Direct Segment Optimization Optimizing conformal plans without IMRT Jennifer M. Steers Jennifer M. Steers 1,2 1,2 , Martha M. Matuszak , Martha M. Matuszak 1,2 1,2 , Benedick , Benedick A. Fraass A. Fraass 1 Departments of Radiation Oncology Departments of Radiation Oncology 1 and and Nuclear Engineering & Radiological Sciences Nuclear Engineering & Radiological Sciences 2 University of Michigan, Ann Arbor, Michigan University of Michigan, Ann Arbor, Michigan
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Direct Segment Optimization Optimizing conformal plans without IMRT Jennifer M. Steers 1,2, Martha M. Matuszak 1,2, Benedick A. Fraass 1 Departments of.
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Direct Segment Optimization Optimizing conformal plans without IMRT
Jennifer M. SteersJennifer M. Steers1,21,2 , Martha M. Matuszak , Martha M. Matuszak1,21,2 , Benedick A. Fraass , Benedick A. Fraass11
Departments of Radiation OncologyDepartments of Radiation Oncology11 and and
University of Michigan, Ann Arbor, MichiganUniversity of Michigan, Ann Arbor, Michigan
Outline
• Introduction– What is DSO?– Why are in we interested in DSO?– Goal
• Methods and Materials• Results– IMRT vs. DSO comparisons
• Conclusions
• Direct segment optimization (DSO)– form of direct aperture optimization (DAO) but
based on flat fields, not on beamlet distribution
• Utilizes user-defined cost functions to optimize the following:– Beam weights– MLC positions
What is DSO?
What is DSO?
Why are we interested in DSO?
• Plans are optimized conformal plans – Can reduce delivery time over IMRT– Can result in fewer MUs when compared to
IMRT
• Plans do not require IMRT QA - plans could be started or adapted much quicker• It may make tweaking and optimizing leaf
positions in conformal plans, such as SBRT, much quicker
Goal
• Can DSO produce simpler plans comparable in quality to IMRT plans with the same beam angles and cost function?
Methods and Materials:Features of DSO
• MLCs and beam weights can be optimized separately or together
• Search strategy options– Ordered and random searches– Step sizes
• DSO offers fewer degrees of freedom per beam when compared to IMRT– User must create segments in a plan before
optimizing
IMRT vs. DSO Setup
• Planning goal: Minimize dose to OARs and normal tissues without compromising target uniformity
• Same gantry angles were used between the IMRT and DSO plans except when needed segments were added to the DSO case
• The same cost function was used to optimize both the IMRT and DSO plans
Evaluation of Comparisons
• Both plans were optimized and evaluated with the following metrics– DVHs – MU/fx and beam-on time/fx– Mean doses to structures– Max structure doses (to 0.5cc or 0.1 cc)