Varian TrueBeam — Engineer Field Guide

Engineer-oriented reference for the TrueBeam and TrueBeam STx. The iX replacement, and the platform most modern SRS / SBRT / VMAT / IMRT programs are built on.

Therapy rules are different — read this first

A linac delivers dose to patients. Downtime cascades into cancer treatment schedules. Daily output QA, monthly TG-142 checks, and annual full physics are mandatory and signed by a qualified medical physicist. Never bypass an interlock. When one trips, document, diagnose, resolve — it is protecting someone.

What changed vs. the Clinac iX

• Digital control chassis — replaces the Clinac analog backbone. Fault logs are richer, but board-level debug is different.
• FFF beams — 6 MV and 10 MV flattening-filter-free beams on TrueBeam; 6 MV FFF on STx. High dose rate changes QA cadence.
• MLC options — Millennium 120 5 mm on TrueBeam; HD120 2.5 mm central leaves on STx. HD120 is the SRS differentiator.
• PerfectPitch 6DoF couch — on STx and optionally on TrueBeam. Mandatory for modern SRS programs.
• Imaging chain — kV / kV CBCT (OBI) with sub-mm setup accuracy; MV portal imager retained.
• Maestro control architecture — different console generation than iX.

Top failure modes

1. Klystron / magnetron end-of-life — filament current drops, RF power sags, interlocks trip. Scheduled consumable — plan replacement, don't wait for a failed treatment.
2. Waveguide vacuum leaks — catastrophic. Circulator, klystron, and bend magnet can take collateral damage. Vacuum logs tell the story.
3. MLC leaf motor failures — stuck leaves stop plans. HD120 leaves are finer-pitch and higher-count; wear patterns differ from Millennium. Leaf position accuracy is an explicit TG-142 number.
4. kV imager (OBI) dead pixels / panel drift — IGRT goes off the rails before anyone notices. Daily Winston-Lutz catches it; phantom-based QA confirms.
5. Portal imager (aS1200 / aS500) — less-noticed failure mode than kV, but MV imaging is the backup path.
6. Cooling / chilled water faults — flow alarm = stop, now. Not optional.
7. Thyratron / solid-state modulator degradation — scheduled consumable on earlier units; newer chassis move to solid-state pulse-forming networks.
8. Couch encoder / PerfectPitch drift — 6DoF accuracy is the SRS foundation. Monthly couch QA is non-negotiable.

Commissioning is a months-long event

• Beam-data collection for Eclipse (AAA / AcurosXB) across all energies and field sizes takes weeks.
• Small-field dosimetry per TRS-483 for SRS cones / HD120 fields is its own sub-project.
• End-to-end SRS test — imaging, MLC, couch, delivery, dose — is the accreditation gate.
• License-specific commissioning — RapidArc, HyperArc, SRS / SBRT packages each require their own validation.

Budget commissioning time in calendar months, not weeks, when planning go-live.

Software and licensing

• Eclipse TPS version must match the chassis. ARIA R&V ecosystem is standard.
• RapidArc / HyperArc / SRS package licenses are per-machine SKUs. Confirm in writing on refurb deals.
• Calypso (beacon tracking) is a separate integration.
• SGRT (AlignRT / Catalyst) is a third-party integration with its own QA chain.

Accepting a refurbished TrueBeam / STx

• Klystron / magnetron install date and hours
• Waveguide vacuum history and pressure logs
• MLC model confirmed (Millennium 120 vs HD120) and leaf-calibration report
• Full leaf-position accuracy table (worst-leaf, drift)
• kV OBI dead-pixel map and flat-field calibration
• CBCT reconstruction calibration (CT-number accuracy)
• MV imager calibration
• PerfectPitch 6DoF couch (if quoted) — end-to-end test, Winston-Lutz
• Thyratron / modulator replacement history
• Cooling-system service records
• Full interlock test pass
• RapidArc / HyperArc / SRS / FFF license list in writing
• Eclipse + ARIA version and TPS-compatibility confirmed
• State radioactive-materials (or radiation-producing-machine) license transferability
• Commissioning plan + physicist budget before patient #1

Things nobody tells you

• The STx is not just "TrueBeam with better MLC." 6DoF couch, HD120, and the SRS commissioning scope are a different clinical program. A department that buys STx without a committed SRS physicist is buying capability it can't deliver.
• FFF beam QA cadence is higher than flattened beams at equivalent dose throughput. Physicist labor line-items up accordingly.
• Klystron lead time — these are not off-the-shelf parts. A site without a parts agreement can sit days-to-weeks waiting on one. Plan.

Related

• TrueBeam
• TrueBeam STx
• Edge
• Halcyon
• Linear Accelerator
• HD120 MLC
• AAPM TG-142
• Rad Onc Physicist
• Brain SRS
• SBRT
• Clinac iX Field Guide — predecessor platform