Medical Physicist's Notes · QA BeamChecker™ Plus
The QA BeamChecker Plus is purpose-built for the dosimetric portion of an AAPM TG-142 / TG-198 daily-QA programme — output and profile constancy across every photon and electron energy in a single setup. The mechanical, safety and imaging daily tests stay on the tools designed for them. This page sets the scope explicitly, with the standards and the manufacturer brochure cited inline.
The four daily-QA categories defined in TG-142 (Klein 2009) and reprinted in TG-198 (Hanley 2021). Only one of them needs a multi-chamber array — that is where the BeamChecker Plus lives.
Output constancy per energy; flatness and symmetry (radial and transverse). The portion of the TG-142 daily list that needs a multi-chamber array detector.
BeamChecker Plus — 8-chamber array
±2 mm laser localisation, optical distance indicator at isocentre, collimator size indicator. These are geometric checks against an external reference.
Stays on a separate mechanical-QA tool
Functional safety interlocks — pass / fail tests, not measurements. Driven by RTT workflow at the start of the day.
Stays on RTT-driven safety checklist
Collision interlocks, positioning / repositioning, imaging-vs-treatment coordinate coincidence for kV, MV and CBCT — required when the linac has imaging.
Stays on a separate imaging-QA tool
One centre chamber + four quadrant chambers at 7.5 cm from centre + three energy-ID chambers, per the Manufacturer brochure. Each row below maps a TG-142 daily test to the chamber set and the tolerance band it answers.
X-ray output constancy
TG-142 daily action threshold ±3% from baseline; no-treat threshold ±5% (Klein 2009). The centre chamber measures output per energy; automatic energy detection lets every photon energy on the machine run in any order without a manual reset.
Source: Klein EE et al., AAPM TG-142, Med Phys 36(9):4197–4212 (2009).
Electron output constancy
Same ±3% / ±5% bands; the same 8-chamber setup covers 6–25 MeV electrons. No second device or energy-by-energy chamber swap.
Source: Klein EE et al., AAPM TG-142 (2009); Manufacturer brochure 1239-26.
Beam-profile constancy
Four quadrant chambers at 7.5 cm from centre give radial and transverse profile constancy on every beam — the basis for the flatness and symmetry trends in routine daily logs (e.g. Chan et al., 5-year Trilogy data).
Source: Chan MF et al., Int J Med Phys Clin Eng Radiat Oncol 4(4):290–299 (2015), PMID 27547595.
Beam-energy constancy
Three energy-ID chambers let the device recognise and verify the delivered energy automatically — the same hardware path used for the energy-constancy daily check.
Source: Manufacturer brochure 1239-26 (chamber layout).
Scope of this page
The page treats BeamChecker Plus as the dosimetric-array piece of a TG-142 / TG-198 daily-QA programme — not a single-tool replacement for the full daily-QA list. The mechanical, safety and imaging daily tests have dedicated tools (collimator-rule, level, room-laser jig, imaging QA phantom, RTT safety checklist). The eight-chamber array does the morning constancy work that needs a multi-point dose measurement.
Sources cited on this page
QA BeamChecker™ Plus
Sibling posts in the QA BeamChecker Plus family.