Special Procedures and Equipment

Question 1

What is the goal of QA?

Answer 1

• reduce the undertainty in treatment and to set an error tolerance limit for SRT treatment

Question 2

What are the uncertainties that contribute to the overall uncertainity of SRT?

Answer 2

• target location
• dosimetry in TPS
• radiation treatment delivery system
• image-guidance system

Question 3

What are the four main patient specific QA checks?

Answer 3

1. delivery of plan dose in a phantom
2. validation of photon fluence using a portal imaging system
3. point dose measurement
4. independent MU validation using MU check software

Question 4

Define isocentre accuracy?

Answer 4

• point in space abour which the collimator, table and gantry rotate

Question 5

Define mechanical isocenter

Answer 5

• point in space about which the linear accelerator and couch rotate
• use lasers and cross hairs to determine this

Question 6

Define radiation isocentre

Answer 6

• point where the radiation beams intersect if the gantry, collimator or couch is rotated

Question 7

What test is used to check the radiation isocentre?

Answer 7

• winston lutz test

Question 8

What is the phantom used and process of the winston lutz test?

Answer 8

• using QUASAR winston lutz wand
  1. phantom attached to linac
  2. ball centre is postioned at linac isocentre defined by lasers of the treatment room
  3. ball is irradiated with several beams at different angulations of the gantry and couch and each shot is imaging using film placed perpendicular to the beam direction or using the EPID on linac

Question 9

What does the winston lutz test show and tolernace?

Answer 9

• measured distances for all shots between the centre of thr ball shadow and radiaiton field reveal isocentre movements
• less then 1mm

Question 10

What are the daily gamma knife checks?

Answer 10

• funcitonality
• daily decayed estimate
• absorbed dose rate computed by TPS
• machine supplied with diode to measure output during a 4 minute exposure for comparison against computed profiles

Question 11

What are the daily QA for tomo and tolerances?

Answer 11

• beam output (3%)

- MVCT image quality (1mm)

Question 12

What are the daily QA checks for cyberknife?

Answer 12

• beam output
• MLC
• beam flatness
• beam symmetry (checking output across beam FOV)

Question 13

What are some applicator QA checks for brachy?

Answer 13

• check source can travel to intended location for treatment length
• check applicator length (anually)

Question 14

What is the source travel distance tolerance?

Answer 14

• 1mm

Question 15

What are the safety checks done daily on a halycon unit?

Answer 15

• door interlock
• audio
• video monitor
• radiaiton monitor
• radiation off at console
• stop treatment with timer
• collision interlock at end of couch and bore