MLC
Multi-Leaf Collimator — array of motorized tungsten leaves that dynamically shape the treatment beam aperture, enabling IMRT, VMAT, SRS / SBRT, and complex conformal plans without the cast-block fabrication of pre-MLC era practice. Leaves move under continuous control during treatment delivery on modulated techniques.
Vendor classes:
- Millennium 120 — Varian standard 5 mm leaf width; on TrueBeam, Trilogy, Clinac iX.
- HD120 — Varian 2.5 mm central / 5 mm outer; on TrueBeam STx, Edge.
- Agility — Elekta 5 mm × 160 leaf; on Versa HD, Infinity, Synergy.
- MLCi / MLCi2 — Elekta predecessor.
- TomoTherapy binary MLC — 64-leaf, 6.25 mm, fully-in / fully-out modulation.
Why it matters to buyers: Leaf count, leaf width, and leaf-position accuracy drive plan conformality. 2.5 mm vs 5 mm is a meaningful clinical-capability difference for SRS / SBRT — sub-centimeter target conformity benefits from finer leaf pitch. License tier and MLC class together determine the clinical envelope the platform can deliver.
Why it matters to engineers: Individual leaf-motor failure is the top MLC fault — stuck leaves stop treatment plans. Leaf-position accuracy is an explicit TG-142 monthly metric (worst-leaf, drift). Carriage wear, leaf-bank alignment drift, and leaf-cleanliness all show up on QA checks before clinical impact.
Related
- Millennium 120
- Agility MLC
- HD120 MLC part
- Clinac iX MLC part
- Linear Accelerator
- CyberKnife (uses Iris variable aperture, not conventional MLC)
- TomoTherapy (binary MLC)
- IMRT
- VMAT
- SBRT
- Brain SRS
- AAPM TG-142
- Rad Onc Physicist
- TrueBeam Field Guide