# Linear accelerator quality assurance: daily, weekly, monthly and annual machine checks

Source: https://onco.cc/protocols/linear-accelerator-quality-assurance/  
OnCo record `linear-accelerator-quality-assurance` (Protocol). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Before patients are treated each day, the radiotherapy team checks that the treatment machine gives the right dose, points at the right place and stops when it should. Bigger checks follow every week, month and year, and after every repair. These checks are why a machine fault very rarely reaches a patient.

## Summary

The AAPM's current list (MPPG 8.b, 2023) sets the minimum: the qualified medical physicist (QMP) designs the programme, chooses tests that fit how the machine is used, and owns the results. Daily, on the beams in use that day: photon and electron output within 3% of the device baseline, profile constancy, the patient-positioning system (lasers within 2 mm if used for final set-up, or the imaging or surface system that replaces them), the distance indicator and a jaw setting, and safety: door interlock, audio and video monitoring of the patient, beam-on indicators and one anti-collision system in rotation. Weekly: quantitative multileaf collimator leaf-position accuracy within 0.5 mm at several gantry angles (a measured picket-fence test; log files alone are not enough). Monthly: output within 2%, energy and profile constancy, couch and angle readouts, a holistic dynamic-delivery (sliding window or VMAT) test within 2%. Annually: absolute calibration in water to TG-51 with a chamber calibrated at an accredited standards laboratory within two years, output within 1% of nominal, beam data compared with the planning system model within 1 to 2%, radiation isocentre by a Winston-Lutz test (all axes within 1 mm), small-field output factors, a full review of machine settings and the emergency procedures. After repairs the QMP's written return-to-service checks apply, and manufacturers' technical bulletins are reviewed at once. SRS and SBRT need the tighter stereotactic tests (MPPG 9).

In the UK, IPEM Report 81 (2018) informs practice in 91% of centres; a 2025 IPEM survey found most centres meeting or exceeding it, with 26% still measuring standard output weekly against the report's monthly recommendation. MPPG 8.b deliberately did not repeat a failure mode analysis and asks each centre to do its own, using its tests as the floor.

## Fields

- Kind: Protocol
- Last checked: 2026-11-11
- Also known as: linac QA; linac quality control; machine QA; morning QA; daily output check; TG-142; MPPG 8.b; IPEM Report 81; Winston-Lutz test; picket fence test

## Connected records

- protocols: [Patient identification and pre-treatment time-out in radiotherapy](https://onco.cc/protocols/radiotherapy-patient-identification-and-time-out/), [Risk-based quality management of the radiotherapy process (TG-100 failure mode and effects analysis)](https://onco.cc/protocols/radiotherapy-risk-analysis-fmea/)
- technologies: [C-arm medical linear accelerators (TrueBeam, Versa HD and others)](https://onco.cc/technologies/c-arm-linac/), [IMRT / IGRT (modern external beam)](https://onco.cc/technologies/imrt-igrt/), [Radiotherapy QA phantoms and dosimeters (Sun Nuclear, IBA Dosimetry, PTW)](https://onco.cc/technologies/radiotherapy-qa-phantoms-dosimeters/)

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