AbstractID: 8250 Title: Dosimetric Study of a Modified Beam Delivery System for IMRT
Our PRIMUS linear accelerator was recent modified with hardware and software
upgrades. The upgrades allow the implementation of a newly designed beam delivery
technique for IMRT. In this new technique, all IMRT segments for a particular gantry
angle are delivered sequentially without switching off the high voltage. Although the
electron gun is continuously emitting electron beam, the electron beam to the target is
controlled using phasing technique with the microwave power. When the electron beam
is needed, the electron beam is injected into the waveguide in-phase with the microwave
power. On the other hand, when the photon beam is not needed during the formation of
segments, electron beam is set de-phased with the microwave power. This new technique
allows a faster delivery of IMRT segments and hence improved treatment time. Because
this technique uses a soft method of switching beam, the beam profile could be affected
by beam leakage during de-phasing stage and beam stabilization. To examine these
effects on the beam profile, two experiments, one with a central cold spot and the other
with a hot spot segmentation configuration were proposed. The beam designed consists
of 4 square fields each is bigger than the other by 2 cm. Our analyses indicate that the
beam profiles are not uniform. However, separation of the tongue-and-groove effect and
leaf transmission lead us to believe that the beam is sufficiently similar to those beams
produced in our standard beam delivery technique.