Varian
Clinac 21EX
The Varian Clinac 21EX is a medical linear accelerator designed for radiation therapy. The Clinac 21EX produces photon beams at 6 MV and up to 25 MV, with a maximum dose rate of 600 MU/min. The Clinac 21EX was manufactured from 1998 to 2012.[1]
How it works
For image guidance, the Clinac 21EX can be equipped with kV (kilovolt) imaging, such as the On-Board Imager (OBI), which is optional on this model. When fitted with OBI, the system can acquire cone-beam CT (CBCT) images for patient positioning and target localization. The Clinac 21EX also supports an optional electronic portal imaging device (EPID), such as the aS500 or aS1000, for verifying treatment field placement.[1]
The Clinac 21EX is designed for 3D conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), and stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) when used with optional cones or a micro-MLC. The system can also support VMAT (volumetric modulated arc therapy) when equipped with OBI and appropriate software upgrades, although this is not a base capability.[1]
Applications
The Clinac 21EX is used for conventional radiation therapy, including 3D-CRT and IMRT, to treat a wide range of cancers. With optional imaging and stereotactic accessories, it can also perform SRS and SBRT for tumors in the brain, lung, liver, and spine. The system supports both photon and electron beam treatments, making it versatile for superficial and deep-seated lesions.[1]
- 3D conformal radiotherapy
- Intensity-modulated radiation therapy (IMRT)
- Stereotactic radiosurgery (SRS) (optional)
- Stereotactic body radiation therapy (SBRT) (optional)
- Volumetric modulated arc therapy (VMAT) (with optional OBI)
Why won't it start?
Documented failure modes, common issues, and field considerations.
- May lack advanced imaging/VMAT unless upgraded
- Older software UI
- Some units have high beam hours
What do the numbers mean?
Dimensions & facilities2
- Multi-Leaf Collimator (MLC)
- 80 leaves (field size 40x40 cm); 120 leaves (field size 40x40 cm, central 20 cm: 5 mm leaf width, outer 20 cm: 10 mm leaf width)[1]
- Multi-Leaf Collimator (MLC)
- 120 leaves (field size 40x40cm; central 20cm of field 5mm leaf width; outer 20cm of field 10mm leaf width)[1]
Configuration & options29
Vintage & configurations
Documented models & variants
| Designation | Generation | Vintage | Changes | Source |
|---|---|---|---|---|
| Clinac 21EX Silhouette | — | — | Silhouette option for smaller room size | oncologysystems.com[1] |
Where are the manuals?
Generated from public-source data on file. Enter your email to access — nothing is published; details are routed privately.
Not publicly documented
Field notes
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Frequently asked questions
What are the photon energy options for the Clinac 21EX?
The Clinac 21EX offers a photon energy configuration of 6 and 10 MV, with options for 15 and 18 MV.[1]
What types of multi-leaf collimator (MLC) are available for the Clinac 21EX?
The Clinac 21EX can be equipped with either an 80-leaf or 120-leaf MLC, both covering a field size of 40x40 cm.[1]
Does the Clinac 21EX support image-guided radiation therapy (IGRT)?
The Clinac 21EX can support IGRT with the optional On-Board Imager (OBI) system, which enables kV imaging and cone-beam CT (CBCT).[1]
Not publicly documented
The following facts about the Clinac 21EX are absent from this record as of this revision. First-hand knowledge or a citation closes a gap; every submission is reviewed before publication.
The control-system platform and OS era of the Clinac 21EX are not on record.
Answerable by: an engineer who operated it or OEM installation records
The process node or technology generation of the Clinac 21EX is not on record.
Answerable by: an OEM datasheet or a fab qualification report
No publicly documented compatible parts, consumables, or accessories for the Clinac 21EX are on record.
Answerable by: an OEM parts catalog or a service engineer
No publicly hosted manuals, SOPs, or datasheets for the Clinac 21EX are on record.
Answerable by: university cleanroom staff or an OEM application specialist
Sources & citations
Sources (1)Every fact above is drawn from these public sources
- [1]oncologysystems.com — oncologysystems.comoncologysystems.com
Last updated Oct 4, 2026.