Report 374 on TG51 Flashcards
Gantry angle
confirm with a physical level
do you level the tank empty or with water in tank?
with water in tank
how can you set SSD if you don’t have a pointer?
- calibrated room lasers
- gantry tilt method
- ODI (least accurate)
Halcyon- use MV imaging
how to ensure detector is on central axis
- use plumb bob
- close jaws to small field size and move detector up and down- watch if it drifts
- mark chamber holder and observe relative position to cross-hairs as chamber is moved up and down
simplified method to check beam quality before doing TG51 annually
-measure at 2 specified depths and calculate ratio, compare to historical
correcting for Pion and Ppol with depth
- should be done to get most accurate results
- Pion with depth is significant for FFF beams
0.6 rcav and 0.5 rcav?
report gives more accurate shifts for each specific detector using MC
how to deal with effect of scan speed?
compare measurements with slowest and fastest speed
use Pf foil or equation for %dd(10)x from %dd(10) for high energy beams?
Pb foil is more accurate
-equation introduces 0.2% error in kq
- even if you cannot put Pb foil at exactly 30 cm or 50 cm, better to say put at 35 cm and use 30 cm equation, then to not use Pb foil at all
- also do this for FFF beams
what does zeroing the electrometer do
essentially subtracts off background
why record Ppol values?
changes over time can indicate problems like poor connections
how can you vary dose per pulse?
- NOT by changing dose rate
- change SSD or depth of measurement
how to verify reference class behavior for a new ion chamber, Pion
-measure Pion for at least 3 values of a dose per pulse
long term stability of a reference ion chamber
- 3% within the 2 years
- can monitor with check sours, Co60 beam, cross-calibrate
what is Prp correction
-introduced in TG51 addendum
-takes into account off-axis variation in the intensity profile of the
radiation field over the sensitive volume of the ionization chamber
