Fixed cone, Iris or MLC
The MLC is 30–40% faster and slightly less conformal — which matters depends entirely on the case.
Built in·updated 2026-08-03
In a brain-metastases comparison, cone/Iris and InCise MLC plans reached the same coverage (98.57% vs 98.75%), but the delivery differed enormously: 166 beams and 58 minutes for cone/Iris against 58 beams and 36 minutes for the MLC.
Conformity indices were slightly better for cone/Iris. So the trade is real but small, and it points one way for most cases and the other way for a specific set:
Choose the MLC when delivery time is the limiting factor — a long treatment, a patient who cannot hold still, a busy machine.
Choose cones or Iris when the target is small, or when an organ at risk abuts the target. That is where the MLC's conformity deficit stops being a rounding error, and it is exactly the geometry a spine or skull-base case presents.
On a scored plan the choice is visible in two places at once: conformity in the plan-quality points, and monitor units in whatever deliverability measure is being used. Decide which one the criteria pay for before you pick.
Where the numbers come from
- Dosimetric comparison between cone/Iris-based and InCise MLC-based CyberKnife plans for single and multiple brain metastases
J Appl Clin Med Phys · 2016
Equal coverage; 166→58 beams, 58→36 min; MLC worse for small targets and abutting OARs
- Clinical impact of the VOLO optimizer on treatment plan quality and clinical treatment efficiency for CyberKnife
J Appl Clin Med Phys · 2020
VOLO vs Sequential: MU −1.1% to −28.4%, time −4.6% to −22.2%