motion managment

Question 1

how to measure motion of tumour and OARs

Answer 1

4DCT data
-fan beam
-3DCT recorded over multiple seconds

Question 2

how is it done

Answer 2

CT sim by either
prospective acquisition or retrospective acquisition

Question 3

prospective acquisition

Answer 3

-images collected at only one phase of respiratory cycle

-decided in advanced
-taking multiple breathes and each phases are added together
-only time we use linear CT anymore

Question 4

retrospective acquistion

Answer 4

scan data acquired at all phases of respiration(continous scanning)

correlation or registration of image w/ the phase is conducted after data has been acquired

most common

uses rpm signal

Question 5

features of 4DCT

Answer 5

-longer than conventional by 5fold
-tf more dose
-requires a signal eg rpm block

Question 6

possible to use CBCT instead of CT

Answer 6

-still free breathing
-instead of axial slices being rebinned , the volume projections are being rebinned

Question 7

motion of :
top of lung
diaphragm

Answer 7

-smallest motion
-largest motion

Question 8

motion direction

Answer 8

-90% sup/inf
-10% ant/post
more time spent on exhale than inhale

Question 9

when is tumour most stable

Answer 9

max expiration

Question 10

slow CT v free breathing CT

Answer 10

-slow CT has blurred images → large errors in delineation
-free breathing CT creates MIP (maximum image projection) +. blurring↓

Question 11

MIP

Answer 11

adding different phase intensities and used for target volume

Question 12

MIP pros

Answer 12

-1 dataset to contour dataset , not 10
-captures 3D range of motion, not just ex and in
-good for lung tumours against background lung

Question 13

MIP Con

Answer 13

-hard defining ITV for tumours in chestwall and diaphragm
-artifically ↑ all CT values
-provides data for only one structure

Question 14

Avip

Answer 14

-takes the average of different intensities
-used for everything but the target volume(egOAR)
-reduces the am of contouring and delineation

Question 15

RPM

Answer 15

-infra-red camera on wall
-only need one camera as rpm block moves in 2 directions

Question 16

phase gating

Answer 16

allows automatic gating acq. and tx delivery based on same phase of patients respitatory cycle
aka motion of block and pattern its showing

Question 17

amplitude based gating

Answer 17

allows auto gating based on position of marker block on patient , regardless of respiratory cycle

aka when block is at particular location … gating is triggered

Question 18

amplitude based gating features

Answer 18

-better at suppressing motion artefacts
-shorter tx time

Question 19

duty cycle

Answer 19

beam on time ÷ total tx time
ie how much of breathing cycle is the beam on for

Question 20

if the duty cycle is 100%

Answer 20

beam always on and tumour always in field

Question 21

duty cycle for:
non-gated treatments
step and shoot IMRT
dynamic IMRT

Answer 21

-100%
-LESS THAN 30%
-50%

Question 22

if theres an increase of beam on time

Answer 22

this ↑duty cycle which then ↑ residual motion

Question 23

if duty cycle is small

Answer 23

tumour wont move alot

Question 24

there is a compromise between

Answer 24

duty cycle (effeciency) and residual motion (normal tissue irradiation)

Question 25

real time-tracking method:electromagnetic field

Answer 25

=calypso system

surgically implanted EM transducer (gold seeds)

Question 26

cyberknife

Answer 26

-600 or 800 cGY per min
-secondary collimnator =radiation cone (between 4 to 60mm)
-6MV