Radiation Safety and Biology – Comprehensive Study Guide (Exam 1)

Comprehensive Study Guide: Radiation Safety and Biology – Exam 1

1. Units of Radiation Measurement

• R – Roentgen

  • Measures exposure in air, specifically ionization created by x-rays or gamma rays.

  • Unit of exposure, not dose; applies to photons in air only.

  • Conversion: 1 R ≈ 0.0087 to 0.009 Gy in air.

• rad – Radiation Absorbed Dose

  • Conventional (old) unit for absorbed dose in tissue or any material.

  • Conversion: 1 rad = 0.01 Gy.

• rem – Roentgen Equivalent Man

  • Conventional unit for equivalent or effective dose.

  • Accounts for radiation type and biological effect.

  • Formula: rem = rad × QF × WT.

  • Conversion: 1 rem = 0.01 Sv.

• Gy – Gray

  • SI unit for absorbed dose.

  • Conversion: 1 Gy = 100 rad.

• Sv – Sievert

  • SI unit for equivalent/effective dose.

  • Conversion: 1 Sv = 100 rem.

  • Approximate identity for photons: 1 R ≈ 1 rad ≈ 1 rem (in soft tissue).

2. Conversions

• Radiation Unit Conversions:

  • R → Gy (air): 1 R ≈ 0.009 Gy_air.

  • rad ↔ Gy: 100 rad = 1 Gy | 1 rad = 0.01 Gy.

  • rem ↔ Sv: 100 rem = 1 Sv | 1 rem = 0.01 Sv.

  • mSv ↔ mrem: 1 mSv = 100 mrem.

3. Personnel Dosimeters

• Film Badge

  • Contains a small film behind filters; darkening is proportional to dose.

  • Pros: cheap; permanent record; can show radiation type (β, γ).

  • Cons: sensitive to heat, humidity, light; less accurate at low doses; single-use.

• TLD – Thermoluminescent Dosimeter

  • Uses crystals (LiF, CaF₂) that trap electrons; heating releases light proportional to dose.

  • Pros: reusable; accurate; suitable for ring badges.

  • Cons: readout erases info; requires special reader; needs annealing.

• OSL – Optically Stimulated Luminescent

  • Utilizes Al₂O₃ crystals that store energy until stimulated by a laser.

  • Pros: extremely sensitive (~1 mrem); can be re-read; stable; wide energy range.

  • Cons: costly; requires a specialized reader.

• Pocket Ion Chamber / Electronic Dosimeter

  • A small ion chamber or solid-state device that provides an instant reading.

  • Pros: immediate feedback.

  • Cons: fragile; possible battery drift; not typically an official record.

Wearing Rules for Dosimeters

• Whole-body badge: worn at collar, outside a lead apron.

• Second badge (if pregnant or applying the two-badge program): waist, under apron.

• Ring badge: worn on the dominant hand with the label facing the palm.

• Store badges in a cool, dry, low-background area at work.

• Important: Do not take badges home or leave them in the car.

• Exchange badges on a monthly (nuclear medicine) or quarterly (X-ray) basis.

Assignment Criteria for Dosimeters

• A badge is issued if an individual is likely to receive more than 10% of 5 rem/year (> 500 mrem).

• This includes staff in fluoroscopy/interventional radiology, C-arm users, nuclear medicine technicians, and declared pregnant workers.

4. Radiation Area Signage and Limits

• Area Types and Limits:

  • Unrestricted: Public access; limit ≤ 2 mrem in 1 h and ≤ 100 mrem/yr; signage: None.

  • Controlled: Occupational area; limit ≤ 5 rem/yr; signage: “Caution – Controlled Area”.

  • Restricted: Limited access; limit > 2 mrem/h; signage: “Caution – Radioactive Materials”.

  • Radiation Area: ≥ 5 mrem/h at 30 cm; signage: “Caution – Radiation Area”.

  • High Radiation Area: ≥ 100 mrem/h at 30 cm; signage: “Caution – High Radiation Area”.

  • Very High Radiation Area: ≥ 500 rad/h at 1 m; signage: “Grave Danger – Very High Radiation Area”.

5. Geiger Counter Operation

• Steps to Operate a Geiger Counter:

  1. Verify that calibration is current.

  2. Inspect the probe, cords, and case for damage.

  3. Check batteries.

  4. Set range to the most sensitive setting; enable audio.

  5. Measure background radiation.

  6. Check against a known check source at fixed geometry; compare with control chart.

  7. Survey slowly (~2 inches per second), approximately 1–2 cm from the surface.

  8. Record instrument ID, units (cpm or mR/h), location, date/time.

6. Survey & Wipe Test Frequencies

• Area Surveys (GM):

  • Daily: Hot lab, dose calibrator bench, injection room, waste storage.

  • Weekly: Storage & decay areas.

  • Monthly: Labs with small quantities (< 200 µCi).

  • Quarterly: Sealed source or brachytherapy storage.

• Removable Contamination (Wipe Tests):

  • Weekly: Hot lab and storage areas.

  • Monthly: Low-use labs.

  • Analyze results in a well counter; action level is approximately 200 disintegrations per minute (dpm) per 100 cm².

7. Dose Limits

• Occupational Dose Limits:

  • Whole body (TEDE): 5 rem (50 mSv)/yr.

  • Lens of the eye: 15 rem (150 mSv)/yr.

  • Skin/Extremity/ Single organ: 50 rem (500 mSv)/yr.

• Public Dose Limits:

  • 0.1 rem (1 mSv)/yr and ≤ 2 mrem/h in unrestricted areas.

• Embryo/Fetus (declared):

  • 0.5 rem (5 mSv) total for gestation.

  • Goal of ≤ 0.05 rem (0.5 mSv) per month after declaration.

• Minors/Students:

  • 0.5 rem (5 mSv)/yr.

• Administrative References:

  • 1 rem × age (lifetime); 3 rem/quarter (legacy guidance).

8. Worker Categories

• Occupational Worker: Those exceeding 10% of the dose limit are required to wear badges.

• General Public: All individuals who are not occupational workers (≤ 100 mrem/yr).

9. Major Radiation Sources to Public

• Natural Sources:

  • Radon (55% of exposure), cosmic radiation, terrestrial radiation, internal radionuclides.

• Man-Made Sources:

  • Medical imaging (CT, nuclear medicine, X-ray), consumer products, air travel, industrial applications.

10. Staff Protection Techniques

• Radiation Protection in X-ray / Fluoroscopy:

  • Use lead aprons (≥ 0.5 mm Pb), thyroid shields, and lead glasses.

  • Stand behind barriers and use mobile shields.

  • Position the tube under-table and stand on the detector side.

  • Collimate tightly to reduce scatter.

  • Utilize Automatic Exposure Control (AEC) and pulsed fluoroscopy.

  • Rotate staff frequently; minimize time the beam is active.

  • Conduct annual inspections of lead shielding.

• Radiation Protection in Nuclear Medicine:

  • Employ L-blocks and lead glass windows.

  • Use vial pigs, syringe shields, tongs/forceps, and lead-lined storage and transport containers.

  • Change gloves frequently and perform wipe tests.

  • Utilize a fume hood for volatile iodine-131.

  • Store materials for decay for at least 10 half-lives prior to disposal.

11. ALARA & Optimization

• ALARA Principle: As Low As Reasonably Achievable

  • Justify every exposure to radiation.

  • Optimize protocols and shielding to ensure minimal exposure.

  • Implement Administrative ALARA I/II levels, which are ¼ and ¾ of limits, respectively.

  • Conduct routine training and review of dosimetry practices.

• Advocacy Campaigns:

  • Image Wisely: Focuses on reducing unnecessary CT scans and optimizing imaging protocols for adults.

  • Image Gently: Emphasizes pediatric care by adjusting mA/kVp based on size, weight-based radiopharmaceutical dosing, and advocating for alternative modalities.

12. Health Physicist Inspection Checklist

• Assessment of:

  • kVp accuracy.

  • mA/time linearity.

  • Output reproducibility.

  • Beam quality assessed via Half-Value Layer (HVL) and filtration.

  • Collimator and Source-to-Image Distance (SID) accuracy.

  • Automatic Exposure Control (AEC) performance.

  • Tube leakage must be less than 100 mR/h at 1 m.

  • Protective barrier integrity.

  • Scatter surveys and Personal Protective Equipment (PPE) inspection.

  • Posting and records review for compliance.

13. Declared Pregnancy Policy

• Declaration Process:

  • Voluntary written declaration to the Radiation Safety Officer (RSO); this can be withdrawn.

  • Issue a fetal badge to be worn at the waist under the apron.

  • Aim for a dose limited to ≤ 0.5 mSv/month; ≤ 5 mSv total during pregnancy.

  • Review previous dose information and adjust tasks if necessary to avoid high-dose procedures (e.g., fluoroscopy or I-131).

  • No automatic job removal as long as limits are met.

  • Ensure privacy and equal treatment for declared pregnant workers.

14. Dosimetry Report Information

• Report should include:

  • Worker ID and Department.

  • Badge type and location.

  • DDE (Deep Dose Equivalent) measured at 1 cm, LDE (Lens Dose Equivalent) at 0.3 cm, and SDE (Shallow Dose Equivalent) at 0.007 cm.

  • Tracking of doses per period, quarter-to-date, year-to-date, and lifetime dose.

  • Indicators in the report: “M” for minimal exposure, “N” for none, “NR” for not returned.

  • ALARA flag if approaching investigation levels for exposure.

15. Badge Assignment Threshold

• Assign dosimeters if a worker is likely to receive ≥ 500 mrem/year (10% of the limit) or is handling unsealed sources, performing fluoroscopy, or is a declared pregnant individual.

16. Radioactive Package Labels & Checks

• Label Types:

  • White-I: Surface limit ≤ 0.5 mR/h; none detectable at 1 m; Transport Index (TI) = 0.

  • Yellow-II: Surface limit ≤ 50 mR/h; < 1 mR/h at 1 m; TI = ≤ 1.

  • Yellow-III: Surface limit ≤ 200 mR/h; < 10 mR/h at 1 m; TI = ≤ 10.

• Receipt Procedure:

  • Wear Personal Protective Equipment (PPE) during receipt.

  • Conduct a visual check for damage/leaks.

  • Survey the package at 1 m and compare to the Transport Index (TI).

  • Perform surface survey (compare to limits).

  • Conduct a wipe test covering a ≥ 300 cm² area.

  • Open carefully, resurvey, and log results.

  • Notify RSO if any results exceed limits or if contamination is detected.

17. Radium Girls Case

• Historical case involving early 1900s dial painters who used Ra-226 paint; the lip-pointing of brushes caused ingestion leading to severe bone necrosis and cancer.

• This incident sparked the development of modern occupational radiation protection laws and worker compensation policies.

18. Attenuation & Shielding Math

• Exponential Law:

  • Describes the relationship between intensity and thickness: I = I₀ e^{- x}.

• To find thickness for a given reduction:

  • x = rac{ ext{ln}igg( rac{1}{1 - rac{ ext{% reduction}}{100}}igg)}{}.

• Using Half-Value Layer (HVL):

  • x = ext{HVL} imes igg[ rac{ ext{ln}igg( rac{1}{1 - rac{ ext{% reduction}}{100}}igg)}{ ext{ln(2)}}igg].

• Half-Value Layer Definition:

  • ext{HVL} = rac{0.693}{}.

  • From measured data, ext{HVL} = rac{x imes 0.693}{ ext{ln}(I₀/I)}.

• Inverse Square Law:

  • I₂ = I₁ imes igg( rac{D₁}{D₂}igg)².

  • To solve for distance: D₂ = D₁ imes ext{sqrt}igg( rac{I₁}{I₂}igg).

19. Example Problems

1. Given linear attenuation coefficient  = 0.173 ext{ cm}^{-1}:

   • ext{HVL} = rac{0.693}{0.173}
     ightarrow ext{HVL} = 4.0 ext{ cm}.

2. To achieve 90% reduction with ext{HVL} = 2 ext{ mm}:

   • ext{# HVLs} = ext{log}_2( rac{1}{0.10})
     ightarrow ext{# HVLs} = 3.32
     ightarrow x = 6.6 ext{ mm}.

3. Given initial intensity I₁ = 2.0 ext{ mR/h} at 1 m:

   • I₂ = 2.0 imes igg( rac{1}{3}igg)²
     ightarrow I₂ = 0.22 ext{ mR/h}.

4. If intensity decreases from 2.0 to 0.5 mR/h:

   • D₂ = 1 imes ext{sqrt}igg( rac{2}{0.5}igg) = 2 ext{ m}.

5. Given I₀ = 150 and I = 37.5 with x = 4 ext{ cm}:

   •  = 0.3466
     ightarrow ext{HVL} = 2.0 ext{ cm}.

20. Common Abbreviations & Conversions

• DDE – Deep Dose Equivalent (1 cm)

• SDE – Shallow Dose Equivalent (0.007 cm)

• LDE – Lens Dose Equivalent (0.3 cm)

• TEDE – Total Effective Dose Equivalent = DDE + CEDE

• CEDE – Committed Effective Dose Equivalent (over 50 years)

• CDE – Committed Dose Equivalent (single organ)

• DAC – Derived Air Concentration

• ALI – Annual Limit on Intake

• AEC – Automatic Exposure Control

• kVp – Kilovoltage Peak

• mA, mAs – Tube current & current × time

• µ – Linear attenuation coefficient

• HVL – Half-Value Layer

• TVL – Tenth-Value Layer

• TI – Transport Index

• RSO – Radiation Safety Officer