American Registry of Radiologic Technologists Certification (ARRT) Radiation Protection and Biology Syllabus

What is the threshold dose for radiation-induced cataracts (lens opacities)?

Historically ~2 Gy acute / 5 Gy chronic, but ICRP has lowered the threshold estimate to about 0.5 Gy (50 rad).

What is the threshold for temporary versus permanent sterility in males?

Temporary sterility ~0.15 Gy; permanent sterility ~3.5–6 Gy to the testes.

What are the three main syndromes of Acute Radiation Syndrome (ARS) in order of increasing dose?

Hematopoietic (bone marrow) syndrome, Gastrointestinal (GI) syndrome, and Cerebrovascular (CNS) syndrome.

What are the four stages (phases) of Acute Radiation Syndrome?

Prodromal, latent, manifest illness, and recovery or death.

At what whole-body dose range does hematopoietic syndrome occur, and what causes death?

Approximately 1–10 Gy (100–1000 rad). Death results from bone marrow depression causing infection, hemorrhage, and anemia.

At what dose range does GI syndrome occur and what is the survival time?

Approximately 6–10 Gy (600–1000 rad). Death occurs within ~3–10 days from loss of intestinal mucosa, fluid/electrolyte loss, and infection.

At what dose does cerebrovascular (CNS) syndrome occur and what is the survival time?

Greater than ~50 Gy (5000 rad). Death occurs within hours to ~3 days from CNS and cardiovascular failure.

What is LD 50/30 and its approximate value for humans?

LD 50/30 is the whole-body dose that is lethal to 50% of an exposed population within 30 days. For humans it is approximately 3–4 Gy (300–400 rad) without medical treatment.

Which gestational period carries the highest risk of radiation-induced congenital malformations (organogenesis)?

Organogenesis (~2–8 weeks / day 10 to week 6) is the period of greatest risk for congenital anomalies and organ malformations.

What is the main radiation risk to the embryo during the first 2 weeks (pre-implantation)?

Prenatal (embryonic) death/resorption — an 'all or nothing' effect; the embryo either dies or survives unaffected.

During which fetal period is the risk of mental retardation and central nervous system effects greatest?

Approximately 8–15 weeks of gestation, when neuronal development is most active.

What is the SI unit of absorbed dose and its traditional equivalent?

Gray (Gy); traditional unit is the rad. 1 Gy = 100 rad; 1 rad = 10 mGy.

What is the SI unit of equivalent dose (and effective dose) and its traditional equivalent?

Sievert (Sv); traditional unit is the rem. 1 Sv = 100 rem.

What is the SI unit of radiation exposure (air kerma) and its traditional unit?

SI: coulomb per kilogram (C/kg) of air; traditional: roentgen (R). 1 R ≈ 2.58 × 10⁻⁴ C/kg.

What is the SI unit of radioactivity and its traditional equivalent?

Becquerel (Bq) = 1 disintegration per second; traditional unit is the curie (Ci). 1 Ci = 3.7 × 10¹⁰ Bq.

How is equivalent dose calculated?

Equivalent dose (Sv) = Absorbed dose (Gy) × radiation weighting factor (W_R). It accounts for the type of radiation's biologic effect.

How is effective dose calculated and what does it account for?

Effective dose = sum of (equivalent dose to each tissue × tissue weighting factor W_T). It accounts for both radiation type and the radiosensitivity of irradiated tissues.

What is the radiation weighting factor (W_R) for x-rays/gamma rays versus alpha particles?

X-rays, gamma rays, and beta particles: W_R = 1. Alpha particles: W_R = 20.

What personnel dosimeter is the current standard, and what is its detection mechanism?

The optically stimulated luminescence (OSL) dosimeter, which uses aluminum oxide stimulated by laser light to release stored energy as light proportional to dose.

How does a thermoluminescent dosimeter (TLD) work and what crystal does it use?

A TLD uses lithium fluoride (LiF) crystals that store absorbed energy; when heated, they emit light proportional to the radiation dose received.

What instrument is the standard for measuring radiation output/exposure in a survey, and how does it work?

The ionization chamber. Radiation ionizes gas in the chamber, producing a measurable current proportional to exposure. It is used for accurate measurement of higher exposure rates (e.g., fluoroscopy output).

What survey instrument is best for low-level radiation detection and contamination surveys?

The Geiger-Müller (GM) counter — very sensitive for detecting low levels of radiation and locating contamination, but not accurate for high exposure rates.

What does ALARA stand for and what is its underlying principle?

As Low As Reasonably Achievable. It directs that radiation doses to patients and workers be kept as low as possible, based on the linear non-threshold model assumption that no dose is risk-free.

What is the annual occupational effective dose limit (whole body)?

50 mSv (5 rem) per year.

What is the cumulative lifetime occupational dose limit formula?

Cumulative dose limit = 10 mSv × age in years (1 rem × age in years).

What is the annual effective dose limit for members of the general public (frequent exposure)?

1 mSv (0.1 rem) per year for continuous/frequent exposure (5 mSv/0.5 rem for infrequent exposure).

What is the occupational dose limit to the lens of the eye and to the skin/extremities?

Lens of the eye: 150 mSv (15 rem)/year. Skin and extremities: 500 mSv (50 rem)/year.

What is the monthly equivalent dose limit for the embryo/fetus of a declared pregnant worker, and the total for the gestation?

0.5 mSv (0.05 rem) per month, and 5 mSv (0.5 rem) for the entire gestation/pregnancy.

What is the average annual effective dose to a person in the US from natural background radiation, and its single largest contributor?

Approximately 3 mSv/year from natural background. The largest single natural source is radon gas.

What are the three cardinal principles of radiation protection (occupational protection)?

Time, distance, and shielding. Minimize time of exposure, maximize distance from the source, and use shielding (lead/barriers).

State the inverse square law and its practical meaning for radiation intensity.

Intensity is inversely proportional to the square of the distance: I₁/I₂ = (D₂)²/(D₁)². Doubling distance reduces intensity to one-fourth.

What patient dose reduction technique has the greatest effect, and what protective measures reduce patient dose?

Proper collimation/beam restriction plus optimal exposure factors. Key measures: collimation, filtration, gonadal shielding (where appropriate), high kVp/low mAs technique, and minimizing repeats.

What is the primary purpose of added filtration in the x-ray beam, and the minimum total filtration above 70 kVp?

Filtration removes low-energy ('soft') photons that would only add to patient skin dose without contributing to the image. Minimum total filtration is 2.5 mm aluminum equivalent for units operating above 70 kVp.

In fluoroscopy, what is the federal limit on entrance skin exposure rate for normal mode and high-level (boost) mode?

Normal mode: 10 R/min (≈88 mGy/min) maximum at the tabletop. High-level control (boost) mode: up to 20 R/min (≈176 mGy/min).

What is the minimum source-to-skin distance (SSD) for stationary and mobile (portable) fluoroscopy units?

Stationary fluoroscopes: at least 38 cm (15 in). Mobile/portable fluoroscopes: at least 30 cm (12 in).

Name fluoroscopy techniques that reduce patient and operator dose.

Last-image hold, pulsed fluoroscopy, reduced frame rate, minimizing beam-on time, keeping the image intensifier close to the patient, increasing source-to-skin distance, collimation, and reducing magnification.

What is the 5-minute reset timer in fluoroscopy for?

An audible alarm/timer that sounds after 5 minutes of cumulative beam-on time to remind the operator of fluoroscopy time and encourage minimizing exposure.

How does the position of the operator relative to the patient affect scatter dose in fluoroscopy?

The patient is the largest source of scatter. Scatter is greatest on the x-ray tube (entrance) side; keeping the under-table tube and over-table image intensifier, and standing away from the entrance side, reduces operator dose.

What is the minimum required lead equivalency of a protective apron?

At least 0.25 mm Pb equivalent; 0.5 mm Pb is commonly used and recommended, attenuating roughly 90%+ of scatter at typical energies.

At what dose level must personnel monitoring (a dosimeter) be provided to occupational workers?

When a worker is likely to receive more than 1/10 (10%) of the annual occupational dose limit — i.e., more than ~5 mSv (0.5 rem) per year.

Where should the primary (collar/whole-body) dosimeter be worn during fluoroscopy when wearing a lead apron?

On the collar, outside the lead apron at the level of the thyroid/neck, to estimate dose to unshielded regions (thyroid and eyes).

What is the difference between a controlled and an uncontrolled area for shielding design?

A controlled area is occupied by radiation workers (design limit 1 mSv/week). An uncontrolled area is occupied by the general public (design limit 0.02 mSv/week / lower).

What is the purpose of the lead-impregnated 'Bucky slot cover' and the protective curtain/drape in fluoroscopy?

They shield the operator from scatter radiation. The Bucky slot cover (≥0.25 mm Pb) covers the opening when the Bucky is moved to the end of the table; the hanging curtain (≥0.25 mm Pb) intercepts scatter from the patient at gonadal/leg level.

What is the effective dose equivalent limit concept (effective dose) intended to limit?

It is intended to limit the overall stochastic risk (cancer and heritable effects) by weighting partial-body and whole-body exposures to an equivalent uniform whole-body risk.

What is the recovery/repair phenomenon known as the 'dose-rate effect' for low-LET radiation?

For low-LET radiation, lowering the dose rate (or fractionating the dose) reduces biologic damage because cells have time to repair sublethal damage between exposures.

What is the target theory in radiation biology?

Target theory holds that there is a specific critical target (DNA) within the cell; a 'hit' to the target by radiation causes cell death or inactivation. Cell survival curves are derived from this concept.

What are free radicals and why are they damaging?

Free radicals are uncharged atoms or molecules with a single unpaired electron in the outer shell, making them extremely chemically reactive; they can break chemical bonds in DNA and other macromolecules.

What is the most likely overall somatic late effect of low-dose radiation, and which malignancy is classically associated with radiation in radiologic technologists historically?

The principal late stochastic effect is carcinogenesis (cancer induction). Leukemia is the classic radiation-induced malignancy historically observed in early radiology workers and atomic-bomb survivors.