Robustness Of Setup Research Articles

State-of-the-art nonstationary hypersurface damage assessment approach for energy harvesters

Since EH (Energy Harvesters) constitute nowadays a vital part of renewable energy engineering, experimental research is required in addition to numerical modeling, serving reliable structural design and ensuring prolonged device service time. The performance of GPEH (GalloPing EH) has been examined in this case study, utilizing comprehensive laboratory wind tunnel tests, carried out under realistic windspeed conditions. Novel structural multivariate risks assessment methodology, presented here, being feasible for nonstationary nonlinear GPEH dynamic systems, that had been either physically measured over a representative period, providing jointly quasi-ergodic time-series, or directly numerically MCS (Monte Carlo Simulated). Based on laboratory-measured GPEH dynamics, the presented analysis demonstrates that the proposed multivariate hypersurface methodology offers robust predictions of the structural failure/damage risks. Furthermore, when dealing with raw measured timeseries, representing the high-dimensional dynamic system, existing risk assessment techniques struggle to handle nonlinear inter-correlations between GPEH critical components. This case study's main objective has been to validate and benchmark the novel multimodal risk assessment methodology, which utilizes multivariate nonstationary lab-recorded time histories to extract relevant design information from the underlying GPEH dynamics.The proposed state-of-the-art nonstationary hypersurface reliability approach being of a generic nature, offering additional capacity for damage/failure risks prognostics for a wide range of nonlinear multidimensional nonstationary systems. Forecasted damage and failure risks have been supplied with confidence bands, demonstrating the experimental setup's robustness, as well as the useful design features of the presented nonstationary hypersurface risks assessment methodology. It should be noted that the presented reliability methodology being mathematically exact, and it does not rely on simplifying assumptions.

Robustness Settings for a Plan-of-the-Day IMPT Strategy for Locally Advanced Cervical Cancer

For the treatment of locally advanced cervical cancer (LACC), proton therapy has been proposed as an alternative to photon therapy to mitigate the treatment-induced morbidities. The large anatomic variations in the pelvis presents a challenge in achieving adequate target coverage and therefore plan-of-the-day (PotD) strategies have been proposed. However, appropriate robustness settings for a PotD strategy for LACC IMPT are currently lacking. The aim of this study is to determine these settings by evaluating the dose of simulated treatment courses. This study included thirteen patients treated for LACC. For each patient, a full and empty bladder planning CT scan (pCT) and three to five weekly repeat CT scans (reCTs) were available. ITVs were constructed by interpolating between the cervix-uteri on the pCTs. Depending on the range of motion, a library of 1 to 4 plans was created. Four-beam IMPT plans were created using our in-house automated treatment planning system. For optimization and evaluation, five set-up robustness (SR) settings were considered, namely 2, 3, 4, 5, or 7 mm set-up error. On top of that, a 3% range robustness (RR) was used. The evaluation was done on 28 error scenarios. The prescribed dose to the targets was V42.75 Gy > 95% on the voxelwise-min dose. Ten treatments per patient were simulated by recalculating the dose on the reCTs, with additional simulated treatment uncertainties. Adequate coverage was assumed when at least 90% of the treatments had a target coverage of V42.75 Gy > 95%. This was evaluated on the low-risk CTV (CTV-LR) and elective CTV (CTV-E) by accumulating the dose on the different reCTs. The volume that gets >40 Gy was also quantified for five different OAR. In total, 125 treatment plans were created. With these plans, 130 treatments were simulated on the reCTs. The table shows the percentage of the 130 treatments that reached the dose criterion for the five SR error scenarios. For a SR of 4 mm and larger, the dose criterion is fulfilled for the CTV-E in at least 90% of the treatments. For the CTV-LR, adequate coverage could not be reached for any of the five robustness settings. The table also shows the relative volume receiving >40 Gy for five OAR. All OAR V40 increase linearly with larger SR. Adequate CTV-E coverage with a PotD strategy was reached with modest robust optimization. For the CTV-LR, however, this could not be achieved, not even with an SR of 7 mm. Since the setup is a global parameter and a larger SR would greatly increase the dose for OAR, we advocate the addition of margins around the ITV to address the underdosages.

An online adaptive plan library approach for intensity modulated proton therapy for head and neck cancer

Background and purposeIn intensity modulated proton therapy (IMPT), the impact of setup errors and anatomical changes is commonly mitigated by robust optimization with population-based setup robustness (SR) settings and offline replanning. In this study we propose and evaluate an alternative approach based on daily plan selection from patient-specific pre-treatment established plan libraries (PLs). Clinical implementation of the PL strategy would be rather straightforward compared to daily online re-planning. Materials and methodsFor 15 head-and-neck cancer patients, the planning CT was used to generate a PL with 5 plans, robustly optimized for increasing SR: 0, 1, 2, 3, 5 mm, and 3% range robustness. Repeat CTs (rCTs) and realistic setup and range uncertainty distributions were used for simulation of treatment courses for the PL approach, treatments with fixed SR (fSR3) and a trigger-based offline adaptive schedule for 3 mm SR (fSR3OfA). Daily plan selection in the PL approach was based only on recomputed dose to the CTV on the rCT. ResultsCompared to using fSR3 and fSR3OfA, the risk of xerostomia grade ≥ II & III and dysphagia ≥ grade III were significantly reduced with the PL. For 6/15 patients the risk of xerostomia and/or dysphagia ≥ grade II could be reduced by > 2% by using PL. For the other patients, adherence to target coverage constraints was often improved. fSR3OfA resulted in significantly improved coverage compared to PL for selected patients. ConclusionThe proposed PL approach resulted in overall reduced NTCPs compared to fSR3 and fSR3OfA at limited cost in target coverage.

Robustness Recipes for Minimax Robust Optimization in Intensity Modulated Proton Therapy for Oropharyngeal Cancer Patients

We aimed to derive a "robustness recipe" giving the range robustness (RR) and setup robustness (SR) settings (ie, the error values) that ensure adequate clinical target volume (CTV) coverage in oropharyngeal cancer patients for given gaussian distributions of systematic setup, random setup, and range errors (characterized by standard deviations of Σ, σ, and ρ, respectively) when used in minimax worst-case robust intensity modulated proton therapy (IMPT) optimization. For the analysis, contoured computed tomography (CT) scans of 9 unilateral and 9 bilateral patients were used. An IMPT plan was considered robust if, for at least 98% of the simulated fractionated treatments, 98% of the CTV received 95% or more of the prescribed dose. For fast assessment of the CTV coverage for given error distributions (ie, different values of Σ, σ, and ρ), polynomial chaos methods were used. Separate recipes were derived for the unilateral and bilateral cases using one patient from each group, and all 18 patients were included in the validation of the recipes. Treatment plans for bilateral cases are intrinsically more robust than those for unilateral cases. The required RR only depends on the ρ, and SR can be fitted by second-order polynomials in Σ and σ. The formulas for the derived robustness recipes are as follows: Unilateral patients need SR = -0.15Σ(2) + 0.27σ(2) + 1.85Σ - 0.06σ + 1.22 and RR=3% for ρ = 1% and ρ = 2%; bilateral patients need SR = -0.07Σ(2) + 0.19σ(2) + 1.34Σ - 0.07σ + 1.17 and RR=3% and 4% for ρ = 1% and 2%, respectively. For the recipe validation, 2 plans were generated for each of the 18 patients corresponding to Σ = σ = 1.5 mm and ρ = 0% and 2%. Thirty-four plans had adequate CTV coverage in 98% or more of the simulated fractionated treatments; the remaining 2 had adequate coverage in 97.8% and 97.9%. Robustness recipes were derived that can be used in minimax robust optimization of IMPT treatment plans to ensure adequate CTV coverage for oropharyngeal cancer patients.