Stride-to-stride variability and fluctuations at intensities around lactate threshold in distance runners.

Stride-to-stride variability and fluctuations in running have been widely investigated in relation to fatigue, injury, and other factors. However, no studies have examined the relationship of stride-to-stride variability and fluctuations with lactate threshold (LT), a well-known performance indicator for distance runners that represents the threshold at which fast-twitch muscle fibers are activated and the glycolytic system is hyperactivated. In this study, we examined a relationship between LT and stride-to-stride variability and fluctuations in trained middle- and long-distance runners (n = 33). All runners were asked to perform multistage graded exercise tests while wearing accelerometers on the upper surface of their shoes. The LT was determined by measuring blood lactate concentrations after each stage. Three gait parameters for each step were calculated based on the acceleration data: stride time (ST), ground contact time (CT), and peak acceleration (PA). The coefficient of variation (CV) and the long-range correlations (α) for each parameter were also calculated. The effects of the runner's group and the relative intensity for CV and α on gait parameters were evaluated using a two-way repeated measures analysis of variance. Although no significant effect was observed in the CV and α of ST, significant intensity main effects were observed for the CV and α of CT and PA. The lack of significant changes in ST might be the result of runners' adequate control of ST to minimize energy cost. All the parameters showing significant changes with increasing intensity decreased dramatically when they were close to LT. This might have been caused by an increase in physiological load near LT and be interpreted as a variation in motor control because of alternations in the mobilized muscle fibers and physiological changes around the LT. The α should be useful for non-invasive LT detection.

VMAT Planning With Xe-CT Functional Images Enables Radiotherapy Planning With Consideration of Lung Function.

Background/Aim: The most severe adverse event of radiotherapy in lung cancer is radiation pneumonitis (RP). Some indices commonly used to prevent RP are evaluated based on the anatomical lung volume. The irradiation dose may be more accurately assessed by using functional lung volume. We evaluated the usefulness of computed tomography (CT) incorporating functional ventilation images acquired by the inhalation of xenon (Xe) gas (Xe-CT functional images). Patients and Methods: Two plans were created for twelve patients: volumetric modulated arc therapy (VMAT) planning using conventional chest CT images (anatomical plans) and VMAT planning using Xe-CT functional images (functional plans), and the dosimetric parameters were compared. Results: Compared to the anatomical plans, the functional plans had significantly reduced V 20Gy in the high-functional lungs (p=0.005), but significant differences were not seen in the moderate-functional and low-functional lungs. Conclusion: The incorporation of Xe-CT functional images into VMAT plans enables radiotherapy planning with consideration of lung function.

Evaluation of geometrical uncertainties on localized prostate radiotherapy of patients with bilateral metallic hip prostheses using 3D-CRT, IMRT and VMAT: A planning study.

OBJECTIVE: Since most radiation treatment plans are based on computed tomography (CT) images, which makes it difficult to define the targeted tumor volume located near a metal implant, this study aims to evaluate and compare three treatment plans in order to optimally reduce geometrical uncertainty in external radiation treatment of localized prostate cancer. METHODS: Experimental subjects were three prostate patients with bilateral hip prosthesis who had undergone radical radiotherapy. The treatment plans were five-field three-dimensional conformal radiation therapy (3D-CRT), fixed 5-field intensity-modulated radiation therapy (IMRT) using similar gantry angles, and single-arc volumetric modulated arc therapy (VMAT). The monitor units (MUs), dose volume histograms (DVHs), the dose indices of planning target volume (PTV), clinical target volume (CTV) and rectum were compared among the three techniques. The geometrical uncertainties were evaluated by shifting the iso-center (2- 10 mm in the anterior, posterior, left, right, superior, and inferior directions). The CTV and rectum dose indexes with and without the iso-center shifts were compared in each plan. RESULTS: The Conformity Index of PTV were 1.35 in 3D-CRT, 1.12 in IMRT, and 1.04 in VMAT, respectively. The rectum doses in 3D-CRT are also higher than those in IMRT and VMAT. The iso-center shift little affected the CTV dose when smaller than the margin size. The rectum dose increased especially after a posterior shift. Additionally, this dose increase was larger in the VMAT plan than in the 3D- CRT plan. However, the VMAT achieved a superior rectum DVH to that of 3D- CRT, and this effect clearly exceeded the rectum-dose increase elicited by the iso-center shift. CONCLUSION: For radiotherapy treatment of localized prostate cancer in patients with hip prosthesis, the dose distribution was better in the VMAT and Metal Artifact Reduction (MAR)-CT image methods than the conventional methods. Because the anatomical structure of the male pelvic region is relatively constant among individuals, we consider that VMAT is a valid treatment plan despite analyzing just three cases.

[Feasibility Study for the Development of an Application for Simulated Virtual Reality Radiation Therapy Experiences Using Android and iOS Devices].

Using virtual reality (VR) technology such as head-mounted displays, users can be immersed in a virtual world and perceive it as reality. In radiation therapy departments, pretreatment patients and students rarely observe treatment rooms and treatment devices, making it difficult to understand the overall flow of radiation therapy. In this study, to facilitate the understanding and teaching of radiation therapy, we suggest the implementation of VR technology and develop software compatible with VR to enable a pertinent comprehension of radiation therapy. With versatility and accessibility in mind, the software is developed as an application for Android and iOS devices.Omnidirectional movies in treatment rooms were acquired from both the patient view and a third-person view using an omnidirectional camera. The Android/iOS devices used were AQUOS R (SHARP), iPhone 7 Plus (Apple), and iPad air (Apple). The software was developed using Unity 2018.4.7f (Unity Technologies). The main components of the software were as follows: (i) a home window featuring a user interface with which people can access arbitrarily rooms by tapping on floor maps or a list of treatment rooms, (ii) a snapshot mode providing 2D images of a treatment room as a slide show, and (iii) a movie mode displaying omnidirectional movies from the patient view or a third-person view. The virtual radiation therapy experience was executed by attaching the Android/iOS devices to 3D VR goggles (SAMONIC).The main components of the application operated in good conjunction on the Android/iOS devices, and live viewing in the virtual world ran smoothly with the VR technology. However, there were resolution limitations due to the specs of the camera and the devices. It will therefore be necessary to adjust the resolution and the frame rate according to the performance of the relevant devices. The application is instructive for both patients and students because the virtual radiation therapy experience is immersive when using the VR technology. In addition, the developed software can transfer data in a single package and has the ability to substitute images and omnidirectional movies with those appropriate for diagnostic radiology and nuclear medicine departments. Therefore, the developed application is highly versatile.