Radiation Physics Memorization

Front 1

What is the rest mass of an electron?

Back 1

0.51 MeV

Front 2

Is an alpha particle charged? If so, what charge does it carry?

Back 2

Yes, +2

Front 3

Is a positron charged? If so, what charge does it carry?

Back 3

Yes, +1

Front 4

Is a neutron charged? If so, what charge does it carry?

Back 4

No

Front 5

Is neutrino charged? If so, what charge does it carry?

Back 5

No

Front 6

Assuming equivalent energy, place the following particles in order of increasing LET:

Neutrons
Alpha particles
Electrons

Back 6

Electron

Front 7

What is the rest mass of a proton?

Back 7

930 MeV (~1 amu)

Front 8

What is the rest mass of a neutron?

Back 8

930 MeV

Front 9

Which of the following particles are directly ionizing?

Protons
Neutrons
Positrons
Alpha particles
Beta rays

Back 9

All are directly ionizing with the exception of neutrons, which are not charged.

Front 10

131Iodine and 125Iodine:

A. Have different chemical properties.
B. Have different Z values.
C. Occupy different columns on the periodic table.
D. Have the same number of neutrons.
E. None of the above.

Back 10

E. I-131 and I-125 are isotopes i.e. they have the same Z value. Their chemical properties are thus the same. They do NOT, however, have the same number of neutrons.

Front 11

If a radionuclide decays by beta minus emission or positron emission, the resultant daughter nuclei will be iso_______.

Back 11

Isobars

Front 12

In Co-60, the number 60 represents what?

Back 12

The number of nucleons i.e. the MASS number (A).

NB: For Co-60, Z=27

Front 13

In standard notation, what does Z represent?

Back 13

Number of protons in an atom. The ATOMIC number

NB: A is the mass number

Front 14

1 MeV = ________ eV

Back 14

10^6 eV

Ex: 930 MeV (mass of a proton) is approximately 1000 MeV or 10^9 eV (1000 x 10^6)

Front 15

Avogadro's Number

What does it represent? What is the constant?

Back 15

Number of atoms of a substance in a mole.

6.02 x 10^23 mol^-1

Front 16

Equation relating half-life and decay constant

Back 16

Where T1/2 is half life and lambda is decay constant.

Front 17

Half life of Ir-192

Back 17

74 days

Front 18

What is the mean life of a radioisotope? (definition)

Back 18

The amount of time the radioisotope would take to decay if the initial activity were constant

Mean life = 1.44 (half life)

NB: Denoted by tau

Front 19

Alpha Decay: What are the products? How do the atomic and mass numbers change?

Back 19

The only products are a daughter nuclide and a helium.

A-4
Z-2

NB: For any given radioisotope, the energy of the emitted alpha particle is always the same.

Front 20

Internal conversion

Back 20

A way of stabilizing an excited nucleus. Excess energy is transferred directly from the nucleus to an electron, which is ejected. The resultant vacancy is then filled by a cascade, which may result in characteristic x-rays and/or Auger electrons.

Front 21

Beta-minus decay

Back 21

Occurs in proton-poor nuclei. A neutron is converted into a proton, electron and antineutrino.

A remains the same, Z increases by one (Z + 1)

Front 22

Beta-plus decay (positron decay)

Back 22

Occurs in proton-rich nuclei. A proton is converted to a neutron, positron and neutrino.

A remains the same, Z decreases by one (Z-1)

Front 23

Electron capture

Back 23

More likely to occur in proton-rich, heavy nuclei. The unstable nucleus grabs an inner shell electron, which combines with a proton to become a neutron. A neutrino is kicked out.

A remains the same, Z decreases by one (Z - 1)

Front 24

Define: Radioactive Equilibrium

Back 24

When the radiation of the activity of a daughter nuclide to the activity of its parent approaches a constant value

Front 25

Secular Equilibrium

Back 25

Occurs when the half-life of a daughter nuclide is much shorter than the half-life of the parent. The activity of the daughter and parent are roughly equal.

Td<
Ex: Sr-90 (half-life 28 yrs) decays into Y-90 (half-life 64 hours)

Front 26

Transient Equilibrium

Back 26

Occurs when the half-life of a daughter nuclide is somewhat shorter than the half-life of its parent

Td~
Ex: Mo-99 (half-life 66.7 hours) decays to Tc-99m (half-life 6.03 hrs)

Front 27

Name four ways of creating radioisotopes

Back 27

1) Naturally occurring
2) Byproduct of nuclear fission
3) Produced in a reactor via neutron bombardment
4) Exposed to a charged particle beam in an accelerator

Front 28

Which radioisotopes are created via nuclear fission?

Back 28

Cs-137, I-131, Sr-90

Front 29

Which radioisotopes are created via neutron bombardment?

Back 29

Co-60, I-125, Ir-192, Pd-103

Front 30

What is the SI unit of activity?

Back 30

Becquerel = 1 decay/sec

Front 31

Curie

Back 31

1 Ci = 3.7 x 10^10 Bq

Old unit of activity (NOT SI)

NB: 1 mCi = 37 MBq

Front 32

What is the equation for calculating activity over a period of time, t?

Back 32

where Ao is the activity at time 0, t is time elapsed and lambda is the decay constant.

Front 33

How would you calculate activity if you know the number of half-lives that have elapsed?

Back 33

where Ao is the activity at time 0 and n is the number of elapsed half-lives.

Front 34

Use factor: Definition and representative values

Back 34

The fraction of time that the beam is pointed at a given barrier

Secondary barrier: 1 (leakage and scatter)
Floor=0.31
Wall=0.21
Ceiling=0.26

Front 35

Occupancy factor: Definition

Back 35

The fraction of a treatment day during which the area is occupied

Front 36

Occupancy (T): Representative values

Back 36

T=1 (full occupancy): Work areas, nurses' station, clinic, console
T=/15 (Partial occupancy): Hallways, staff restroom, employee lounge
T=1/20 (Occasional occupancy): Public restrooms, lobby, storage areas
T=1/40 (Transient occupancy): Stairways, elevators

Front 37

Workload: Definition

Back 37

The number of patients treated per WEEK* the dose equivalent delivered per patient at a distance of 1 m

Front 38

Per regulations, how much leakage is allowed from the head of a linac?

Back 38

No more than 0.1% of the useful dose rate at 1 m

Front 39

For safety purposes and shielding, where are radiation levels calculated or measured?

Back 39

1 foot beyond the outside surface of a shielded wall

Front 40

Barrier transmission factor (B): Definition

Back 40

The multiplicative factor by which the radiation level must be reduced so that it matches the design limit (P)

Front 41

With regard to room shielding, how do you solve for the required barrier transmission factor (Bp) for a primary barrier?

Back 41

where P is the allowable weekly dose in Sievert, W is workload, T is occupancy, U is use factor and d is the distance from the source to the protection point (in METERS)

This is only for the primary barrier.

Front 42

With regard to room shielding, how do you solve for the leakage barrier transmission factor (BL) for a secondary barrier?

Back 42

where P is the allowable weekly dose in Sievert, dL is the distance from the isocenter to the protection point, W is workload and T is occupancy.

W is multiplied by 0.001 to reflect the fact that regulations allow 0.1% of the useful dose via leakage.

Front 43

1 Sv = ______ rem

Back 43

100 rem

Front 44

What is a radiation weighting factor? What's it used for?

Back 44

Used in calculating equivalent dose for various particles.

Front 45

What is the radiation weighting factor (Wr) for x-rays? Electrons? Neutrons? Alpha particles?

Back 45

Xrays and electrons: Wr=1
Neutrons: Wr=20 (dpdt on energy)
Alpha particles: Wr=20

Front 46

What is a deterministic effect? Examples?

Back 46

Effects that increase in severity with increasing dose above a given threshold

Ex: Skin erythema, hair loss, cataracts, fibrosis

Front 47

What is a stochastic effect? Examples?

Back 47

The probability of the effect increases with dose; however, the severity of the effect does not. All or nothing.

Ex: Carcinogenesis, genetic effects

Front 48

A medical event occurs. What sort of documentation is required?

Back 48

1) Notify the NRC within 24 hours by phone
2) Submit a written report within 15 days
3) Notify the patient and the referring physician within 24 hours

Front 49

What constitutes an NRC medical event?

Back 49

1) Total dose differs by 20% or more
2) A single dose within a fractionated regimen differs by 50% or more
3) Wrong patient
4) Wrong mode of treatment
5) Leaking sealed source
6) Dose to the wrong site that exceeds 500 mSV and 50% of the prescribed dose

Front 50

LD50 for humans

Back 50

4 Gy to the whole body (without medical intervention)

Front 51

Effective dose for a CXR? CT?

(in mSv)

Back 51

Chest x-ray: 0.1 mSv
CT: 10 mSv

Front 52

What is the average annual effective dose to the public? Daily dose? How much is natural?

Back 52

6.2 mSv/year
0.017 mSv/day
About half is due to medical procedures and half is naturally occurring.

Front 53

Define: Effective dose

Back 53

The dose received, taking into account the radiation sensitivities of various organs and tissues

He = Ht x Wt where Ht is the mean equivalent dose and Wt is the tissue weighting factor

Front 54

Define: Equivalent dose

Back 54

The dose absorbed, taking into account the type and energy of the radiation

Ht = Dt x Wr where Dt is the average absorbed dose in a tissue and Wr is the radiation weighting factor

Ex: Wr for neutrons is 20

Front 55

What is the excess lifetime risk of developing a fatal cancer due to a given dose of radiation?

Back 55

The risk is 4 in 100 per Sievert i.e. 4x10^-2 per Sv effective dose

Ex: A chest xray delivers 10 mrad to the lungs only. Equivalent dose = 10 mrad * 1 (weighting factor of xrays) = 10 mrem
Effective dose = (10 mrem)(1 rem/1000 mrem)(1 Sv/100 rem)(0.12) = 1.2 x 10^-5 Sv
(1.2 x 10^-5 Sv)(4x10^-2 risk/Sv) = 5x10^-7

Front 56

What units are associated with an exposure rate constant?

Back 56

Front 57

What is the equation relating exposure and charge?

Back 57

X = Q/m

where X is exposure, Q is the charge collected and m is the mass of the air in the sample volume

Front 58

At what energy do free air ionization chambers become impractical?

Back 58

Above 3 MeV. The plate separation and chamber size required to maintain equilibrium is too big to be practical.

Front 59

For each of the following devices, is it an absolute or relative dosimeter?

Free air ionization chamber
Calorimeter

Back 59

Free air ionization chamber: Absolute (exposure)
Calorimeter: Absolute (dose)

Front 60

What is standard temperature and pressure?

Back 60

22 C (295 K) and 760 mm-Hg

Front 61

How do you convert Celsius to Kelvin?

Back 61

Add 273

Front 62

How do you calculate a temperature and pressure correction factor?

Back 62

where STP are 295 K and 760 mm-Hg. T is in Celsius.

Front 63

Geiger-Muller Counters: What can they detect? On what principle are they based? What are they good for?

Back 63

GM counters work on the principle of gas amplification, making them very sensitive. They can detect a single charged particle but canNOT discriminate energy. GM counters do have refractory period, or "resolving time," which can cause spuriously low counts in a high radiation field. They are best used for locating lost sources or detecting radioactive contamination.

Front 64

What are the advantages of TLDs as an in vivo dosimeter?

Back 64

Small
No wires
Reusable
Can be used over a wide dose range (less than a cGy up to 10 Gy?)
Near tissue equivalence (if using LiF)
Nearly linear relationship between dose and response up to ~3-4 Gy

Front 65

What are the disadvantages of a TLD?

Back 65

Delayed reading, can only be read once (so write it down!)

Front 66

What is the formula for optical density?

Back 66

Front 67

Diodes: Benefits? What can they be used for?

Back 67

Advantages: Very sensitive, rugged, reliable, real-time readout
Uses: Daily machine output constancy, pt dosimetry

NB: canNOT be used for beam calibration

Front 68

MOSFETs: Advantages? Uses?

Back 68

Advantages: Small, lightweight, reusable
Disadvantages: Shorter lifetime than a diode
Uses: Patient dosimetry

Front 69

Film Dosimetry: Benefits? Disadvantages?

Back 69

Advantages: High spatial resolution, creates a permanent record, widely available, relatively cheap
Disadvantages: Has to be developed, not tissue equivalent, energy dependent, sensitive to light

Front 70

Define: Electron stopping power

Back 70

Energy lost per unit path length in the medium (dependent on density)

Units = MeV/cm

Front 71

Define: Mass Stopping Power (electrons)

Back 71

Energy loss per unit path length in the medium divided by density i.e. stopping power divided by density

Units = MeVcm2/g

Front 72

How are electrons beams defined?

Back 72

R50 i.e. the depth (cm) at which the dose is 50% of the maximum

Front 73

How do you calculate the electron energy at a given depth?

Back 73

Ez = Eo[1-(z/Rp)]

where Ez is the energy at depth z, Eo is the incident electron energy and Rp is the practical range of the given electron energy (~energy/2)

Front 74

Rule of thumb for blocking electrons with Pb

Back 74

The minimum thickness (in mm)= incident energy/2

Front 75

A photon and electron field abut. Describe the distribution of hot and cold spots.

Back 75

Hot spot in the photon field due to greater scattering of the electrons.
Cold spot in the electron field

Front 76

What is the minimum ICRU-recommended field size for an electron field?

Back 76

An electron field cutout should be at least as large as the electrons' practical range to achieve lateral scatter equilibrium

i.e. Minimum field size > Rp = E/2

Front 77

How do photon and proton dose distributions differ?

Back 77

Photons: Superior skin sparing, more forgiving of changes in target position and inhomogeneity
Protons: Generally lower integral dose (no exit dose), smaller lateral penumbra, fewer beams usually used, can use "patch fields" given the lack of exit dose

Front 78

What is the typical maximum range of a proton therapy beam?

Back 78

30 cm (corresponding to an energy of 23-240 MeV)

Front 79

What is the typical maximum energy of a therapeutic proton beam?

Back 79

~250 MeV

Front 80

In PET, what is actually detected to produce the image?

Back 80

511 keV (0.511 MeV) photons

- These are created via an annihilation reaction between a position and electron.

Front 81

Per NRC CFR Part 20 and 10 CFR Part 35, how often does a radiation shielding survey of adjacent areas need to be conducted for an I-192 source?

Back 81

Whenever the source is changed in the HDR unit.

Front 82

Exposure

Back 82

- Measure of the ability of photon radiation to ionize air
- DEFINED ONLY FOR AIR AND PHOTONS
- Units: R or C/kg (SI)
- Only practical under 3 MeV (due to the limitations of ionization chambers)

Front 83

Roentgen

Back 83

- Unit of exposure
- NOT SI
- Equals 2.58 x 10^-4 C/kg

Front 84

Equation for Exposure

Back 84

X=Q/m


where X is exposure, Q is the electrical charge produced in air, and m is mass in kg

Front 85

A photon beam has an energy of 6 MV. What does this mean? What is the maximum and average energy produced?

Back 85

A 6x beam is produced using a stream of 6 MeV electrons. The maximum photon energy produced is thus 6 MV with an average energy of 2 MV (~energy/3).

Front 86

What is a typical dose rate for an EBRT treatment?

Back 86

200-600 MU/minute

Higher for SBRT and SRS

Front 87

What roles do a linac monitor ion chamber serve?

Back 87

1) Provide feedback to maintain a constant dose rate
2) Track the total or integrated dose i.e. total MU delivered
3) Monitor beam flatness and symmetry

Front 88

Where is the collimator-produced field size defined? i.e. where is it measured?

Back 88

At SAD (usually 100 cm)

Front 89

How much radiation is transmitted through the movable jaws of the collimator?

Back 89

<=0.5%

Front 90

Half-life of Co-60

Back 90

5.26 years

Front 91

How does Co-60 decay?

Back 91

Beta-minus

Front 92

For Co-60 units, how often should the timer error be measured?

Back 92

Monthly (NRC regulation)

Front 93

A collimator is set to a field size of 20x20 cm. How large is the field at a depth of 30 cm?

Back 93

Collimator field size is defined at isocenter (100 cm)

fr = f x r/SAD
fr = 20 x (30 cm/100 cm) = 6 cm

Front 94

You are given a beam profile. How is the field size defined?

Back 94

The field size is defined as the distance between the 50% intensity points. In the example below, the ion chamber is at 110 cm (not isocenter), so the field size needs to account for this.

Beam profile field size = Isocenter field size(r/SAD)
22 cm = f(110 cm/100 cm)
f = 20 cm

Front 95

Over what portion of a beam profile is flatness assessed?

Back 95

Inner 80%

NB: It would be unrealistic to expect the beam edges to be completely flat.

Front 96

Equation for beam flatness

Back 96

NB: This is ONE definition of many. Tolerance is generally +/-3%

Front 97

Name three sources of penumbra

Back 97

1) Non-point source (ex: Co-60)
2) Transmission penumbra: collimator jaws or blocks
3) Scattered photons and secondary electrons

Front 98

Define: physical penumbra

Back 98

- The measured penumbra, incorporating all possible causes, including geometric, transmission and scatter
- Commonly defined as the lateral distance between the 80% and 20% intensity levels in a beam profile measured at a depth of 10 cm using a 10x10 cm2 field

Front 99

How does field size affect scatter?

Back 99

- Direct relationship
- As field size increases, more matter is irradiated --> increased scatter

Front 100

Dmax of Co-60

Back 100

0.5 cm

Front 101

Dmax of a 10x beam

Back 101

2.5 cm

Front 102

Dmax of a 15 MV beam

Back 102

3 cm

Front 103

Dmax of a 6x beam

Back 103

1.5 cm

Front 104

Dmax of an 18 MV beam

Back 104

3.3 cm

Front 105

How does depth dose change with beam energy?

Back 105

With increasing beam energy:
1) Deeper dmax
2) Greater skin sparing
3) Higher PDD for a given depth when d>dmax
4) Usually LOWER PDD for a given depth when d

Front 106

Define: Mayneord f factor

Back 106

- Factor used to convert between two PDDs with different SSDs
- F is >1 when the second SSD is larger than the first (bc PDD increases with SSD)
- In the equation below, dm is dmax.

Front 107

Formula: Equivalent Circle

Back 107

Set the area of a circle and square equivalent to each other -->

Radius = Equivalent square/sqrt(pi)

Front 108

Draw a diagram of a TAR set-up.

Back 108