AbstractID: 8872 Title: Simultaneous optimization of beam orientations, wedges and
field weights for planning with pre-defined MLC fields
As an alternative between forward planning and beamlet-based IMRT, we have developed an optimization system for inverse planning
with predefined anatomy-based MLC fields. In this system, the orientation (table and gantry), the wedge filter and the field weights
are simultaneously optimized for every beam. Optimal wedge angles and wedge orientations are determined using the concept of the
super-omni wedge. A bound-constrained quasi-Newton algorithm performs field weight optimization, while a fast simulated annealing
algorithm selects the optimal beam orientations. Plan evaluation is based on quasi-random sampling and on a quadratic objective
function with penalty-like constraints. As the system is coupled to Pinnacle3 by means of the PinnComm interface, it uses its fast
convolution/superposition dose calculation engine. Moreover, in order to generate directly deliverable plans, the following practical
issues have been incorporated in the system: collision between gantry and table, radio-opaque elements of table top and minimal
number of MUs for virtual wedge. We illustrate the performance of the new system on two patients. In a rhabdomyosarcoma case, the
system improved both the target coverage and the sparing of the salivary gland, as compared to a manually designed plan. In a similar
experience for a prostate case, we observed an increased dose conformity around the PTV with a reduced rectum toxicity. For the
many cases where full IMRT may not be necessary, the system efficiently produces very satisfactory plans meeting the clinical
objectives, while treatment and verification are comparatively much simpler.