exam 3- radiation protection pt 1

§Gamma rays are always higher energy than x-rays. §A. True B. False

false they are the same

relationship between time and exposure

1:1 relationship §This means ½ the time = ½ the exposure

1 R = ______ C/kg

2.58 x 10^-4

1 Ci = ____ Bq

3.7 x 10^10 Bq

what is the threshold for ioniziation in keV

1 keV

§Which photon might contribute to fog? §A. 1 §B. 2 §C. 3 D. 4

B. 2

§Which type(s) of diagnostic imaging are considered ionizing radiation? §A. MRI §B. Ultrasound §C. CT §D. A and C E. All of the above

CT

§What is the largest source of man-made radiation exposure on average in the US? §A. CT scans §B. Nuclear medicine §C. Radiography §D. Nuclear fallout

CT scans

§Historical: Roentgen (R) SI: ?

Coulombs/kilogram (C/kg)

§How many Becquerel (or disintegrations per second) are there in 1 Ci of F-18? §A. 2.58 x 104 §B. 2.58 x 1010 §C. 3.7 x 104 D. 3.7 x 1010

D. 3.7 x 1010

§What is the primary purpose of filtration? §A. To improve image quality §B. To produce characteristic X-rays §C. To increase beam energy D. To reduce patient dose

D. To reduce patient dose

§Which of the following is not an effective way to reduce radiation exposure? §A. Time §B. Distance §C. Shielding §D. Wear your dosimeter

D. Wear your dosimeter

§A standard chest radiograph is roughly equivalent to which of the following exposure levels? §A. 2.7% of the average U.S. annual background dose §B. 10 days BERT §C. A transatlantic flight D. All of the above

D. all of the above

unit for absorbed dose

Gray (Gy) 1 rad = 1 Gy 1 Gy = 1 J/kg

§Which of the following will reduce your exposure the most? §A. Cut your time in the room in half §B. Double your distance from the radiation source §C. Put 1 HVL of shielding between you and the source D. Put 1 TVL of shielding between you and the source

Put 1 TVL of shielding between you and the source

RAM vs RGE

RAM: radioactive materials - nuclear medicine, brachy, gamma knife (Co-60) RGE: radiation generating equipment - diagnostic radiography and fluoro, therapy linac and OBI

what does scattered photons do to images and the patient

Scattered photons can lead to fog in the image as well as radiation exposure beyond the primary beam

§Techniques to reduce the noise and fog effects of these photons on image quality include:

air gap techniques and grids

Mass density (ρ) has an effect on attenuation at what kind of energies

all

Thickness has an effect on attenuation at what kind of energies

all

§The proper way to assure minimum exposure in a diagnostic imaging procedure is to start with the minimum mAs and kVp and increase them gradually until the resulting image is acceptable. T or F

false

image quality, patient dose, and scatter are all dependent on

beam energy and intensity

§Which of the following types of particulate radiation is most commonly encountered in medicine? §A. Alphas §B. Betas §C. Protons D. Neutrons

beta

§Which interaction results in excitation of the tissue atom but not ionization? §A. Compton §B. Photoelectric §C. Classical §D. Pair Production

classical

§During a typical exam the dose to the radiographer is most likely to be caused by which of the following interactions? §A. Classical §B. Compton C. Pair Production

compton

primary interaction that produces scatter radiation

compton scatter

equation to determine mAs (intensity)

current x exposure time

§Photons that pass through without interacting are called:

direct transmission create the image

§Microwaves are what type of radiation?

electromagnetic

examples of particulate radiation

electrons (beta) protons neutrons alpha particles (He nucleus)

relationship between exposure and distance

exposure = 1/(distance)^2 §This means doubling your distance divides your exposure by 4 §Also know as the "inverse square law"

If a facility does not possess or use radioactive materials, they do not have to worry about exposure limits or the ALARA principle. T or F

false

§A microwave oven produces ionizing radiation. §A. True B. False

false

§Non-ionizing radiation has no potential negative health effects. §A. True §B. False

false

§Photodisintegration is a common interaction in diagnostic radiography. §A. True B. False

false

which particulate radiation has the highest mass? lowest?

highest: alpha particles lowest: electrons

secondary source of radiation - leakage

leakage radiation §X-rays produced by the x-ray tube that are not in the direction of the useful beam §Shielded by x-ray tube housing §Limited to 0.1% of primary beam @ 1 m by FDA regulations §Is a potential source of personnel exposure §Source is the x-ray tube

Atomic number (Z) has an effect on attenuation at what kind of energies

low energies (photoelectric effect)

§Which of the following involves an inner shell interaction and total absorption of the photon? §A. Classical §B. Compton §C. Photoelectric §D. Photodisintegration

photoelectric

§What is the largest source of natural background radiation for most of the U.S. population? §A. Cosmic rays §B. Terrestrial radiation §C. Radon gas D. Bananas

radon gas

effective dose indicates risk for what kind of effects

stochastic effects (primarily cancer)

the three principles to reduce exposure to radiation

time distance shielding

BERT is a way to express exposure levels in a way that may help reassure patients and make it easier to understand. T or F

true

§Prior to 1990, natural background sources of radiation contributed more than half of the total exposure to radiation in the United States. §A. True B. False

true

the largest benefit vs risk ratio is achieved by

using the smallest radiation exposure that will produce useful images and by producing optimal images with the first exposure

relationship between shielding and exposure

§1 HVL (half-value layer) - reduces exposure to 1/2 §1 TVL (tenth-value layer) - reduces exposure to 1/10

§Which unit is appropriate for expressing the exposure, in air, of a radiography exam? §A. Roentgen §B. Gray §C. Sievert §D. Curie §E. None of the above

§A. Roentgen

how to find annual effective dose given an absorbed dose

§Absorbed dose x radiation weighting factor = equivalent dose §Equivalent dose x tissue weighting factor = effective dose ex: §Assume an annual absorbed dose of 1 mGy to the lungs from radon gas. What is the annual effective dose? §Equivalent dose §wr for alpha particles is 20 §1 mGy x 20 = 20 mSv §Effective dose §wt for lung is 0.12 20 mSv x 0.12 = 2.4 mSv

effective dose accounts for what

§Accounts for the type and amount of tissue irradiated as well as the type of radiation

ALARA

§As Low As Reasonably Achievable §Must show reasonable steps have been taken to limit exposure to patients, staff, and the general public

§What is attenuation?

§Attenuation is the loss of photons due to interactions as they pass through matter. §Attenuation includes: §Absorption (the entire photon is absorbed) and §Scatter (the photon changes direction and may deposit a portion of its energy)

what is the average x ray energy

§Average X-ray energy will be closer to kVp/3, or 33 keV

§Which unit is appropriate for expressing the absorbed dose to a patient from a 6 MV photon therapy beam? §A. Roentgen §B. Gray §C. Sievert §D. Curie E. None of the above

§B. Gray

§Beam Hardening average energy after passing through filter

§Because lower energy photons have a higher probability of interaction, the exit dose always has higher average energy than the entrance dose

units for activity

§Becquerel (Bq) §1 Bq is one disintegration per second (dps) Quantifies the total amount of radioactivity

Radioactive materials (RAM)

§Byproducts of nuclear reactors §Regulated by the NRC and through agreement states §Produced by particle accelerators Produce a spectrum of gamma rays based on decay properties

§1.02 MeV is required for which interaction? §A. Compton §B. Photoelectric §C. Pair Production D. Photodisintegration

§C. Pair Production

§Which unit is appropriate for expressing the effective dose to a radiation worker from an accidental exposure? §A. Roentgen §B. Gray §C. Sievert §D. Curie §E. None of the above

§C. Sievert

§Which unit is appropriate for expressing the equivalent dose to a patient from a CT scan? §A. Roentgen §B. Gray §C. Sievert §D. Curie §E. None of the above

§C. Sievert

§Some of the consequences of ionization in human cells

§Creation of unstable atoms §Production of free electrons §Production of low-energy x-ray photons §Creation of reactive free radicals capable of producing substances poisonous to the cell §Creation of new biologic molecules detrimental to the living cell §Injury to the cell that may manifest itself as abnormal function or loss of function

how are diagnostic images formed

§Diagnostic images are formed by photons that pass through the patient without interacting

§Photodisintegration

§Does not occur at diagnostic energies §Neutron production becomes a concern in radiation therapy above ~10 MeV

§Pair Production

§Dominant at energies > ~25 MeV §Requires photon energy > 1.022 MeV §Contributes to dose in radiation therapy

§Photoelectric Absorption

§Dominant interaction < ~25 keV §Contributes to contrast in diagnostic imaging §Primary source of contrast in mammography §Highly Z and E dependent §~ Z^3/E^3 §Characteristic x-rays

§Compton Scattering

§Dominant interaction between ~25 keV and ~25 MeV §Contributes to contrast in diagnostic imaging §Primary source of contrast in CT §Radiation therapy dose §Depends on physical density §Relatively independent of Z and E §Characteristic x-rays

§Which unit is appropriate for expressing the exposure, in air, of a 6 MV photon therapy beam? §A. Roentgen §B. Gray §C. Sievert §D. Curie §E. None of the above

§E. None of the above

definition of radiation protection

§Effective measures employed by radiation workers to safeguard patients, personnel, and the general public from unnecessary exposure to ionizing radiation This is any radiation exposure that does not provide a medical benefit

energy (beam quality) of primary radiation

§Energy of electrons determines "peak" energy of X-rays §kVp - peak accelerating voltage §100 kVp translates to a peak electron energy of 100 keV

§Total effective dose equivalent

§Essentially the sum of all sources of radiation exposure (external and internal, natural and man-made) §Designed to give an estimate of an individuals total radiation exposure from all sources §Regulatory limits are imposed by NRC

what does filtration due to energy of beam

§Filtration changes the spectrum §"Hardens" the beam §Removes low energy X-rays §Produces characteristic X-rays

x ray beam production in x ray tube

§High-speed electrons produced by a filament (thermionic emission) §Negatively charged (cathode) §Electrons strike target §Positively charged (anode) §Most commonly tungsten §High melting point and high "Z" §X-rays are produced §Via bremsstrahlung §X-rays exit tube through window §Typically pass through metal filter

Photons that scatter may still hit the imager. Such photons are called:

§Indirect transmission §These photons contribute to noise or "fog"

sources of ionizing radiation

§Internal - Naturally occurring radioactive isotopes in food (e.g. K-40 in bananas) §Cosmic - Radiation from cosmic rays that penetrate the atmosphere §Terrestrial - Radioactive isotopes in soil or building materials §Air - Naturally occurring radioactive gases that are inhaled (principally radon) man made- CT, nuclear medicine, radiography, interventional

C/kg applies to only what kind of photons

§Is a measure of the number of ion pairs created in air §Is only defined for photons <3 MeV in air

what is the leakage radiation regulation by the FDA

§Limited to 0.1% of primary beam @ 1 m by FDA regulations

§Classical (Coherent) Scattering

§Occurs mostly at low energies (< 25 keV) §Can contribute to scatter (fog) in imaging §No energy is lost §Does not affect dose

§Entrance skin exposure

§Often referred to simply as "patient dose" in radiography §Can be measured with TLDs §Can also be estimated from nomogram §Units are mR

importance of patient education for their protection

§Patient's should be informed of the type of procedure they are to undergo and what it entails §They should also be informed of any follow-up required §When radiation is involved it is also important to be able to answer concerns about the radiation exposure involved in the procedure

definition of absorbed dose

§Radiation dose to the patient comes from photons that interact with the patient The energy absorbed by the patient from these interactions is called: absorbed dose

§How to reduce patient exposure from diagnostic exams

§Reduce the amount of the x-ray "beam-on" time. §Use as much distance as warranted between the x-ray tube and the patient for the examination. §Always shield the patient with appropriate gonadal and/or specific area shielding devices.

RGE: radiation generating equipment

§Regulated at the state level §Produce a spectrum of X-rays based on energy, target, and filtration properties

§Air kerma

§SI quantity replacing exposure §Kerma stands for "kinetic energy released in matter" §Thus "air kerma" is the kinetic energy released in a unit mass (kg) of air §Units are J/kg (i.e. Gy) §When units of air kerma are given in Gy, it can be denoted as "Gya"

units for equivalent dose

§SI: Sievert (Sv) Historical: Radiation equivalent man (rem) §1 rem = 10 mSv

§How to reduce personnel exposure from diagnostic exams

§Shortening the length of time spent in a room where x-radiation is produced §Standing at the greatest distance possible from an energized x-ray beam §Interposing a radiation-absorbent shielding material between the radiographer and the source of radiation

§Mean marrow dose

§Simply the average dose to the active bone marrow §Concept similar to effective dose §For single radiograph, simply multiply the dose times the fraction of total active bone marrow in the beam §Relevant for assessing potential hematologic effects §Almost no chance of observing such effects from diagnostic procedures §Has relevance in assessing total population risk of leukemia §The average mean marrow dose in the US due to diagnostic x-ray procedures is approximately 1 mGy/yr

diagnostic efficacy

§The degree to which the diagnostic study accurately reveals the presence or absence of disease in the patient §The largest benefit vs. risk ratio is achieved by using the smallest radiation exposure that will produce useful images and by producing optimal images with the first exposure

the linear no threshold model related to ALARA principle

§The risk of cancer development is proportional to dose without threshold §The probability of cancer risk is assumed to accumulate linearly with dose

§Collective Effective Dose

§Used to describe radiation exposure of populations from low doses of different sources of ionizing radiation §E.g. for evaluating radiation protection standards or radiological technologies §Not a relevant unit for epidemiological studies §SI unit is the person-sievert (traditional is man-rem)

§Dose area product (DAP)

§Used to quantify surface dose from diagnostic exams §Sum total of air kerma over the exposed patient surface §Typical units are mGy cm2 §Calculated by taking the air kerma in mGy and multiplying by the surface area irradiated

§Dose length product (DLP)

§Used to quantify volumetric dose from CT exams §Typical units are mGy cm §Calculated by taking the CTDIvol in mGy and multiplying by the length of the scan §Gives a quick relative comparison of risk to patient from different exams §E.g. if you change the protocol and DLP doubles, risk to the patient has approximately doubled.

§Genetically significant dose (GSD)

§Weighted average dose to the gonads for a population §Weighted by reproductive potential §i.e. age, sex, expected number of offspring §Attempts to estimate the relevant dose that could cause genetic effects in a population §Reported GSD for the US is 2 mGy/yr §The genetic effects of this level of dose are not statistically detectable

secondary source of radiation - scatter

§X-rays from the primary beam that interact with objects and are deflected outside the useful beam area §Primary interaction is Compton scatter §Is a potential source of personnel exposure §Source is the patient or any other object in the primary beam

Primary beam

§X-rays produced by the x-ray tube that are in the direction of the useful beam §Useful beam is filtered and collimated to reduce patient dose §Personnel should never be exposed to primary beam §Source is the x-ray tube