ESTRO 2023 - Abstract Book

S466

Sunday 14 May 2023

ESTRO 2023

These doses can also be used to compute the fluence reduction at the leaf sides as a function of the distance to the leaf tip (s) (Fig 2a) as well as its first derivative, which is proportional to the effective tongue-and-groove width (Fig 2b). RayStation and Monaco did not account for this effect, which made trade-offs in the MLC parameters necessary and greatly varied the final MLC parameters used by different centres (Fig 2c).

The parameters used by each centre strongly depended on the procedure used for its determination (e.g., FOURL test vs tuning with clinical plans). In comparison, these leaf tip effects were much less pronounced for the Millennium MLC. Raytracing showed that these challenging effects were directly related to the MLC geometry and that the characteristics responsible for the large leaf tip effects of the Agility were its tilting design and its small source-to-collimator distance.

Conclusion