Radiation Safety for Radiologic Technologists: Essential Knowledge for the ARRT Exam

Radiation protection is included in the ARRT Radiography Examination Content Specifications and is central to safe practice. A radiologic technologist must produce the images needed for care while optimizing patient exposure and keeping occupational and public exposure As Low As Reasonably Achievable (ALARA).

This guide distinguishes U.S. legal limits from international recommendations and patient-dose optimization. It covers ALARA, time-distance-shielding controls, pregnancy, dosimetry, biological effects, and strategies that reduce avoidable exposures.

The ALARA Principle

ALARA stands for As Low As Reasonably Achievable. In U.S. regulation it means making every reasonable effort to keep occupational and public exposure below dose limits, considering technology, economics, and societal factors. For patients, the complementary principles are justification (the examination's expected benefit outweighs its radiation risk) and optimization (dose is appropriate for the clinical task, not simply the lowest possible). Understanding the physics of X-rays supports that optimization.

Keep these related but distinct principles clear:

The Three Cardinal Rules of Radiation Protection

Time, distance, and shielding are practical controls used chiefly for occupational and public protection. Patient protection additionally requires justification and optimization; shortening an acquisition or adding shielding must never compromise the needed examination.

1. Time

For a constant dose rate, dose is proportional to exposure time: half the beam-on time gives half the dose. In fluoroscopy, use the lowest pulse rate and beam-on time that preserve the clinical information; pulsed mode is not automatically lower dose if other system settings compensate.

2. Distance

For a small point source in free space, intensity follows the inverse square law: doubling distance reduces intensity to one quarter. Clinical scatter fields are more complex, but distance remains powerful. During mobile and fluoroscopic work, the patient is usually the main scatter source: maximize distance as circumstances allow, avoid the primary beam, and use a fixed or mobile barrier when available.

3. Shielding

Use barriers and protective equipment appropriate to the exposure pathway:

• Primary barriers — structures designed to attenuate the useful primary beam
• Secondary barriers — structures designed for scatter and tube-leakage radiation rather than the useful beam
• Occupational protective equipment — aprons, thyroid collars, eyewear, ceiling-suspended shields, table skirts, and mobile barriers selected under the facility program. Protective gloves attenuate scatter but must never be placed in the primary beam.
• Patient contact shielding — not routinely recommended for gonadal or fetal protection by AAPM and ASRT because benefit is negligible with modern equipment and a misplaced shield can obscure anatomy or interfere with automatic exposure control. Follow controlling state rules and facility policy.

U.S. NRC Dose Limits—and What They Mean

The values below are federal limits in 10 CFR Part 20 for NRC licensees; Agreement States regulate byproduct material under compatible rules, while state programs generally regulate diagnostic X-ray machines. OSHA requirements may also apply. These legal ceilings are not ALARA targets, patient dose limits, or universal international limits. ICRP/IAEA recommendations are generally more restrictive for occupational effective dose: 20 mSv per year averaged over five years (100 mSv in five years), with no more than 50 mSv in one year.

Category	NRC limit	Scope / note
Adult occupational total effective dose equivalent (TEDE)	50 mSv (5 rem) in a year	Annual legal limit; no NRC “10 mSv × age” cumulative limit
Adult occupational lens dose equivalent	150 mSv (15 rem) in a year	NRC annual limit; ICRP recommends a lower lens limit
Adult occupational shallow dose equivalent to skin or an extremity	500 mSv (50 rem) in a year	NRC annual limit
Embryo/fetus of a declared pregnant worker	5 mSv (0.5 rem) for the entire pregnancy	Exposure should be substantially uniform; about 0.5 mSv (0.05 rem) per month is regulatory guidance, not a separate limit
Individual member of the public	1 mSv (0.1 rem) in a year	From licensed operations; excludes background and the person's medical exposure. Also 0.02 mSv (0.002 rem) in any one hour in an unrestricted area.

Patient Dose Reduction Strategies

Patient protection starts with a justified examination and a protocol matched to patient size and the clinical question. Accurate positioning, collimation, appropriate exposure factors, use of automatic exposure control when suitable, and quality control reduce avoidable exposure. Repeating one identical projection adds roughly another projection's dose; it does not necessarily double the dose of a multi-image examination.

Choose kVp and mAs Together

Higher kVp increases penetration, but it reduces patient dose only when mAs is reduced appropriately while preserving adequate detector exposure and task-specific image quality. Higher kVp by itself can increase dose. Use validated, anatomy- and size-specific technique charts; chest technique commonly uses relatively high kVp (see the chest X-ray guide).

Collimate to the Required Anatomy

Collimation to the anatomy required by the clinical question reduces irradiated tissue and scatter and generally improves contrast. Do not crop electronically as a substitute for proper beam collimation.

Use the Protocol SID

Use the protocol-specified source-to-image distance (SID)—commonly about 100–110 cm for table/wall work and about 180 cm for upright chest imaging. SID changes receptor exposure by the inverse-square relationship; whether patient dose changes depends on how technique or automatic exposure control compensates. Correct SID also controls magnification and geometric unsharpness.

Do Not Substitute Patient Shielding for Optimization

AAPM Position Statement PP 32-A and the ASRT statement support discontinuing routine gonadal and fetal patient shielding. Modern equipment and collimation have made the potential reduction very small, while a shield can cover needed anatomy, trigger a repeat, or alter automatic exposure control. It does not protect tissue from internal scatter. Use correct collimation and technique instead; accommodate a patient's concern when it can be done safely and follow controlling law and facility policy.

Pregnancy and Radiation Safety

Pregnancy requires careful communication and procedure-specific assessment—not automatic cancellation of needed imaging:

• Patient screening — Before an examination that could deliver a meaningful conceptus dose, follow facility policy to ask any patient who could be pregnant about pregnancy possibility and menstrual history, and document the result. The historical “10-day rule” is not universal; IAEA guidance describes a 28-day approach for most low-dose studies and a missed-period approach for high-dose lower-abdomen/pelvis procedures.
• Needed imaging — Pregnancy is not, by itself, a reason to withhold a justified examination. If pregnancy is known or uncertain and the uterus may receive direct or appreciable scatter exposure, involve the radiologist/authorized practitioner and medical physicist as local policy requires; optimize the protocol and estimate conceptus dose when warranted.
• Patient shielding — Do not routinely place fetal or gonadal contact shielding. It provides negligible protection from internal scatter and can compromise the examination. Collimation and optimized technique are effective controls.
• Worker declaration — Under NRC rules, declaration is voluntary and must be in writing. Once declared, the embryo/fetus limit is 5 mSv (0.5 rem) for the entire pregnancy, with dose kept substantially uniform; guidance uses about 0.5 mSv per month. IAEA/ICRP recommendations use working conditions that make it unlikely the unborn child will exceed about 1 mSv after declaration.
• Work assignment — Declaration does not automatically bar a technologist from radiographic work. The radiation-safety officer reviews likely dose and controls; declaration may be withdrawn in writing under NRC guidance.

Stochastic Effects and Tissue Reactions

Stochastic effects, principally cancer and heritable effects, are modeled for protection purposes as having increasing probability with dose and no assumed threshold; severity does not increase with dose. Tissue reactions (formerly deterministic effects), such as skin injury or lens opacities, generally have a threshold, and severity increases as dose rises above it. Routine diagnostic radiography is normally far below tissue-reaction thresholds, but prolonged or repeated fluoroscopically guided procedures can produce high localized skin dose. Track available dose metrics, follow notification and follow-up policy, and never confuse displayed reference-point air kerma with a patient's exact peak skin dose.

Personal Dosimetry

Not every person who works near radiation is automatically required by federal rule to wear a dosimeter. Under 10 CFR 20.1502, NRC licensees must monitor adults likely to exceed 10% of an occupational limit and declared pregnant workers likely to receive more than 1 mSv deep dose equivalent during the pregnancy, among other specified groups. OSHA, state rules, accreditation requirements, or facility policy can be more inclusive.

Type	How It Works	Use
OSL (Optically Stimulated Luminescence)	Aluminum oxide crystal stores energy from radiation; read with laser stimulation	Common passive whole-body or extremity monitoring technology
TLD (Thermoluminescent Dosimeter)	Lithium fluoride crystal stores energy; read by heating	Passive whole-body, extremity, or area monitoring
Film Badge	Photographic film darkens with exposure; read by densitometry	Passive monitoring; use has declined but depends on the program
Electronic personal dosimeter / pocket ion chamber	Provides a direct or real-time indication; technology and limitations vary	Supplemental alarming or task-based monitoring when specified; it replaces the official dosimeter only if the program approves it

Badge placement follows the radiation-safety program. With one badge and an apron, collar level outside the apron is common. In a two-badge program, wear one at the collar outside and the other on the torso under the apron so the approved algorithm can estimate effective dose. A declared pregnant worker's embryo/fetus badge is worn at waist level under the apron and is additional to—not a replacement for—the occupational badge. Ring dosimeters face the source on the most exposed hand as the program directs. Never share a badge or wear it during your own medical imaging.

Positioning Tips to Avoid Repeat Exposures

An avoidable repeat adds radiation dose; one repeated identical projection adds approximately another projection's dose, while the percentage increase for a multi-view examination depends on which image is repeated. Accurate positioning and clear communication help avoid repeats without sacrificing diagnostic quality.

Chest X-Ray (PA)

For an upright PA chest, elevate the chin and roll the shoulders forward to move the scapulae laterally. Center according to the receptor and facility protocol, commonly near T7, and expose after full inspiration when the patient can cooperate. Check rotation, inspiration, coverage, motion, and exposure before deciding that a repeat is clinically necessary.

Knee AP

Align the knee without rotation, center to the knee joint according to the department's positioning protocol, and adjust central-ray angulation when required for patient habitus. Include the distal femur and proximal tibia/fibula. Do not repeat solely for a minor positioning difference if the image answers the clinical question.

Shoulder Y Projection

The scapular Y view can help assess alignment in suspected dislocation. With the affected shoulder near the upright receptor, rotate into a PA oblique position until the scapular body is approximately perpendicular to the receptor; the required obliquity varies by patient. Center to the scapulohumeral region and use trauma-safe movement. Confirm that repeat imaging is necessary before re-exposing.

Lumbar Spine Lateral

In a lateral recumbent position, flex the knees for stability, bring the arms clear of the spine, superimpose the shoulders and pelvis, and support the waist when needed to make the lumbar spine parallel to the receptor. Center and collimate according to the requested coverage and protocol—commonly around L3, above the iliac crest for a routine lateral lumbar image.

Effective Dose for Common Exams

Effective dose is a population-level radiation-protection quantity, not a patient-specific prediction of cancer risk. The approximate adult values below are broad educational examples compiled by RadiologyInfo (ACR/RSNA); actual dose varies with equipment, protocol, patient size, and number of images. Use facility dose data and diagnostic reference levels for optimization rather than treating these values as limits.

Examination	Effective Dose (mSv)	Comparable to
Chest X-ray (PA & Lateral)	0.1 mSv	10 days of background radiation
Extremity X-ray	<0.001 mSv	Less than about 3 hours of natural background
Abdomen X-ray (AP)	0.7 mSv	4 months of background radiation
Lumbar Spine (3 views)	About 1.4 mSv	6 months of background radiation
CT Head	About 1.6 mSv	About 7 months of background radiation
CT Abdomen/Pelvis	About 7.7 mSv	About 2.6 years of background radiation

ARRT Exam Practice Questions

Test your knowledge with these exam-style questions:

Q1: An adult worker receives 12 mSv TEDE in a year at an NRC-licensed facility. How far below the 10 CFR 20.1201 annual legal limit is that value?

A: 38 mSv below the 50 mSv ceiling. This arithmetic does not mean the worker has a 38 mSv “allowance”; ALARA and facility investigation levels still apply.

Q2: After a worker voluntarily declares pregnancy in writing, what NRC dose limit applies to the embryo/fetus?

A: 5 mSv (0.5 rem) over the entire pregnancy, with exposure kept substantially uniform; approximately 0.5 mSv per month is NRC guidance.

Q3: The cardinal rule of radiation protection that states "doubling the distance reduces exposure by a factor of four" is based on which principle?

A: The inverse square law

Q4: Which of the following is the most effective way to reduce patient dose during a knee X-ray?

A) Using a faster screen speed
B) Increasing the SID to 120 cm
C) Ensuring correct positioning to avoid repeats
D) Using a higher mA

A: C — Correct positioning helps avoid an unnecessary additional exposure. A repeated identical projection adds approximately another projection's dose, not necessarily twice the dose of the complete examination.

Summary

Radiation safety is not just exam material — it's your daily responsibility as a radiologic technologist. The key principles to remember:

• Justification and optimization govern patient exposure; ALARA and dose limits protect workers and the public
• Three Cardinal Rules — Time, Distance, Shielding
• Know scope and units — NRC: 50 mSv annual adult occupational TEDE, 5 mSv embryo/fetus for an entire declared pregnancy, and 1 mSv annual public dose from licensed operations
• Prevent avoidable repeats through appropriate positioning, communication, technique, collimation, and image review
• Screen for possible pregnancy when relevant under facility policy; do not automatically deny needed imaging
• Do not use routine fetal/gonadal patient shielding; follow law and facility policy and optimize the examination
• Wear dosimetry as directed; badge number and placement depend on the monitoring program and apron use

For more detailed positioning techniques and their specific radiation safety considerations, check out the X-Ray and CT Scan modality pages.

Authoritative Sources

• U.S. NRC, 10 CFR 20.1201, Occupational dose limits for adults
• U.S. NRC, 10 CFR 20.1208, Dose equivalent to an embryo/fetus
• U.S. NRC, 10 CFR 20.1301, Dose limits for individual members of the public
• U.S. NRC, 10 CFR 20.1502, Conditions requiring individual monitoring
• U.S. NRC, Regulatory Guide 8.13, Instruction Concerning Prenatal Radiation Exposure
• IAEA, Radiation protection of pregnant women in radiology and Female workers during and after pregnancy
• ICRP, Publication 103: The 2007 Recommendations and Publication 118: Tissue reactions
• AAPM, Communicating Advances in Radiation Education for Shielding (CARES) and archived Position Statement PP 32-A
• OSHA, 29 CFR 1910.1096, Ionizing radiation
• FDA, Medical X-ray imaging
• ARRT, Examination Content Specifications
• RadiologyInfo (ACR/RSNA), Radiation Dose from X-Ray and CT Exams