  Robust fine tuning of multi-leaf collimator (MLC) Treatment Planning System
(TPS) modeling parameters is crucial for creating an optimal beam model,
particularly with the ever-increasing accuracy required for advancing
techniques. Challenges arise from balancing the trade-off between multiple
parameters and therefore the quality of tuning depends on the experience of the
physicist and the procedures used. This is in part due to limitations of the
MLC modeling within the TPS. As a result, the actual values used have been
shown to vary widely between centers. We present and evaluate two different MLC
transmission maps to improve the modeling of the Elekta Agility MLC in the
RayStation TPS. The model prototypes were developed with discrete and
continuous MLC transmission maps assigned to the tongue-and-groove and leaf tip
regions. The prototypes aimed to replicate the average doses for synchronous
and asynchronous sweeping gap fields, measured using a Farmer chamber in a
solid water phantom. This study investigated the impact of these improvements
using test fields and a wide variety of measured clinical plans in three
different centers. The models achieved good accuracy and the improvements
facilitated the standardization of the configuration and commissioning
processes and extended the range of validity of TPS dose calculations in wide
variety of treatment plans and measuring systems. The simpler MLC prototype
with discrete transmission maps performed similarly to the more sophisticated
one both in tests and clinical plans and constitutes a good option for routine
clinical practice. The need for trade-offs were reduced and the models were
successfully configured using a common set of parameters across the three
centers, which is useful for reducing the workload and the risks associated
with the configuration process, thus improving the accuracy and safety of
radiotherapy treatments.
