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Treatment Planning I > Radiation Physics Terminology > Flashcards

Radiation Physics Terminology Flashcards

1
Q

what is conventional sim

A
  1. Fluoroscopy X-ray require

2. Doctor draws field borders on x-ray images

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2
Q

What is CT sim

A
  1. requires CT scanner and virtual sim workstation
  2. patient CT scan is required
  3. relative points or other landmarks marked at sim
  4. field setup are created virtually
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3
Q

why are bbs used at simulation

A

BBs used to indicate where marked isocenter is located

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4
Q

why are solder wires used at simulation

A

solder wires can be used to mark the anatomic locations of structures (scar, border, breast, etc), to serve as a marker that is visible to the dosimetrist on the CT

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5
Q

what point(s) are marked during simulation

A

marked isocenter(s)

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6
Q

what is marked isocenter

A
  1. marked at simulation

2. in Pinnacle, you can only localize to one marked iso

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7
Q

what is final isocenter

A
  1. placed during planning by dosimetrist or physician
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8
Q

what is final isocenter

A
  1. placed during planning by dosimetrist or physician

2. usually if you have a final iso, there will be an iso shift

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9
Q

what is iso shift

A

directions for therapist indicating how to get from the marked isocenter to the final isocenter by adjusting the treatment chair

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10
Q

what is calc point

A

placed by dosimetrist during treatment planning if the marked or final iso does not follow rules of calc point

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11
Q

in which orientation are CT slides obtained

A

axial/ transverse

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12
Q

define image segmentation

A

slide by slide delineation of anatomic regions of interest

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13
Q

define critical structures

A

non target structures that we want to monitor how much radiation dose they receive

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14
Q

examples of critical structures

A

lung, heart, rectum, etc,…

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15
Q

define normal tissue and list examples

A

non target structures. could be critical (rectum) or non critical (fat)

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16
Q

define tolerance

A

each critical structure has a maximum dose. if the critical structure receives more dose than the tolerance, will have negative consequences

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17
Q

what are the consequences for exceeding tolerance

A

depends upon type of critical structures
pneumonitis for lungs
cataracts for eyes

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18
Q

GTV (ICRU 50)

A

gross tumor volume

gross demonstrable extent and location of the disease

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19
Q

CTV (ICRU 50)

A

clinical target volume

demonstrated tumor if present and any other tissue with presumed tumor

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20
Q

PTV (ICRU 50)

A

planning target volume

includes CTV and a setup margin compensate for patient movement and setup uncertainties

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21
Q

IM (ICRU 62)

A

internal margin

added to CTV to compensate for internal physiologic movement during treatment

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22
Q

ITV (ICRU 62)

A

internal target volume

volume that includes CTV with internal margin

23
Q

SM ( ICRU 62)

A

setup margin

margin for patient movement and setup uncertainty

24
Q

OR (ICRU 62)

A

organ at risk

25
Q

PRV (ICRU 62)

A

planning organ at risk volume

margins to compensate for internal movement and setup variability of organ at risk

26
Q

what is absorbed dose

A

energy deposited by ionizing radiation per unit mass (Gy)

1 Gy= 1 J/kg

27
Q

what is a fraction

A

each time radiation is administered equals to one fraction
if the patient comes once a day, it’s 1 fx per day
if the patient comes twice a day, it’s two fx per day

28
Q

what is the current unit for prescribed radiation dose

A

Gy or cGy

29
Q

What is the previous unit for prescribed radiation dose

A

Rad (radiation absorbed dose)

30
Q

what is the conversion unit between the older radiation unit and the current radiation unit

A

100 rad= 1 Gy

31
Q

What is the approved dose calculation algorithm at MDACC

A

CC Convolution

32
Q

What happens when an x-ray beam passes through a material

A

when an x-ray (or gamma) passes through a medium, photons and matter interact with the result that energy is transferred to medium

33
Q

what is the first step in the interaction between the photon and the matter

A

ejection of electrons from the atoms of the absorbing medium, called secondary electrons

34
Q

what do the high speed electrons that are produced do

A
  1. high speed electrons transfer energy by absorbing ionization and excitation of the atoms along their path
  2. if the absorbed medium consists of body tissues, sufficient energy may be deposited within cells, destroying their reproductive capacity
35
Q

what happens to most of the absorbed energy

A

converted into heat, producing no biological effect

36
Q

what happens when a photon interacts with the electrons in the material

A

a part or all energy of photons convert into kinetic energy of electron

37
Q

describe photon scattering in the medium

A
  1. if only part of photon energy is given to electron, then photon is scattered with reduced energy
  2. the scattered photon may interact again with a partial or complete transfer of energy to the electron
  3. photon may experience one or multiple interaction in which energy lost by the photon is converted into kinetic energy of electrons
38
Q

what is bremsstrahlung or braking radiation

A
  1. high speed electron passes near a nucleus
  2. electron is accelerated and deflected from its path by the attractive Coulomb force of the nucleus.
  3. The deflected electron will lose all part or all of its energy as electromagnetic radiation
39
Q

what is the maximum energy of the resulting bremsstrahlung photon

A

the interaction may result in partial or complete loss of electron energy, the resulting bremsstrahlung photon may have energy up to the initial energy of electron

40
Q

define buildup region

A

area from surface to dmax

41
Q

define buildup region

A

area from surface to dmax

42
Q

why cant we place a calc point in the build up

A

not correctly modeled in Pinnacle

not adequate tissue to allow for complete buildup

43
Q

what is attenuation

A

gradual loss of intensity of x-ray through some material

44
Q

what causes attenuation

A
  1. coherent scattering
  2. photoelectric effect
  3. Compton effect
  4. pair production
  5. annihilation radiation
45
Q

define photoelectric effect

A

incident photon strike an electron bound to an atom

46
Q

what happens to the energy in photoelectric effect

A

the entire energy of photon is transferred to the electron, which is ejected as photoelectron.
the incident photon vanishes, giving an energy equal to incident photon energy- Eb to the electron

47
Q

define Compton effect

A

an incident photon strikes a weakly bound electron

48
Q

what happens to the energy in Compton effect

A

a portion of the photon’s energy is absorbed by the electron which is emitted at an angle (theta). the photon is scattered with reduced energy

the photon leaves the site in a direction from that of the original photon (scattered at an angle phi)

49
Q

what happens to the energy in Compton effect

A

a portion of the photon’s energy is absorbed by the electron which is emitted at an angle (theta). the photon is scattered with reduced energy

the photon leaves the site in a direction from that of the original photon (scattered at an angle phi)

50
Q

define pair production

A

a photon is absorbed in the vicinity of the nucleus. If disappears, and gives rise to an electron and position

51
Q

define annihilation radiation

A

a slowly moving position (created as a result of pair production) combines with a free electron and produces two photons. The photons are ejected opposite directions of each other.

52
Q

an example of converting mass into energy

A

annihilation radiation

53
Q

define penumbra

A

region near the edge of the field margin where the dose falls rapidly

the region, at the edge of a radiation beam, over which the dose rate changes rapidly as a function of distance from the beam axis.

Treatment Planning I (1 decks)

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