Physical characteristics of a miniature multileaf collimator

A preliminary study of the physical characteristics of a miniature multilea f collimator (mMLC) used with 4 MV x rays is reported. The mMLC attached to the accessory mount of a class C or D Varian linear accelerator (Varian On cology Systems, Palo Alto, CA) with a source to aperture distance of 65 cm. The field penumbra using the small leaves was found to be consistent with the anticipated field penumbra using photon jaws at the same source to aper ture distance as the mMLC. The percentage depth dose values of square field s were found to be consistent with the fields collimated with the upper and lower jaws. Output factors for the very small fields were found to vary ra pidly. Circular fields could be produced with depth dose characteristics si milar to those produced using conical tertiary collimators, commonly used f or radiosurgery, but with a broader penumbra. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)01401-7].