Radiation Physics Terminology

Question 1

what is conventional sim

Answer 1

1. Fluoroscopy X-ray require

2. Doctor draws field borders on x-ray images

Question 2

What is CT sim

Answer 2

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

Question 3

why are bbs used at simulation

Answer 3

BBs used to indicate where marked isocenter is located

Question 4

why are solder wires used at simulation

Answer 4

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

Question 5

what point(s) are marked during simulation

Answer 5

marked isocenter(s)

Question 6

what is marked isocenter

Answer 6

1. marked at simulation

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

Question 7

what is final isocenter

Answer 7

1. placed during planning by dosimetrist or physician

Question 8

what is final isocenter

Answer 8

1. placed during planning by dosimetrist or physician

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

Question 9

what is iso shift

Answer 9

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

Question 10

what is calc point

Answer 10

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

Question 11

in which orientation are CT slides obtained

Answer 11

axial/ transverse

Question 12

define image segmentation

Answer 12

slide by slide delineation of anatomic regions of interest

Question 13

define critical structures

Answer 13

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

Question 14

examples of critical structures

Answer 14

lung, heart, rectum, etc,…

Question 15

define normal tissue and list examples

Answer 15

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

Question 16

define tolerance

Answer 16

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

Question 17

what are the consequences for exceeding tolerance

Answer 17

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

Question 18

GTV (ICRU 50)

Answer 18

gross tumor volume

gross demonstrable extent and location of the disease

Question 19

CTV (ICRU 50)

Answer 19

clinical target volume

demonstrated tumor if present and any other tissue with presumed tumor

Question 20

PTV (ICRU 50)

Answer 20

planning target volume

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

Question 21

IM (ICRU 62)

Answer 21

internal margin

added to CTV to compensate for internal physiologic movement during treatment

Question 22

ITV (ICRU 62)

Answer 22

internal target volume

volume that includes CTV with internal margin

Question 23

SM ( ICRU 62)

Answer 23

setup margin

margin for patient movement and setup uncertainty

Question 24

OR (ICRU 62)

Answer 24

organ at risk

Question 25

PRV (ICRU 62)

Answer 25

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

Question 26

what is absorbed dose

Answer 26

energy deposited by ionizing radiation per unit mass (Gy) | 1 Gy= 1 J/kg

Question 27

what is a fraction

Answer 27

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

Question 28

what is the current unit for prescribed radiation dose

Answer 28

Gy or cGy

Question 29

What is the previous unit for prescribed radiation dose

Answer 29

Rad (radiation absorbed dose)

Question 30

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

Answer 30

100 rad= 1 Gy

Question 31

What is the approved dose calculation algorithm at MDACC

Answer 31

CC Convolution

Question 32

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

Answer 32

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

Question 33

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

Answer 33

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

Question 34

what do the high speed electrons that are produced do

Answer 34

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

Question 35

what happens to most of the absorbed energy

Answer 35

converted into heat, producing no biological effect

Question 36

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

Answer 36

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

Question 37

describe photon scattering in the medium

Answer 37

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

Question 38

what is bremsstrahlung or braking radiation

Answer 38

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

Question 39

what is the maximum energy of the resulting bremsstrahlung photon

Answer 39

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

Question 40

define buildup region

Answer 40

area from surface to dmax

Question 41

define buildup region

Answer 41

area from surface to dmax

Question 42

why cant we place a calc point in the build up

Answer 42

not correctly modeled in Pinnacle | not adequate tissue to allow for complete buildup

Question 43

what is attenuation

Answer 43

gradual loss of intensity of x-ray through some material

Question 44

what causes attenuation

Answer 44

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

Question 45

define photoelectric effect

Answer 45

incident photon strike an electron bound to an atom

Question 46

what happens to the energy in photoelectric effect

Answer 46

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

Question 47

define Compton effect

Answer 47

an incident photon strikes a weakly bound electron

Question 48

what happens to the energy in Compton effect

Answer 48

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)

Question 49

what happens to the energy in Compton effect

Answer 49

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)

Question 50

define pair production

Answer 50

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

Question 51

define annihilation radiation

Answer 51

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.

Question 52

an example of converting mass into energy

Answer 52

annihilation radiation

Question 53

define penumbra

Answer 53

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.