4,165 research outputs found
Beam Orientation Optimization for Intensity Modulated Radiation Therapy using Adaptive l1 Minimization
Beam orientation optimization (BOO) is a key component in the process of IMRT
treatment planning. It determines to what degree one can achieve a good
treatment plan quality in the subsequent plan optimization process. In this
paper, we have developed a BOO algorithm via adaptive l_1 minimization.
Specifically, we introduce a sparsity energy function term into our model which
contains weighting factors for each beam angle adaptively adjusted during the
optimization process. Such an energy term favors small number of beam angles.
By optimizing a total energy function containing a dosimetric term and the
sparsity term, we are able to identify the unimportant beam angles and
gradually remove them without largely sacrificing the dosimetric objective. In
one typical prostate case, the convergence property of our algorithm, as well
as the how the beam angles are selected during the optimization process, is
demonstrated. Fluence map optimization (FMO) is then performed based on the
optimized beam angles. The resulted plan quality is presented and found to be
better than that obtained from unoptimized (equiangular) beam orientations. We
have further systematically validated our algorithm in the contexts of 5-9
coplanar beams for 5 prostate cases and 1 head and neck case. For each case,
the final FMO objective function value is used to compare the optimized beam
orientations and the equiangular ones. It is found that, our BOO algorithm can
lead to beam configurations which attain lower FMO objective function values
than corresponding equiangular cases, indicating the effectiveness of our BOO
algorithm.Comment: 19 pages, 2 tables, and 5 figure
IMRT beam angle optimization using electromagnetism-like algorithm
The selection of appropriate beam irradiation directions in radiotherapy â beam angle optimization (BAO) problem â is very impor- tant for the quality of the treatment, both for improving tumor irradia- tion and for better organs sparing. However, the BAO problem is still not solved satisfactorily and, most of the time, beam directions continue to be manually selected in clinical practice which requires many trial and error iterations between selecting beam angles and computing ïŹuence patterns until a suitable treatment is achieved. The objective of this pa- per is to introduce a new approach for the resolution of the BAO problem, using an hybrid electromagnetism-like algorithm with descent search to tackle this highly non-convex optimization problem. Electromagnetism- like algorithms are derivative-free optimization methods with the ability to avoid local entrapment. Moreover, the hybrid electromagnetism-like algorithm with descent search has a high ability of producing descent directions. A set of retrospective treated cases of head-and-neck tumors at the Portuguese Institute of Oncology of Coimbra is used to discuss the beneïŹts of the proposed algorithm for the optimization of the BAO problem.Fundação para a CiĂȘncia e a Tecnologia (FCT
Searching standard parameters for volumetric modulated arc therapy (VMAT) of prostate cancer
Background
Since December 2009 a new VMAT planning system tool is available in OncentraÂź MasterPlan v3.3 (Nucletron B.V.). The purpose of this study was to work out standard parameters for the optimization of prostate cancer.
Methods
For ten patients with localized prostate cancer plans for simultaneous integrated boost were optimized, varying systematically the number of arcs, collimator angle, the maximum delivery time, and the gantry spacing. Homogeneity in clinical target volume, minimum dose in planning target volume, median dose in the organs at risk, maximum dose in the posterior part of the rectum, and number of monitor units were evaluated using studentâs test for statistical analysis. Measurements were performed with a 2D-array, taking the delivery time, and compared to the calculation by the gamma method.
Results
Plans with collimator 45° were superior to plans with collimator 0°. Single arc resulted in higher minimum dose in the planning target volume, but also higher dose values to the organs at risk, requiring less monitor units per fraction dose than dual arc. Single arc needs a higher value (per arc) for the maximum delivery time parameter than dual arc, but as only one arc is needed, the measured delivery time was shorter and stayed below 2.5 min versus 3 to 5 min. Balancing plan quality, dosimetric results and calculation time, a gantry spacing of 4° led to optimal results.
Conclusion
A set of parameters has been found which can be used as standard for volumetric modulated arc therapy planning of prostate cancer
- âŠ