AbstractID: 4452 Title: IMRT Modeling influence on planning
The quality of an intensity modulated radiation therapy (IMRT) treatment plan can be strongly influenced by the physical and
mathematical models underlying a clinical planning system. This lecture provides an overview of the models that are commonly
employed for purposes of treatment planning for megavoltage (MV) photon-beam IMRT achieved through multi-leaf collimator
(MLC) delivery. IMRT treatment planning models will be examined which include models of: ionizing-radiation dose computation;
fluence-map optimization; MLC delivery sequence optimization; dosimetric plan evaluation; and “biologic” plan evaluation. Models
will be studied with focus on the assumptions, merits, and limitations involved with different models. The differences between reality
and the models will be explored. Emphasis will be placed on plan characteristics that exist in reality but are not reflected in the model
of the IMRT delivery. The influence of the algorithms employed to implement the models will also be discussed including methods
that involve discretization, rounding, and limited numerical precision. Practical examples that demonstrate the influence of modeling
differences on IMRT plan quality will be presented.
Educational Objectives:
1. Understand the influence of the choice of physical models employed in clinical IMRT
2. Understand the assumptions, merits, and limitations involved with different IMRT planning models
3. Review the conditions where IMRT modeling is suspect and requires careful scrutiny in clinical implementation