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 Dpr = 100 Gy) 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 1% = 2.9 Gy, 1 mm showed a pass rate of 98.5%. The dose parameters were V 100 = (99.1 +/- 0.3) %, V 150 = (76.4 +/- 2.5) %, V 200 = (44.5 +/- 5.5) % and D90 = 125.9 +/- 3.6 Gy and 10.7 +/- 1.3 needles with 34.0 +/- 0.8 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.

Automated summary

This article introduces a treatment planning system (TPS) that combines multiple direction needle-path planning with inverse dose optimization algorithms for assisting low-dose rate brachytherapy. The experimental results show that the TPS can generate treatment plans with acceptable dose coverage in a reasonable amount of time, and the results are in good accordance with a commercial TPS.