TG-142: Complete LINAC QA Guide (AAPM Protocol)
The international reference protocol for radiotherapy quality assurance — tests, tolerances, frequencies and recommended equipment
📑 Table of Contents
What is TG-142?
The AAPM Task Group 142 (TG-142) is the reference report from the American Association of Physicists in Medicine that defines the quality assurance (QA) programme for medical linear accelerators (LINACs). Published in 2009, it replaced and significantly expanded the TG-40, becoming the international standard for radiotherapy QA.
- Updated TG-40 (1994) recommendations
- Added specific tests for multi-leaf collimators (MLC)
- Included QA for IMRT, VMAT, and stereotactic techniques (SRS/SBRT)
- Defined tolerances for integrated imaging systems (CBCT, EPID, kV)
- Established test frequencies: daily, monthly, and annual
Why is TG-142 Important?
Compliance with TG-142 ensures radiotherapy treatments are delivered with maximum precision and safety. A robust QA programme based on TG-142:
- Ensures dosimetric accuracy — essential for tumour control
- Detects deviations before they affect patients
- Meets regulatory and hospital accreditation requirements
- Supports advanced techniques like IMRT, VMAT and SRS/SBRT safely
- Meets requirements of the European Directive 2013/59/Euratom on radiation protection
Daily Daily Tests
Daily tests verify basic accelerator functionality before starting treatments. With equipment like the Daily QA 4 Pro, these checks can be completed in under 5 minutes.
| Parameter | Non-IMRT Tolerance | IMRT Tolerance | SRS/SBRT Tolerance |
|---|---|---|---|
| Output (Dose Rate) | ±3% | ±3% | ±3% |
| Field Size | ±2 mm | ±2 mm | ±2 mm |
| Alignment Lasers | ±2 mm | ±2 mm | ±1 mm |
| Distance Indicator (ODI) | ±2 mm | ±2 mm | ±2 mm |
| Safety: door, audio/video | Functional | Functional | Functional |
Monthly Monthly Tests
Monthly tests evaluate more detailed beam and mechanical system parameters. The IC Profiler and MapCHECK 3 are reference equipment for these checks.
| Parameter | Non-IMRT Tolerance | IMRT Tolerance | SRS/SBRT Tolerance |
|---|---|---|---|
| Output Constancy (photons) | ±2% | ±2% | ±2% |
| Output Constancy (electrons) | ±2% | ±2% | N/A |
| Profile Symmetry | ±3% | ±2% | ±2% |
| Flatness | ±2% | ±2% | ±1% |
| Beam Quality (energy) | ±2% | ±2% | ±1% |
| Mechanical Isocentre | ±2 mm diameter | ±2 mm diameter | ±1 mm diameter |
| MLC Accuracy | ±2 mm | ±1 mm | ±1 mm |
| CBCT Image Quality | Baseline | Baseline | Baseline |
Annual Annual Tests
Annual tests are the most comprehensive and include absolute calibration per the TG-51 protocol. Equipment such as the PC Electrometer and SunScan 3D are essential.
| Parameter | General Tolerance | SRS/SBRT Tolerance |
|---|---|---|
| Absolute Calibration (TG-51) | ±1% | ±1% |
| PDD/TMR Verification | ±2% | ±2% |
| Field Factors | ±2% | ±2% |
| Light-Radiation Coincidence | ±2 mm | ±1 mm |
| Mechanical-Radiation Isocentre | ±2 mm | ±1 mm |
| Collimator Accuracy | ±2 mm | ±1 mm |
| MLC Transmission | Baseline ±0.5% | Baseline ±0.5% |
| MLC Leaf Speed | Per manufacturer specifications | |
MLC and IMRT-Specific Tests
TG-142 includes dedicated sections for MLC quality assurance, essential for modern techniques such as IMRT and VMAT.
| MLC/IMRT Test | Frequency | IMRT Tolerance |
|---|---|---|
| Leaf Positional Accuracy | Monthly | ±1 mm |
| Leaf Speed | Monthly | Per manufacturer spec |
| Inter-leaf Transmission | Annual | ≤2% of reference |
| Tongue-and-groove Effect | Annual | Periodic verification |
| Picket Fence Test | Monthly | ±1 mm |
| VMAT Verification | Monthly | Baseline |
Imaging Systems QA (IGRT)
A major innovation of TG-142 over TG-40 is the inclusion of QA recommendations for integrated imaging systems:
- CBCT (Cone-Beam CT): Image quality, geometric accuracy, patient dose
- kV Imaging: Spatial calibration, image quality, isocentre coincidence
- EPID (Electronic Portal Imaging): Uniformity, spatial resolution, calibration
- Image-isocentre coincidence: ±2 mm (±1 mm for SRS)
Action Levels in TG-142
Level 1 — Inspection
Document and monitor trends. Repeat measurement to confirm.
Level 2 — Scheduled Action
Correct within a defined timeframe. Assess impact on ongoing treatments.
Level 3 — Immediate Action
Suspend treatments until correction and verification. Do not treat patients.
Recommended Equipment for TG-142 Compliance
Sun Nuclear, represented by Interphysix in Europe, offers comprehensive solutions for implementing a TG-142-compliant QA programme:
☀️ Daily QA 4 Pro
Checks output, symmetry, energy, field size and uniformity in a single setup — results in under 5 minutes.
View product →📊 IC Profiler
2D ionisation chamber array for beam profile, symmetry and flatness measurements.
View product →🎯 MapCHECK 3
High-resolution 2D diode array for IMRT plan QA with automatic gamma analysis.
View product →🌀 ArcCHECK
Cylindrical 3D phantom with 1386 detectors for VMAT and IMRT verification.
View product →⚡ PC Electrometer
High-precision electrometer for absolute calibration per TG-51.
View product →TG-142 vs TG-40: Key Differences
❌ TG-40 (1994)
- Conventional radiotherapy only
- Basic MLC mention
- No imaging systems QA
- Uniform tolerances
- No SRS/SBRT coverage
✅ TG-142 (2009)
- IMRT, VMAT, SRS, SBRT included
- Dedicated MLC test section
- CBCT, kV, EPID covered
- Technique-specific tolerances
- Tighter SRS/SBRT tolerances
Need Equipment for Your QA Programme?
Interphysix is an exclusive Sun Nuclear representative in Europe. We help implement complete TG-142-compliant QA programmes.
Contact us for a quoteReferences
- Klein EE, et al. “Task Group 142 report: Quality assurance of medical accelerators.” Med Phys. 2009;36(9):4197-4212. DOI: 10.1118/1.3190392
- Hanley J, et al. “AAPM Task Group 198 Report.” Med Phys. 2021;48(10):e771-e921. DOI: 10.1002/mp.14992
- AAPM Report No. 142 — Official AAPM page
Última actualização: 26/04/2026