AbstractID: 7913 Title: Optimizing beam orientations and virtual wedges in multifield
conformal radiotherapy
In radiotherapy treatment planning, the objective is to deliver a prescribed dose to the
target volume while sparing surrounding normal tissues as much as possible. This task is
best accomplished with computer optimization. In this context, we have developed an
algorithm for multifield conformal radiotherapy (MFCRT), where subfields are generated
automatically for each beam. The first subfield is adjusted to the target volume
projection. The subsequent subfields are generated from this first one by removing the
overlapping surface of each organ at risk (OAR) respectively. Each subfield can be
realized with a multileaf collimator, and the effect of a virtual wedge can be added to this
segmentation without compromising treatment automation. In this perspective, we
propose to optimize simultaneously beam weights and orientations, along with wedge
angles and orientations, using fast simulated annealing. In this way, one can think of
finding the best plans in MFCRT, in order to compare with full intensity-modulated
radiotherapy (IMRT). There are some pragmatic advantages in proceeding with MFCRT:
plans directly deliverable, intuitive beam apertures and simpler verifications. We present
our first results, using a simplified dose calculation algorithm and physical criteria, for a
tumor located in the thorax. Considering the need in IMRT to convert ideal beam profiles
into deliverable ones, MFCRT appears as an interesting alternative to IMRT.