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=100Gy) 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%=2.9Gy, 1mm showed a pass rate of 98.5%. The dose parameters were V100=99.1±0.3%, V150=76.4±2.5%, V200=44.5±5.5% and D90=125.9±3.6Gy and 10.7±1.3 needles with 34.0±0.8 seeds were used. The median of the TPS total running time was 4.4minutes. 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.

An anthropomorphic pelvis phantom for MR-guided prostate interventions.

PURPOSE: To design and manufacture a pelvis phantom for magnetic resonance (MR)-guided prostate interventions, such as MRGB (MR-guided biopsy) or brachytherapy seed placement. METHODS: The phantom was designed to mimic the human pelvis incorporating bones, bladder, prostate with four lesions, urethra, arteries, veins, and six lymph nodes embedded in ballistic gelatin. A hollow rectum enables transrectal access to the prostate. To demonstrate the feasibility of the phantom for minimal invasive MRI-guided interventions, a targeted inbore MRGB was performed. The needle probe was rectally inserted and guided using an MRI-compatible remote controlled manipulator (RCM). RESULTS: The presented pelvis phantom has realistic imaging properties for MR imaging (MRI), computed tomography (CT) and ultrasound (US). In the targeted inbore MRGB, a prostate lesion was successfully hit with an accuracy of 3.5 mm. The experiment demonstrates that the limited size of the rectum represents a realistic impairment for needle placements. CONCLUSION: The phantom provides a valuable platform for evaluating the performance of MRGB systems. Interventionalists can use the phantom to learn how to deal with challenging situations, without risking harm to patients.

Comparison of the Oxford Sleep Resistance Test and the Multiple Sleep Latency Test.

OBJECTIVE: The Oxford Sleep Resistance Test (OSLER) consists of four tests over 40 min conducted in a dark and quiet room. If a dim light flashes the patient has to briefly depress a button and then press it again immediately, which indicates that the patient resists sleep. The Maintenance of Wakefulness test (MWT) is another test to assess the ability to maintain wakefulness. Previous studies found a good correlation between the sleep latencies measured with the Osler and the MWT. The most widely used Multiple Sleep Latency Test (MSLT) measures the propensity to fall asleep and not the inability to stay awake. Up to this date there have been no studies comparing the Osler and the MSLT, which is the aim of the study presented here. APPROACH: After a night of polysomnography we investigated the sleep latencies the following day with the Osler and the MSLT in 43 patients suffering from moderate or severe obstructive sleep apnea (OSA) (33 men and 10 women; median age 59 years; median apnea hypopnea index 30.5 per hour sleep). We analysed the correlation between these two tests and between values in the Epworth Sleepiness Scale (ESS) and the Karolinska Sleepiness Scale (KSS) and these two tests. MAIN RESULTS: We did not find a correlation between the Osler and the MSLT nor between these two tests and the questionnaires (ESS, KSS). The only significant correlation was found between the mean MSLT latency and the sleep onset latency in the polysomnography the night before. Seven patients stayed awake during the Osler and showed a decreased mean sleep latency in the MSLT. SIGNIFICANCE: The Osler, the MSLT and the questionnaires measure different objective and subjective aspects of sleepiness. In untreated OSA patients an increased propensity to fall asleep was not automatically associated with the inability to stay awake.