L 17: IGRT

Question 1

Answer 1

Question 2

Image Guidance is done for

Answer 2

• Patient data acquisition
• Treatment planning & simulation
• Patient set up and target localization before and during treatment

Question 3

On board imagers

Answer 3

• K-V Imaging
• M V - EPID

Question 4

Both of the imagers have

Answer 4

Flat panel image detector
256 x 256 solid detectors consisting of amorphous silicon photo diodes

Question 5

K-V Imager uses

Answer 5

• CBCT
• Fluoroscopic
• Radiographic
• check set up or track fiducial markers during respiration

Question 6

M-V Imager uses
EPIDs

Answer 6

• Portal verification before and during treatment
• Online monitoring of the targetduring treatment

Question 7

K-V CBCT

Answer 7

• 1 mm resolution at isocenter
• Soft tissue constrast
• Better than MV CBCT
• Disadvantages:
• Sagging (correction ~2mm)
• beam hardening (software correction)
• X-ray scatter (anti scatter grids)

Question 8

M-V CBCT when compared to KV CBCT

Answer 8

Disadvantages
* Less contrast and spatial resolution
* Less soft tissue visibility
* Less compatibility with treatment plan images
* Less flexibility

Advantages
* Less artifacts of metal objects like implants, dental fillings
* CT numbers directly corelate with electron density
* More accurate calculation of imaging dose

Question 9

Helical tomotherapy

Answer 9

• Combines LINAC and helical CT scanner features
• Images are less susceptible to imaging artifacts from surgical clips, hip implants and dental fillings.
• Xenon ion chamber

Question 10

Ultrasound

Answer 10

Disadvantages of using US for IGRT:
* Poor image quality
* Anatomic distortions

Advantages:
* Real time tracking
* non radiographic
* non invasive

Question 11

4D-CT

Answer 11

• Needed if more than 5mm motion
• Tracks patients breathing frequency
• The pitch needs to be less than regular CT scans

Question 12

Real time tumor tracking is seen in

Answer 12

• Fluroscopy based tracking
• Exac trac
• Cyber knife
• Electromagnetic tracking
• MRI Guided IGRT

Question 13

Exac-trac

Answer 13

• For srs/sbrt

Question 14

Cyber knife

Question 15

F

Fiducials

Question 16

Electromagnetic field tracking
CALYPSO

Question 17

MRI Guided IGRT

Question 18

PET-CT
F-18 half life

Answer 18

2 hours
* PET Activity is due to glycolysis in the tumor cells
* This effect is called warburg effect

Question 19

Images and radiation doses

Answer 19

• KV 2D: Milligray
• KV CBCT: 0.1-10 cGy
• Port Film: 2-10 cGy
• MV CBCT: 1 - 30 cGy

Question 20

High quality diagnostic X-Ray films Unit

Answer 20

kVp, mA, time
This combo is referred to as technique

Question 21

Data required to store each CT image slice

Answer 21

512 Kilobytesnmm

Question 22

Co-60 used in teletherapy activity

Answer 22

around 10,000 Ci

Question 23

5 parameters used to assess image quality

Answer 23

1. Geometric accuracy
2. constrast
3. Spatial resolution
4. Noise
5. Uniformity

Question 24

CT scan filter techniques

Answer 24

CT scans have electron density information

Question 25

Anti-Scatter grid

Answer 25

Increases exposure time and increased radiation dose to patient

Question 26

Digital subtraction angiography is used for

Answer 26

AVM SRS treatment

Question 27

PET SUV (std uptake value) unit

Answer 27

g/ml

Question 28

Intensifying screen

Answer 28

* Made of phosphor * Use of this shortens the exposure time and reduces dose to the patient

Question 29

CT Sim

Answer 29

* Estimated dose is 3-5cGy * Less the pitch more the overlap between each slice of CT Scan. * Radiation dose is inversly proportional to the pitch setting

Question 30

Types of electromagnetic radiation

Answer 30

Good Xylophones Use Very Important Music Recorders Gamma > X-rays > UV rays > Visible light > ifrared rays > Microwave > Radio

Question 31

MRI Scan

Answer 31

T1: due to differences in Longitudinal & Spin relaxation time T2: relaxation time

Question 32

CBCT

Answer 32

* Full Fan = to obtain small fielf of view, 180 deg rotation * Half fan = to obtain large view of field, 360 deg rotation, half bow tie filter

Question 33

Pelvic kV-CBCT Dose

Answer 33

2cGy

Question 34

Ultrasound

Answer 34

* Mechanical waves- no radiation * Images display the US signal attenuation properties of tissues * The speed of sound is dependent on material thrugh which it is traversed * Bone has higher attenuation co-ef than muscle. * The direction of US wave propagation is parallel to the particle displacement in tissues

Question 35

Electromagnetic Beacon tracking is affected by

Answer 35

* Patient thickness * PResence of mettalic implants * insufficient number of beacons

Question 36

Knowledge based treatment planning

Answer 36

Utilizes previously treated plans to generate model which can predict treatment planning results and guide optimization * DVH * Predicts DVH in the above manner

Question 37

Patient specific IMRT QA, pre treatment can be done by

Answer 37

* EPID * Film and an ion chamber in solid water phantom * An ionization chamber array * A diode array