TG-142: Quality Assurance of Medical Accelerators

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AAPM TG-142: Quality assurance of medical accelerators (External link)

Overview

TG-142 updates TG-40 recommendations for linear accelerator quality assurance recommendations. By setting different tolerances based on the intended use of the accelerator (non-IMRT, IMRT, SRS/SBRT), TG-142 attempts to balance the costs of implementing a QA program against it's costs. TG-142 also adds information on Asymmetric jaws, multileaf collimators (MLCs), and dynamic/virtual wedges. The report also gives specific recommendations regarding setup of a QA program regarding QA team members, procedures, training, and end-to-end system checks.

Machine Check Tables

Daily Checks

Category Procedure Non-IMRT IMRT SRS/SBRT
Dosimetry X-ray output constancy (all energies) 3% 3% 3%
Dosimetry Electron output constancy (weekly test) 3% 3% 3%
Mechanical Laser Localization 2mm 1.5mm 1mm
Mechanical Distance Indicator (ODI) @ iso 2mm 2mm 1mm
Mechanical Collimator size indicator 2mm 2mm 1mm
Safety Door Interlock Functional Functional Functional
Safety Door Closing Safety Functional Functional Functional
Safety Audiovisual monitors Functional Functional Functional
Safety Stereotactic area monitor NA NA Functional
Safety  Radiation area monitor Functional Functional Functional
Safety Beam on indicator Functional Functional Functional

Monthly Checks

Category Procedure Non-IMRT IMRT SRS/SBRT
Dosimetry X-ray output constancy 2% 2% 2%
Dosimetry Electron output constancy 2% 2% 2%
Dosimetry Backup monitor chamber constancy 2% 2% 2%
Dosimetry Typical dose rate constancy NA 2% 2%
Dosimetry Photon beam profile constancy 1% 1% 1%
Dosimetry Electron beam profile constancy 1% 1% 1%
Dosimetry Electron beam energy constancy 2%/2mm 2%/2mm 2%/2mm
Mechanical Light/Radiation field coincidence 2mm/1% an a side 2mm/1% an a side 2mm/1% an a side
Mechanical Light/Radiation field coincidence 1mm/1% an a side 1mm/1% an a side 1mm/1% an a side
Mechanical Distance check device for lasers compared with front pointer 1mm 1mm 1mm
Mechanical Gantry/collimator angels indicator 1.0° 1.0° 1.0°
Mechanical Accessory trays 2mm 2mm 2mm
Mechanical Jaw position indicators (symmetric) 2mm 2mm 2mm
Mechanical Jaw position indicators (asymmetric) 1mm 1mm 1mm
Mechanical Cross-hair centering (walkout) 1mm 1mm 1mm
 Mechanical Treatment couch position indicators 2mm/1.0°  2mm/1.0°  1mm/0.5°
Mechanical Wedge placement accuracy 2mm 2mm 2mm
Mechanical Compensator placement accuracy 1mm 1mm 1mm
Mechanical Latching of wedges/blocking tray Functional Functional Functional
Mechanical Localization lasers 2mm 1mm 1mm
Safety Laser guard interlock Functional Functional Functional

Annual Checks

 Category  Procedure  Non-IMRT IMRT SRS/SBRT
 Dosimetry X-ray & Electron Flatness Change from Baseline 1% 1% 1%
Dosimetry X-ray and Electron symmetry change from baseline 1% 1% 1%
Dosimetry SRS arc rotation mode; MU setting vs delivered NA NA 1.0MU or 2%
Dosimetry SRS arc rotation mode; Gantry arc setting vs delivered NA NA 1.0 degree or 2%
 Dosimetry X-ray/electron output calibration (TG-51) 1% 1% 1%
Dosimetry  Spot check of field size dependent output factors 2% for < 4x4cm2 

1% for ≥ 4x4cm2

2% for < 4x4cm2 

1% for ≥ 4x4cm2

2% for < 4x4cm2 

1% for ≥ 4x4cm2

 Dosimetry Output factors for electron applicators  2% 2% 2%
 Dosimetry X-ray beam quality (PDD10 or TMR2010) 1% 1% 1%
Dosimetry  Electron beam quality (R50) 1mm 1mm 1mm
Dosimetry Physical Wedge Transmission Factor 2% 2% 2%
Dosimetry X-ray MU linearity (output constancy) 2% ≥ 5MU 5% (2-4MU), 

2% ≥ 5MU

5% (2-4MU), 

2% ≥ 5MU

Dosimetry Electron MU linearity (output constancy) 2% ≥ 5MU 2% ≥ 5MU 2% ≥ 5MU
Dosimetry X-ray output constancy vs dose rate 2% 2% 2%
Dosimetry X-ray output constancy vs gantry angle 1% 1% 1%
Dosimetry Electron output constancy vs gantry angle 1% 1% 1%
Dosimetry Electron and X-ray off-axis factor constancy vs gantry angle 1% 1% 1%
Dosimetry Arc Mode (expected MU, degrees) 1% 1% 1%
Dosimetry TBI/TSET mode Functional Functional Functional
Dosimetry PDD or TMR and OAF constancy 1% (TBI) or 1mm PDD shift (TSET) 1% (TBI) or 1mm PDD shift (TSET) 1% (TBI) or 1mm PDD shift (TSET)
Dosimetry TBI/TSET output calibration 2% 2% 2%
Dosimetry TBI/TSET accessories 2% 2% 2%
Mechanical Collimator rotation isocenter 1mm 1mm 1mm
Mechanical Gantry rotation isocenter 1mm 1mm 1mm
Mechanical Couch rotation isocenter 1mm 1mm 1mm
Mechanical Electron applicator interlocks Functional Functional Functional
Mechanical Coincidence of radiation and mechanical isocenter 2mm 2mm 1mm
Mechanical Table top sag 2mm 2mm 2mm
Mechanical  Table angle
Mechanical Table travel maximum range 2mm 2mm 2mm
Mechanical Stereotactic accessories, lockouts, etc NA NA Functional
Safety Follow manufacturer’s test procedures Functional Functional Functional

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