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 | 2mm |
| 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 (symmetric) | 2mm or 1% on a side | 2mm or 1% on a side | 2mm or 1% on a side |
| Mechanical | Light/Radiation field coincidence (asymmetric) | 1mm or 1% on a side | 1mm or 1% on a side | 1mm or 1% on 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 | 1° | 1° | 1° |
| 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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