AbstractID: 7681 Title: Enhancing IMRT with MLC Rotation
MLC based IMRT techniques are well established but suffer several physical limitations. Dosimetric spatial resolution is limited by
the MLC leaf width, interleaf leakage and tongue and groove effects degrade dosimetric accuracy, small MLC sub-fields reduce
treatment efficiency and the mechanical range of leaf motion limits the maximum deliverable field size. Still, MLC based techniques
are the most popular because they can be implemented on the majority of manufacturer’s linacs. Collimator rotation is used in
standard radiation therapy to improve the conformity of the MLC shape to the target volume. Until now, collimator rotation has not
been fully exploited in IMRT due to the complexity of deriving the MLC leaf configurations for rotated sub-fields. Here we report on
a new way that MLC based IMRT is delivered which incorporates collimator rotation. Rotation of the MLC provides another degree
of freedom when calculating the leaf sequences for a desired fluence map. We have developed a series of specialized algorithms that
are capable of determining rotated MLC segments*. The fields may be delivered statically (with the collimator not rotating and the
leaves stationary during irradiation) or dynamically (with the collimator rotating and leaves moving simultaneously during
irradiation). We present results of our leaf motion and collimator rotation algorithms by comparing measured and desired dose
distributions. Comparisons are also made between our method and conventional sliding window and step-and-shoot techniques.
Improvements in spatial resolution, interleaf effects, MU efficiency and maximum deliverable field size are observed.
*Patent Pending