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Simultaneous optimization of beam orientations, wedge filters and field weights for inverse planning with anatomy‐based MLC fields
Author(s) -
Beaulieu Frédéric,
Beaulieu Luc,
Tremblay Daniel,
Roy René
Publication year - 2004
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1755492
Subject(s) - computer science , wedge (geometry) , algorithm , simulated annealing , guidance system , mathematical optimization , mathematics , engineering , geometry , aerospace engineering
As an alternative between manual planning and beamlet‐based IMRT, we have developed an optimization system for inverse planning with anatomy‐based MLC fields. In this system, named Ballista , the orientation (table and gantry), the wedge filter and the field weights are simultaneously optimized for every beam. An interesting feature is that the system is coupled to Pinnacle 3 by means of the PinnComm interface, and uses its convolution dose calculation engine. A fully automatic MLC segmentation algorithm is also included. The plan evaluation is based on a quasi‐random sampling and on a quadratic objective function with penalty‐like constraints. For efficiency, 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. Moreover, in order to generate directly deliverable plans, the following practical considerations have been incorporated in the system: collision between the gantry and the table as well as avoidance of the radio‐opaque elements of a table top. We illustrate the performance of the new system on two patients. In a rhabdomyosarcoma case, the system generated plans improving both the target coverage and the sparing of the parotide, as compared to a manually designed plan. In the second case presented, the system successfully produced an adequate plan for the treatment of the prostate while avoiding both hip prostheses. For the many cases where full IMRT may not be necessary, the system efficiently generates satisfactory plans meeting the clinical objectives, while keeping the treatment verification much simpler.