Varian Clinac 23EX
Family: Varian Clinac EX (legacy) · Modality: Linear Accelerator
Higher-energy dual-energy C-arm linear accelerator in Varian's Clinac EX-series. Positioned above the Clinac 21EX on photon-energy range — 23EX ships with 6 MV and 18 MV photon energies plus an extended electron suite up to 22 MeV. Direct predecessor to the Clinac iX 6+18 MV configuration. Deployed broadly for treatment of deep-seated or bulky disease where the 15 MV top energy on 21EX / Clinac iX 6+15 MV isn't adequate.
What 23EX adds over 21EX
- 18 MV photon beam (vs 21EX's 15 MV typical high-energy). Higher beam energy means deeper dose maximum and different secondary-radiation / neutron-shielding considerations.
- 22 MeV electron capability at the top of the electron energy suite.
- Neutron shielding requirements — at 18 MV, photoneutron production becomes a meaningful secondary-radiation concern; maze, door, and vault shielding are designed for 18 MV neutron dose on 23EX installations. Standard 21EX vault shielding at 15 MV may be inadequate for 23EX without re-engineering.
Platform highlights
- 6 MV and 18 MV photon energies — dual-energy operator-selectable.
- Electron energies — 6 / 9 / 12 / 15 / 18 / 22 MeV.
- Millennium MLC — 120-leaf or 80-leaf (configuration-dependent).
- 600 MU/min maximum dose rate.
- Klystron-based RF — shared with 21EX; klystron is the primary wear item.
- On-Board Imager (OBI) — kV imaging on late-production 23EX units.
- Head geometry — shared with Clinac iX / Trilogy / Novalis TX.
Specs
- Dual photon energies: 6 MV + 18 MV
- Electron energies: 6 / 9 / 12 / 15 / 18 / 22 MeV
- Millennium 120-leaf or 80-leaf MLC
- 600 MU/min dose rate
- Klystron RF · SF6 waveguide
- OBI (late-production)
- ±185° gantry rotation · 100 cm SID
Clinical positioning
- Deep-seated and bulky disease — prostate, lung, thoracic, abdominal, complex pelvic.
- Bariatric patient populations — 18 MV beam penetration benefits large-patient dosimetry.
- 3D-CRT, IMRT, IGRT — the clinical workhorse workflows.
- Electron therapy up to 22 MeV — used for select electron-boost applications and mycosis fungoides / skin / chest-wall treatments.
Service reality
- Vault neutron shielding is a specific consideration on 18 MV platforms. Replacing a 23EX with a 15 MV-only successor typically doesn't require vault rework; the reverse (installing 23EX into a 15 MV vault) does.
- Klystron / waveguide / thyratron service patterns same as 21EX.
- Head and MLC parts-compatibility with Clinac iX is a meaningful advantage.
- TG-142 commissioning and periodic QA per AAPM TG-142 (TG-142).
Market position (secondary / refurb)
- Mid-volume refurb platform. 23EX is less common than 21EX in the secondary market because fewer sites specified 18 MV at the outset; clinically, most treatment volume is served by 6 MV and 10–15 MV beams.
- Service ecosystem shared with the rest of the Clinac EX / iX generation; parts supply mature.
- Upgrade pathway — Clinac iX 6+18 MV → TrueBeam (chassis replacement).
Relationship to siblings and successors
- Clinac 21EX — lower-high-energy sibling (6 + 10/15 MV).
- Clinac 2100C / 2300C — predecessor-class.
- Clinac iX 6+18 MV — direct successor.
- TrueBeam — current-generation chassis replacement.