Static Delivery Research Articles

A static beam delivery device for fast scanning proton arc-therapy

Arc-therapy is a dose delivery technique regularly applied in photon radiation therapy, and is currently subject of great interest for proton therapy as well. In this technique, proton beams are aimed at a tumor from different continuous ranges of incident directions (so called ‘arcs’). This technique can potentially yield a better dose conformity around the tumor and a very low dose in the surrounding healthy tissue. Currently, proton-arc therapy is performed by rotating a proton gantry around the patient, adapting the normally used dose-delivery method to the arc-specific motion of the gantry. Here we present first results from a feasibility study of the conceptual design of a new static fast beam delivery device/system for proton-arc therapy, which could be used instead of a gantry. In this novel concept, the incident angle of proton beams can be set rapidly by only changing field strengths of small magnets. This device eliminates the motion of the heavy gantry and related hardware. Therefore, a reduction of the total treatment time is expected. In the feasibility study presented here, we concentrate on the concept of the beam transport. Based on several simple, but realistic assumptions and approximations, proton tracking calculations were performed in a 3D magnetic field map, to calculate the beam transport in this device and to investigate and address several beam-optics challenges. We propose and simulate corresponding solutions and discuss their outcomes. To enable the implementation of some usually applied techniques in proton therapy, such as pencil beam scanning, energy modulation and beam shaping, we present and discuss our proposals. Here we present the concept of a new idea to perform fast proton arc-scanning and we report on first results of a feasibility study. Based on these results, we propose several options and next steps in the design.

Six degrees of freedom dynamic motion-including dose reconstruction in a commercial treatment planning system.

Intrafractional motion during radiotherapy delivery can deteriorate the delivered dose. Dynamic rotational motion of up to 38 degrees has been reported during prostate cancer radiotherapy, but methods to determine the dosimetric consequences of such rotations are lacking. Here, we create and experimentally validate a dose reconstruction method that accounts for dynamic rotations and translations in a commercial treatment planning system (TPS). Interplay effects are quantified by comparing dose reconstructions with dynamic and constant rotations. The dose reconstruction accumulates the dose in points of interest while the points are moved in six degrees of freedom (6DoF) in a precalculated time-resolved four-dimensional (4D) dose matrix to emulate dynamic motion in a patient. The required 4D dose matrix was generated by splitting the original treatment plan into multiple sub-beams, each representing 0.4s dose delivery, and recalculating the dose of the split plan in the TPS (Eclipse). The dose accumulation was performed via TPS scripting by querying the dose of each sub-beam in dynamically moving points, allowing dose reconstruction with any dynamic motion. The dose reconstruction was validated with film dosimetry for two prostate dual arc VMAT plans with intra-prostatic lesion boosts. The plans were delivered to a pelvis phantom with internal dynamic rotational motion of a film stack (21 films with 2.5mm separation). Each plan was delivered without motion and with three prostate motion traces. Motion-including dose reconstruction was performed for each motion experiment using the actual dynamic rotation as well as a constant rotation equal to the mean rotation during the experiment. For each experiment, the 3%/2mm γ failure rate of the TPS dose reconstruction was calculated with the film measurement being the reference. For each motion experiment, the motion-induced 3%/2mm γ failure rate was calculated using the static delivery as the reference and compared between film measurements and TPS dose reconstruction. DVH metrics for RT structures fully contained in the film volume were also compared between film and TPS. The mean γ failure rate of the TPS dose reconstructions when compared to film doses was 0.8% (two static experiments) and 1.7% (six dynamic experiments). The mean (range) of the motion-induced γ failure rate in film measurements was 35.4% (21.3-59.2%). The TPS dose reconstruction agreed with these experimental γ failure rates with root-mean-square errors of 2.1% (dynamic rotation dose reconstruction) and 17.1% (dose reconstruction assuming constant rotation). By DVH metrics, the mean (range) difference between dose reconstructions with dynamic and constant rotation was 4.3% (-0.3-10.6%) (urethra ), -0.6% (-5.6%-2.5%) (urethra ), 1.1% (-7.1-7.7%) (GTV ), -1.4% (-17.4-7.1%) (GTV ), -1.2% (-17.1-5.7%) (GTV ), and -0.1% (-3.2-7.6%) (GTV mean dose). Dose reconstructions with dynamic motion revealed large interplay effects (cold and hot spots). A method to perform dose reconstructions for dynamic 6DoF motion in a TPS was developed and experimentally validated. It revealed large differences in dose distribution between dynamic and constant rotations not identifiable through dose reconstructions with constant rotation.

Coriolis-induced liquid breakup and spray evolution in a rotary slinger atomizer: Experiments and analysis

Understanding the physics of primary liquid breakup process and its correlation with the evolution of spray characteristics in a rotary slinger atomizer is the goal of the present research. Experiments were conducted in a high-speed slinger test rig that houses a static liquid delivery manifold to uniformly supply the liquid to the rotating slinger disc that contains a single row of orifices carved on its peripheral surface for liquid injection.The atomizer was operated for a wide range of conditions by varying the rotational speed and liquid feed rate. The liquid breakup structure at the exit of the slinger orifices was visualized using front light illumination technique, while the droplet size was measured at different radial stations away from the slinger surface by application of the Interferometric Laser Imaging for Droplet Sizing (ILIDS) technique. The visualization images highlighted strong influence of Coriolis force as the liquid tends to accumulate on one side of the channel (that is opposite to the rotational direction) for all cases. It was observed that while the liquid thickness is smaller for higher rotational speed, it does not vary much with liquid feed rate at the same speed and, instead, in such case the span of the liquid is wider. A theoretical analysis was developed to describe the in-channel liquid behaviour that accounts for the effect of Coriolis and surface tension forces. Interestingly, the theory could explain the above observations. The differences in the predictions in comparison to the analysis by Dahm et al. (2006a) was attributed to the assumption of annular film flow in the latter. The liquid breakup mode (stream, sheet or transition mode) could be described by Coriolis Bond number (Bo) that refers to the ratio of Coriolis to surface tension forces and proportional to the spread parameter (span to thickness ratio), while the liquid breakup regimes were identified on a Bo−q plot, where q is the liquid to air momentum flux ratio. The variation of characteristic droplet sizes with both rotational speed and feed rate were examined, and again some interesting trends are identified. The correlation between liquid breakup mode/regime with the measured droplet size was established using the above non-dimensional numbers.

Significance of post-pacing intervals shorter than tachycardia cycle length for successful catheter ablation of atypical flutter.

During entrainment mapping of macro-reentrant tachycardias, the time difference (dPPI) between post-pacing interval (PPI) and tachycardia cycle length (TCL) is thought to be a function of the distance of the pacing site to the re-entry circuit and dPPI < 30 ms is considered within the re-entry circuit. This study assessed the importance of PPI < TCL as a successful target for atypical flutter ablation. A total of 177 ablation procedures were investigated. Surface electrocardiograms (ECGs) were evaluated and combined activation and entrainment mapping were performed to choose ablation sites. Each entrainment sequence immediately preceding static radiofrequency delivery at the same site was analysed. A total of 545 entrainment sequences were analysed. dPPI < 0 ms was observed in 45.3% (247/545) sequences. Ablation resulted in tachycardia termination more often at sites with dPPI < 0 (27.8% vs. 14.5%, P < 0.001) and with a progressively increasingly inverse correlation between dPPI duration and ablation success [odds ratio (OR): 0.974; 95% confidence interval (CI) 0.960-0.988; P < 0.001]. Tachycardia termination or cycle length prolongation also occurred more often at sites with dPPI < 0 (50.6% vs. 33.2%, P < 0.001) and with a similar inverse correlation with dPPI duration (OR: 0.972; 95% CI 0.960-0.984; P < 0.001). Twelve-lead synchronous isoelectric intervals were observed in 64.4% (163/253) flutter ECGs and were associated with a dPPI < 0 (75.3% vs. 55.8%, P < 0.001). When combined with activation mapping, a negative dPPI is a more effective parameter for identifying a target for successful ablation compared to a dPPI = 0-30 ms. Its occurrence is associated with a critical small narrow slow-conducting isthmus at the target site.

4D in vivo dose verification for real‐time tumor tracking treatments using EPID dosimetry

The use of sophisticated techniques such as gating and tracking treatments requires additional quality assurance to mitigate increased patient risks. To address this need, we have developed and validated an in vivo method of dose delivery verification for real-time aperture tracking techniques, using an electronic portal imaging device (EPID)-based, on-treatment patient dose reconstruction and a dynamic anthropomorphic phantom. Using 4DCT scan of the phantom, ten individual treatment plans were created, 1 for each of the 10 separate phases of the respiratory cycle. The 10 MLC apertures were combined into a single dynamic intensity-modulated radiation therapy (IMRT) plan that tracked the tumor motion. The tumor motion and linac delivery were synchronized using an RPM system (Varian Medical Systems) in gating mode with a custom breathing trace. On-treatment EPID frames were captured using a data-acquisition computer with a dedicated frame-grabber. Our in-house EPID-based in vivo dose reconstruction model was modified to reconstruct the 4D accumulated dose distribution for a dynamic MLC (DMLC) tracking plan using the 10-phase 4DCT dataset. Dose estimation accuracy was assessed for the DMLC tracking plan and a single-phase (50% phase) static tumor plan, represented a static field test to verify baseline accuracy. The 3%/3 mm chi-comparison between the EPID-based dose reconstruction for the static tumor delivery and the TPS dose calculation for the static plan resulted in 100% pass rate for planning target volume (PTV) voxels while the mean percentage dose difference was 0.6%. Comparing the EPID-based dose reconstruction for the DMLC tracking to the TPS calculation for the static plan gave a 3%/3 mm chi pass rate of 99.3% for PTV voxels and a mean percentage dose difference of 1.1%. While further work is required to assess the accuracy of this approach in more clinically relevant situations, we have established clinical feasibility and baseline accuracy of using the transmission EPID-based, in vivo patient dose verification for MLC-tracking treatments.

Tomographic-based 3D scintillation dosimetry using a three-view plenoptic imaging system.

To demonstrate the feasibility of a three-plenoptic camera projection, scintillation-based dosimetry system for measuring three-dimensional (3D) dose distributions of static photon radiation fields. Static x-ray photon beams were delivered to a cubic plastic scintillator volume embedded within acrylic blocks. For each beam, three orthogonal projections of the scintillating light emission were recorded using a multifocus plenoptic camera. Experimental 3D reconstructions of the light distribution were obtained using an iterative maximum likelihood-expectation maximization (ML-EM) algorithm. For this purpose, the elements of the system matrix representing the contribution of the scintillator volume voxels to the camera sensor pixels were calculated using optical design software. A reconstruction-specific correction was applied to light reconstructions to account for scintillating light imaged by the camera but not directly resulting from dose deposition. Cross beam profiles (CBPs) and percentage depth dose (PDD) curves were compared to treatment planning system data for square fields. Three-dimensional and 3D gamma analyses were performed for concave-shaped dose distributions and the Pearson correlation coefficient and reconstruction error were employed to assess the quality of the measured relative 3D dose distributions. A full and accurate model of the plenoptic camera-based scintillation dosimetry system was implemented using the light ray tracing capabilities of optical design software. With this model, light distributions were successfully reconstructed over a volume of 60×60×60mm at a resolution of 2mm. For relative 3D measurements of square radiation fields of , and compared with treatment planning system reference distributions, the maximum root-mean-square error of the CBPs evaluated at two different depths was of 3.2%, 1.2%, and 1.1%, respectively; as for the corresponding linearly fitted PDDs of the square fields, the slopes of the reconstructed dose distributions overestimated those of the reference distributions by at most 0.2%/cm. The 2D gamma passing rate with a criterion of 2%/2mm for the concave-shaped photon field was of 61.6%, 66.1%, and 76.4% using one, two, and three plenoptic projections; the respective success rates become 77.1%, 87.5%, and 94.9% using a criterion of 3%/3mm. The 3D correlation coefficient for the corresponding reconstructions was of 0.688, 0.905, and 0.976, respectively. Three-dimensional light distributions emitted from within a plastic scintillator volume were successfully recovered using optical design software to establish a complete tomographic model of a plenoptic camera-based prototype. The tomographic model can equivalently extend to dynamic dose delivery measurements, providing temporal resolution limited by the camera's exposure time. This feasibility study enables a simplified design-to-implementation process for volumetric scintillation dosimetry prototypes toward fully meeting the clinical needs of 3D dose measurements for static and dynamic delivery techniques.

Evaluation of the target dose coverage of stereotactic body radiotherapy for lung cancer using helical tomotherapy: A dynamic phantom study.

To evaluate the target dose coverage for lung stereotactic body radiotherapy (SBRT) using helical tomotherapy (HT) with the internal tumor volume (ITV) margin settings adjusted according to the degree of tumor motion. Lung SBRT with HT may cause a dosimetric error when the target motion is large. Two lung SBRT plans were created using a tomotherapy planning station. Using these original plans, five plans with different ITV margins (4.0-20.0mm for superior-inferior [SI] dimension) were generated. To evaluate the effects of respiratory motion on HT, an original dynamic motion phantom was developed. The respiratory wave of a healthy volunteer was used for dynamic motion as the typical tumor respiratory motion. Five patterns of motion amplitude that corresponded to five ITV margin sizes and three breathing cycles of 7, 14, and 28 breaths per minute were used. We evaluated the target dose change between a static delivery and a dynamic delivery with each motion pattern. The target dose difference increased as the tumor size decreased and as the tumor motion increased. Although a target dose difference of <5 % was observed at ≤10mm of tumor motion for each condition, a maximum difference of -9.94 % ± 7.10 % was observed in cases of small tumors with 20mm of tumor motion under slow respiration. Minimizing respiratory movement is recommended as much as possible for lung SBRT with HT, especially for cases involving small tumors.

Construction and Application of a Static Load Performance Testing Platform for Truck-Mounted Drilling Rigs

Abstract In this paper, a static load performance testing platform for truck-mounted drilling rigs is constructed, which can directly test the static torque and static lifting force on the truck-mounted drilling rig, and replace current methods of theoretical calculation and construction experience for obtaining the above parameters. This platform detection is intuitive, accurate and efficient, and thus has been successfully applied to static load performance tests and delivery inspections on truck-mounted drilling rigs.

Order Now, Pickup in 30 Minutes: Managing Queues with Static Delivery Guarantees

Order Now, Pickup in 30 Minutes: Managing Queues with Static Delivery Guarantees

A two-phase optimization model for the demand-responsive customized bus network design

This paper proposes a new optimization model for the network design problem of the demand-responsive customized bus (CB). The proposed model consists of two phases: inserting passenger requests dynamically in an interactive manner (dynamic phase) and optimizing the service network statically based on the overall demand (static phase). In the dynamic phase, we propose a hierarchical decision-making model to describe the interactive manner between operator and passengers. The CB network design problem is formulated in a mixed-integer program with the objective of maximizing operator’s revenue. The CB passenger’s travel behavior is measured by a discrete choice model given the trip plan provided by the operator. A dynamic insertion method is developed to address the proposed model in the dynamic phase. For the network design problem in the static phase, the service network is re-optimized based on the confirmed passengers with strict time deviation constraints embedded in the static multi-vehicle pickup and delivery problem. An exact solution method is developed based on the branch-and-bound (B&B) algorithm. Numerical examples are conducted to verify the proposed models and solution algorithms.

Effect of Atomized Delivery of Nutrients on the Growth Characteristics and Microstructure Morphology of Bacterial Cellulose.

This work demonstrates a general strategy for introducing remarkable changes in matrix organization and, consequently, functional properties of bacterial cellulose (BC). BC-producing cells were induced, using a well-defined atomized droplet nutrient delivery (ADND) system, to form pellicles with a regular layered morphology that persists throughout the mat depth. In contrast, the morphology of mats formed by conventional static medium nutrient delivery (SMND) is irregular with no distinguishable pattern. ADND also resulted in larger meso-scale average pore sizes but did not alter the fibril diameter (∼70 nm) and crystallinity index (92-95%). The specific modulus and specific tensile strength of ADND mats are higher than those of SMND mats. This is due to the regularity of dense layers that are present in ADND mats that are able to sustain tensile loads, when applied parallel to these layers. The density of BC films prepared by ADND is 1.63-fold lower than that of the SMND BC film. Consequently, the water contents (g/g) of ADND- and SMND-prepared BC mats are 263 ± 8.85 and 99.6 ± 2.04, respectively. A model that rationalizes differences in mat morphology resulting from these nutrient delivery methods based on nutrient and oxygen concentration gradients is proposed. This work raises questions as to the extent that ADND can be used to fine-tune the matrix morphology and how the resulting lower density mats will alter the diffusion of actives from the films to wound sites and increase the ability of cells to infiltrate the matrix during tissue engineering.

Kv Intrafraction Verification for SBRT Amplitude-Gated Rapidarc Treatments: An Initial Experience

To report the workflow and the quality assurance program established for the first kV-IGRT intrafraction verification gated RapidArc (RA) treatment successfully delivered in our institution. One patient with stage I NSCLC was treated using the gating technique on a medical linear accelerator. Prescription dose was 48 Gy in four fractions and one fiducial marker was implanted near the tumor. During simulation a gated CT in a Stable Exhale (SE) phase (breath hold pause = 20 sec) was acquired. A 6 MV FFF plan was generated on the gated CT using four partial arcs; the fiducial and its 3 mm PRV were delineated in the planning CT. During each fraction a gating amplitude window of 2.5 mm was set, a gated CBCT on the SE was acquired and positioning was performed according to a tumor fusion. Two orthogonal kV images were then collected to verify the position of the marker. Triggered kV images were acquired immediately before beam-on to verify the intrafraction fiducial position during treatment and to perform an a posteriori evaluation of the marker displacements in the superior-inferior (SI) direction with respect to DRR images. Pretreatment quality assurance was performed using a Delta4 phantom (static delivery) and with EBT3 Gafchromic films coupled with a Quasar moving phantom (gated delivery) using three breathing pattern (BP): 1) FB: free BP of the patient, 2) EX1: SE obtained by modifying the FB pattern and 3) EX2: a random SE. A film irradiated in static delivery was taken as a reference to evaluate the gating deliveries and compared with TPS dose as additional static QA. Beam-on time was 1.8 ± 0.5 min per arc and 7.2 ± 1.4 min per fraction. The duty cycle averaged over all arcs was 42 ± 3.9 % and 56 ± 17 kV triggered images per fraction were acquired. The SI distance between the marker and its expected position was 1.7 ± 0.4 mm on average and 2.9 ± 0.7 mm at 95th percentile (range: 0 - 4.2 mm). During treatment the fiducial was always displayed inside its PRV, except during the delivery of arc 3 in fraction 3. This is in agreement with shifts evaluation, where we found an average displacement of 3.6 ± 0.3 mm. 2%/2mm gamma agreement for the static delivery was 97.8% and 100% for the Delta4 phantom and films, respectively. The gated deliveries were dosimetrically equivalent to the static procedure, with dose differences at isocenter below 1% and gamma pass-rates above 98.2%. Good agreement was also found with TPS (gamma scores > 98.9%). The system capability to superimpose marker PRV on real-time kV images made the clinicians confident during the delivery and the evaluation of the fiducial shifts has proven to be consistent to what was observed during the treatment. A 3 mm margin was required to account for 95% of the gating intrafraction uncertainties. Gated treatments were delivered to a moving phantom and no significant differences were found with respect to a static delivery. The use of a small gate coupled with a SE BP allows delivering acceptable dose distributions with reasonable duty cycles.

Hybrid metaheuristic for the Pickup and Delivery Problem designed for passengers and goods transportation

This paper introduces a new formulation for a variant of static Pickup and Delivery Problem involving passengers and goods, time windows, multiple visits and transfer operations with or without storage. This model contributes to address mobility and logistics requirements for stakeholders with the rise of Smart Cities. Solutions of good quality are found thanks to a hybrid metaheuristic based on an evolutionary algorithm. Our results are compared on small instances for which optimal solutions have been found using MILP. We discuss perspectives and upcoming challenges such as the scalability of the model.

What Works in Family Planning Interventions in Sub-saharan Africa: A Scoping Review

Introduction: This scoping review was aimed to map the available evidence on family planning intervention in Sub Saharan Africa. Even though there were systematic reviews conducted in this setting on family planning interventions, the need for this scoping review stems from the need to provide an updates on family planning intervention across Sub Saharan Africa. It is essential to establish an adequate evidence base to support the design of policies aimed at improving family planning interventions. Furthermore, condensing evidence across different settings allows a meaningful comparison of experiences and facilitates knowledge transfer across countries. Therefore, this scoping review tried to summarize what works in family planning interventions in Sub Saharan Africa. Methods: The overall focus was to review the overall body of evidence on a given topic, with focus on width rather than depth. We conducted our scoping review according to the ‘York Methodology’ described by Arksey & O’Malley. This allowed us to appraise and condense evidence across study types into one single interpretation. Result: Five studies were reviewed in this study. All of the studies were specific to countries in Sub-Saharan Africa. Among the five quantitative studies, the majority used cross-sectional study design while the remaining used quasiexperimental study design. From studies reviewed, demand creation through (mass media, community mobilizations), messages from religious leaders, advocacy, social franchising, establishment of family planning task force, mobile outreach, and static service delivery were mentioned as means of family planning interventions. Conclusion: Mass media coverage, demand generation, and advocacy and community mobilization were commonly used in family planning interventions across different Sub-Saharan African Countries. Accordingly, family planning interventions which used different these strategies were characterized by better use of modern contraception in these setups.

Interplay Effect of Target Motion and Pencil-Beam Scanning in Proton Therapy for Pediatric Patients.

Purpose:To investigate the effect of interplay between spot-scanning proton beams and respiration-induced tumor motion on internal target volume coverage for pediatric patients.Materials and Methods:Photon treatments for 10 children with representative tumor motions (1–13 mm superior-inferior) were replanned to simulate single-field uniform dose–optimized proton therapy. Static plans were designed by using average computed tomography (CT) data sets created from 4D CT data to obtain nominal dose distributions. The motion interplay effect was simulated by assigning each spot in the static plan delivery sequence to 1 of 10 respiratory-phase CTs, using the actual patient breathing trace and specifications of a synchrotron-based proton system. Dose distributions for individual phases were deformed onto the space of the average CT and summed to produce the accumulated dose distribution, whose dose-volume histogram was compared with the one from the static plan.Results:Tumor motion had minimal impact on the internal target volume hot spot (D2), which deviated by <3% from the nominal values of the static plans. The cold spot (D98) was also minimally affected, except in 2 patients with diaphragmatic tumor motion exceeding 10 mm. The impact on tumor coverage was more pronounced with respect to the V99 rather than the V95. Decreases of 10% to 49% in the V99 occurred in multiple patients for whom the beam paths traversed the lung-diaphragm interface and were, therefore, more sensitive to respiration-induced changes in the water equivalent path length. Fractionation alone apparently did not mitigate the interplay effect beyond 6 fractions.Conclusion:The interplay effect is not a concern when delivering scanning proton beams to younger pediatric patients with tumors located in the retroperitoneal space and tumor motion of <5 mm. Children and adolescents with diaphragmatic tumor motion exceeding 10 mm require special attention, because significant declines in target coverage and dose homogeneity were seen in simulated treatments of such patients.

Development of a deformable phantom for experimental verification of 4D Monte Carlo simulations in a deforming anatomy

PurposeTo verify the accuracy of 4D Monte Carlo (MC) simulations, using the 4DdefDOSXYZnrc user code, in a deforming anatomy. We developed a tissue-equivalent and reproducible deformable lung phantom and evaluated 4D simulations of delivered dose to the phantom by comparing calculations against measurements. MethodsA novel deformable phantom consisting of flexible foam, emulating lung tissue, inside a Lucite external body was constructed. A removable plug, containing an elastic tumor that can hold film and other dosimeters, was inserted in the phantom. Point dose and position measurements were performed inside and outside the tumor using RADPOS 4D dosimetry system. The phantom was irradiated on an Elekta Infinity linac in both stationary and moving states. The dose delivery was simulated using delivery log files and the phantom motion recorded with RADPOS. ResultsReproducibility of the phantom motion was determined to be within 1 mm. The phantom motion presented realistic features like hysteresis. MC calculations and measurements agreed within 2% at the center of tumor. Outside the tumor agreements were better than 5% which were within the positional/dose reading uncertainties at the measurement points. More than 94% of dose points from MC simulations agreed within 2%/2 mm compared to film measurements. ConclusionThe deformable lung phantom presented realistic and reproducible motion characteristics and its use for verification of 4D dose calculations was demonstrated. Our 4DMC method is capable of accurate calculations of the realistic dose delivered to a moving and deforming anatomy during static and dynamic beam delivery techniques.

Agent-based microsimulation conceptual model for urban freight distribution

Abstract In this paper, we develop a conceptual model that integrates the microsimulation and the multi-agent systems in the urban goods distribution processes. The proposed model, which it is defined between the agent-based microsimulation models, allows to analyze the different behaviors and actions that are the result of an urban freight distribution process, facilitating the decision making to improve the efficiency of the logistic process. The model is formulated as a multi-layer urban freight distribution network which involve the street city network and the microsimulation of passenger trips, the use of a distribution center, the design of initial static pick-up and delivery routes, the behaviors of the agents of the system and their interactions that give feedback to the model, and finally assess the impact of the agents in the improvement of the re-routing optimization process at urban freight distribution, according to the multiple types of dynamics variables such as dynamic travel time by traffic conditions in different travels.

Load transfer operations for a dynamic vehicle routing problem with mixed backhauls

We consider a dynamic vehicle routing problem with mixed backhauls (DVRPMB) that seeks to plan, in the most efficient way, the delivery of dynamic pickup orders that arrive in real time, while a predefined plan of serving static delivery orders is being executed. Maintaining the original assignment of delivery orders to vehicles may limit system performance, since the changes in the system state caused by the arriving dynamic orders may grant re-assignments of such orders advantageous. Thus, in this paper, we introduce and solve a variant of DVRPMB that allows orders to be transferred between vehicles during plan implementation. We refer to this problem as the DVRPMB with load transfers (DVRPMB-LT). Since the problem is solved with periodic re-optimization, we focus on the underlying optimization problem, develop an appropriate model using an arc-based formulation, and compare the exact solutions to the ones of the corresponding problem that does not allow transfers. Furthermore, we develop a practical heuristic framework to address the complexity of DVRPMB-LT and solve cases of practical relevance. Subsequently, we employ the proposed framework to solve and analyze the full dynamic problem.

Clinical efficacy and safety of a highly conformal, supine, hybrid forward and inverse planned intensity modulated radiation therapy technique for craniospinal irradiation

Purpose: To demonstrate the clinical efficacy and safety of a highly conformal, supine, hybrid forward and inverse planned intensity modulated radiation therapy (IMRT) technique for photon craniospinal irradiation (CSI).Methods: Patients who received supine, hybrid IMRT CSI from 2009 to 2014 were included in this retrospective review. Clinical target volume (CTV) was defined as intracranial contents and thecal sac, including nerve roots. Dose was prescribed such that >99% of CTV received >99% of prescription and >95% of the planning target volume received >95% of prescription, with no attempt to include vertebral bodies. Lateral fields were utilized at the cranium and upper cervical spine. Spine fields were either single posterior or 2–3 obliques. Plans were generated with a hybrid of forward and inverse planned IMRT. Inferior borders of the cranium fields and superior border of the lower spine field were designed with 6–15 cm long, gradual dose gradients by sequential closing of multileaf collimator leaves using forward planned multiple static segment IMRT delivery. The sliding window upper spine IMRT field was created by the inverse planning system to match gradients of the brain and lower spine fields. The lower spine field gradient was similarly completed.Results: The cohort consisted of 34 patients. Median CSI dose was 36 Gy (range: 18–39.6 Gy). With a median follow up of 59.4 months, there were no isolated recurrences or spinal myelopathies at CTV margins or field gradients. Eleven patients had recurrence, all of which were intracranial.Conclusions: Our hybrid forward and inverse planned IMRT supine CSI technique did not result in any isolated recurrences or myelopathies at CTV margins or field gradients. This suggests our target volumes and blended gradients are appropriate for highly conformal three-dimensional planning.

Evaluation of ArcCHECK SNC Machine QA tool for Modern Linear Accelerator

Purpose: ArcCHECK SNC Machine QA tool is used to test geometric and delivery aspects of linear accelerator. Methods: In this study we evaluated the performance of this tool. For each item analyzed by the tool, wherever possible, tests across the same time period using portal dosimetry were also evaluated. Machine QA feature allows user to perform quality assurance tests using ArcCHECK phantom. Following tests can be performed 1) Gantry Speed, Rotation and Angle 2) MLC/Collimator 3) Beam Profile Flatness and Symmetry. Data was collected on true BEAM STx for a year. All plans were created for 6 and 10 MV beams as per the SNC patient user manual in Eclipse v.13. Results: The Gantry speed was 3.9 deg/sec with speed maximum deviation around 0.3 deg/sec. The Gantry Isocenter for arc delivery was 0.9 mm and static delivery was 0.4 mm which was well consistent with MPC (0.4 mm). The average maximum percent positive and negative diff was found to be 1.9%, -0.25% and average maximum distance positive and negative diff was 0.4 mm, -0.3 mm for MLC/Collimator QA. The average gamma error at 1% 1 mm criteria was 1.4% using portal Dosimetry for 6 MV. The Flatness for Arc delivery was 1.8% and Symmetry for Y was 0.8% and X was 1.8%. Conclusion: ArcCHECK SNC Machine QA tool is useful for quality assurance of modern linear accelerators as it tests both geometric and delivery aspects. This test can be incorporated in the regular quality assurance protocol for VMAT delivery.