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Automatic single-isocenter multiple-target cranial stereotactic treatment plan optimization via planning system
Kurtis H Dekker1,2,3, Jennifer A Everaars4
1Medical Physics Department, Cancer Centre of Southeastern Ontario, Kingston Health Sciences Centre, Kingston, Ontario, Canada.
Background:
Single-isocenter multiple-target stereotactic radiation treatments delivered on C-arm linear accelerators are increasingly common due to practical advantages in both accessibility and speed compared to multiple isocenter treatments. Optimization of high-quality treatment plans can be a time-consuming process requiring substantial manual effort. In our institution, the planning workflow for these treatments was entirely manual and involved the generation of optimization structures and repeated recalculation and input of optimization objectives during the iterative optimization process. Although commercial automated planning solutions are available, their implementation may impose operational constraints, including reliance on specific immobilization and image/surface guidance hardware, motivating the development of an immobilization-independent automation tool for cranial stereotactic treatment plan optimization.
Purpose:
To develop and implement a treatment planning optimization tool for multiple-target cranial stereotactic treatments in the Varian Eclipse treatment planning system, to reduce manual planner input and planning time while improving plan quality.
Methods:
A software tool was written using the Varian Eclipse Scripting Application Programming Interface to automatically generate target-specific ring structures and facilitate the iterative process of plan generation. Twenty cases were retrospectively re-planned with this tool and compared with the corresponding clinical plans to evaluate plan quality using qualitative and quantitative metrics of conformality and complexity. Automated plans were verified using portal dosimetry to ensure clinical deliverability. For ten cases, a timing study was performed to compare optimization time between the software tool and manual re-optimization.
Results:
The automatic optimization tool produced plans with similar modulation and complexity, but consistently lower dosimetric falloff metrics (R50% and Paddick Gradient Index) than the corresponding clinical plans. All plans passed patient-specific QA (portal dosimetry) following institutional practice. For the ten cases included in the timing study, the software had a mean runtime of 5.8 min (range: 2-12 min), with variation depending on case characteristics such as number of targets and arcs employed. In comparison, manual plan generation required 21.5 min on average (range: 4-49 min).
Discussion:
The automated planning tool produced clinically acceptable, deliverable plans with better dose falloff compared to the previous manual planning approach. The tool is estimated to save an average of 15 min of optimization time per plan.
Conclusions:
A treatment planning optimization tool has been developed that provides improvement in both dosimetric plan quality and treatment planning efficiency for single-isocenter multiple-target cranial stereotactic treatments.
