Analysis and Accuracy Improvement of UWB-TDoA-Based Indoor Positioning System.

Positioning systems are used in a wide range of applications which require determining the position of an object in space, such as locating and tracking assets, people and goods; assisting navigation systems; and mapping. Indoor Positioning Systems (IPSs) are used where satellite and other outdoor positioning technologies lack precision or fail. Ultra-WideBand (UWB) technology is especially suitable for an IPS, as it operates under high data transfer rates over short distances and at low power densities, although signals tend to be disrupted by various objects. This paper presents a comprehensive study of the precision, failure, and accuracy of 2D IPSs based on UWB technology and a pseudo-range multilateration algorithm using Time Difference of Arrival (TDoA) signals. As a case study, the positioning of a 4×4m2 area, four anchors (transceivers), and one tag (receiver) are considered using bitcraze's Loco Positioning System. A Cramér-Rao Lower Bound analysis identifies the convex hull of the anchors as the region with highest precision, taking into account the anisotropic radiation pattern of the anchors' antennas as opposed to ideal signal distributions, while bifurcation envelopes containing the anchors are defined to bound the regions in which the IPS is predicted to fail. This allows the formulation of a so-called flyable area, defined as the intersection between the convex hull and the region outside the bifurcation envelopes. Finally, the static bias is measured after applying a built-in Extended Kalman Filter (EKF) and mapped using a Radial Basis Function Network (RBFN). A debiasing filter is then developed to improve the accuracy. Findings and developments are experimentally validated, with the IPS observed to fail near the anchors, precision around ±3cm, and accuracy improved by about 15cm for static and 5cm for dynamic measurements, on average.

Validation of the Computerized Pediatric Triage Tool, pediaTRI, in the Pediatric Emergency Department of Lenval Children's Hospital in Nice: A Cross-Sectional Observational Study.

Introduction: A reliable pediatric triage tool is essential for nurses working in pediatric emergency departments to quickly identify children requiring priority care (high-level emergencies) and those who can wait (low-level emergencies). In the absence of a gold standard in France, the objective of our study was to validate our 5-level pediatric triage tool -pediaTRI- against the reference tool: the Pediatric Early Warning Score (PEWS) System. Materials and Methods: We prospectively included 100,506 children who visited the Pediatric Emergency Department at Lenval Children's Hospital (Nice, France) in 2016 and 2017. The performance of pediaTRI to identify high-level emergencies (severity levels 1 and 2) was evaluated in comparison with a PEWS ≥ 4/9. Data from 2018-19 was used as an independent validation cohort. Results: pediaTRI agreed with the PEWS score for 84,896 of the patients (84.5%): 15.0% (14.8-15.2) of the patients were over-triaged and 0.5% (0.5-0.6) under-triaged compared with the PEWS score. pediaTRI had a sensitivity of 76.4% (74.6-78.2), a specificity of 84.7% (84.4-84.9), and positive and negative likelihood ratios of 5.0 (4.8-5.1) and 0.3 (0.3-0.3), respectively, for the identification of high-level emergencies. However, the positive likelihood ratios were lower for patients presenting with a medical complaint [4.1 (4.0-4.2) v 10.4 (7.9-13.7 for trauma), and for younger children [1.2 (1.1-1.2) from 0 to 28 days, and 1.9 (1.8-2.0) from 28 days to 3 months]. Conclusion: pediaTRI has a moderate to good validity to triage children in a Pediatric Emergency Department with a tendency to over-triage compared with the PEWS system. Its validity is lower for younger children and for children consulting for a medical complaint.

Indoor Intruder Tracking Using Visible Light Communications.

This paper proposes a comprehensive study of indoor intruder tracking using visible light communication (VLC). A realistic indoor VLC channel was developed, taking into consideration reflections, shadowing, and ambient noise. The intruder was considered smart and aiming to escape tracking. This was modelled by adding noise and disturbance to the intruder's trajectory. We propose to extend the application of minimax filtering from state estimation in the radio frequency (RF) domain to intruder tracking using VLC. The performance of the proposed method was examined and compared with Kalman filter for both VLC and RF. The simulation results showed that the minimax filter provided marginally better tracking and was more robust to the adversary behavior of the intruder than Kalman filter, with less than 0.5 cm estimation error. In addition, minimax was significantly better than Kalman filter for RF tracking applications.

IGRT/ART phantom with programmable independent rib cage and tumor motion.

PURPOSE: This paper describes the design and experimental evaluation of the Methods and Advanced Equipment for Simulation and Treatment in Radiation Oncology (MAESTRO) thorax phantom, a new anthropomorphic moving ribcage combined with a 3D tumor positioning system to move target inserts within static lungs. METHODS: The new rib cage design is described and its motion is evaluated using Vicon Nexus, a commercial 3D motion tracking system. CT studies at inhale and exhale position are used to study the effect of rib motion and tissue equivalence. RESULTS: The 3D target positioning system and the rib cage have millimetre accuracy. Each axis of motion can reproduce given trajectories from files or individually programmed sinusoidal motion in terms of amplitude, period, and phase shift. The maximum rib motion ranges from 7 to 20 mm SI and from 0.3 to 3.7 mm AP with LR motion less than 1 mm. The repeatability between cycles is within 0.16 mm root mean square error. The agreement between CT electron and mass density for skin, ribcage, spine hard and inner bone as well as cartilage is within 3%. CONCLUSIONS: The MAESTRO phantom is a useful research tool that produces programmable 3D rib motions which can be synchronized with 3D internal target motion. The easily accessible static lungs enable the use of a wide range of inserts or can be filled with lung tissue equivalent and deformed using the target motion system.

Couch-based motion compensation: modelling, simulation and real-time experiments.

The paper presents a couch-based active motion compensation strategy evaluated in simulation and validated experimentally using both a research and a clinical Elekta Precise Table™. The control strategy combines a Kalman filter to predict the surrogate motion used as a reference by a linear model predictive controller with the control action calculation based on estimated position and velocity feedback provided by an observer as well as predicted couch position and velocity using a linearized state space model. An inversion technique is used to compensate for the dead-zone nonlinearity. New generic couch models are presented and applied to model the Elekta Precise Table™ dynamics and nonlinearities including dead zone. Couch deflection was measured for different manufacturers and found to be up to 25 mm. A feed-forward approach is proposed to compensate for such couch deflection. Simultaneous motion compensation for longitudinal, lateral and vertical motions was evaluated using arbitrary trajectories generated from sensors or loaded from files. Tracking errors were between 0.5 and 2 mm RMS. A dosimetric evaluation of the motion compensation was done using a sinusoidal waveform. No notable differences were observed between films obtained for a fixed- or motion-compensated target. Further dosimetric improvement could be made by combining gating, based on tracking error together with beam on/off time, and PSS compensation.

Geometric accuracy of a novel gimbals based radiation therapy tumor tracking system.

PURPOSE: VERO is a novel platform for image guided stereotactic body radiotherapy. Orthogonal gimbals hold the linac-MLC assembly allowing real-time moving tumor tracking. This study determines the geometric accuracy of the tracking. MATERIALS AND METHODS: To determine the tracking error, an 1D moving phantom produced sinusoidal motion with frequencies up to 30 breaths per minute (bpm). Tumor trajectories of patients were reproduced using a 2D robot and pursued with the gimbals tracking system prototype. Using the moving beam light field and a digital-camera-based detection unit tracking errors, system lag and equivalence of pan/tilt performance were measured. RESULTS: The system lag was 47.7 ms for panning and 47.6 ms for tilting. Applying system lag compensation, sinusoidal motion tracking was accurate, with a tracking error 90% percentile E(90%)<0.82 mm and similar performance for pan/tilt. Systematic tracking errors were below 0.14 mm. The 2D tumor trajectories were tracked with an average E(90%) of 0.54 mm, and tracking error standard deviations of 0.20 mm for pan and 0.22 mm for tilt. CONCLUSIONS: In terms of dynamic behavior, the gimbaled linac of the VERO system showed to be an excellent approach for providing accurate real-time tumor tracking in radiation therapy.

A multiple model approach to respiratory motion prediction for real-time IGRT.

Respiration induces significant movement of tumours in the vicinity of thoracic and abdominal structures. Real-time image-guided radiotherapy (IGRT) aims to adapt radiation delivery to tumour motion during irradiation. One of the main problems for achieving this objective is the presence of time lag between the acquisition of tumour position and the radiation delivery. Such time lag causes significant beam positioning errors and affects the dose coverage. A method to solve this problem is to employ an algorithm that is able to predict future tumour positions from available tumour position measurements. This paper presents a multiple model approach to respiratory-induced tumour motion prediction using the interacting multiple model (IMM) filter. A combination of two models, constant velocity (CV) and constant acceleration (CA), is used to capture respiratory-induced tumour motion. A Kalman filter is designed for each of the local models and the IMM filter is applied to combine the predictions of these Kalman filters for obtaining the predicted tumour position. The IMM filter, likewise the Kalman filter, is a recursive algorithm that is suitable for real-time applications. In addition, this paper proposes a confidence interval (CI) criterion to evaluate the performance of tumour motion prediction algorithms for IGRT. The proposed CI criterion provides a relevant measure for the prediction performance in terms of clinical applications and can be used to specify the margin to accommodate prediction errors. The prediction performance of the IMM filter has been evaluated using 110 traces of 4-minute free-breathing motion collected from 24 lung-cancer patients. The simulation study was carried out for prediction time 0.1-0.6 s with sampling rates 3, 5 and 10 Hz. It was found that the prediction of the IMM filter was consistently better than the prediction of the Kalman filter with the CV or CA model. There was no significant difference of prediction errors for the sampling rates 5 and 10 Hz. For these sampling rates, the errors of the IMM filter for 0.4 s prediction time were less than 2.1 mm in terms of the 95% CI criterion or 1.1 mm in terms of the standard deviation (SD) or root mean squared errors (RMSE) criterion. For the prediction time of 0.6 s the errors were less than 3.6 mm in terms of the 95% CI criterion or 1.8 mm in terms of the SD/RMSE criterion. The prediction error analysis showed that the average percentage of the target lies outside the 95% CI margin was 5.2% and outside the SD/RMSE margin was 24.3%. This indicates the effectiveness of the 95% CI criterion as a margining strategy to accommodate prediction errors.

A new approach to quantify the mechanical and radiation isocentres of radiotherapy treatment machine gantries.

In this paper a new method is proposed to quantify and reduce the radiation beam position uncertainty due to the radiotherapy treatment machine gantry deflection. A new tool has been designed and manufactured to provide the means to measure the alignment of the collimator axis and of the beam central axis in space, using the NDI Polaris optical tracking system and Gafchromic films. The tool can be mounted onto the accessory tray of the linacs from different manufacturers. The approach has been demonstrated with measurements of the mechanical isocentre being performed on ten linacs from three major manufacturers at four clinical sites. Measurements of the radiation isocentre were performed on a single linac. The collimator axis trajectory is modelled using a vector-end effector in order to provide more information than standard mechanical assessment methods. The method uses a mathematical optimization technique to calculate the position of the mechanical isocentre and the 'size' of the collimator axes intersection locus. Deviations of the collimator axes from the isocentre are expressed in terms of systematic and random error. The effects of measurement uncertainties are evaluated both via simulations and experimentally. The use of optical tracking and optimization techniques combined with an operator-induced measurement error compensation algorithm leads to a faster measurement of the mechanical isocentre (20 min for 24 angles) and eliminates operator-induced uncertainties. The uncertainty of the measurement of the mechanical isocentre was between 40 microm and 70 microm in terms of standard deviation. For some of the linacs assessed, the mechanical isocentre obtained using a standard approach with an adjustable pointer was displaced by over 1 mm from that found with the proposed method. The radii of the collimator axes intersection locus found with the proposed method were between 0.4 mm and 0.72 mm for the linacs assessed. Film measurement revealed a misalignment of the mechanical isocentre and the radiation isocentre by 0.4 mm. The proposed method potentially enables a reduction of the beam position uncertainty. This may be achieved at the planning stage by compensating for the identified systematic collimator axes deviations which were found to be reproducible. The method also creates a potential for using different setup margins independently for each axis and for each gantry angle, calculated specifically for a given linac.

How many nodes must be examined to accurately stage gastric carcinomas? Results from a population based study.

BACKGROUND: There are few population based data about lymphadenectomy practices in resections for stomach carcinoma. The aim of the current study was to describe these practices and to determine how many nodes must be examined in order to accurately stage gastric carcinoma. METHODS: The current study included all patients (749 patients total) with TNM Stage I, II, or III resected gastric carcinoma diagnosed over a 21 year period (1976-1996) in a well-defined French population. A model of the relationship between the proportion of positive nodes and the number of examined nodes was performed. The relationship between the proportion of positive nodes and the number of nodes examined was modeled to determine the number of nodes beyond which the proportion of N+ tumors no longer changed. RESULTS: The average number of examined lymph nodes was 8.4 per patient. More than 15 lymph nodes were examined in 17.6% of patients. Under 10 examined nodes, the proportion of N+ classified tumors significantly decreased with the number of examined nodes, whereas it remained stable beyond this value. The type of gastrectomy and patient age were the two factors independently associated with the resection of at least 10 nodes, whereas the diagnosis period was not associated. After adjustment for the type of surgical resection, three variables independently influenced the prognosis of TNM Stage I or II tumors: extension within the gastric wall (extension T3/T4 vs. T1/T2; odds ratio [OR] = 2.05, P < 0.001), age at diagnosis (age >or= 70 years vs. < 70 years; OR = 4.06, P < 0.001), and the number of examined nodes (10 resected lymph nodes vs. 0-9; OR = 0.57, P < 0.001). CONCLUSIONS: The current study strongly suggests that staging is not reliable when fewer than 10 lymph nodes are examined. The number of examined lymph nodes should be used as a stratification criterion in clinical trials and as an adjustment variable in survival studies.