \text{LDE} = 11.25\text{ mSv} LDE = 11.25 mSv ( 1125 mrem 1125\text{ mrem} 1125 mrem ); SDE/TODE = 37.5 mSv \text{SDE/TODE} = 37.5\text{ mSv} SDE/TODE = 37.5 mSv ( 3750 mrem 3750\text{ mrem} 3750 mrem ).

Action: RSO must conduct a formal written root-cause investigation, interview the worker, inspect shielding apparatus and techniques, recommend corrective actions, and submit findings to the Radiation Safety Committee (RSC).

Annual Program Review (10 CFR 20.1101(c)): Licensees must review radiation protection program content and implementation at least annually.

Summary of 10 CFR Part 20 Limits & Worked Clinical Calculation

Exposure Category Applicable Regulation Annual Statutory Limit (SI) Annual Statutory Limit (Conventional) Measurement Depth ALARA Level I (Quarterly) ALARA Level II (Quarterly)

Occupational Whole Body (TEDE) 10 CFR 20.1201(a)(1)(i) 50 mSv 50\text{ mSv} 50 mSv 5 rem 5\text{ rem} 5 rem ( 5000 mrem 5000\text{ mrem} 5000 mrem ) 1.0 cm 1.0\text{ cm} 1.0 cm ( 1000 mg/cm 2 1000\text{ mg/cm}^2 1000 mg/cm 2 ) 1.25 mSv 1.25\text{ mSv} 1.25 mSv 3.75 mSv 3.75\text{ mSv} 3.75 mSv

Occupational Lens of Eye (LDE) 10 CFR 20.1201(a)(2)(i) 150 mSv 150\text{ mSv} 150 mSv 15 rem 15\text{ rem} 15 rem ( 15000 mrem 15000\text{ mrem} 15000 mrem ) 0.3 cm 0.3\text{ cm} 0.3 cm ( 300 mg/cm 2 300\text{ mg/cm}^2 300 mg/cm 2 ) 3.75 mSv 3.75\text{ mSv} 3.75 mSv 11.25 mSv 11.25\text{ mSv} 11.25 mSv

Occupational Skin / Extremity (SDE) 10 CFR 20.1201(a)(2)(ii) 500 mSv 500\text{ mSv} 500 mSv 50 rem 50\text{ rem} 50 rem ( 50000 mrem 50000\text{ mrem} 50000 mrem ) 0.007 cm 0.007\text{ cm} 0.007 cm ( 7 mg/cm 2 7\text{ mg/cm}^2 7 mg/cm 2 ) 12.5 mSv 12.5\text{ mSv} 12.5 mSv 37.5 mSv 37.5\text{ mSv} 37.5 mSv

Occupational Organ / Tissue (TODE) 10 CFR 20.1201(a)(1)(ii) 500 mSv 500\text{ mSv} 500 mSv 50 rem 50\text{ rem} 50 rem ( 50000 mrem 50000\text{ mrem} 50000 mrem ) 1.0 cm 1.0\text{ cm} 1.0 cm ( 1000 mg/cm 2 1000\text{ mg/cm}^2 1000 mg/cm 2 ) 12.5 mSv 12.5\text{ mSv} 12.5 mSv 37.5 mSv 37.5\text{ mSv} 37.5 mSv

Embryo / Fetus (Declared Worker) 10 CFR 20.1208 5 mSv 5\text{ mSv} 5 mSv gestation 0.5 rem 0.5\text{ rem} 0.5 rem ( 500 mrem 500\text{ mrem} 500 mrem ) Waist (under apron) ≤ 0.5 mSv/mo \le 0.5\text{ mSv/mo} ≤ 0.5 mSv/mo N/A

Occupational Minors (< 18 yrs) 10 CFR 20.1207 10% of adult limits 10% of adult limits Standard depths 10% adult Level I 10% adult Level II

General Public (Annual TEDE) 10 CFR 20.1301(a)(1) 1 mSv 1\text{ mSv} 1 mSv 0.1 rem 0.1\text{ rem} 0.1 rem ( 100 mrem 100\text{ mrem} 100 mrem ) Whole body N/A N/A

Public Unrestricted Hourly Rate 10 CFR 20.1301(a)(2) 0.02 mSv 0.02\text{ mSv} 0.02 mSv in 1 hr 2 mrem 2\text{ mrem} 2 mrem in 1 hr 1.0 cm 1.0\text{ cm} 1.0 cm ( 1000 mg/cm 2 1000\text{ mg/cm}^2 1000 mg/cm 2 ) N/A N/A

Worked Clinical Calculation: Dual-Limit Compliance Evaluation

Scenario: A radiopharmacist receives an external deep-dose equivalent of DDE = 16 mSv \text{DDE} = 16\text{ mSv} DDE = 16 mSv during hot-lab compounding. Routine thyroid bioassay after handling unsealed 131 I ^{131}\text{I} 131 I detects an internal uptake resulting in an estimated committed dose equivalent to the thyroid of CDE thyroid = 380 mSv \text{CDE}_{\text{thyroid}} = 380\text{ mSv} CDE thyroid ​ = 380 mSv . Given a thyroid tissue weighting factor of w thyroid = 0.03 w_{\text{thyroid}} = 0.03 w thyroid ​ = 0.03 :

Calculate Committed Effective Dose Equivalent (CEDE): CEDE = w thyroid × CDE thyroid = 0.03 × 380 mSv = 11.4 mSv \text{CEDE} = w_{\text{thyroid}} \times \text{CDE}_{\text{thyroid}} = 0.03 \times 380\text{ mSv} = 11.4\text{ mSv} CEDE = w thyroid ​ × CDE thyroid ​ = 0.03 × 380 mSv = 11.4 mSv

Calculate Total Effective Dose Equivalent (TEDE): TEDE = DDE + CEDE = 16 mSv + 11.4 mSv = 27.4 mSv \text{TEDE} = \text{DDE} + \text{CEDE} = 16\text{ mSv} + 11.4\text{ mSv} = 27.4\text{ mSv} TEDE = DDE + CEDE = 16 mSv + 11.4 mSv = 27.4 mSv

TEDE Compliance: 27.4 mSv ≤ 50 mSv 27.4\text{ mSv} \le 50\text{ mSv} 27.4 mSv ≤ 50 mSv (Compliant with annual whole-body occupational limit).

3. Calculate Total Organ Dose Equivalent (TODE) to the thyroid: TODE thyroid = DDE + CDE thyroid = 16 mSv + 380 mSv = 396 mSv \text{TODE}_{\text{thyroid}} = \text{DDE} + \text{CDE}_{\text{thyroid}} = 16\text{ mSv} + 380\text{ mSv} = 396\text{ mSv} TODE thyroid ​ = DDE + CDE thyroid ​ = 16 mSv + 380 mSv = 396 mSv

TODE Compliance: 396 mSv ≤ 500 mSv 396\text{ mSv} \le 500\text{ mSv} 396 mSv ≤ 500 mSv (Compliant with annual non-stochastic organ limit). Operational Conclusion: Both limits are met. However, even if the 16 mSv 16\text{ mSv} 16 mSv external dose were spread evenly over four quarters ( 4 mSv 4\text{ mSv} 4 mSv each), every quarter would exceed the Level II investigational level of 3.75 mSv 3.75\text{ mSv} 3.75 mSv , so the RSO must investigate and report corrective actions to the RSC.