Radiation Protection

1
Radiation Protection

• Review of Units of Measurements
• Protection for Patient and Personnel
• Review of Radiobiology
• Follows the ARRT Content Specifications

2
Sources of Radiation Exposure

• Natural or background - ground, cosmic,
  naturally occurring isotopes, etc.
• Artificial or man-made - Medical and dental
  largest contributor to population dose

3
Units of Measurement - Know traditional and
Standard International Units

• Roentgen (R) - traditional unit of exposure in
  air - equipment related x and gamma rays
  Coulomb/Kg or C/Kg
• rad (r) - traditional unit of absorbed dose
  all
• Gray (Gy)
• rem - traditional unit of dose equivalent x,
  beta, gamma
• Seivert (Sv)
• Curie (Ci) - measure of radioactivity
• Becquerel (Bq) in Nuc Med

4
Detection MethodsPersonnel Field
Instruments

• Ionization Counter
• Cutie Pie,Geiger Counter
• spills, more industrial
• Scintillation detector
• more technical use
• used in CT,NM

• Film Badges - month
• photographic film
• TLD - 3 months
• Sensitive to 5 mrem
• Expensive
• Ionization chamber
• pocket dosimeter
• drifts / not accurate
• Larger one for NM or more industrial

5
OSL

• Aluminum Oxide
• Laser beam releases light
• Sensitive to exposures as low as 1 mrem
• 3 months at a time
• Can be reanalized

6
Monitoring Agencies

• NCRP -National Council on Rad Protection
• dose limitations control
• DRH - Devices for Radiological Health
• radiation control (more equipment related)
• NRC - Nuclear Regulatory Commission - radiation
  protection standards (formerly- Atomic Energy
  Comm)
• Maryland State Dept. Health Hygiene
• EPA - Environmental Protection Agency
• more industrial application related matters

7
Recommendations for Dose

• ALARA - As Low As Reasonably Achievable for
  patient and occupational worker
• Cumulative Dose Limit for Occupational Worker -
  simply your age x 1 rem
• ie. 47yo male RT, 47 rem
• Embyro or fetus -- 50mrem/month or 500 mrem total
• Member of public frequently, exposed 100mrem

8
Interactions with Matter

• Coherent ( Classicial or Thompson) scattering
  lt 30kVp
• Photoelectric Effect 30-150 kVp
• Comptons Scatter 30-150 kVp
• ie. 70kVp 40 PE and 60 Compton
• vs 100kVp 10 PE and 90 Compton
• Pair Production and Photodisintegration MeV as
  in Rad Therapy

9
Estimated Patient Doses

• Skin - TLD 15, 000mrem and extremities 30,000
  mrem
• Gonad -- genetic responses at 20rads/yr
• Bone Marrow (mean) - rad induced leukemia 100
  rad/yr
• Gonadal and bone doses are estimates!

10
Estimated Doses

• Fluoroscopic are harder to measure
• 2rad/mA/minute
• remember patient becomes the hazard since the
  scatter is what gets the radiographer
• Exams with higher patient doses are
• Fluoro
• Angio
• Portables
• General - around pelvic region, hip femur,
  lumbar, coccyx, sacrum

11
Cardinal Principles

• Time ? time, ? dose OR ? time, ? dose
• Distance ? distance, ? dose OR if you
  conversely ? distance, ? dose (dont forget the
  inverse square law or direct square law)
• Shielding reduces dose as much as 95 in male
  patients

12
Patient Protection

• Film Screen Combo
• Beam limitation
• PBL - automatic collimation
• Cones
• Cylinders
• aperture diaphragms
• ? field, scatter, dose
• Avoid Repeats
• techniques charts
• good communication
• restraining devices
• good QA program

• Cardinal Principles
• time, distance, shielding
• Exposure Factors
• kVp, mA, time, distance
• directly related
• ? kVp - ? interactions
• ?time - ? dose
• fluoro time -keep it short
• ?mA and ? (fast) time
• Filtration - inherent
• 0.5mm al lt50kVp
• 1.5mm al 50-70kVp
• 2.5mm al gt70kVp

13
Patient Protection - continued

• Shielding - not lt 0.25mm Pb
• long bones in peds
• all eyes
• gonadal - 5cm primary
• flat rubber lead strips
• shadow shield
• shaped or cup
• eye shields
• If patient holds cassette, Pb glove needs to be
  0.5 mm to protect hand

• Air Gap technique
• High Dose to Gonads
• hip upper femur
• pelvis lumbar
• lumbo-scaral
• abdomen
• sacrum coccyx
• S-I Joints
• BE, IVP, Cysto, Hystero

14
Personnel Protection

• Cardinal Principles
• Time, Distance, Shielding
• Protective wear
• Pb aprons 0.5mm
• Pb gloves 0.25mm
• thyroid - ? dose 10 6mrad per exam
• Pb glasses 0.75mm
• ? dose 98
• Pb sterile gloves

• Barriers - 7 high
• primary 1/16th inch
• secondary 1/32 inch
• Pb glass port
• mobile in OR
• Mobile exposure cord length - no less 6

15
Personnel Protection Continued

• Never hold Patients - use immobilization
  devices
• Wear monitoring devices
• film badge
• TLD
• Pocket dosimeter

• Fluoro equipment - apron on tower, bucky slot
  cover, fluoro timer
• Clear room when doing portables or provide with
  Pb apron
• Stand 2 m from table

16
Pregnancy

• Radiographer
• self disclosure voluntary
• fetus 50mrem per month or 500 mrem or 5mSv over
  term
• Baby badge at waist
• 0.5mm Pb aprons are 88 effective gt 70 kVp

• Patient
• ask about LMP
• ALARA
• double shield or limit exam views
• 10 day rule for high dose exams

17
Rad Protection - Equipment General Radiographic

• Control panel light, meters and sound
• SID within ? 2 variance
• PBL within ? 2 of SID
• Beam alignment
• Filtration 2.5mm Al equivalent total
• Reproducibility output , not to exceed 5
• Linearity intensity across mA stations, not
  be exceed 10
• Personnel shield short cords so exposures are
  made behind 7 barriers

18
Rad Protection - EquipmentFluoro and Mobile

• Mobile C-Arm not lt 12 (30cm) source to tabletop
  distance
• Stationary Fluoronot lt 15 (38cm) source to
  tabletop distance
• Primary Barrier IA assembly 2mm Pb equivalent
  when gt125kVp (usually 80-120 kVp fluoro)
• Filtration 2.5mmAl total just in overhead tube
  lt100mR/Hr leakage at 1 meter
• PBL on Fluoro tower borders on monitor when IA
  is 14 from tabletop
• Exposure switch Dead man - intermittent ? dose

19
Rad Protection - EquipmentFluoro and Mobile

• Bucky Slot Cover 5cm wide at gonadal level and
  0.25mm Pb thick
• Protective Apron on Tower 0.15- 0.25mm Pb
  between patient operator
• Cumulative Timer for Fluoro 5 min/audible
• X-Ray Intensity should not gt2.1R/min at tabletop
  per mA at 80 kVp
• Dose Rate must not gt 10R/min maximum, should not
  5
• Front loaded cassette vs back load front less
  dose
• Spot cassette vs spot film camera -- dose to
  patient 3x more for cassette over camera

20
RADIOBIOLOGY

• In addition to the technical side, we must
  understand the biological effects!

21
Characteristics of Radiation

• Physical
• LET - efficiency of radiation to produce
  excitation and ionization ( energy deposit per
  unit path length)
• LET of dx is 3 keV/?m
• RBE - Relative Biological Effectiveness

22
Biological Aspects

• Review the mitosis and meiosis cycles
• The most sensitive time for DNS is G2 and rest of
  mitotic stages (least during G1 and Synthesis)
• Keep in mind that in meiosis, DNS replicates only
  once
• What about other factor affecting cellular
  response?

23
Laws of Sensitivity

• High mitotic activity -- more sensitive
• Cell differentiation -- less, more sensitive
• Long dividing future -- more sensitive
• All these Bergonie and Tribondeau
• Biological Stress
• Pre/post irradiation conditions
• Chemicals -- enhancers, protectors
• Ancel and Vitemberger -- more environment related

24
Effects---

• Direct - photon strikes DNA --breaks in ladder
  either rungs or side rails
• Indirect - photon strikes water -- most abundant
  so most likely to happen more frequently
• Target Theory -- variations, but striking a
  critical DNA area where lethality occurs
  immediately or may take two hits to achieve death
• Cell survival curves - curve representing the
  dose and proportion of cells surviving

25
Mean Survival Curves

• Relationship between the dose and number of cells
  that survive
• Lethal Dose
• human LD 50/60 -- 350 rad
• previously 50/30 - Chernobyl changed figures

26
Dose Response Relationships

• Linear, non-linear
• Threshold or non-threshold
• (non-stochastic) (stochastic, random)
• We practice by Linear, non-threshold

27
Cellular Responses

• Interphase death
• Division Delay
• Reproductive failure

28
Stages of ResponseDose Dependent

• Prodromal -- NVD
• Latent
• Manifest
• hematologic --dose between 100-1000
• 200-600/200-1000
• GI syndrome - dose between 1000-5000
• 600-1000
• CNS - dose gt 5000
• Recovery or Death

29
Radiation Reduced Malignancy

• Historical populations
• Dose related
• Risks associated
• 20 population USA will die of Ca
• how do you tell if rad caused?
• Children? Leukemia is common

30
In Utero -- Fetal Irradiation

• neonatal death - 2-3 week of gestation
• malformations
• growth stunting
• congenital defects - functional defects after
  week 20
• cancer induction
• Week 4-11 severe abnormalities, especially CNS
  and skeletal, while 11- 16 mental retardation
  microcephaly