Radiation Safety and Radiography Fundamentals Flashcards

Principles of Radiation Safety, Patient Holding, and Personal Protective Equipment

• Patient Holding Restrictions:

  • Student radiographers must never hold a patient during an X-ray exposure under any circumstances.
  • Graduated, licensed radiographers should also refrain from holding patients because scatter radiation emitted from the patient represents the primary source of occupational exposure in diagnostic radiography.
  • When a patient cannot maintain the required position independently, non-radiation workers who are not routinely exposed to the department's radiation environment should be utilized (e.g., a family member, security guard, nurse, or admissions staff member).

• Personal Protective Equipment (PPE) in Healthcare:

  • Standard healthcare PPE includes disposable gowns, gloves, surgical masks, $N95$ respirators, face shields, hair coverings (bonnets), and shoe coverings.
  • $N95$ respirators are mandatory when interacting with patients known or suspected to have airborne pathogens, such as COVID-19.

• Radiation Personal Protective Equipment (Radiation PPE):

  • Required for all personnel remaining inside a room where live radiation is produced, such as Operating Rooms (OR) during fluoroscopic or mobile imaging.
  • Lead Aprons: Must be worn by all individuals in the room except the patient. Surgeons and surgical technologists wear lead aprons underneath their sterile surgical gowns.
  • Thyroid Shields: Protect the radio-sensitive thyroid gland from scatter exposure.
  • Lead Caps/Hats: Protect the cranium from scatter radiation.
  • Leaded Eyewear/Goggles: Contain leaded glass to protect the lenses of the eyes from developing radiation-induced cataracts.
  • Lead-Lined Gloves: Shield the hands, provided the hands are kept outside the direct primary radiation beam.
  • Full-Body Lead Aprons: Provide core body shielding against scattered radiation.

Radiation Protective Barriers and Personal Dosimetry

• Occupational Exposure and Cardinal Principles of Protection:

  • Radiation received by radiation workers during the performance of their professional duties is classified as occupational exposure.
  • The Three Cardinal Principles of Radiation Protection:
  • Time: Minimize the amount of time spent in proximity to live radiation.
  • Distance: Maximize the physical distance between the worker and the radiation source.
  • Shielding: Position appropriate lead-equivalent attenuation barriers between the worker and the source.
  • Distance is the most effective principle: Increasing distance from the radiation source exponentially decreases radiation exposure.

• Structural Protective Barriers:

  • Structural barriers shield hospital personnel and the public from primary, scatter, and leakage radiation.
  • Primary Protective Barrier:
  • Defined as any barrier located in the direct path of the primary X-ray beam (e.g., the wall behind the wall Bucky unit, or the floor beneath the X-ray table).
  • Prevents the unattenuated primary beam from penetrating into adjacent hallways or occupied rooms.
  • Required lead content: Minimum of $\frac{1}{16}\,\text{inch}$ ($1.58\,\text{mm}$) lead ($\text{Pb}$) or lead equivalent.
  • Secondary Protective Barrier:
  • Defined as any barrier positioned outside the direct primary path of the beam (e.g., side walls of the radiography room, control booth barriers).
  • Designed to attenuate scatter radiation (produced as the primary beam diverges in a cone shape and interacts with objects) and tube leakage radiation.
  • Required lead content: Minimum of $\frac{1}{32}\,\text{inch}$ ($0.79\,\text{mm}$) lead ($\text{Pb}$) or lead equivalent.
  • Chemical Symbols in Radiology:
  • $\text{Pb}$ = Lead (from the Latin Plumbum).
  • $\text{Al}$ = Aluminum.

• Personnel Monitoring and Dosimetry:

  • Personal dosimeters record accumulated radiation dose to personnel over time.
  • Dosimeter Placement:
  • Standard Placement: Worn continuously during working hours at the collar level outside the lead apron to monitor dose to the thyroid and eye lenses.
  • Pregnant Radiographers: Wear a secondary fetal dosimeter at the waist level underneath the lead apron to record the embryonic/fetal dose.
  • Nuclear Medicine Technologists: Wear ring/extremity dosimeters on the fingers to monitor direct localized dose to the hands when handling radioactive isotopes.
  • Storage Protocol: When leaving the department at the end of a shift, dosimeters must be left in a designated lead-shielded or non-radiation storage area within the facility.
  • Regulatory Compliance: Wearing a assigned personnel dosimeter is mandatory under federal and state regulations. Technologists and students are prohibited from working or entering clinical sites without their dosimeters.

• Types of Personnel Monitoring Devices:

  • OSL (Optically Stimulated Luminescence Dosimeter):
  • Contains aluminum oxide ($\text{Al}_2\text{O}_3$) crystalline detectors.
  • Processing laboratories read accumulated exposure by stimulating the detector with laser light, causing it to luminesce proportionally to the radiation dose received.
  • TLD (Thermoluminescent Dosimeter):
  • Contains lithium fluoride ($\text{LiF}$) crystals.
  • Read by heating the crystals to high temperatures, causing them to emit visible light proportional to the absorbed radiation dose.

Occupational Radiation Exposure Limits and ALARA

• Annual and Lifetime Dose Limits:

  • Equivalent and effective dose limits are measured using the International System of Units (SI) unit Sievert ($\text{Sv}$) or millisievert ($\text{mSv}$).
  • Occupational Dose Limits (Radiation Workers):
  • Annual Whole-Body Limit: $50\,\text{mSv}$ ($5\,\text{rem}$) per year.
  • Cumulative (Lifetime) Limit: $10\,\text{mSv} \times \text{age in years}$.
    • Formula: $\text{Cumulative Limit (mSv)} = 10\,\text{mSv} \times \text{Age}$.
    • Calculation Example: For a $22$-year-old technologist, the lifetime dose limit is $10\,\text{mSv} \times 22 = 220\,\text{mSv}$.
    • Note: Fractional age in months is not used; calculations strictly use whole years.
  • Lens of the Eye Annual Equivalent Limit: $150\,\text{mSv}$.
  • Skin, Hands, and Feet Annual Equivalent Limit: $500\,\text{mSv}$.
  • General Public Dose Limits:
  • Frequently Exposed Public: $1\,\text{mSv}$ per year.
  • Infrequently Exposed Public: $5\,\text{mSv}$ per year.
  • Embryo/Fetus Dose Limits (Declared Pregnant Worker):
  • Monthly Equivalent Limit: $0.5\,\text{mSv}$ per month.
  • Total Gestational Limit: $5.0\,\text{mSv}$ (or $0.5\,\text{mSv}$ per month across the gestational duration).

• The ALARA Principle:

  • ALARA stands for As Low As Reasonably Achievable.
  • Mandates utilizing the lowest possible radiation exposure factors necessary to yield diagnostic-quality images.
  • Applying excessively low exposure factors causes quantum mottle (graininess), destroying image quality and necessitating repeated exposures that double patient dose.

Technical Factors and Patient Dose Reduction Strategies

• Optimizing Technical Factors:

  • Digital Radiography Protocol: Employs High ${\text{kVp}}$ and Low ${\text{mAs}}$ parameters to reduce total patient absorbed dose.
  • Kilovoltage Peak ($\text{kVp}$):
  • Controls the electrical potential across the X-ray tube, dictating the energy, quality, and penetrability of the X-ray beam.
  • Higher $\text{kVp}$ increases beam energy, allowing photons to penetrate tissue rather than being absorbed by the patient's body.
  • Milliampere-Seconds ($\text{mAs}$):
  • Product of tube current ($\text{mA}$) and exposure time in seconds ($\text{s}$).
  • Controls the quantity (total number) of X-ray photons produced.
  • Lowering $\text{mAs}$ directly reduces patient radiation dose.
  • Exposure Time: Shorter exposure times reduce the probability of patient motion, preventing image blurring and avoiding repeat exposures, which is vital in pediatric imaging.

• Source-to-Image Receptor Distance ($\text{SID}$):

  • Standard clinical $\text{SID}$ values are $40\,\text{inches}$ ($101.6\,\text{cm}$) and $72\,\text{inches}$ ($182.88\,\text{cm}$).
  • $\text{SID}$ should never be reduced below $40\,\text{inches}$.
  • Increasing $\text{SID}$ moves the X-ray tube source farther from the patient, reducing patient skin entrance exposure.

• Quality Assurance and Verification:

  • Preventable errors must be eliminated prior to exposure.
  • Verify requisitions: Match patient full name, date of birth, and medical record number (MRN) between the physician's order and the electronic worklist.
  • Artifact Removal: Ensure all radio-opaque objects (e.g., necklaces, zippers, metallic clothing attachments) are removed prior to positioning.

Biological Effects of Radiation, Radiosensitivity, and Gonadal Shielding

• Law of Bergonié and Tribondeau:

  • States that the radiosensitivity of biological tissues and cells is directly proportional to their reproductive/mitotic activity and inversely proportional to their degree of differentiation.
  • Four Key Determinants of Radiosensitivity:
  1. Cell Age: Immature, stem, or precursor cells are significantly more sensitive than mature, fully differentiated cells.
  2. Complexity / Differentiation: Simple, unspecialized cells are more radiosensitive than complex, highly specialized cells.
  3. Mitotic Rate: Cells with high rates of replication and division are highly radiosensitive.
  4. Metabolic Rate: Cells that utilize energy rapidly (high metabolic activity) exhibit elevated radiosensitivity.

• Radio-sensitive Organs and Biological Categories:

  • Radio-sensitive Tissues: Gonads (germ cells: ova in females, sperm in males), eye lenses, thyroid gland, and active breast tissue.
  • Somatic Effects: Radiation damage occurring to the body tissues of the exposed individual during their lifetime (e.g., skin erythema, organ dysfunction, radiation-induced malignancies, or congenital birth defects in a fetus exposed in utero).
  • Genetic (Hereditary) Effects: Radiation damage inflicted upon the germ cells (sperm/ova), resulting in unexpressed gene mutations that manifest in future generations/offspring.

• Gonadal Shielding Guidelines:

  • Lead Equivalent Standard: Gonadal shields must contain at least $0.5\,\text{mm}$ lead ($\text{Pb}$) equivalent.
  • Dose Reduction: Proper placement reduces gonadal exposure by up to $95\%$.
  • Clinical Indications:
  • Patient is of reproductive age or younger.
  • The gonads lie directly within or within $5\,\text{cm}$ of the primary beam path.
  • The shield does not obscure critical diagnostic anatomy.
  • Childbearing Age Parameters: Defined from the onset of menses at puberty (typically $10\text{--}11\,\text{years}$ of age, occasionally as young as $9\,\text{years}$) through menopause (typically $50\text{--}55\,\text{years}$ of age).
  • Anatomical Placement Considerations:
  • Females: Reproductive organs (ovaries, uterine tubes) are situated higher in the pelvic cavity; shielding must be placed anteriorly above the pubic symphysis.
  • Males: Reproductive organs (testes) lie externally; shielding must be placed directly over and inferior to the pubic symphysis.
  • Anatomical Landmarks: The pubic symphysis is a non-palpable landmark located in a personal area. Radiographers must locate positioning boundaries using adjacent palpable landmarks (such as the anterior superior iliac spine, or ASIS) and measured distances rather than direct palpation of private areas.

Pregnancy Protocols for Radiographers and Patients

• Embryonic and Fetal Radiation Risks:

  • First Trimester Sensitivity: The first $12\,\text{weeks}$ of gestation represents the most critical period of developmental organogenesis. Embryonic exposure during this frame carries high risk for embryonic death, spontaneous abortion (miscarriage), severe congenital structural malformations, and increased susceptibility to childhood malignancies.
  • Gestation Progression: Radio-resistance gradually increases in the second and third trimesters as fetal tissues differentiate and mature.

• Occupational Pregnancy Policies:

  • Voluntary Declaration: Pregnancy declaration by a radiation worker is entirely voluntary and must be submitted in writing.
  • Workplace Accommodation Options:
  • Maintain standard clinical rotation without modifications.
  • Request schedule modifications (e.g., restriction from performing mobile/portable procedures or fluoroscopy/OR duty during the first trimester).
  • Request a formal leave of absence.
  • Dose Tracking: A declared pregnant radiographer wears a second waist-level fetal dosimeter beneath the lead apron to strictly enforce the gestational limit of $0.5\,\text{mSv}$ per month.

• Patient Screening and Protection Protocols:

  • Pre-Exposure Screening: Inquire regarding Last Menstrual Period (LMP) and potential pregnancy status for all female patients of childbearing potential ($9\text{--}55\,\text{years}$).
  • Surgical Context: A total hysterectomy eliminates pregnancy capability. A tubal ligation ("tubes tied") does not completely eliminate the presence of functional ovaries or potential ectopic/gestational risk; screening protocols must still be applied.
  • Modifications for Pregnant Patients:
  • Restrict light field via strict collimation.
  • Provide full abdominal and pelvic lead shielding.
  • Consult the ordering physician to reduce total projections (e.g., reducing a standard 3-view extremity examination to a 2-view series).
  • Ensure pregnancy tests ordered in emergency or inpatient settings are confirmed negative prior to exposure.

Beam Modification Devices: Filtration, Grids, and Collimation

• Filtration:

  • Metal sheets (typically aluminum) placed inside the X-ray tube housing.
  • Absorbs low-energy, long-wavelength X-ray photons ("soft" radiation) from the primary beam.
  • Low-energy photons lack sufficient energy to penetrate the patient and reach the image receptor; without filtration, they would only contribute to patient skin entrance exposure.

• Anti-Scatter Grids:

  • Constructed of alternating thin lead strips and radiolucent interspace materials, placed between the patient and the image receptor inside the Bucky assembly or portable grid caps.
  • Absorbs scattered radiation generated within the patient's body before it reaches the image receptor, preventing fog and loss of contrast.

• Collimation and Positive Beam Limitation (PBL):

  • Collimation: Variable lead shutters that limit the dimensions of the useful X-ray field.
  • Increasing Collimation: Closing the shutters to make the light field smaller; decreases scatter production and lowers patient dose.
  • Decreasing Collimation: Opening the shutters to make the light field larger; increases patient dose.
  • Positive Beam Limitation (PBL):
  • Automatic collimation system present in modern X-ray equipment.
  • Sensors detect the size and orientation of the image receptor placed in the Bucky tray and automatically collimate the primary beam light field to match the exact dimensions of the image receptor.

Inverse Square Law Mathematics and Calculations

• Inverse Square Law Principle:

  • The intensity ($I$) of radiation is inversely proportional to the square of the distance ($d$) from the radiation source.
  • Conceptual Rules:
  • Doubling the distance ($2 \times d$) from the source reduces radiation intensity to one-fourth ($\frac{1}{4}$) of its original value.
  • Halving the distance ($\frac{1}{2} \times d$) quadruples ($4 \times$) the radiation intensity.

• Mathematical Formula:   $\frac{I_1}{I_2} = \left(\frac{d_2}{d_1}\right)^2 \quad \text{or} \quad \frac{I_1}{I_2} = \frac{d_2^2}{d_1^2}$

  • Where:
  • $I_1$ = Initial Radiation Intensity
  • $I_2$ = New Radiation Intensity
  • $d_1$ = Initial Distance
  • $d_2$ = New Distance

• Step-by-Step Calculation Walkthrough:

  • Problem: A radiographer performs a PA chest examination yielding an intensity of $5\,\text{mGy}$ at a distance of $10\,\text{feet}$. The X-ray tube is subsequently moved to a distance of $15\,\text{feet}$. What is the new radiation intensity ($I_2$)?
  • Step 1: Identify given variables:
  • $I_1 = 5\,\text{mGy}$
  • $d_1 = 10\,\text{feet}$
  • $d_2 = 15\,\text{feet}$
  • $I_2 = x$
  • Step 2: Set up the proportion:     $\frac{5}{I_2} = \left(\frac{15}{10}\right)^2$
  • Step 3: Square the distances:     $15^2 = 225$$10^2 = 100$$\frac{5}{I_2} = \frac{225}{100}$
  • Step 4: Cross-multiply:     $225 \times I_2 = 5 \times 100$$225 \times I_2 = 500$
  • Step 5: Solve for $I_2$:     $I_2 = \frac{500}{225} \approx 2.22\,\text{mGy}$

Radiation Protection & Radiobiology Review Concepts

• Determinants of Radiosensitivity (Law of Bergonié and Tribondeau Review):

  • Depends on cell age, structural complexity, rate of cell replication, and metabolic rate (rate of energy utilization by the cell).

• Short-Term vs. Long-Term Radiation Effects:

  • Short-Term Radiation Effects:
  • Predictable, deterministic threshold responses occurring shortly after exposure.
  • Result from receiving high radiation doses over a brief time frame.
  • Manifests clinically as Acute Radiation Syndrome (ARS), which is subdivided into three biological stages:
    1. Hematologic (blood-forming system disruption).
    2. Gastrointestinal (GI) (intestinal mucosal damage).
    3. Central Nervous System (CNS) (neurological collapse).
  • Long-Term Radiation Effects (Stochastic Effects):
  • Random, non-threshold probabilistic effects where the likelihood of occurrence (rather than severity) increases with dose.
  • Require no minimum threshold dose to occur (e.g., radiation-induced carcinogenesis or genetic mutations).

• Terminology and Acronym Key:

  • $\text{SID}$: Source-to-Image Receptor Distance (distance from X-ray tube target to image receptor surface).
  • $\text{OID}$: Object-to-Image Receptor Distance (distance between the patient's body part being imaged and the image receptor surface).
  • $\text{kVp}$: Kilovoltage Peak (controls beam penetrability and image contrast).
  • $\text{OSL}$: Optically Stimulated Luminescence (laser-read dosimeter containing aluminum oxide).
  • $\text{TLD}$: Thermoluminescent Dosimeter (heat-read dosimeter containing lithium fluoride).