lecture 7 radiation saf

0.5 mm lead apron reduces exposure by at least a factor of [...] 

10 

A [...] usually disrupts many molecular bonds and produces visible chromosomal damage

hit

Acute deterministic radiation syndromes include? [...]

Local tissue damage, Hematologic depression and cytogenic damage

Acute Radiation Lethality

• Mega-radiation levels – like Hiroshima or Chernobyl
  

  • LD 50/30 is the lethal dose to kill 50% of the population in about 30 days

    • Humans LD is [...] to [...] rads 

• 300 to 400 rads 

Acute Radiation Lethality

• Less than 100 dose (rad) is not lethal

• More than 100 is [...] death

• More than 1,000 is [...] death

• More than 10,000 is [...] death 

1. hematologic

2. gastrointestinal

3. central nervous system

   
   look at stages below

   
   

   

Age

• Highest risk is [when?]
  

  • Younger patients have more rapidly dividing cells and higher metabolic rates so they are associated with more radiation damage 

• Increases again when you get older

before birth

Age

• Law of Bergonie & Tribondeau
  

  • Greater maturity of cells (adulthood) increases resistance against radiation

  • Things that increase radiosensitivity (all associated with childhood)

    • Increased [...]

    • Increased [...]

    • Increased [...] 

1. metabolic activity

2. cell proliferation rate

3. tissue growth rate 
   
   

   

ALARA stands for [...]

As Low As Is Resonably Achievable

All unnecessary exposure must be avoided and all absorbed doses be kept [...]

As Low As Is Resonably Achievable

Anoxic environments are [...]

more protected from radiation

Average dose for extremity exam of hand or foot is [...] mSv 

0.001 mSv

Biologic tissue is [more or less] sensitive under aerobic conditions 

more

Biological tissue is more sensitive under [...]

aerobic conditions

Cataract Formation

• Acute threshold
  

  • Probably about [...] Gy

• Fractionated threshold
  

  • As high as [...] gy

  • Indicates fractionating the dose (breaking up the dose over a set period of time) is safer for cataracts

• Latent period
  

  • 15 year average (but reported from 5 to 30 years)

  • May be dose related – 8 years following 2.5 to 6.5 Gy doses 

1. 2 Gy

2. 10 Gy

• Latent period
  

  • [...] year average (but reported from 5 to 30 years)

  • May be dose related – [...] years following 2.5 to 6.5 Gy doses 

1. 15

2. 8

Cataract Formation

• lens radiosensitivity is [dependent on what]

• Len shield is not necessary usually, unless working with fluoroscopy 

age dependent

• Len shield is not necessary usually, unless working with [...] 

• fluoroscopy 

greater effect and shorter latent period with older age
different effect than normal (old age usually protects you)

Cataract Formation

• [what type of effect?] 

• [threshold?]

• [linear?] 

• Deterministic 

• threshold

• nonlinear 

Cataract Formation

• [greater or lesser] effect and [longer or shorter] latent period with older age 

1. greater

2. shorter

• [...] 

  • halogenated pyrimidines

• [...] 

  • contains -SH- group which competes with O2 for free radical binding

• Protects the patient 

1. Radiosensitizers 

2. Radioprotectors 

Congenital abnormalities

• [...]% increase in congenital abnormalities from the normal averages following a 100 mGy  (10 rad) fetal dose
  

  • Normally, 5% of all live births exhibit congenital abnormality

1%

Lower than 1% increase if the dose is lower 

Cytogenic Damage

• 2 types
  

  • [...]

    • At very low radiation doses

    • Linear 

    • non-threshold 

    • dose-response

  • [...] – the most significant latent human damage

    • At high doses: frequency increases when dosages increase 100 rad

    • Nonlinear

    • non-threshold

    • dose response

    • Results in

      • Rings – from multi-damage on the same chromosome

      • Dicentrics – reciprocal translocations from adjacent hits

1. single hit

2. multi hit aberrations

Cytogenic Damage

• 2 types
  

  • Single hit

    • At very low radiation doses

    • [linear or nonlinear] 

    • [threshold?] 

    • [dose response?]

  • Multi hit aberrations – the most significant latent human damage

    • At high doses: frequency increases when dosages increase 100 rad

    • [linear or nonlinear]

    • [threshold?]

    • [dose response?]

    • Results in

      • Rings – from multi-damage on the same chromosome

      • Dicentrics – reciprocal translocations from adjacent hits

• Linear 

• non-threshold 

• dose-response

• Nonlinear

• non-threshold

• dose response

• [...] – from multi-damage on the same chromosome

• [...] – reciprocal translocations from adjacent hits

• Rings

• Dicentrics

Cytogenic Damage

• Damage is usually manifest during the next cellular mitosis 
  

  • Significant radiation damage can cause chromosomal aberrations in the next 1 to 2 cell divisions (therefore is [what type of] effect) 

an acute deterministic

Cytogenic Damage

• Damage
  

  • [threshold?] 

  • [dose-response?] 

  • Damage is difficult to identify with low doses (less than 5 rads) 

• Non-threshold 

• dose-response 

• (any amount of damage will produce an effect)
  

  
  

  

Cytogenic damage of acute determinisitic effects we can infer genetic changes, however we are only actually [...]

looking at the physical structure change to DNA

Data from Mega-mouse experiments

• Doubling dose
  

  • Found the doubling dose for genetic mutation was much [higher or lower] in mice than fruit flies. Since mice are more comparable to humans, this mean the doubling dose is more like [...] or [...].

• higher

• 100 or 200

Governmental standards did not change however since the world was already used to the 5 rad limit, why increase it.  

Data from Mega-mouse experiments

• Pertinent conclusions
  

  • A dose of 1.0 rem per generation increases the natural of spontaneous mutation rate by approximately [...]%

• 1%

Even though 1.0 rem is a lot of radiation, it actually caused a 1% increase in mutation which is not a lot 

Data from Mega-mouse experiments

• Pertinent conclusions
  

  • Most mutations are harmful

  • Any dose of radiation, however, small, entails some genetic risk

  • Number of mutations are proportional to dose

    • Linear extrapolation from high dose is a [valid or invalid] estimate of low-dose effects

valid

Data from Mega-mouse experiments

• Substantial dose rate effect
  

  • Since mice, like us, have an ability to heal (unlike fruit flies)

  • Same dose administered over a period of time results in [more or fewer] mutations than an acute exposure

  • Dose rate effect in gonads

    • Chronic irradiation is considerably less effective in inducing mutations in spermatogonia and oocytes

    • greater in females (oocytes > spermatogonia)

      • Indicates why spermatogonia are more radiosensitive; because they can’t heal as fast as oocytes

  • Absolute frequency of radiation induced genetic mutations are very low

fewer

Data from Mega-mouse experiments

• Substantial dose rate effect
  

  • Since mice, like us, have an ability to heal (unlike fruit flies)

  • Same dose administered over a period of time results in fewer mutations than an acute exposure

  • Dose rate effect in gonads

    • Chronic irradiation is considerably [more or less] effective in inducing mutations in spermatogonia and oocytes

    • greater in females (oocytes > spermatogonia)

      • Indicates why spermatogonia are more radiosensitive; because they can’t heal as fast as oocytes

  • Absolute frequency of radiation induced genetic mutations are very low

less

Data from Mega-mouse experiments

• Substantial dose rate effect
  

  • Since mice, like us, have an ability to heal (unlike fruit flies)

  • Same dose administered over a period of time results in fewer mutations than an acute exposure

  • Dose rate effect in gonads

    • Chronic irradiation is considerably less effective in inducing mutations in spermatogonia and oocytes

    • greater in females (oocytes > spermatogonia)

      • Indicates why spermatogonia are more radiosensitive; because they can’t heal as fast as oocytes

  • Absolute frequency of radiation induced genetic mutations are very [high or low]

low

Decrease age of tissue/organs = [...]

increase radiosensitivity

Deterministic effects aka Nonstochastic effects 

• Linear threshold curve

• Sigmoid threshold curve

• Linear quadratic threshold curve
  

  • Linear at first but becomes quadratic (exponential) at higher doses

  • Examples:

    • [...]

    • [...]

    • [...] 

• Leukemia

• Breast cancer

• Heritable damage 

Distance

• Scatter is generally [...]% of beam entrance skin intensity at 1.0 meter (about 3 feets) 

0.1%

Meaning that that the intensity of the scatter is 1/1000th of what it is at the source of the scatter if you get 1 meter away (about 3 feet)

SO most effective means of protection from scatter radiation is distance (for the clinician at least, it doesn’t reduce scatter radiation, just prevents it from hitting you)

Earliest sign of radiation injury is [...]

erythema

Estimates

• [...]
  

  • Slope of linear dose response

• [...]
  

  • Observed cases – expected cases

• [...]
  

  • Observed cases : expected cases

• Absolute risk

• Excess risk

• Relative risk

Relative risk

Ex: if I expect to see 10 cases of a given cancer, but I see 30, then that’s a 3:1 ratio increase in relative risk 

Estimates

• Absolute risk
  

  • Slope of linear dose response

• Excess risk
  

  • [...] cases – [...] cases

• Relative risk
  

  • [...] cases : [...] cases

• Observed cases – expected cases

• Observed cases : expected cases

Relative risk

Ex: if I expect to see 10 cases of a given cancer, but I see 30, then that’s a 3:1 ratio increase in relative risk 

Exposure reduction principles

1. Minimize [...]

2. Maximize [...]

3. Employ [...] 

1. time

2. distance

3. shielding

Exposure time

• Exposure rate x time

• Scatter exposure rate expressed in [...] 

mR/hr 

Factors affecting scatter

• Field size = (irradiated voxel)²

• This is something we can actively control by using [...]

• proper collimation

• Increasing area the x-ray beam can come out of, increases the dimensions of the x-ray beam and increases the field size

• Purpose of collimation

  • Lowers patient dose by restricting the volume of irradiated tissue

  • Safe and improves image contrast by decreasing scatter

Factors affecting scatter

• Field size = ([...])²

• This is something we can actively control by using proper collimation

irradiated voxel

• Increasing area the x-ray beam can come out of, increases the dimensions of the x-ray beam and increases the field size

• Purpose of collimation

  • Lowers patient dose by restricting the volume of irradiated tissue

  • Safe and improves image contrast by decreasing scatter

Factors affecting scatter

• Orientation of body part and tube – you want the body part to be [...] 

parallel 

Factors affecting scatter

• Thickness of body part
  

  • [thicker or thinner] body parts have more scatter radiation

Thicker

Foot is pretty thin but the ankle might give off some scatter

Abdomen is thick and gives off a lot of scatter

Fetal Effects

• 1st trimester is the most sensitive!

• High risk of prenatal death, congenital deformities and neonatal death

• Risk of [...] extends to the 2nd trimester 

leukemia

Fetal Effects

• [...] trimester is the most sensitive!

1st

Fetal exposure

• 2nd to 10th week = period of [...]
  

  • If radiation dose is sufficiently high:

    • Temporary growth retardation

    • Early in the period = severe skeletal anomalies

    • Later in the period = congenital abnormalities 

major organogenesis

Fetal exposure

• 2nd to 10th week = period of major organogenesis
  

  • If radiation dose is sufficiently high:

    • [...]

    • Early in the period = [...]

    • Later in the period = [...] 

• Temporary growth retardation

• Early in the period = severe skeletal anomalies

  

• Later in the period = congenital abnormalities 

Fetal exposure

• After 10th week = period of [...]
  

  • Functional CNS disorders

    • Mental retardation

      • ~4% chance of occurrence per 10 Rads (0.1 Sv)

  • Structural CNS disorders

    • Microcephaly

  • Permanent growth retardation is likely 

CNS development

Fetal exposure

• After 10th week = period of CNS development
  

  • Functional CNS disorders

    • [...]

      • ~4% chance of occurrence per 10 Rads (0.1 Sv)

  • Structural CNS disorders

    • [...]

  • Permanent growth retardation is likely 

• Mental retardation

• Microcephaly

• Mental retardation

  • [...]% chance of occurrence per 10 Rads (0.1 Sv)

~4%

Fetal exposure

• First two weeks
  

  • High dose (250 mG)

    • Results in [...] or [...]

  • Low does

    • Increased normal incidence of spontaneous abortion by only [...]%

      • Normal incidence is about 25 to 50%

      • Very LOW rate

• resorption of embryo or spontaneous abortion & death

• 0.1%

Fetal Risks

• Below 50 mGy
  

  • [...]

• Between 50 to 100 mGy 

  • [...]

• After 100 mGy
  

  • [...] effects

  • [...] during organogenesis (2nd to 10th weeks)

  • [...] (8th to 15th weeks) 

• Probably no risk of embryonic death or major malformation during organogenesis (2nd to 10th week)

• Deterministic

• Malformations

• Microcephaly/mental defects

Fluoroscopy & Basic Operator Safety

• Distancing and Positioning
  

  • One step back from the table cuts down exposure rate by a factor of [...]

• Shielding
  

  • 0.5 mm lead apron attenuates scatter factor by a factor of [...] 

• 4

• 20

Fluoroscopy & Basic Operator Safety

• Good rule of thumb:
  

  • Getting 1 feet away from the table decreases the dose by [...]

  • Getting 1 meter away decreases dose by [...] 

• 100

• 1000

Fluoroscopy & Basic Operator Safety

• Orientation of the image intensifier can change the location of the scatter radiation
  

  • [...] dose reduction on intensifier side with lateral fluoroscopy 

5x

Fluoroscopy & Basic Operator Safety

• Time
  

  • Use [...] whenever possible

  • Use [...] fluoroscopy (if designed to reduce dose

  • Use [...] only when permanent record is required

  • Do not expose patient unless [...] is viewing image 

• freeze frame (last image hold)

• pulsed

• record mode

• physician

Fluoroscopy & Basic Operator Safety

• Where should you stand?
  

  • Most of the scatter radiation is by the [...] so you should stand by the [...] 

• x-ray tube

• x-ray intensifier 

Genetic Mutations

• Data from drosophila (fruit fly studies)
  

  • [linear?] non-threshold curves

  • [dose rate?] according to fruit fly data

    • Meaning genetic effects are cumulative; doesn’t matter if it’s a little or a lot or spread out over time

  • Doubling dose from 5 to 150 rads!

    • Meaning the natural mutation rate is doubled in as little as 5 rads 

• Linear

• No “dose rate” effect

• Doubling dose from [...] to 150 rads!

  • Meaning the natural mutation rate is doubled in as little as [...] rads 

5

5

Greater maturity of cell = [...]

increase resistance

High dose non-specific lifespan shortening groups have [...]

decrease parenchymal cells, decrease in number of fine blood vessels, and increase density of connective tissue

H_T = quality factor in [what unit?]

Rems (not rads)

In fluoroscopy where is safer to stand on the image intensifier side or xray tube side? [...]

Image intensifier
Scatter radiation is higher at the tube side

In terms of gonads [...] will decrease the number of spermatozoa, [...] temporary sterility, [...] permanent sterility

• 10 rads

• 200 rads

• 500 rads

Increase cell proliferation rate = [...]

increase radiosensitivity

Increase metabolic activity = [...]

increase radiosensitivity

Increase tissue growth rate = [...]

increase radiosensitivity

Irradiation of macromolecular solutions

Produces many smaller molecules and viscosity decreases describes which irradiation type? [...]

Produces side chains that become sticky, and the viscosity increases describes which irradiation type? [...]

Considered to be the primary mechanism of cellular damage from low dose of radiation accounting for late effects of radiation describes which radiation type? [...]

• Main Chain Scission

• Cross-linking

• Point Lesions

Is radiation an effective cancer-causing agent?

• [...]

• No! It is not highly effective

For about 300 A-bomb survivors, only one died due to malignancy 

Lead glass

• [...] mm lead equivalent

• The shield should be double the thickness of lead
  

• Lead glass used bc by law, you should be able to see the patient the entire time 

1.5 mm

Lead safety garments

• [...] mm lead typical for primary beam

• [...] mm lead for secondary beam

• All gonadal shields should have at least [...] mm of lead

• .5

• .25

• .5

Life span Shortening

• Since 1965, radiologic occupations are safe. Mortality is the same as the general population

• Currently, we might lose about [...] days due to dealing with radiation

• Linear 

• non-threshold 

• does response 

12

Life span Shortening

• Since 1965, radiologic occupations are safe. Mortality is the same as the general population

• Currently, we might lose about 12 days due to dealing with radiation

• [linear?] 

• [threshold?] 

• [dose response?] 

• Linear 

• non-threshold 

• does response

Major forms of DNA damage

• Main chain scission
  

  • One side rail

    • [can it be repaired]

    • Mis-repair possible via [...]

  • Both side rail

    • [can it be repaired] & can result in [...]

• Main chain scission with cross-linking

• Rung breakage
  

  • Simple

    • 2 nitrogenous bases separated by an ionizing event

    • Typically reparable

  • Base separation/loss of base

    • Typically irreparable

    • Results in a frame shift

• Often quickly repaired

• point mutation

• Generally irreparable & can result in frame shift

• Rung breakage
  

  • [...]

    • 2 nitrogenous bases separated by an ionizing event

    • Typically reparable

  • [...]

    • Typically irreparable

    • Results in a frame shift

• Simple

• Base separation/loss of base

• • Simple

    • 2 nitrogenous bases separated by an ionizing event

    • Typically reparable

  • Base separation/loss of base

    • Typically irreparable

    • Results in a [...]

frame shift

Maximum permissible dose (MPD)

• Cumulative lifetime limit
  

  • [...] rem (10 mSv) x age

  • Ex: if you’re 20 years old, your exposure limit is [...] rems

• Got rid of MPD in 1990 and began to use effective dose limits 

• 1 rem

• 20 rems

Miscellaneous statistics

• Newborns are 3 times [more or less] radiosensitive for cancer than a 25 year old

• 70 year old’s are about 3 times [more or less] radiosensitive than a 25 year old 

• more

• less

Most medical procedures result in a [...] dose distribution within the patient

nonuniform

Most to least cells sensitive to radiation

1. [...]

2. [...]

3. [...]

4. [...]

5. [...]

6. [...]

7. [...]

8. [...]

9. [...]

10. [...] 

1. Lymphocytes

2. Erythroblasts (a lot of these are in red bone marrow)

3. Myeloblasts

4. Spermatogonia/oocytes

5. Endothelial cells

6. Epithelial cells

7. Bones

8. Nerve

9. Brian

10. Muscle

Multi-hit chromosomal aberration are considered to be the most significant in terms of [...]

latent human damage

Observed / Expected cases = [...]

Relative Risk

Observed cases - Expected cases = [...]

Excess risk

Occupational dose monitoring is required when there is any likelihood that an individual will receive more than [...] the recommended dose limit

1/10

Occurs at very low radiation doses. In the G1 phase of the cell cycle, produces chromatid deletion. Replication during S-phase of mitosis. This describes which cytogenic damage? [...]

Single hit chromosomal abberations

Occurs in higher dose greater than 0.5Gy, generally results from cell death or organ atrophy. Describes those for which incidence and severity depends on dose, but for which there is a threshold dose? [...]

Nonstochastic Effects

Occurs in lower doses less than 0.5Gy. Severity of effect is independent of the dose. Usually no threshold to damage. As dose increases chance of occurrence increases describes? [...]

 Non-Deterministic Effects

Once above [...] kVp , you have to put lead in the walls :/

70 kVp

One step back from table can cut exposure rate by a factor of [...]

4

OSLD is [...] can read as low as [...]

• most sensitive

• 1 mrem (0.0001 rem) 

Ovaries

• Pre-puberty radiation
  

  • [...]

  • [...]

• Post-puberty irradiation: (same numbers as the testes)
  

  • As little as 10 rads can cause delay or suppression of menstruation

  • 200 Rads – temporary sterility

  • 500 Rads – permanent sterility 

• Germ cell death

• Ovarian atrophy

• Post-puberty irradiation: (same numbers as the testes)
  

  • As little as [...] rads can cause delay or suppression of menstruation

  • 200 Rads – [...]

  • 500 Rads – [...] 

• 10 rads

• 200 Rads – temporary sterility

• 500 Rads – permanent sterility 

Overall lifetime cancer risk increases about [...]% for every 10 rad ([...]% natural incidence) 

• 1% for every 10 rad (33% natural incidence) 

Overall Quantitative Radiation-Induced Cancer risks  -- BEIR committee Report

• A single exposure to a lot of radiation (10 rads) [does or doesn't] result in as much excess mortality as does continuous exposure to low doses (1 rad, or 100 mrads)

doesn’t

This describes occupational hazard of the clinician 

Overall, females are about [...]% [more or less] radiosensitive to cancer than males

• Breast, lung cancer

70% more

Oxygen effect

• Biologic tissue is more sensitive under aerobic conditions

• Oxygen Enhancement Ratio (OER) = [...] dose / [...] dose
  

  • Always takes less radiation to cause damage in an aerobic environment so OER will always be [positive or negative]

  • OER is LET (linear energy Transfer) dependent – inverse relationship

    • Greatest for low-LET – max at 3.0

    • About 1.0 for high-LET radiations

    • X-rays are low LET

    • Heavier radiation like alpha particles are high-LET 

• anoxic dose / aerobic dose

• positive

• OER is LET (linear energy Transfer) dependent – [direct or inverse] relationship

inverse

Oxygen effect radiation is dependent on [...]

Linear energy transfer