ARC

Question 1

step and shoot

Answer 1

-beam is off in between movements tf less radiation leakage
-easier to deliver and plan

-more time consuming

Question 2

dynamic IMRT

Answer 2

faster
has smooth intensity modulation

beam on throughout—-leakage ↑
more susceptible to tumor motion
another QA needed for MLC motion accuracy

Question 3

what do you need for VMAT

Answer 3

• CBCT imaging system with soft tissue matching
• A high number of MLC leaves (122)
• Arc Planning software
• Modifications to the gantry

Question 4

Control IMRT

Answer 4

dynamic dose delivery defined as segments/subfields
* Fixed aperture shape
* Fixed gantry angle
* Fixed number of MUs

Question 5

superimposed field segments:

Answer 5

step and shoot
fixed gantry

Question 5

dynamic MLC

Answer 5

sliding window
fixed gantry

Question 6

tomotherapy

Answer 6

fan beam
non-linear
-binary leafs
dynamic gantry

Question 7

VMAT

Answer 7

dynamic gantry

Question 8

leaf motion between adjcent angles is limited by

Answer 8

leaf travel and gantry rotation speed

Question 9

vmat collimator angles

Answer 9

-variable
-more freedom
- reduce leakage in stationary leaves

Question 10

VMAT MLC shape

Answer 10

variable
-as the gantry rotates and the MLC moves ,the bealmets of the adjcent beam angles must be similar
ie smooth transition and small distances to travel

Question 11

Vmat dose rate

Answer 11

-variable
-if the dose rate required is to high or low the gantry speed can be adjusted to an extent

Question 12

gantry speed

Answer 12

-variable
-only tolerate small and smooth variations because of its weight
-up. to 1 rev per minute is irrelevant

Question 13

interplay occurs in

Answer 13

any dynamic MLC tx
happens in lung

Question 14

interplay is

Answer 14

relationship of motion of MLC and motion of lung

if these motion coincide the interplay ocurs

Question 15

when is interplay likely to be a problem

Answer 15

smallno.of fractions

if. theres large no. , interplay artefact is averaged out

Question 16

excessive modulation =

Answer 16

more uncertianity
can lead to differences in planned dose and delivered dose

Question 17

Modulation of the hardware creates

Answer 17

*Dose calculation uncertainty ↑
* Mechanical uncertainty ↑

Question 18

overall IMRT:
plan

Answer 18

simplish
single arc
fewer MLC movements tf less wear on machine

Question 19

overall IMRT:
plan quality

Answer 19

dose conformity and tissue sparing improve
VMAT similar plan quality

Question 20

overall IMRT:
tx time

Answer 20

reduced

-↑ comfort
-↓ external motion
-can be used w FFF to ↓ tx time more

Question 21

overall IMRT:
MU

Answer 21

30-60% reduction

tf reduced:
secondary cancer
head scatter
MLC scatter
out of field dose
integral dose