Prediction-based compensation for gate on/off latency during respiratory-gated radiotherapy

During respiratory-gated radiotherapy (RGRT), gate on and off latencies cause deviations of gating windows, possibly leading to delivery of low- and high-dose radiations to tumors and normal tissues, respectively. Currently, there are no RGRT systems that have definite tools to compensate for the delays. To address the problem, we propose a framework consisting of two steps: 1) multi-step-ahead prediction and 2) prediction-based gating. For each step, we have devised a specific algorithm to accomplish the task. Numerical experiments were performed using respiratory signals of a phantom and ten volunteers, and our prediction-based RGRT system exhibited superior performance in more than a few signal samples. In some, however, signal prediction and prediction-based gating did not work well, maybe due to signal irregularity and/or baseline drift. The proposed approach has potential applicability in RGRT, and further studies are needed to verify and refine the constituent algorithms.Comment: 12 pages, 12 figures, accepted by Computational and Mathematical Methods in Medicin

Non-LTE Line-Formation and Abundances of Sulfur and Zinc in F, G, and K Stars

Extensive statistical-equilibrium calculations on neutral sulfur and zinc were carried out, in order to investigate how the non-LTE effect plays a role in the determination of S and Zn abundances in F, G, and K stars. Having checked on the spectra of representative F-type stars (Polaris, Procyon, and alpha Per) and the Sun that our non-LTE corrections yield a reasonable consistency between the abundances derived from different lines, we tried an extensive non-LTE reanalysis of published equivalent-width data of S I and Zn I lines for metal-poor halo/disk stars. According to our calculations, S I 9212/9228/9237 lines suffer significant negative non-LTE corrections amounting to <~ 0.2--0.3 dex, while LTE is practically valid for S I 8683/8694 lines. Embarrassingly, as far as the very metal-poor regime is concerned, a marked discordance is observed between the [S/Fe] values from these two abundance indicators, in the sense that the former attains a nearly flat plateau (or even a slight downward bending) while the latter shows an ever-increasing trend with a further lowering of metallicity. The reason for this discrepancy is yet to be clarified. Regarding Zn, we almost confirmed the characteristic tendencies of [Zn/Fe] reported from recent LTE studies (i.e., an evident/slight increase of [Zn/Fe] with a decrease of [Fe/H] for very metal-poor/disk stars), since the non-LTE corrections for the Zn I 4722/4810 and 6362 lines (tending to be positive and gradually increasing towards lower [Fe/H]) are quantitatively of less significance (<~ 0.1 dex).Comment: 33 pages, 7 figures, PASJ, Vol. 57, No. 5 (2005) in pres

Drift-Induced Step Instabilities Due to the Gap in the Diffusion Coefficient

On a Si(111) vicinal face near the structural transition temperature, the $1 \times 1$ structure and the $7 \times 7$ structure coexist in a terrace: the $1 \times 1$ structure is in the lower side of the step edge and the $7 \times 7$ structure in the upper side. The diffusion coefficient of adatoms is different in the two structures. Taking account of the gap in the diffusion coefficient at the step, we study the possibility of step wandering induced by drift of adatoms. A linear stability analysis shows that the step wandering always occurs with step-down drift if the diffusion coefficient has a gap at the step. Formation of straight grooves by the step wandering is expected from a nonlinear analysis. The stability analysis also shows that step bunching occurs irrespective of the drift direction if the diffusion in the lower side of the step is faster. The step bunching disturbs the formation of grooves. If step-step repulsion is strong, however, the step bunching is suppressed and the straight grooves appear. Monte Carlo simulation confirms these predictions.Comment: 5 pages, 6 figure

Factual survey of the clinical use of deformable image registration software for radiotherapy in Japan

Deformable image registration (DIR) has recently become commercially available in the field of radiotherapy. However, there was no detailed information regarding the use of DIR software at each medical institution. Thus, in this study, we surveyed the status of the clinical use of DIR software for radiotherapy in Japan. The Japan Society of Medical Physics and the Japanese Society for Radiation Oncology mailing lists were used to announce this survey. The questionnaire was created by investigators working under the research grant of the Japanese Society for Radiation Oncology (2017–2018) and intended for the collection of information regarding the use of DIR in radiotherapy. The survey was completed by 161 institutions in Japan. The survey results showed that dose accumulation was the most frequent purpose for which DIR was used in clinical practice (73%). Various commissioning methods were performed, although they were not standardized. Qualitative evaluation with actual patient images was the most commonly used method (28%), although 30% of the total number of responses (42% of institutions) reported that they do not perform commissioning. We surveyed the current status of clinical use of DIR software for radiotherapy in Japan for the first time. Our results indicated that a certain number of institutions used DIR software for clinical practice, and various commissioning methods were performed, although they were not standardized. Taken together, these findings highlight the need for a technically unified approach for commissioning and quality assurance for the use of DIR software in Japan

Control of chaotic wandering of an isolated step by the drift of adatoms

金沢大学総合メディア基盤センターThe drift of adatoms strongly influences the wandering pattern of an isolated step moving in a surface diffusion field. When the drift velocity has a component against the step motion and exceeds a critical value, the straight step becomes unstable with long wavelength fluctuations, and wanders. This wandering pattern can be controlled by changing the direction of the drift. When the drift has no component parallel to the step edge, the unstable step obeys the Kuramoto-Sivashinsky equation and shows a chaotic pattern. When the drift has a component parallel to the step edge, the step obeys the Benney equation. If the parallel component is sufficiently large, the step shows a regular pattern

Instabilities of steps induced by the drift of adatoms and effect of the step permeability

金沢大学総合メディア基盤センターWe theoretically study step wandering and step bunching induced by the drift of adatoms with attention to the permeability of steps. The critical drift velocity to induce the instability is calculated, and Monte Carlo simulation is performed to test the linear analysis. In sublimation, when the step distance is small in comparison with the surface diffusion length, the wandering and bunching of steps can occur simultaneously with the step-down drift if steps are impermeable. The instabilities do not occur simultaneously if steps are permeable: the bunching occurs with the step-up drift, and the wandering with the step-down drift. In growth, when the step distance is small, the bunching occurs with the step-down drift and the step wandering occurs with the step-up drift irrespective of the permeability, in agreement with Métois and Stoyanov [Surf. Sci. 440, 407 (1999)]. The change of the permeability with increasing temperature can explain the instabilities observed in Si(111) vicinal face

Evaporation and impingement effects on drift-induced step instabilities on a Si(001) vicinal face

金沢大学総合メディア基盤センターWe theoretically study the effect of evaporation and impingement of atoms on step wandering induced by the drift of adatoms. With a Si(001) vicinal face in mind, the anisotropy in diffusion coefficient is assumed to alternate on consecutive terraces. Without evaporation, steps wander in-phase with step-up drift and grooves perpendicular to the steps appear. The form of the wandering steps is sinusoidal with the width increasing in time as t12. Evaporation of adatoms suppresses the step wandering and introduces two surface diffusion lengths. When they are longer than the step distance, the step width still increases in proportion to t12, but with a smaller coefficient than that in the case without evaporation. When one of the surface diffusion lengths is comparable or shorter than the step distance, the saturation of the step width occurs. Impingement of atoms, on the other hand, changes the form of the wandering steps: their front becomes flat and wide and the grooves become steep and narrow. The growth rate of the step width becomes small, but the step width increases with the same exponent 12.© 2005 The American Physical Society

Increased B7-H1 and B7-H4 Expressions on Circulating Monocytes and Tumor-Associated Macrophages are Involved in Immune Evasion in Patients with Gastric Cancer

Expression of the costimulatory molecule B7-H4, a member of the inhibitory B7 family, has been reported to be upregulated on tumor-associated macrophages, and this overexpression may be involved in immune evasion in cancer patients. The present study was designed to investigate B7-H4 expression on monocytes/macrophages and its relationship with immune evasion in gastric cancer patients. B7-H4 expression on circulating monocytes and tumor-associated macrophages was evaluated by multicolor flow cytometry. Carboxyfluorescein succinimidyl ester proliferation assays and quantitative interferon-gamma enzyme-linked immunosorbent assays were carried out to determine the inhibitory effect of B7-H4+ monocytes on CD4+ T cells. B7-H4 expression on circulating monocytes was upregulated and these B7-H4+ monocytes showed immunosuppressive properties. B7-H4 expression was closely related to the depth of invasion, as well as the presence of lymphatic and venous invasion. There were significant correlations between B7-H4 expression and B7-H1 or HLA-DR expression on monocytes/macrophages in gastric cancer patients. B7-H4 expression was remarkably upregulated in gastric cancer tissues compared with peripheral blood samples. Complete surgical removal of the tumor decreased B7-H4 expression on circulating monocytes from gastric cancer patients. Cocultures of gastric cancer cell lines and monocytes led to upregulation of B7-H4 expression on monocytes. Increased B7-H4 expression on circulating monocytes and tumor-associated macrophages may be one of the key mechanisms responsible for immune evasion by tumors in gastric cancer