[Verification of Dose Distribution in Cervical Cancer Brachytherapy Using Metal and Plastic Applicators].

PURPOSE: To validate the point-A dose and dose distribution of metal and resin applicators in comparison with those of TG-43U1. METHODS: The metal and resin applicators consisting of tandem and ovoid were modeled by the egs_brachy. The doses to point A and dose distributions considering each applicator were calculated and compared to those of TG-43U1. RESULTS: The dose to point A considering the metal applicator was 3.2% lower than that of TG-43U1, but there was no difference in the dose to point A considering the resin applicator. The dose distribution considering the metal applicator was lower than that of TG-43U1 at all calculation points, but there was no difference in the dose distribution considering the resin applicator at almost all calculation points. CONCLUSION: In this study, the dose distribution considering the metal applicator was lower than that of TG-43U1 at all calculation points, but there was no difference in the dose distribution considering the resin applicator at almost all calculation points. Therefore, TG-43U1 can accurately calculate the dose distribution when changing from the metal applicator to the resin applicator.

Mouthpiece polymer-gel dosimeter for in vivo oral dosimetry during head and neck radiotherapy.

In this study, we developed a mouthpiece-type gel dosimeter to prevent the oral mucositis caused by the perturbation effect of dental alloys in the radiotherapy of the head and neck regions and to enable in vivo dosimetry. Understanding the dose distribution in the oral cavity during radiotherapy helps identify the possible site for oral mucositis during treatment. Here agarose, which has a higher melting point than gelatin, was added as a coagulant to stabilize the shape of the dosimeter. The strength and dose response of the dosimeter were investigated. The strength was measured at room temperature, 20°C-40 °C, which is higher than the intraoral temperature. The dose-response curves were obtained by magnetic resonance imaging with R2 ranging from 0 to 25 Gy. The strength and dose response of the mouthpiece-type gel dosimeter were approximately 4 and 2.1 times higher than those of polyacrylamide gel and tetrakis hydroxymethyl phosphonium chloride dosimeters commonly used in the prescribed doses per fraction of treatment. The dosimeter is composed of 4 wt% MgCl2 and 1.5 wt% agarose; thus, it can retain the water equivalence. Through in vivo oral dosimetry in three dimensions for head and neck radiotherapy with dental alloys using the mouthpiece-type gel dosimeter, we obtained three-dimensional dose distributions in the dosimeter. The properties of the dosimeter show that it can be used in the clinic, depending on the prescribed dose.

Quantitative analysis of the intra-beam respiratory motion with baseline drift for respiratory-gating lung stereotactic body radiation therapy.

This study aimed to quantitatively clarify the baseline drift for each respiratory cycle in two respiratory-gating methods using the intra-beam respiratory motion data of lung cancer patients. The residual motion and dose distribution were calculated based on intra-beam respiratory motion data with the baseline drift. To quantify the baseline drift $\Delta$ during irradiation, it was defined as the inclination between the detected expiration point and the expiration point in the next cycle in the anterior-posterior (AP), cranial-caudal (CC) and left-right (LR) directions obtained using an in-house programme. The baseline drift value reached up to 0.74 mm/s in the CC direction as per the respiratory motion data of 10 patients. The homogeneity index (HI) of the phase-gating method tended to increase because the target was irradiated even when the amplitude position of the target differed from period to period. In contrast, the amplitude-gating method enabled irradiation considering the amplitude position of the target because the gating window was set considering the amplitude position of the respiratory motion. The respiratory-gating methods and respiratory phase in respiratory-gating lung stereotactic body radiation therapy (SBRT) must be determined based on the respiratory motion of the patients.

Sparse random feature maps for the item-multiset kernel.

Random feature maps are a promising tool for large-scale kernel methods. Since most random feature maps generate dense random features causing memory explosion, it is hard to apply them to very-large-scale sparse datasets. The factorization machines and related models, which use feature combinations efficiently, scale well for large-scale sparse datasets and have been used in many applications. However, their optimization problems are typically non-convex. Therefore, although they are optimized by using gradient-based iterative methods, such methods cannot find global optimum solutions in general and require a large number of iterations for convergence. In this paper, we define the item-multiset kernel, which is a generalization of the itemset kernel and dot product kernels. Unfortunately, random feature maps for the itemset kernel and dot product kernels cannot approximate the item-multiset kernel. We thus develop a method that converts an item-multiset kernel into an itemset kernel, enabling the item-multiset kernel to be approximated by using a random feature map for the itemset kernel. We propose two random feature maps for the itemset kernel, which run faster and are more memory efficient than the existing feature map for the itemset kernel. They also generate sparse random features when the original (input) feature vector is sparse and thus linear models using proposed methods . Experiments using real-world datasets demonstrated the effectiveness of the proposed methodology: linear models using the proposed random feature maps ran from 10 to 100 times faster than ones based on existing methods.

Quantifying temperature-equilibrium time using temperature analysis inside a Farmer ionization chamber.

In this study, we propose a methodology for temperature determination of the temperature and pressure correction factor, PTP, by analyzing the temperature distribution of the modeled ionization chamber taking into account the thermal effect of a water phantom on neighboring materials in the process. Additionally, we present an appropriate temperature-equilibrium time for conducting measurements. The temporal response in the cavity is acquired at 20-s intervals using a Farmer ionization chamber and an electrometer. The initial temperature of the water phantom is 20-25°C with continuous heating/cooling. The temporal response is measured until temperature equilibrium is confirmed, specifically when a temperature difference of 1-5°C is observed between the ionization chamber and the water phantom. Using an ionization-chamber model, temperature distribution is simulated between 20 and 25°C with various parameters set to receive heating and cooling from surrounding media. The results suggest that the temporal response of the ionization chamber essentially coincides with the temperature change at the tip and middle; moreover, the predicted temperature change for temporal response and the simulated temperature of water are different by ~0.16°C at the tip and ~0.79°C at the bottom. Overall, the temperature-equilibration time for absorbed dosimetry is affected by two factors: the cavity wall and the stem side of the cavity; moreover, 400 s is required to obtain complete temperature equilibrium in the water phantom. This analytical study supports the experimental value obtained in previous research. Therefore, analytical representation of the temperature distribution in the ionization chamber is possible.

Design and characteristics of an agar additive polymer gel dosimeter.

Herein, we investigate the use of agar and gelatin in a polymer gel dosimeter. The polymer gel is enclosed in a vinyl film to obtain a dosimeter of arbitrary shape and maintain the shape at room temperature. The resulting polymer gel dosimeter could preserve its shape across a wide temperature range. Excluding the surface region, the obtained dose distribution was within 3% of that determined in an ionization chamber.

Why Does Large Batch Training Result in Poor Generalization? A Comprehensive Explanation and a Better Strategy from the Viewpoint of Stochastic Optimization.

We present a comprehensive framework of search methods, such as simulated annealing and batch training, for solving nonconvex optimization problems. These methods search a wider range by gradually decreasing the randomness added to the standard gradient descent method. The formulation that we define on the basis of this framework can be directly applied to neural network training. This produces an effective approach that gradually increases batch size during training. We also explain why large batch training degrades generalization performance, which previous studies have not clarified.

Effective neural network training with adaptive learning rate based on training loss.

A method that uses an adaptive learning rate is presented for training neural networks. Unlike most conventional updating methods in which the learning rate gradually decreases during training, the proposed method increases or decreases the learning rate adaptively so that the training loss (the sum of cross-entropy losses for all training samples) decreases as much as possible. It thus provides a wider search range for solutions and thus a lower test error rate. The experiments with some well-known datasets to train a multilayer perceptron show that the proposed method is effective for obtaining a better test accuracy under certain conditions.

Effects of stroke education using an animated cartoon and a manga on elementary school children.

BACKGROUND: Stroke education for the youth is expected to reduce prehospital delay by informing the bystander of appropriate action to take and providing knowledge to prevent onset of stroke in future. Previously, we developed effective teaching materials consisting of an animated cartoon and a Manga for junior high school students. The aim of this study was to evaluate the feasibility and effectiveness of our educational materials for stroke education taught by schoolteachers to elementary school children. METHODS: Using our teaching materials, a 30-minute lesson was given by trained general schoolteachers. Questionnaires on stroke knowledge (symptoms and risk factors) and action to take on identification of suspected stroke symptoms were filled out by school children before, immediately after, and at 3 months after completion of the lesson. RESULTS: A total of 219 children (aged 10 or 11 years) received the stroke lesson. Stroke knowledge significantly increased immediately after the lesson compared with before (symptoms, P < .001; risk factors, P < .001); however, correct answer rates decreased at 3 months immediately after completion of the lesson (symptoms, P = .002; risk factors, P = .045). The proportion of the number of children calling emergency medical service on identifying stroke symptoms was higher immediately after the lesson than baseline (P = .007) but returned to the baseline at 3 months after the lesson. CONCLUSIONS: Stroke lesson by schoolteachers using our teaching materials consisting of an animated cartoon and a Manga that was previously used for junior high school students was feasible for elementary school children. However, revision of the materials is required for better retention of stroke knowledge for children.

Experimental demonstration of adaptive quantum state estimation.

The first experimental demonstration of an adaptive quantum state estimation (AQSE) is reported. The strong consistency and asymptotic efficiency of AQSE have been mathematically proven [A. Fujiwara, J. Phys. A 39, 12489 (2006)]. In this Letter, the angle of linear polarization of single photons, the phase parameter between the right and the left circularly polarization, is estimated using AQSE, and the strong consistency and asymptotic efficiency are experimentally verified. AQSE will provide a general useful method in both quantum information processing and metrology.

Reduction of light reflection at silicon-plate surfaces by means of subwavelength gratings in terahertz region.

We investigate triangular surface-relief gratings for reducing reflection at a planar silicon surface for light in the terahertz frequency region of 0.3-3.0THz. Structural parameters of the one- and two-dimensional (1D 2D) subwavelength gratings required for the antireflection (AR) layer were obtained numerically. Experimental results for the AR effects agreed well with those obtained numerically, except for gratings fabricated with laser ablation, which causes structural fluctuations of the grating. In the 1D grating, a high transmittance exceeding 90% for the TM wave was obtained. 2D gratings comprised of arrayed micropyramids were experimentally confirmed to be polarization insensitive.