Linac QA

acceptance testing

performed upon equipment installation, by physicists and vendor representative

commissioning

performed by qualified physicist, establishes baselines

QA testing

performed by physicist, equipment calibrated by ADL (accredited dosimetry callibration laboratory)

spot checks

• performed by therapist, equipment less precise

• array detectors

• multiple tests in 1 exposure (output, symmetry, constancy)

daily QA dosimetry

• x-ray output constancy: 3%

• electron output constancy: 3% (all energies at least 2x weekly)

daily QA mechanical

• lasers: 2mm (non IMRT), 1.5 (IMRT), 1mm (SBRT)

• ODI: 2mm

• collimator size: 2mm (non IMRT/IMRT), 1mm (SBRT)

daily QA safety

door interlock & audiovisual monitor: functional

daily QA checks

• water level/temp/pressure

• gas pressure SF6!!

• general conditions

• tx devices

• supplies

monthly QA check - dosimetry

• x-ray output constancy: 2%

• x-ray beam profile constancy: 1%

• electron output constancy: 2%

• electron beam profile constancy: 1%

• backup monitor: 2%

• dose rate constancy: 2%

monthly QA check safety

emergency off & wedge interlocks: functional

monthly QA check mechanical

• lasers 2mm (non IMRT), 1mm (IMRT, SBRT, SRS)

• light vs x-ray: 2mm/1mm (asym)

• FS indicators: 2mm/1mm (asym)

• tx couch position (2mm/1 degree

• gantry/collimator: 1 degree

• cross hair center: 1 mm

• light field intensity & tray/wedge latches: functional

temperature and pressure corrections

• most ion chambers unsealed

• chamber sensitivity changes with temp and pressure

• increased temp, reading goes up

• increased pressure, reading goes down

monthly QA respiratory gating

• beam output constancy: 2%

• phase, amplitude beam control: functional

• in room respiratory monitoring system & gaing interlock: functional

annual QA check dosimetry

• x-ray flatness.symmetry: 1%

• electron flatness/symmetry: 1%

annual QA check safety

per manufacturer

annual QA check mechanical

• collimator rotation iso: 1mm

• coincidence of radiation and mechanical iso: 2mm

• table top sag: 2mm

• table angle: 1 degree

• electron applicator interlocks: functional

stability of isocenter

• stable: convergence @ iso

• wobble: non-convergence @ iso

• split field test: used to QA POP fields

split field test

materials: film, plastic tray on 4 feet, 2 shielding blocks

split field technique

• gantry @ 0, film on tray

• shielding block on top of film

• shielding block under tray, opposite side/jaw

• expose film @ 0 and 180

couch isocenter

• gantry @ 0, ref. marj w. table at iso height, rotate through various angles

• not exceed 1mm

• error: bad ref. mark, collimator, light crosshair alignment

machine dose rate constancy

• constancy: machine output, cGy/MU

• spot check confirms baseline parameters

• often combined with flatness, symmetry, beam penetragtion

• possible reasons: magnetron current, electron gun current, change in monitor ion chamber

• instruments: ion chamber, diodes, film, TLD

flatness

• maximum difference from CA dose over 80% field dimension

• defined at a depth of 10cm

symmetry

• difference in dose rate between any 2 points within 80% of field of dimension

FFF

ff removed in beam to attenuate photons

beam penetrative quality

• PDD/HVL - established upon commissioning using precision instruments

• spot check - standardize SSD and FS

• materials: tissue equivalent, ion chamber/diods

• technique: 2 measurements, compare ratio to established baseline usually at dmax and some depth <70%

imagers QA - kV and MV

• daily: collision/door interlock, warning lights.sounds, laser/image.tx iso coincidence (2mm), phantom localization and couch shift

• monthly: kV/MV/laser alignment (1mm), high contrast spatial resolution, CT # accuracy

• annual: imaging dose and x-ray generator performance