Simultaneous optimization of beam orientations, wedge filters and field weights for inverse planning with anatomy‐based MLC fields

Abstract

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 Pinnacle3 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.

Performance evaluation of an algorithm for fast optimization of beam weights in anatomy-based intensity modulated radiotherapy

“…However, all the parameters were stringently kept within the desired limits in ABIP plans for both the cases. As suggested in recent investigations,[3132] it will be necessary to optimize the beam orientations, couch and wedge angles to reach more competitive plans.…”

Multiobjective optimization with a modified simulated annealing algorithm for external beam radiotherapy treatment planning

“…BALLISTA is an inverse planning software developed recently at our institution. 6 It is very useful for cases where full intensity-modulated radiation therapy ͑IMRT͒ is not absolutely needed, but manual forward planning in threedimensional ͑3D͒ conformal therapy ͑3D-CRT͒ often leads to suboptimal plans. BALLISTA is capable of optimizing treatment plans with various degrees of freedom: gantry angle, couch angle, collimator angle, wedge angle, and segment weight.…”

“…The main features of BALLISTA have already been described in length, 6 but will be briefly presented here for the sake of completeness. A simulated annealing algorithm optimizes the beam configuration ͑gantry, couch, and collimator angles͒.…”

“…A popular approach is to introduce importance factors in the objective function to mimic the planner's preferences between the often contradictory goals of treatment planning. 3,5,6 Another suggested approach consists of a number of hard constraints, which must be satisfied, with a single remaining objective being optimized consistently with the constraints. 4 However, both these objective functions need their parameters fixed before the optimization.…”

Towards Conformal Interstitial Light Therapies: Modelling Parameters, Dose Definitions and Computational Implementation

“…Simulated annealing has been used as an optimization technique for radiation treatment planning in the clinical setting, with successes reported in both external beam radiation therapy (EBRT) (Aubry et al, 2006;Beaulieu et al, 2004;Morrill et al, 1995) and high dose-rate (HDR) brachytherapy (Lessard & Pouliot, 2001;Martin et al, 2007). For EBRT, the basic optimization problem is the determination of the appropriate temporal and spatial arrangements of multiple external radiation beams, which can be tailored in highly sophisticated and precise ways in modern 3-D conformal radiation therapy.…”