Establishment of multilateral evaluation method of exercise effect using skeletal muscle MRI

科学研究費助成事業 研究成果報告書：若手研究(B)2011-2013 課題番号：2379139

General ion recombination effect in a liquid ionization chamber in high-dose-rate pulsed photon and electron beams

Liquid ionization chambers (LICs) are highly sensitive to dose irradiation and have small perturbations because of their liquid-filled sensitive volume. They require a sensitive volume much smaller than conventional air-filled chambers. However, it has been reported that the collection efficiency has dependencies on the dose per pulse and the pulse repetition frequency of a pulsed beam. The purpose of this study was to evaluate in detail the dependency of the ion collection efficiency on the pulse repetition frequency. A microLion (PTW, Freiburg, Germany) LIC was exposed to photon and electron beams from a TrueBeam (Varian Medical Systems, Palo Alto, USA) linear accelerator. The pulse repetition frequency was varied, but the dose per pulse was fixed. A theoretical evaluation of the collection efficiency was performed based on Boag’s theory. Linear correlations were observed between the frequency and the relative collection for all energies of the photon and electron beams. The decrease in the collected charge was within 1% for all the flattened photon and electron beams, and they were 1.1 and 1.8% for the 6 and 10 MV flattening filter-free photon beams, respectively. The theoretical ion collection efficiency was 0.990 for a 10 MV flattened photon beam with a dose rate of 3 Gy·min−1. It is suggested that the collected charge decreased because of the short time intervals of the beam pulse compared with the ion collection time. Thus, it is important to correctly choose the pulse repetition frequency, particularly when flattening filter-free mode is used for absolute dose measurements

Radiobiological response of U251MG, CHO-K1 and V79 cell lines to accelerator-based boron neutron capture therapy

In the current article, we provide in vitro efficacy evaluation of a unique accelerator-based neutron source, constructed at the Budker Institute of Nuclear Physics (Novosibirsk, Russian Federation), for boron neutron capture therapy (BNCT), which is particularly effective in the case of invasive cancers. U251MG, CHO-K1 and V79 cells were incubated and irradiated in various concentrations of boric acid with epithermal neutrons for 2–3 h in a plexiglass phantom, using 2.0 MeV proton energy and 1.5–3.0 mA proton current, resulting in a neutron fluence of 2.16 × 1012 cm−2. The survival curves of cells loaded with boron were normalized to those irradiated without boron (to exclude the influence of the fast neutron and gamma dose components) and fit to the linear–quadratic (LQ) model. Colony formation assays showed the following cell survival rates (means ± SDs): CHO-K1: 0.348 ± 0.069 (10 ppm), 0.058 ± 0.017 (20 ppm), 0.018 ± 0.005 (40 ppm); V79: 0.476 ± 0.160 (10 ppm), 0.346 ± 0.053 (20 ppm), 0.078 ± 0.015 (40 ppm); and U251MG: 0.311 ± 0.061 (10 ppm), 0.131 ± 0.022 (20 ppm), 0.020 ± 0.010 (40 ppm). The difference between treated cells and controls was significant in all cases (P < 0.01) and confirmed that the neutron source and irradiation regimen were sufficient for control over cell colony formation. We believe our study will serve as a model for ongoing in vitro experiments on neutron capture therapy to advance in this area for further development of accelerator-based BNCT into the clinical phase

Influence of secondary neutrons induced by proton radiotherapy for cancer patients with implantable cardioverter defibrillators

<p>Abstract</p> <p>Background</p> <p>Although proton radiotherapy is a promising new approach for cancer patients, functional interference is a concern for patients with implantable cardioverter defibrillators (ICDs). The purpose of this study was to clarify the influence of secondary neutrons induced by proton radiotherapy on ICDs.</p> <p>Methods</p> <p>The experimental set-up simulated proton radiotherapy for a patient with an ICD. Four new ICDs were placed 0.3 cm laterally and 3 cm distally outside the radiation field in order to evaluate the influence of secondary neutrons. The cumulative in-field radiation dose was 107 Gy over 10 sessions of irradiation with a dose rate of 2 Gy/min and a field size of 10 × 10 cm². After each radiation fraction, interference with the ICD by the therapy was analyzed by an ICD programmer. The dose distributions of secondary neutrons were estimated by Monte-Carlo simulation.</p> <p>Results</p> <p>The frequency of the power-on reset, the most serious soft error where the programmed pacing mode changes temporarily to a safety back-up mode, was 1 per approximately 50 Gy. The total number of soft errors logged in all devices was 29, which was a rate of 1 soft error per approximately 15 Gy. No permanent device malfunctions were detected. The calculated dose of secondary neutrons per 1 Gy proton dose in the phantom was approximately 1.3-8.9 mSv/Gy.</p> <p>Conclusions</p> <p>With the present experimental settings, the probability was approximately 1 power-on reset per 50 Gy, which was below the dose level (60-80 Gy) generally used in proton radiotherapy. Further quantitative analysis in various settings is needed to establish guidelines regarding proton radiotherapy for cancer patients with ICDs.</p

Whole‐body vibration for patients with nonalcoholic fatty liver disease: a 6‐month prospective study

Physical exercise has demonstrated benefits for managing nonalcoholic fatty liver disease (NAFLD). However, in daily life maintaining exercise without help may be difficult. A whole‐body vibration device (WBV) has been recently introduced as an exercise modality that may be suitable for patients who have difficulty engaging in exercise. We tested WBV in patients with NAFLD and estimated its effectiveness. We studied the effects of a 6‐month WBV program on hepatic steatosis and its underlying pathophysiology in 25 patients with NAFLD. Seventeen patients with NAFLD were designated as a control group. After WBV exercise, body weight in the study group decreased by only 2.5% compared with the control group. However, we found significant increases in muscle area (+2.6%) and strength (+20.5%) and decreases in fat mass (−6.8%). The hepatic (−9.9%) and visceral (−6.2%) fat content also significantly decreased (P < 0.05). There was substantial lowering of hepatic stiffness (−15.7%), along with improvements in the levels of inflammatory markers; tumor necrosis factor alpha (−50.9%), adiponectin (+12.0%), ferritin (−33.2%), and high‐sensitivity C‐reactive protein (−43.0%) (P < 0.05). These results suggest that WBV is an exercise option for patients with NAFLD that is effective, efficient, and convenient

機能画像情報を利用した非アルコール性脂肪性肝疾患の非侵襲的病態評価法の確立

科学研究費助成事業 研究成果報告書：基盤研究(C)2014-2016課題番号 : 2635088