Gradient Index Research Articles

OptImal Gamma kNife lIghTnIng sOlutioN (IGNITION) score to characterize the solution space of the Gamma Knife FIP optimizer for stereotactic radiosurgery.

The objective of this study is to evaluate the user-defined optimization settings in the Fast Inverse Planning (FIP) optimizer in Leksell GammaPlan® and determine the parameters that result in the best stereotactic radiosurgery (SRS) plan quality for brain metastases, benign tumors, and arteriovenous malformations (AVMs). Thirty patients with metastases and 30 with benign lesions-vestibular schwannoma, AVMs, pituitary adenoma, and meningioma-treated with SRS were evaluated. Each target was planned by varying the low dose (LD) and beam-on-time (BOT) penalties in increments of 0.1, from 0 to 1. The following plan quality metrics were recorded for each plan: Paddick conformity index (PCI), gradient index (GI), BOT, and maximum organ-at-risk (OAR) doses. A novel objective score matrix was calculated for each target using a linearly weighted combination of the aforementioned metrics. A histogram of optimal solutions containing the five best scores was extracted. A total of 7260 plans were analyzed with 121 plans per patient for the range of LD/BOT penalties. The ranges of PCI, GI, and BOT across all metastatic lesions were 0.58-0.97, 2.1-3.8, and 8.8-238 min, respectively, and were 0.13-0.97, 2.1-3.8, and 8.8-238 min, respectively, for benign lesions. The objective score matrix showed unique optimal solutions for metastatic lesions and benign lesions. Additionally, the plan metrics of the optimal solutions were significantly improved compared to the clinical plans for metastatic lesions with equivalent metrics for all other cases. In this study, FIP optimizer was evaluated to determine the optimal solution space to maximize PCI and minimize GI, BOT and OAR doses simultaneously for single metastatic/benign/non-neoplastic targets. The optimal solution chart was determined using a novel objective score which provides novice and expert planners a roadmap to generate the most optimal plans efficiently using FIP.

Beamforming Phased-Array-Fed Lenses With >0.5λ-Spaced Elements

We propose a phased-array-fed lens (PAFL) antenna that is capable of beamforming like a phased array but with array elements spaced beyond <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5\lambda $ </tex-math></inline-formula> . The PAFL produces high-quality scanned beams using only five active feeds. This architecture represents dramatic cost and power savings over conventional phased arrays while providing many of the features. We present an optimal beamforming method to achieve the maximum gain at any angle using a subset of feeds and a multiobjective optimizer using particle swarm optimization for more granular pattern control. The method is applied to several simulated state-of-the-art lens antennas with good performance confirming the generality of the method. The theory is demonstrated with a prototype PAFL comprising a 4 inch aperture gradient-index (GRIN) lens antenna, an 8-element <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.725\lambda $ </tex-math></inline-formula> -spaced linear patch array operating at 29 GHz, and a commercial Ka-band SATCOM beamformer integrated circuit (IC). The prototype achieves the maximum gain at all angles and improves the scan loss by 4 dB at ±50°.

Inverse design of high-NA metalens for maskless lithography

Abstract We demonstrate an axisymmetric inverse-designed metalens to improve the performance of zone-plate-array lithography (ZPAL), one of the maskless lithography approaches, that offer a new paradigm for nanoscale research and industry. First, we derive a computational upper bound for a unit-cell-based axisymmetric metalens. Then, we demonstrate a fabrication-compatible inverse-designed metalens with 85.50% transmission normalized focusing efficiency at 0.6 numerical aperture at 405 nm wavelength; a higher efficiency than a theoretical gradient index lens design (79.98%). We also demonstrate experimental validation for our axisymmetric inverse-designed metalens via electron beam lithography. Metalens-based maskless lithography may open a new way of achieving low-cost, large-area nanofabrication.

Morphotectonic Analysis of Wadi Al-Batin Alluvial Fan, South of Iraq, Using Remote Sensing and GIS Techniques

This research aimed to know the tectonic activity of the Wadi Al-Batin alluvial fan using hydrological and morphotectonic analyses. Wadi Al-Batin alluvial fan is deposited from Wadi Al-Rimah in Saudi Arabia, which extended to Iraqi and Kuwait international boundaries. The longitudinal and transverse faults that characterize this region were common. The Abu- Jir-Euphrates faults have a significant impact on the region. The faults zone consists of several NW- SE trending faults running from the Rutba in western Iraq to the south along the Euphrates through Kuwait and meeting the Al-Batin fault to the Jal Al-Zor fault. The Hydromorphometric analysis of the present fan shows five watersheds having asymmetry shapes, more elongated and activity from the elongation ratio and asymmetry factor values. In contrast, transverse topographic symmetry and mountain front sinuosity factor have moderate to low activity from the stream length gradient index. The morphotectonic analysis suggests that the Wadi Al-Batin alluvial fan has a moderate tectonic activity due to the tectonic activity of the subsurface lineaments and the oil field activities found in the region.

Morphomertic and neotectonic study of Upper Teesta River basin, Sikkim Himalaya using geospatial techniques

This study is done on the basis of the surface and subsurface faults and active tectonic processes which disrupt the pattern of the drainage system present in the basin. The pattern of the drainages and their morphological features shown in the morphometric drainage basin areas which are used as a sign of neotectonics activity. This study is focused on the Upper Teesta River basin of the Sikkim Himalayan. For the study of the morphometric and morphotectonic analysis of the Upper Teesta River basin, ALOS PALSAR DEM was used to generate the drainage order of the basin with the help of the Arc GIS Software. The estimated drainage order of the basin is 6th. In this study, morphotectonic parameters such as asymmetry factor, elongation ratio, transverse topography asymmetry, mountain-front sinuosity, ratio of valley floor width to valley height, and hypsometric Integral was estimated 45.66, 0.55, 0.25, 1.08, 0.94, 0.44 respectively. These all-parameters value show the Upper Teesta River Basin is tectonically active. The stream gradient index of the basin was calculated >500 indicate the study region tectonically active. This research is validated using 50 years (1971–2020) earthquake data. Therefore, geospatial tool is an important tool to know the area is neo tectonically active.

Comparison of Eucalyptus spp. wood quality in solar and conventional drying

The aim of the study was to compare the quality of sawn Eucalyptus spp. wood under solar and conventional drying, focusing on parameters such as drying rate, moisture gradient, drying stresses, and wood defects. For this purpose, a comparison was made between samples dried in a solar kiln and a conventional drying chamber. As a preliminary analysis, the specific gravity and initial moisture content of the wood were evaluated, and the quality and drying parameters of the wood were assessed both before and after the drying process. It was observed that the drying rate in the conventional chamber was twice as high above the fiber saturation point and four times higher in the diffusion phase compared to solar drying. Regarding the moisture gradient and defect index, there was no statistical difference between the two processes. However, the percentage of pieces with defects was significantly higher in conventional drying, as well as demonstrating higher drying stresses, which may hinder mechanical processing after water removal. Therefore, it can be concluded that solar drying presents a quality similar to conventional drying and can be a good alternative for drying processes.

Evaluation of plan quality and treatment efficiency in cranial stereotactic radiosurgery treatment plans with a variable source-to-axis distance.

Radiotherapy deliveries with dynamic couch motions that shorten the source-to-axis distance (SAD) on a C-arm linac have the potential to increase treatment efficiency through the increase of the effective dose rate. In this investigation, we convert clinically deliverable volumetric modulated arc therapy (VMAT) and dynamic conformal arc (DCA) plans for cranial radiosurgery into virtual isocenter plans through implementation of couch trajectories that maintain the target at a shortened but variable SAD throughout treatment. A randomly sampled population of patients treated with cranial radiosurgery from within the last three years were separated into groups with one, two, and three lesions. All plans had a single isocenter (regardless of number of targets), and a single prescription dose. Patient treatment plans were converted from their original delivery at a standard isocenter to a dynamic virtual isocenter in MATLAB. The virtual isocenter plan featured a variable isocenter position based upon the closest achievable source-to-target distance (referred to herein as a virtual source-to-axis distance [vSAD]) which avoided collision zones on a TrueBeam STx platform. Apertures were magnified according to the vSAD and monitor units at a given control point were scaled based on the inverse square law. Doses were calculated for the plans with a virtual isocenter in the Eclipse (v13.6.23) treatment planning system (TPS) and were compared with the clinical plans. Plan metrics (MU, Paddick conformity index, gradient index, and the volume receiving 12 Gy or more), normal brain dose-volume differences, as well as maximum doses received by organs at risk (OARs) were assessed. The values were compared between standard and virtual isocenter plans with Wilcoxon Sign Ranked tests to determine significance. A subset of the plans were mapped to the MAX-HD anthropomorphic phantom which contained an insert housing EBT3 GafChromic film and a PTW 31010 microion chamber for dose verification on a linac. Delivering plans at a virtual isocenter resulted in an average reduction of 20.9% (p = 3×10-6 ) and 20.6% (p = 3.0×10-6 ) of MUs across all VMAT and all DCA plans, respectively. There was no significant change in OAR max doses received by plans delivered at a virtual isocenter. The low dose wash (1.0-2.0 Gy or 5-11% of the prescription dose) was increased (by approximately 20 cc) for plans with three lesions. This was equivalent to a 2.7%-3.8% volumetric increase in normal tissue receiving the respective dose level when comparing the plan with a virtual isocenter to a plan with a standard isocenter. Gamma pass rates with a 5%/1mm analysis criteria were 96.40% ± 2.90% and 95.07% ± 3.10% for deliveries at standard and virtual isocenter, respectively. Absolute point dose agreements were within -0.36% ± 3.45% and -0.55% ± 3.39% for deliveries at a standard and virtual isocenter, respectively. Potential time savings per arc were found to have linear relationship with the monitor units delivered per arc (savings of 0.009 s/MU with an r2 = 0.866 when fit to plans with a single lesion). Converting clinical plans at standard isocenter to a virtual isocenter design did not show any losses to plan quality while simultaneously improving treatment efficiency through MU reductions.

Identifying predictors of on-table adaptation for pancreas stereotactic body radiotherapy (SBRT)

PurposeTo identify any clinical or dosimetric parameters that predict which individuals may benefit from on-table adaptation during pancreas stereotactic body radiotherapy (SBRT) with MRI-guided radiotherapy. Methods and materialsThis was a retrospective study of patients undergoing MRI-guided SBRTfrom 2016 to 2022.Pre-treatment clinical variables and dosimetric parameters on the patient’s simulation scan were recorded for each SBRT course, and their ability to predict for on-table adaptation was analyzed using ordinal logistic regression. The outcome measure was number of fractions adapted. ResultsSixty-three SBRT courses consisting of 315 fractions were analyzed. Median prescription dose was 40 Gy in five fractions (range, 33–50 Gy); 52% and 48% of courses were prescribed ≤40 Gy and >40 Gy, respectively. The median minimum dose delivered to 95% (D95) of the gross tumor volume (GTV) and planning target volume (PTV) was 40.1 Gy and 37.0 Gy, respectively. Median number of fractions adapted per course was three, with 58% (183 out of 315) total fractions adapted. On univariable analysis, the prescription dose (>40 Gy vs ≤40 Gy), GTV volume, stomach V20 and V25, duodenum V20 and dose maximum, large bowel V33 and V35, GTV dose minimum, PTV dose minimum, and gradient index were significant determinants foradaptation (all p < 0.05). On multivariable analysis, only the prescription dose was significant (adjusted odds ratio 19.7, p = 0.005), but did not remain significant after multiple test correction (p = 0.08). ConclusionsThe likelihood of needing on-table adaptation could not be reliably predicted a priori using pre-treatment clinical characteristics, dosimetry to nearby organs at risk, or other dosimetric parameters based on the patient’s anatomy at the time of simulation, suggesting the critical importance of day-to-day variations in anatomy and increasing access to adaptive technology for pancreas SBRT. A higher (ablative) prescription dose was associated with increased use of adaptation.

Analysis of CyberKnife intracranial treatment plans using ICRU 91 dose reporting: A retrospective study.

ICRU 91, published in 2017, is an international standard for prescribing, recording, and reporting stereotactic treatments. Since its release, there has been limited research published on the implementation and impact of ICRU 91 on clinical practice. This work provides an assessment of the recommended ICRU 91 dose reporting metrics for their use in clinical treatment planning. A set of 180 intracranial stereotactic treatment plans for patients treated by the CyberKnife (CK) system were analyzed retrospectively using the ICRU 91 reporting metrics. The 180 plans comprised 60 trigeminal neuralgia (TGN), 60 meningioma (MEN), and 60 acoustic neuroma (AN) cases. The reporting metrics included the planning target volume (PTV) near-minimum dose ( ), near-maximum dose ( ), and median dose ( ), as well as the gradient index (GI) and conformity index (CI). The metrics were assessed for statistical correlation with several treatment plan parameters. In the TGN plan group, owing to the small targets, was greater than in 42 plans, whereas both metrics were not applicable in 17 plans. The metric was predominantly influenced by the prescription isodose line (PIDL). The GI was significantly dependent on target volume in all analyses performed, where the variables were inversely related. The CI was only dependent on target volume in treatment plans for small targets. The ICRU 91 and metrics breakdown in plans for small target volumes below 1 cm3 ; the Min and Max pixel should be reported in such cases. The metric is of limited use for treatment planning. Given their volume dependence, the GI and CI metrics could potentially serve as plan evaluation tools in the planning of the sites analyzed in this study, which would ultimately improve treatment plan quality.

Comparison between the HyperArc™ technique and the CyberKnife® technique for stereotactic treatment of brain metastases

PurposeThe purpose of this study was to compare the planimetric capacities between HyperArc™-based stereotactic radiosurgery and robotic radiosurgery system-based planning using CyberKnife® M6 for single and multiple cranial metastases. Materials and methodsWe evaluated 51 treatment plans for cranial metastases, including 30 patients with a single lesion and 21 patients with multiple lesions, treated with the CyberKnife® M6. These treatment plans were optimized using the HyperArc™ (HA) system with the TrueBeam. The comparison of the quality of the treatment plans between the two treatment techniques (CyberKnife and HyperArc) was performed using the Eclipse treatment planning system. Dosimetric parameters were compared for target volumes and organs at risk. ResultsCoverage of the target volumes was equivalent between the two techniques, whereas median Paddick conformity index and median gradient index for all target volumes were 0.9 and 3.4, respectively for HyperArc plans, and 0.8 and 4.5 for CyberKnife plans (P<0.001). The median dose of gross tumor volume (GTV) for HyperArc and CyberKnife plans were 28.4 and 28.8, respectively. Total brain V18Gy and V12Gy-GTVs were 11cm3 and 20.2cm3 for HyperArc plans versus 18cm3 and 34.1cm3 for CyberKnife plans (P<0.001). ConclusionThe HyperArc provided better brain sparing, with a significant reduction in V12Gy and V18Gy, associated with a lower gradient index, whereas the CyberKnife gave a higher median GTV dose. The HyperArc technique seems to be more appropriate for multiple cranial metastases and for large single metastatic lesions.

GRIN-lens-based in-line digital holographic microscopy.

In-line digital holographic microscopy (DHM) provides three-dimensional images with large fields of view and depths of field and micrometer-scale resolution, using a compact, cost-effective, and stable setup. Here, we develop the theoretical background and experimentally demonstrate an in-line DHM based on a gradient-index (GRIN) rod lens. In addition, we develop a conventional pinhole-based in-line DHM with different configurations to compare the resolution and image quality of both GRIN-based and pinhole-based systems. We show that in a high-magnification regime, where the sample is positioned near a source that produces spherical waves, our optimized GRIN-based setup provides better resolution (∼1.38µm). Furthermore, we employed this microscope to holographically image dilute polystyrene micro-particles with diameters of 3.0 and 2.0µm. We investigated the effect of light source-detector and sample-detector distances on the resolution, by both theory and experiment. Our theoretical and experimental results are in good agreement.

Dispersion controlled nanocomposite gradient index lenses

The degrees of freedom afforded by nanocomposite materials and additive manufacturing allow for the precise control over the chromatic properties of gradient index (GRIN) optics. The ability to engineer nanocomposite optical materials using blends of three or more constituents makes it possible to independently specify the refractive index gradient and the dispersion of optical materials. The refractive index spectra of the primary nanocomposite feedstock are defined relative to one another using various concentrations of monomers and nanofillers. Inkjet deposition is then used to print-compose specific feedstock to form refractive index gradients with precise control over dispersion. Arrays of 4-mm-diameter spherical GRIN lenses were fabricated using different nanomaterial compositions. The ability to positively and negatively control dispersion and to obtain achromatic performance was demonstrated. Control over partial dispersion is also shown.

Assessment of soil quality in a heavily fragmented micro-landscape induced by gully erosion

Soil quality degradation induced by erosion significantly inhibits sustainable development worldwide. For assessment of soil quality variations in an area with a heavily fragmented micro-landscape induced by gully erosion, 16 soil quality indicators were tested in laboratory settings and selected by principal component analysis (PCA). Meanwhile, soil quality prediction was conducted by the random forest (RF) model with its quality indicators derived from a 3-dimensional structure of the landscape (resolution, 0.01 m) obtained with an unmanned aerial vehicle (UAV). During RF modelling, 80 % of the Soil Quality Indices (SQIs) estimated by PCA were randomly selected as training data, and the remaining was used to validate the prediction result. The optimal SQIs were shown to include Mnd, bulk density, silt content, and cation exchange capacity (CEC). Additionally, the PCA-calculated SQI ranging from 0.33 to 0.85 decreased with decreasing elevation in the gully erosional area. Moreover, the spatial soil quality predicted by RF with a satisfied accuracy (R2 = 0.83 ∼ 0.86; RMSE = 0.03 ∼ 0.04) was comparable to PCA-calculated SQI. Overall, the spatial variation of soil quality in the gully was attributed to elevation (13.4 ∼ 24.1 %), slope gradient (8.0 ∼ 13.4 %), relief amplitude (9.8 ∼ 12.9 %), and terrain roughness index (10.3 ∼ 11.9 %). This study confirmed the excellent performance of RF for SQI prediction, and also indicated that ultra-high-resolution (0.01 m) terrain obtained by unmanned aerial vehicle (UAV) was a competent tool for soil quality assessment in areas with complicated microtopography and limited availability for soil sampling.

Analysis of Bending Properties of FG-SMA Beam Under Thermo-Mechanical Coupling

The mechanical properties of functional-graded shape memory alloy (FG-SMA) is of highly significance for its applications and structural design. This paper establishes a constitutive model of the FG-SMA beam, considering the influence of the temperature variation and the tension-compression asymmetry coefficient. The fiber element method and the virtual work principle were employed to establish the governing equation of the bending of FG-SMA beam, which is solved using the Newton–Raphson algorithm. Furthermore, the effect of the tension-compression asymmetry coefficient, temperature, gradient index, bending moment, and axial load on the mechanical properties of the FG-SMA beams was analyzed. The results showed that the tension-compression asymmetry coefficient, gradient index, bending moment, and axial load significantly have relatively obvious influence on the cross-sectional mechanical response of the FG-SMA beams, while the effect of the temperature was not noticeable.

Higher order finite element models for transient analysis of strain gradient functionally graded microplates

In the study, three different higher order finite element models (HOFEMs) are developed to perform the transient analysis of functionally graded (FG) microplates subjected to different dynamic loads, namely, sinusoidally distributed step and exponential blast loads. A normal and shear deformable plate theory with five unknowns is used to present displacement field and modified strain gradient theory is employed for small-scale effect. A rectangular four-noded element and Newmark's method is used to solve transient analysis of FG microplates. The effects of boundary condition, type of dynamic loading, thickness to material length parameter, aspect ratio, gradient index and CPU time are investigated. It is found that two of the HOFEMs developed based on the C1 and C2 continuity requirements produced almost same numerical results. However, the one with 36 unknows per element yields slightly different results than the others. The HOFEM satisfying the C1 continuity requirement consumes the minimum computational time.

Improvement of angina after treating focal coronary artery disease undetected in resting conditions.

A 65-year-old woman without cardiovascular risk factors presented with stable angina Canadian Cardiovascular Society (CCS) Class II. The 7-item Seattle Angina Questionnaire (SAQ-7) indicated frequent angina, moderate physical limitation, and low quality of life for a summary score of 50/100. Coronary CT and invasive angiography revealed severe stenosis in the mid-left anterior descending (LAD) coronary artery with a minimum lumen area (MLA) of 0.9 mm2 and mixed plaque (Figures 1A and B). Intravascular ultrasound (IVUS) confirmed small MLA and 84% plaque burden (Figure 1A, right panels). The resting full-cycle ratio (RFR) was negative (0.93), whereas fractional flow reserve (FFR) was positive (0.75) with a focal pressure step-up in the pullback curve as quantified by a high pullback pressure gradient (PPG) index of 0.79 (Figures 1C and D). The patient underwent percutaneous coronary intervention (PCI) with one drug-eluting stent (Figure 1E). Post-PCI IVUS confirmed good stent expansion. Post-PCI FFR increased to 0.92 without residual focal pressure gradients in the pullback curve (Figure 1F), and normal microcirculation function demonstrated by a coronary flow reserve (CFR) of 7.8 and index of microvascular resistance (IMR) of 16 (Figure 1G). RFR remained unchanged at 0.94. The SAQ-7 at 1-year follow-up showed complete symptoms resolution and improvement in all domains (Figure 1H). A symptomatic patient with obstructive focal epicardial disease yet a negative resting index experienced relief from angina after PCI. This case highlights the usefulness of a comprehensive physiological assessment in cases considered for revascularization, particularly with focal lesions.

Monitor unit restrained hybrid approach using conformal arcs for radiosurgery of solitary brain metastasis

PurposeThis study appraises the efficacy of monitor unit (MU) restrained hybrid planning approach for solitary brain metastasis combining dynamic conformal and volumetric modulated arcs. The optimal level of monitor unit restrainment is ascertained by plan metric analysis. Besides, dependence of efficiency index (η50%) on beam modulation (BM) and association of normal brain receiving 12Gy (V12) with gradient index (GI) under the applied MU constraints is assessed. MethodsSixteen cases were planned to a dose of 20 Gy using 2–3 non-coplanar DCAT arcs and a coplanar VMAT arc, combined in a 7:3 dose ratio. All VMAT optimizations were based on DCA dose. A baseline VMAT plan was generated without using the MU-tool. Then MUs of the baseline plan were reduced using the MU-tool by 10%, 20%, 30%, and 40% to develop alternate plan types. Alternate plans were compared to baseline plan using the mean difference of plan metrics. The relationship of η50% with BM and that of V12 with GI was assessed using Pearson's r. ResultsEfficiency index, η50% reduced significantly across all plan types except MU-10. CI increased from 90.8% to 91.4% on reducing MU restraint. GI did not deteriorate for MU-10 and MU-20 but increased for MU-30 and MU-40, P < 0.006. Brain receiving 12Gy, V12 increased about 0.1 cm3 for MU-40, P = 0.001. Also, the probability of symptomatic necrosis, S-NEC(V12), increased by 0.1% for MU-40 and MU-30, P < 0.012. BM reduced from MU-20 through MU-40 by at least 5.7% (P < 0.001). Beam-on-time and MU factor reduced maximally by 0.6 min and 15.7%, for MU-40. For all plan types, η50% correlated directly with BM, whereas V12 showed an inverse relationship with GI. ConclusionsModerately constrained, MU-20 type hybrid plans demonstrated optimal overall efficiency, achieving plan objectives with reasonable delivery simplicity. Efficiency index reduced gradually with decreasing beam modulation.

Identifying predictors of on-table adaptation for pancreas stereotactic body radiotherapy (SBRT).

702 Background: There is growing interest in the use of stereotactic body radiotherapy (SBRT) to treat pancreatic cancer. The purpose of this study was to identify any clinical or dosimetric parameters that predict which individuals may benefit from on-table adaptation during pancreas SBRT with MRI-guided radiotherapy. Methods: This was a single center retrospective study of patients undergoing MRI-guided SBRT to the pancreas from 2016 to 2022. An online daily adaptive workflow was in place for all fractions according to pre-specified criteria. Pre-treatment clinical variables and dosimetric parameters on the patient’s simulation scan were recorded for each SBRT course, and their ability to predict for on-table adaptation was analyzed using ordinal logistic regression. The outcome measure was number of fractions adapted. Results: Seventy-three SBRT courses consisting of 365 fractions were included in this study. Median prescription dose was 40 Gy in five fractions (range, 33-50 Gy); 56% and 44% of courses were prescribed ≤ 40 Gy and &gt; 40 Gy, respectively. Median gross and planning target volume (GTV and PTV) coverage were 94.7% and 84.3%, respectively. Median number of fractions adapted per course was three, with overall 58% (211 out of 365) total fractions adapted. On univariable analysis, the prescription dose ( &gt; 40 Gy vs ≤ 40 Gy), GTV size, stomach V20 and V25, duodenum V20 and Dmax, large bowel V33 and V35, heterogeneity index, and gradient index were significant determinants of the use of on-table adaptation (all p &lt; 0.05). On multivariable analysis, only prescription dose remained significant (adjusted odds ratio 7.66, p = 0.003). Conclusions: Prescription dose in MRI-guided pancreas SBRT is the only reliable predictor of on-table adaptation. Providers should strongly consider utilization of adaptive technology when delivering ablative doses to the pancreas.[Table: see text]

Multiple Brain Metastases Radiosurgery with CyberKnife Device: Dosimetric Comparison between Fixed/Iris and Multileaf Collimator Plans.

In our institution, stereotactic radiosurgery of multiple brain metastases is performed with the CyberKnife® (CK) device, using fixed/Iris collimators. In this study, nineteen fixed/Iris plans were recalculated with the multileaf collimator (MLC), to assess if it is possible to produce plans with comparable dosimetric overall quality. For consistent comparisons, MLC plans were re-optimized and re-normalized in order to achieve the same minimum dose for the total planning target volume (PTVtot). Conformation number (CN), homogeneity index (HI) and dose gradient index (DGI) metrics were evaluated. The dose to the brain was evaluated as the volume receiving 12 Gy (V12) and as the integral dose (ID). The normal tissue complication probability (NTCP) for brain radionecrosis was calculated as a function of V12. The reoptimized plans were reviewed by the radiation oncologist and were found clinically acceptable according to the The American Association of Physicists in Medicine (AAPM) Task Group-101 protocol. However, fixed/Iris plans provided significantly higher CN (+8.6%), HI (+2.2%), and DGI (+44.0%) values, and significantly lower ID values (-35.9%). For PTVtot less than the median value of 2.58cc, fixed/Iris plans provided significantly lower NTCP values. On the other side, MLC plans provided significantly lower treatment times (-18.4%), number of monitor units (-33.3%), beams (-46.0%) and nodes (-21.3%). CK-MLC plans for the stereotactic treatment of brain multi metastases could provide an important advantage in terms of treatment duration. However, to contain the increased risk for brain radionecrosis, it could be useful to calculate MLC plans only for patients with large PTVtot.

Dynamic Behavior of a Spinning Exponentially Functionally Graded Shaft With Unbalanced Load

Abstract The dynamic behaviors of a pinned–pinned spinning exponentially functionally graded shaft with unbalanced loads are investigated. The shaft is simulated in the Rayleigh beam model considering rotary inertia and gyroscopic effects. The governing equation for the flexural vibration of the shaft is derived via the Hamilton principle. Based on the boundary conditions, both the exact and approximate whirl frequency equations of the system are obtained analytically. Also, the validity of the proposed model is confirmed by comparing it with the results reported in the literature. Finally, a numerical study on the basis of the analytical solutions is performed to evaluate the main parameters, including slenderness ratio (α), gradient index (β), mass ratio (μ), and eccentric distance (γ) on the whirl frequency, critical spinning speed, mode shapes, and stability of the system. The results reveal that the vibration and instability of the spinning shaft are strongly dependent on the unbalanced load and material gradient.