1.1 Linear Accelerator Components

flow of internal components of linac

1. modular (magnetron/klystron) — pulse into waveguide (microwaves)

2. electron gun injects electrons into waveguides (electrons come from tungsten filaments)

3. microwaves accelerate electrons through the accelerating waveguide (@ SOL), using steering magnets used to focus beam

4. magnets deflect the beam to the tungsten xray target and when electrons interact, theyre converted into photos/xrays

5. photons/xrays focused thru primary collimator to rid of scatter

6. shape the beam thru the flattening filter — to uniformly distribute photon into cone shape of beam

7. beam pass thru 2 ion chambers (dual ionization chambers) — measuring dose thats delivered

8. pass thru treatment head (jaws: form x and y field size) and multi-leaf collimator (MLC: conforms beam to unique shapes)

gantry

 large, rotating arm-like structure that houses and moves the radiation-producing components around the patient during radiation therapy

• Rotates 360 deg.

how far does the gantry rotate vs collimator vs floor

gantry + collimator = both 360 deg.

floor = 180 deg.

how does the couch move?

• move laterally. longitudinally, verticaly, (some beds allow for pitch and roll tilting ⟹ “6-degrees of freedom”)

onboard kv imaging

Onboard kV (CBCT) imaging: source panel/detector 

• Kv produces diagnostic level xrays for pictures (orthogonal pictures)

hand pendant

handheld control device to control linac/couch/positioning

mechanical isocentre

invisible point in the room where everything is centered and everything rotates relative to this point

radiaiton isocentre

point in space where the radiation beam intersect when the gantry is rotated and the beam is on

CAX

central axis

SSD

source-skin distance

SAD

source-axis distance (axis = isocentre in pt)

SID

source-imager distance

TTH

tabletop height (isocenter to flat top of table)

laser

thin beams of light that intersect at the isocentre, acting as visual reference for the isocentre, used to position pt and accurately align the isocentre in the body

where are the lasers in the linac room

• Ceiling laser: used when gantry is rotated, bisects pt into R/L planes AND superior-inferior plans  

• Sagittal laser: shine from foot of bed and splits pt into R/L planes  

• right/left laser: bisect into superior-inferior AND anterior-posterior

is the linac room light or dark

Ū light (esp during cleaning and entry/exit), but during treatment = dim lighting to see field and lasers for setup