motion management

Question 1

motion interplay effect

Answer 1

significant for smaller lesions, small number of fracitons, highly modulated plans

Question 2

5 categories of motion management

Answer 2

motion-encompassing
respiratory-gating
breath-hold
forced shallow breathing
repiration-synchronized (tracking)

Question 3

different CT Sims for breathing motion

Answer 3

4DCT
DIBH/DEBH
free breathing with slow scan

Question 4

how much time does gating add to treatment time?

Answer 4

-4-15X

depends on dose rate

Question 5

what use DIBH for breast?

Answer 5

during inhalation the diaphragm pulls the heart posteriorly and inferiorly away from the breast, and thus the is potential reduction of both cardiac and lung toxicity

Question 6

what does DIBH do wrt lung?

Answer 6

-increases lung volume, thus decreasing V20Gy

Question 7

prospective vs retrospective 4DCT

Answer 7

prospective = only acquire data at certain points in cycle
retrospective= acquire throughout all cycles, put data into bins for cycles later

Question 8

4 requirements of a tumor tracking system

Answer 8

) identify tumor position in real ime

2) anticipate tumor motion to allow for time delays in response of beam positioning system
3) reposition the beam
4) adapt the dosimetry to allow for changing lung volume and critical structure locations during the breathing cycle

Question 9

why use multiple fiducials?

Answer 9

-If one moves, cannot know if fudicial moved wrt to tumour. With more fiducials, one can deduce this

Question 10

4 ways to locate the tumor during tumor tracking

Answer 10

1. real time imaging of tumor istelf (ex fluoroscopy)
2. real time imaging of fiducials implanted in the tumor
3. inference of tumor position from surrogate breathing signals
4. nonradiograpjhic tracking of active or passive signaling device implanted in the tumor (ex. RF transponders)

Question 11

what is the time delay for repositioning with cyberknife?

Answer 11

100-200 ms

Question 12

2 ways treatment beam can be repositioned in real time in response to tumor motion

Answer 12

• MLC repositioning

- cyberknife-entire linac moves (can adapt to full 3D motion of tumor)

Question 13

what is the concern with realigning the beam to the tumor position?

Answer 13

beam may pass through an OAR that was avoided during the planning process

Question 14

how long can the time delay of a real-time tracking method be?

Answer 14

< 0.5 s, irregularity of breath cycle makes it difficult to predict more than 0.5 s ahead

Question 15

2 important QA aspects of motion tracking for dose delivery

Answer 15

1. how position as a function of time is determined

2. calibrating the spatial coordinate system with the beam delivery coordinate system

Question 16

how often should the E2E test be performed for cyber knife?

Answer 16

monthly

Question 17

what is “average tumor trajectory”

Answer 17

stable input trace that reflects the target;s motion during respiration

Question 18

what is a problem with optical tracking techniques?

Answer 18

assumes that external marker motion correlates with internal tumor/organ motion- this is not necessarily true especially in lung

Question 19

what are things that affect the effectiveness of gating?

Answer 19

• reproducibility of patient breathing patterns
• increases treatment time
• some studies show no benefit for motion < 2 cm

Question 20

What does align RT do?

Answer 20

• surface tracking (uses 3D cameras)
• no contact
• fluoro with SBRT
• uses speckles on skin

Question 21

pros and cons of phase vs amplitude gating

Answer 21

amplitude- more robust to changes in breathing rate. less prone to sorting errors.
phase- more robust to changes in baseline- more interruptions

Question 22

what is active breathing coordination

Answer 22

holds the patient’s breathing cycle at a treshold using a spirometer

verify reproducibility with fluoro, CT scan