A simple model for dynamic jaw dosimetry

Dynamic beam delivery promises to become an important component in radiotherapy. Dynamic jaw treatment fields allow each jaw to move independently of the others during beam delivery. A treatment segment is the simplest dynamic-jaw treatment field that can be given, whereby each jaw is in a state of uniform motion during the dose delivery. More complex radiation fields may be constructed by concatenating treatment segments together. Thus before the dosimetry of the general dynamic jaw field can be understood, it is important to understand the dosimetry of a treatment segment. A simple model for the dosimetry has been developed relating the dose delivered by the dynamic beam to a dose delivered by a corresponding static beam. This model presents a number of important conceptual ideas that can be generalized to describe more complex dynamic fields. Essentially, the dynamic dose at a point is a spatial average of doses from the static beam´s profile. The model was tested experimentally by measuring with a diode array, dynamic beams generated on a linear accelerator. Their profiles were compared to those generated by the model and were found to be typically within 2% of one another