Multiple direction needle-path planning and inverse dose optimization for robotic low-dose rate brachytherapy

PURPOSE: Robotic systems to assist needle placements for low-dose rate brachytherapy enable conformal dose planning only restricted to path planning around risk structures. We report a treatment planning system (TPS) combining multiple direction needle-path planning with inverse dose optimization algorithms. METHODS: We investigated in a path planning algorithm to efficiently locate needle injection points reaching the target volume without puncturing risk structures. A candidate needle domain with all combinations of trajectories is used for the optimization process. We report a modular algorithm for inverse radiation plan optimization. The initial plan with V100 > 99% is generated by the “greedy optimizer”. The “remove-seed algorithm” reduces the number of seeds in the high dose regions. The “depth-optimizer” varies the insertion depth of the needles. The “coverage-optimizer” locates under-dosed areas in the target volume and supports them with an additional amount of seeds. The dose calculation algorithm is benchmarked on an image set of a phantom with a liver metastasis (prescription dose [Formula: see text]) and is re-planned in a commercial CE-marked TPS to compare the calculated dose grids using a global gamma analysis. The inverse optimizer is benchmarked by calculating 10 plans on the same phantom to investigate the stability and statistical variability of the dose parameters. RESULTS: The path planning algorithm efficiently removes 72.5% of all considered injection points. The candidate needle domain consists of combinations of 1971 tip points and 827 injection points. The global gamma analysis with gamma [Formula: see text] , [Formula: see text] showed a pass rate of [Formula: see text] The dose parameters were [Formula: see text] , [Formula: see text] , [Formula: see text] and [Formula: see text] and [Formula: see text] needles with [Formula: see text] seeds were used. The median of the TPS total running time was 4.4 minutes. CONCLUSIONS: The TPS generates treatment plans with acceptable dose coverage in a reasonable amount of time. The gamma analysis shows good accordance to the commercial TPS. The TPS allows taking full advantage of robotic navigation tools to enable a new precise and safe method of minimally invasive low-dose-rate brachytherapy.