WEEK 6 RADIATION BIOLOGY & PROTECTION RTEC A 2006
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Ionization process removal or addition of an electron
INTERACTIONS in the TUBE
Interactions In The Patient
HEAT
COHERENT
BREMSTRAHLUNG(BREMS)
PHOTOELECTRIC
CHARACTERISTIC
COMPTON
PAIR PRODUCTION
PHOTODISINTEGRATION
Sources of Ionizing Radiation
Natural Radiation
Man – made Radiation
Units of Measurement
ALARA
DOSE –
MEDICAL IMAGING
MEDICAL X-RAYS
DENTAL X-RAYS
GREATES SOURCES OF MAN-MADE
RADIATION
Terminology to cover
Cumulative
Annual
UNITS OF RADIATION MEASUREMENT
To quantify the amount of radiation a patient or worker receives
Conventional (British)Units vs. SI Units
Conventional (British) Units Used Since The 1920’s
1948 - A System Of Units Based On Metric Measurements Was Developed By The
International Committee For Weights And Measures. SI Units
SI Units Were Officially Adopted In 1985
Conv. Units
SI Units
RADS
REMS
R - ROENTGEN
GRAYS
SIEVERT
C/KG
R - ROENTGEN
THE QUANTITY OF X-RADIATION
ONLY EXPOSURE IN AIR
OUTPUT OF XRAY TUBE
DOES NOT INDICATE ACTUAL
PATIENT EXPOSURE OR
ABSORBTION
RADIATION ABSORBED DOSE
(RAD) SI = GRAY (Gy)
MEASURES THE AMOUNT OF
ENERGY ABSORBED IN ANY MEDIUM.
(the patient) 1 Gy = 100 rads1/100 Gy
Radiation Absorbed Dose
= 1 rad
ABSORBED DOSE – Used for patient
Traditional Unit = rad
SI Unit = GRAY (Gy)
Measures the amount of energy absorbed in any medium
WEEK 6 RADIATION BIOLOGY & PROTECTION RTEC A 2006
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1 Gy = 100 rads
REM / SIEVERT
Used for occupational exposure
1 Sv = 100 REM
EMPLOYEE EXPOSURE
1/100 sv = 1 REM
RADIATION EQUIVALENT MAN
THE PRODUCT OF THE
(REMS) SI UNITS = SEIVERT
GRAY x QUALITY FACTOR (QF)
Not all types of radiation produce the same responses in living tissue
The unit of dose equivalence, expressed as the product of the absorbed dose in rad and
quality factor.
Radiation Equivalent Man
DOSE EQUIVALENT – Used for
employee
Traditional Unit = rem
SI Unit = Sievert (Sv)
1 Sv = 100 rem
The product of the Gray and the quality
factor
1 RAD X QF = 1 REM
1 GRAY X QF = 1 SIEVERT
QF FOR X-RAYS = 1 So…… Rads = Rems
QUALITY FACTOR Qualifies what the damage is from different types of radiation
Example: QF for X-ray is 1
QF for alpha is 20
Alpha is 20 x more damaging to tissue
Why did the bunny die??
BUNNY A Received 200 rads
BUNNY B Received 200 rads
Why did the bunny die??
BUNNY A 200 rads of X-RAY =200 RADS BUNNY B 200 rads of alpha = 4000 rads
Response of cells to radiation
CELL SENSITIVITY TO RADIATION
TYPE OF CELL
TYPE OF DAMAGE RECEIVED
KIND OF RADIATION EXPOSED TO
SENSITIVITY TO RADIAITION
Which (Male or Female) GONADs are external vs internal
Which gender has gonads from birth? vs Which gender constantly produces new cells?
Which GENDER is more sensitive to radiation at birth? Why?
Annual dose
5 Rem/year 50mSv/year
(5000 mrem)
Permissible Occupational Dose
Cumulative Dose
1 rem x age 10mSv x age
PUBLIC EXPOSURENON MEDICAL EXPOSURE
10 % of Occupational exposure
50 % of Occupational exposure
0.5 rad or 500 mrad or 50mgray
0.1 rem 10 mrem 1mSv
Under age 18 and Students
Fetus Exposu
Radiation exposure is most harmful during the first trimester of pregnancy
Embryo-Fetus Exposure limit (Monthly) 0.05 rem or 0.5 mSv
WEEK 6 RADIATION BIOLOGY & PROTECTION RTEC A 2006
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Radiation Monitoring
MONITORS MEASURE THE QUANTITY OF RADIATION RECEIVED.
ANY RADIATION WORKIER MUST BE MONITORED TO DETERMINE ESTIMATED DOSE
EXPOSURE
PERSONNEL MONITORING DEVICES MOST COMMON
Film Badges
Thermoluminescent Dosimeters (TLD)
Pocket Dosimeters
Optically Stimulated Luminescence (OSL Dosimeters)
Field Survey Instruments
Geiger Muller counter
Biological Response to Ionizing Radiation
X-ray interactions with matter (human tissue) can cause biological changes.
Technologists must understand cellular biology and how radiation interacts with cells in order
to protect oneself and the patient.
CELL TYPES
BIOLOGIC RESPONSE TO IONIZING RADIATION.
CELL STRUCTURE
NUCLEUS & CYTOPLASM
Most important part of the cell…….
CHROMOSOMES, WHICH ARE MADE UP OF GENES.
Cell Type Examples
Radiosensitive: Skin cells, small intestine cells, germ cells
Resistant cells: Specialized in structure and function, do not undergo repeated mitosis –
Nerve, muscle & brain cells
Basic Cell Structure Two parts: Nucleus Cytoplasm
Nucleus contains chromosomes – genetic info (DNA)
DNA is at risk when a cell is exposed to ionizing radiation
Cytoplasm – 80% water
Cellular Absorption
Direct vs. Indirect Hit
Direct Hit Theory:
Indirect Hit Theory:
When radiation interacts with DNA.
Occurs when water molecules are ionized
Break in the bases or phosphate bonds
Produces chemical changes – injury or
Can injure or kill the cell
cell death
Vast majority of cellular damage is from
indirect hit.
TARGET THEORY
[Photons hit master molecule DNA = cell dies
Or doesn’t hit nucleus – and just passes through
No essential damage
WEEK 6 RADIATION BIOLOGY & PROTECTION RTEC A 2006
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Hormoresis – repair that can occur when below 5 rads of expsoure
Radiosensitivity of Cells
Bergonie & Tribondeau (1906) – method of classifying a cell’s response to radiation according
to sensitivity.
Cells are most sensitive during active division (primitive in structure & function).
RADIOSENSITIVITY OF CELLS
Mitotic activity
Structure
Specific characterisitics of the cell
Function
(primative)
The Law of Bergonie & Tribondeaux
Cells that are most sensitive to radiation
Young – immature cells
Stem Cells
Highly dividing (mitotic) cells
Highly metabolic
EFFECTS OF RADIATION
LATE EFFECTS SOMATIC EFFECTS = INDIVIDUAL EXPOSED
GENETIC EFFECTS = FUTURE GENERATIONS
Somatic Cells
Germ Cells
Perform all the body’s functions.
Reproductive cells of an organism.
Possess 2 of every gene on two different
Half the number of chromosomes as the
chromosomes.
somatic cells.
Divide through the process of mitosis
Reproduce through the process of meiosi
Cellular Response to Radiation
Die before mitosis
Delayed mitosis
Failure to divide at normal mitotic rate
Total Body Response to Radiaiton
Acute Radiation Syndrome – full body exposure given in a few minutes.
3 stages of response:
1. Prodromal Stage: NVD stage
(nausea, vomiting, diarrhea)
2. Latent Period: Feels well while
undergoing biological
changes
3. Manifest Stage: Full effects felt,
recovery or death
3 Radiation Syndromes
Bone marrow syndrome: results in infection, hemorrhage & anemia
Gastrointestinal syndrome: results in diarrhea, nausea & vomiting, fever
Central nervous syndrome: results in convulsions, coma, & eventual death from increased
intracranial pressure.
WEEK 6 RADIATION BIOLOGY & PROTECTION RTEC A 2006
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Late Effects of Radiation
Somatic Effects: develop in the individual who is exposed
Most common: Cataract formation & Carcinogenesis
Genetic Effects: develop in future generations as a result of damage to germ cells.
PROTECTING THE PATIENT
THE PATIENT MUST BE EXPOSED TO IONIZING RADIATION FOR A DIAGNOSTIC
IMAGE TO BE PRODUCED.
RISK VS. REWARD
ALARA AS LOW AS REASONABLY ACHIEVABLE
The RADIOGRAPHER has the responsibility of maximizing
the quality of the radiograph while minimizing the risk to the patient
Cardinal Principles of Protection Triad of Radiation Safety
Time
Distance
Shielding
*Apply to the patient & Technologist
Time
The exposure is to be kept as short as possible because the exposure is directly proportional
to time. Over Radiation to Skin Too much time under beam
Shielding
A lead protective shield is placed between the x-ray tube and the individuals exposed
absorbing unnecessary radiation
Thickness of Lead Shielding
LEAD APRONS MUST BE:
0.25 mm of Pb or equivalent
GONAD SHIELDS:
0.50 mm of Pb or equivalent
Rules for Shielding
Patients radiosensitive organs must be shielded whenever the primary beam is within
4 to 5 cm of the reproductive organs.
TYPES OF SHEILDING
FLAT /CONTACT
SHAPED
SHADOW
Distance - Distance from the radiation source should be kept as great as possible
Physical Law: Inverse Square Law
Intensity is Spread Out
INVERSE SQAURE LAW FORMULA
More to come on
Inverse Square Law… next week