Test 1 Flashcards
Radiation that has the ability to make an atom a charged particle (remove an electron)
Ionizing radiation
Radiation in which electric and magnetic fields vary simultaneously (ex: x-ray, gamma rays, etc)
Electromagnetic radiation
What is the difference between x-rays and gamma rays?
X-rays come from Brems interactions (manmade); gamma from nucleus (natural)
A stream of atomic or subatomic particles that may be charged positively (ex: alpha particles), negatively (ex: beta) or not at all
Electrons don’t go as far as photons (superficial treatment); short travel range and don’t penetrate wall so don’t have to worry about shielding)
Particulate radiation
2 forms of ionizing radiation
Electromagnetic radiation
Particulate radiation
Plank’s equation
E=hv or E=hc/λ
Plank’s constant (h)
6.62 x 10^-34
6 types of electromagnetic radiation (from highest to lowest frequency)
Gamma rays Ultraviolet light Visible light Infrared light Microwaves Radio and television
7 types of visible light (from low to high frequency)
Red Orange Yellow Green Blue Indigo Violet (ROYGBIV)
Average wavelength (λ) (m) and frequency (v) (Hz) of gamma rays
λ = 10^-12 m v = 10^20 Hz
Average wavelength (λ) (m) and frequency (v) (Hz) of ultraviolet light
λ = 10^-8 m v = 10^17 Hz
Average wavelength (λ) (m) and frequency (v) (Hz) of visible light
λ = 10^-6 m v = 10^14 Hz
Average wavelength (λ) (m) and frequency (v) (Hz) of infrared light
λ = 10^-5 m v = 10^13 Hz
Average wavelength (λ) (m) and frequency (v) (Hz) of microwaves
λ = 10^-2 m v = 10^10 Hz
Average wavelength (λ) (m) and frequency (v) (Hz) of radio and television waves
λ = 10^2 m v = 10^6 Hz
Energy and frequency are ___________; energy and wavelength are _____________________
Proportional; inversely proportional
2 major groups of radiation in a therapy department
External beam
Brachytherapy sources
2 types of external beams
Linear accelerators (linacs) Cobalt-60
Machines that produce x-ray, gamma rays, and electrons; most popular
Ex: SRS/SBRT
External beams
Machines that emit gamma rays, x-rays, alpha, and beta particles
Ex: 137Cs, 192Ir, 125I
Brachytherapy sources
2 types of beams made by linacs based on what is being treated
Photon
Electron
3 categories of linacs based on types of energies (want different energies for different part thicknesses)
Low
High
Dual-energy (most common)
Cobalt-60 delivers gamma rays with dual-energies of what MeV, averaging what MeV?
1.7 and 1.33 MeV
Average = 1.25 MeV
Amount of energy delivered to tissue (keV/um)
Linear energy transfer (LET)
What is the charge, atomic mass number, and origin of alpha particles (a)?
Charge = +2
Atomic mass number = 4
Origin = nucleus
What is the charge, atomic mass number, and origin of negatrons (B-) (beta particles)?
Charge = -1
Atomic mass number = 0
Origin = nucleus
What is the charge, atomic mass number, and origin of positrons (B+) (beta particles)?
Charge = +1
Atomic mass number = 0
Origin = nucleus
What is the charge, atomic mass number, and origin of neutrinos (v)?
Charge = 0
Atomic mass number = 0
Origin = nucleus
What is the charge, atomic mass number, and origin of x-rays?
Charge = 0
Atomic mass number = 0
Origin = electron shells
What is the charge, atomic mass number, and origin of gamma rays (y)?
Charge = 0
Atomic mass number = 0
Origin = nucleus
Basically a helium nuclei that has been stripped of its two electrons
Emitted by heaviest nuclides/large unstable atoms that have a large amount of excess energy
Damage done with ingestion
Can be stopped by paper
Ex: uranium decays to produce daughters radium and radon
Alpha particles (a)
How many protons and neutrons do alpha particles have?
2 protons
2 neutrons
Alpha particles have a very _____ LET because it distributes all its energy when it hits
High
Can be positively or negatively charged Emitted from the nucleus; not natural, created through decay Have the rest mass of an electron Shielded best with plastics or glass Dependent on Z^2/mass^2 Greater Z = more photon production, small mass = more Brems Energy range = energy/2 In range = dissipated, 90% = shallow
Beta particles (B- or B+)
Rest mass of electrons and beta particles (B- or B+)
0.511 MeV
1 MeV beta particle has a range of _______ centimeters of tissue
2 cm
Similar to electrons but carry no charge; not affected by electromagnetic forces but by a “weak” subatomic force of much shorter range and are therefore able to pass through great distances in matter
Neutrino
No mass and no charge; manmade by Brems (85%) or characteristic (15%) interactions
X-rays
No mass and no charge; natural from nucleus
Gamma rays
What are photoelectric interactions dependent on?
Z^3/E^3
What are Compton interactions dependent on?
Electron density (why we can treat with radiation therapy; if it was photoelectric they’d all be absorbed by bone)
3 types of natural background radiation
Cosmic
Terrestrial
Internal exposure
What percent of human-absorbed radiation doses arise from natural background radiation?
82%
Radiation that reaches our planet from high-energy photon emissions beyond our atmosphere (sun/stars)
Atmosphere absorbs some of the emitted radiation before they reach the planet’s surface
Depends on location/height on earth
Cosmic radiation
What is the dose per year of natural background radiation?
1 mSv/yr + 2 mSv/yr radon = 3 mSv/yr
What is the dose per year of cosmic radiation?
26 mrem/yr = 0.26 mSv/yr
Radiation from earth; naturally occurring radioactive materials
Terrestrial radiation
What is the cosmic radiation dose in Denver compared to at sea level?
2 times as much in Denver than at sea level = 5mrem/0.5 mSv
What is the terrestrial radiation dose in the Rocky Mountains?
0.63 mSv
Accounts for 2/3 of natural background radiation
Second cause of lung cancer in the US
Can be found in cement in basements
Radon
What is the dose per year of terrestrial radiation (not including radon)?
16 mrem/yr = 0.16 mSv/yr
What is the dose per year from radon?
200 mrem/yr = 2 mSv
Naturally occurring radiation in the body
Internal exposure
What is the dose per year from internal exposure?
20 mrem/yr = 0.2 mSv
What is the radiation dose from man-made sources?
0.6 mSv
What is the radiation dose from medical sources?
0.5 mSv
What is the radiation dose from consumer products?
0.11 mSv
2 types of man-made sources of radiation
Medical
Consumer products
Amount of ionization produced by photons in air per unit mass of air, only applicable to photons while they interact with air
Exposure
Traditional and SI units of exposure
Traditional: Roentgen (R)
SI: Coulomb/kg of air
Unit of charge
Coulomb (C)
1 R = ? C per gram of air
2.48x10^-4 C per gram of air
The use of exposure is limited to photons with energies below what MeV?
3 MeV
Amount of energy absorbed per mass of any material while radiation interacts in the material
Absorbed dose
Traditional and SI units of absorbed dose
Traditional: rad
SI: gray (Gy)
2 units of energy
Erg
Joule (J)
1 rad = ? erg per gram of material
100 erg per gram of material
1 Gy = ? J per kg of material = ? rad
1 J per kg of material = 100 rad
1 Gy = ? rad = ? cGy
100 rad = 1 cGy
Product of absorbed dose and a quality factor, which takes into account the biological effects of different types of radiation
Dose equivalent
Traditional and SI units of dose equivalent
Traditional: rem
SI: Sievert (Sv)
Radiation weighting factor, specific to specific types of radiation; accounts for the biological effectiveness of the specific radiation
Quality factor (QF)
Rad x QF
rem
Gray x QF
Sievert (Sv)
1 Sv = ? rem
100 rem
Number of radioactive disintegrations (transformations) per unit of time; how quickly isotopes decay
Activity
Traditional and SI units of of activity
Traditional: curie (Ci)
SI: becquerel (Bq)
curie = ? disintegrations/second
3.7 x 10^10 disintegrations/second
1 Bq = ? disintegrations/second
1 disintegrations/second
1 Ci = ? Bq
3.7 x 10^10 Bq
What is the quality factor (QF) of x-rays and gamma rays (y), beta particles, positrons, and muons, and high energy external protons?
1
What is the quality factor (QF) of protons other than recoil protons and energy greater than 2 MeV?
2
What is the quality factor (QF) of thermal neutrons (slower)?
5
What is the quality factor (QF) of fast neutrons, alpha particles, and fission fragments other than heavy nuclei?
20
Higher quality factor = ________ dose
Higher
Detects the ionizations produced by the interactions in a gas, simplest measurement device
Sensitivity depends on the mass of the gas
Voltage affects ion saturation; if not enough voltage ions will reassemble and readings will be innacurate
Used for QA on linacs
Ionization chambers
What is the calibration of ionization chambers?
2%
What is the average voltage of ionization chambers?
200-300 V
2 types of gas-filled detectors
Ionization chamber
Geiger-Muller (GM) detector
Very sensitive to radiation, doesn’t measure dose
High voltage
Used for detection of contamination (detecting the presence of radioactive materials in areas or on surfaces where they aren’t wanted)
Geiger-Muller (GM) detector
Consists of crystal substance that when irradiated has electrons displaced in its crystal lattice
When the crystal is heated, the electrons return to their normal location (original energy states/valence bands) with the emission of characteristic energy that can be seen as light by using a detector
Dose stored for days or weeks, good personal monitor
More responsive than film, mimics tissue
Dose received is proportional to the radiation damage in the crystal
Thermoluminescent dosimeter (TLD)
3 materials TLDs may be made of
Lithium fluoride (Lif)
Lithium borate
Calcium fluoride
TLDs are accurate within what percent?
5%
What is the annealing process of TLDs?
Preheat TLD for 1 hour at 400 °C and at 24 hours at 80 °C to get rid of glow peaks
Inexpensive personnel monitor with different filters for different doses, depths, and radiation energy (ex: lead, tin, no filter)
Film badge
What is the deep and shallow dose of film badges in centimeters?
Deep = 1 cm Shallow = 0.0007 cm
What is the accuracy of dose readings of film badges?
+/-20 (inaccurate)
Film badges are more responsive to low energy with no response for ____ MeV or greater
10 MeV
Initially expensive, gas-filled dosimeter
Offers immediate readout
Used for infrequently exposed people
Have to charge it to zero it out or you could get false readings
Pocket dosimeter
2 neutron detectors
Rascal
Bubble counter
3 materials a rascal detector can be made of
Boron trifluoride (BF3)
Argon
Propane
How do you read a bubble counter?
5 bubble/mrem
Radiation is stored in this dosimter, then scanned by a laser and emits light
More sensitive than film
Uses filters to distinguish dose (deep, eye, etc.)
Personnel monitoring device commonly used today
Optically stimulated luminescence (OSL)
What is the OSL made of?
Aluminum oxide detector
What energy range do linacs use and at what energy are neutrons emitted?
Linacs use 8-18 MeV and neutrons are emitted at greater than 10 MeV
What shielding material is used for neutrons?
Borated polyethylene
Set standards; agencies authorized by congress to establish mandates and regulations that explain the technical, operational, and legal details necessary to implement laws
Regulatory agencies
Set exposure levels, voluntary regulatory agency
Reports cover all radiation-associated industries
National Council on Radiation Protection and Measurement (NCRP)
Regulatory agency that sets exposure levels
International Commission on Radiation Protection
2 regulatory agency that set exposure levels
National Council on Radiation Protection and Measurement (NCRP)
International Commission on Radiation Protection
Independent agency of the US government that’s charged with overseeing reactor safety, security, licensing, and renewal, radioactive material safety, and spent fuel management; responsible for isotope usage (need license for brachytherapy)
Nuclear Regulatory Commission (NRC)
Federal regulatory agency that licenses and okays linacs
Reviews radiopharmaceuticals and radiation-producing equipment (Title 21)
Food and Drug Administration (FDA)
Federal regulatory agency that governs shipment of radioactive materials (Title 49)
Department of Transportation
Administrative regulatory agency requiring employers to ensure safety of workers
Workplace safety and health
Regulations that relate to the use of radiation in regards to employees
Occupational Safety and Health Administration (OSHA)
Have a threshold for induction and severity increases with dose (ex: erythema, epilation, cataracts)
Have to reach threshold to see certain effects
Nonstochastic/deterministic effects
No induction threshold and are proportional to the dose received (ex: cancer, genetic effects, teratogenic effects)
Probability increases with dose, sensitivity doesn’t
Stochastic effects
Embryologic malformations; developmental effects
Effects on kids exposed in utero/fetus
Correlation: earlier trimester = greatest effect from radiation exposure
Teratogenic effects
Lethal effect of acute whole-body exposure in which 50% of the total population exposed is affected in 30 days
LD 50/30
What is the LD 50/30?
4.5 Gy (450 rads)
3 effects of radiation
Somatic/carcinogenesis
Genetic/mutagenesis
Developmental/teratogenesis
Effects that take place in the exposed individual
Somatic effects/carcinogenesis
Abnormalities occurring in future kids/subsequent generations
Exposure to gonads, usually presents as cancer
Genetic effects/mutagenesis
What is the chance of the exposed individual developing fatal cancer per rem due to low level exposure?
1 chance in 2500 of developing fatal cancer per rem due to low level exposure
There is no known threshold for genetic effects but models predict what occurance?
1 in 10,000 per rem occurrence
What can happen in the 1st 3 weeks if a fetus is exposed and what can happen after?
1st 3 weeks = failure to implant
After = different types of childhood cancers
Comparisons for radiation workers are made with workers in “safe” industries in which risk of injury is about 1 in 10,000 per year; because radiation-induced effects may exhibit a latent period, these comparisons are difficult
Comparable risk
Measure of the genetic risk to the population as a whole from exposure to ionizing radiation to some or all members of the population
Dose that, if received by every member of the population, would be expected to result in the same total genetic effect on the population as the sum of the individual doses
Gives measurement of what general risk can take place from exposure in a population
Takes natural and manmade radiation into account
Genetically significant dose (GSD)
Lifetime cancer rise for acute whole body exposure to low LET radiation
8 in 10,000 per rem (8 per 10,000 people per rem)
Effective dose equivalent limit (stochastic effects) of annual occupational exposures
50 mSv (5 rem)
Dose equivalent limits for tissues and organs (nonstochastic effects) of lens of the eye of annual occupational exposures
150 mSv (15 rem)
Dose equivalent limits for tissues and organs (nonstochastic effects) of all others (ex: red bone marrow, breast, lung, gonads, skin, and extremities) of annual occupational exposures
500 mSv (50 rem)
Cumulative exposure
10 mSv x age in years (1 rem x age in years)
Planned special occupational exposure, effective dose equivalent limit and guidance for emergency occupational exposure
50 mSv (5 rem)/year
Annual public exposure effective dose equivalent limit, continuous or frequent exposure
1 mSv (0.1 rem)
Annual public exposure effective dose equivalent limit, infrequent exposure
5 mSv (0.5 rem)
Effective dose equivalent when remedial action is recommended
> 5 mSv (>0.5 rem)
Remedial action recommended exposure to radon and its decay products
> 0.007 Jhm^-3 (>2 WLM)
Annual public exposure dose equivalent limits for lens of eye, skin, and extremeties
50 mSv (5 rem)
Effective dose equivalent limit for annual education and training exposure
1 mSv (0.1 rem)
Dose equivalent limit for lens of eye skin, and extremities for annual education and training exposure
50 mSv (5 rem)
Total dose equivalent limit for embryo-fetus exposures
5 mSv (0.5 rem)
Dose equivalent in a month for embryo-fetus exposures
0.5 mSv (0.05 rem)
Negligible individual risk level (annual) effective dose equivalent per source or practice
0.01 mSv (0.001 rem)
3 major rules
Time (Cobalt-60 machine examples)
Distance (inverse square law)
Shielding (HVL)
Exposure from a Cobalt-60 machine must be less than ____ mR/hr at any point one meter from the source; if the average exceeds ____ mR/hr it’s outside of limit (shielding not working)
10 mR/hr; 2 mR/hr
Thickness of absorbing material necessary to reduce the x-ray intensity to half its original value
Half-value layer (HVL)
Most dense shielding material (written in mm versus others in cm)
Lead
Number of patients per week times the amount of radiation for each (cGy/week or rad/wk)
Time interval of the absorbed dose rate (cGy/min or rad/min) determined at the depth of the maximum absorbed dose, 1 meter from the “source”
Workload (W)
Fraction of time the primary beam is aimed at a particular wall
Use factor (U)
Fraction of time the shielded space is occupied
Occupancy factor (T)
Percent of radiation transmitted through the wall, ceiling, etc. Helps determine HVL
Transmission factor (B)
Permissible dose (P) of a controlled area
0.1 cGy/wk
Permissible dose (P) of an uncontrolled area (don’t control who is going in and out of space)
0.01 cGy/wk
