Transcript Radiographers – Radiation Dosimetry

Radiation Dosimetry
John Gough, MS, CHP
Radiation Safety Officer
Swedish Medical Center
Introduction
Swedish Medical Center
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Established in 1910
3 Hospital locations
Multiple specialty clinics
Cancer, Heart, Surgery institutes
12 primary-care clinics
Full range nuclear med, radiation oncology
Research Hospital
Type A Medical Broad Scope License
History
History
• X-rays discovered in 1895
• Radioactivity discovered in 1896
• First document radiation fatality – 1904
– Clarence Daly severely burned in
1986 by an x-ray fluoroscope
History
• First attempt at establishing a radiation
dose limit – Skin Erythema Dose – 1920
• 200 mR/day dose limit established in 1931
• 25,000 mrem/year established during
WWII.
Radiation Dosimeters
Radiation Dosimetry
• scientific determination of amount, rate,
and distribution of radiation emitted from a
source of ionizing radiation, in biological d.
measuring the radiation-induced changes
in a body or organism, and in physical d.
measuring the levels of radiation directly
with instruments.
Types of Dosimeters
• Immediate Read
– Pocket Ionization Chambers, Solid state
detectors, handheld GM/Ionization detectors
with dose accumulation function
• Delayed read / Personnel monitors
– Film Badges, TLD (Thermo Luminescent
Dosimeters), OSL (Optically Stimulated Lightemitting Dosimeters)
Film Badges
• Most common type of radiation
dosimeter used.
• Works by darkening of x-ray
film in proportion to radiation
absorbed.
• Cheap
• Not durable
• Short monitoring period per
badge (6 months or less)
TLD
• “Captures” radiation dose
information in a crystal matrix
• Releases light when heated,
light intensity proportional to
radiation dose absorbed
• Durable
• Can be expensive (reusable
chips)
• Information destroyed when
processed
OSL
• “Captures” information in an Aluminum
Oxide matrix
• Releases information by laser
stimulation
• Can be reread after processing
• Durable
• Landauer Only
Pocket Ionization
• Electro-statically charged “leaf”
discharges as it is exposed to
ionizing radiation
• Not considered a “legal” record
• Low accuracy (+/- 20%)
• Physical impacts can affect
radiation dose readings
Solid State
• Provides instantaneous
information regarding dose
accumulation
• Simple to use
• Not a “legal” record
• Dose range device dependent
Handheld Radiation
Detectors
• Ability to perform both dose
rate and dose accumulation
• Good for spot checks
• Direction dependent
• Not considered a “legal”
personnel dose record
Dose Limits
Occupational Dose
"Occupational dose" means the dose received by an
individual in the course of employment in which the
individual's assigned duties involve exposure to radiation
or to radioactive material from licensed and unlicensed
sources of radiation, whether in the possession of the
licensee, registrant, or other person. Occupational dose
does not include dose received: From background
radiation, from any medical administration the
individual has received, from exposure to individuals
administered radioactive material and released under
chapter 246-240 WAC, from voluntary participation in
medical research programs, or as a member of the
public.
Radiation Doses Comparison
Activity
Dose (mrem)
1 day of background radiation
1 mrem
1 Chest x-ray
10 mrem
Public Dose Limit
100 mrem
Nuclear Stress Test
500+ mrem
Whole Body CT
1000+ mrem
Occupational Dose Limits
NRC / WA DOH
Part of Body
Whole Body (TEDE)
Annual Limit
(mrem)
5,000
Organ or Extremity
50,000
Lens of the Eye
15,000
Dose to Fetus
500
Occupational Dose Limits
NRCP Recommendations
Part of Body
Whole Body (TEDE)*
Annual Limit
(mrem)
5,000*
Organ or Extremity
50,000
Lens of the Eyes
15,000
* Not to exceed 1000 mrem x Individual’s Age for
Cumulative Lifetime exposure.
ALARA Concept
“As Low As Reasonably Achievable” means
making every reasonable effort to
minimize the dose received when working
with sources of radiation. Essentially it
means minimizing the risks while
understanding that the cost vs. benefit for
the dose reduction.
Typical ALARA Levels
Part of Body
Quarterly Action Level
(mrem)
Level I
Level II
Whole Body
125
375
Organ or Extremity
1250
3750
Lens of the Eyes
375
1125
Fetal
n/a
150
Dosimetry Reports
Expected Doses
from Radiography Sources
Radiography Sources
Isotope
Typical
Activity (Ci)
Gamma
Constant (R/hr
– Ci @1 meter)
Dose rate
(R/hr @ 1m)
Ir-192
100
0.48
48
Co-60
20
1.32
26.4
Se-75
100
0.2
20
X-ray
n/a