A simulation study on estimation of Bragg-peak shifts via machine learning using proton-beam images obtained by measurement of secondary electron bremsstrahlung

We investigated an estimation method of Bragg-peak shifts via machine learning using proton-beam images obtained by measurement of secondary electron bremsstrahlung (SEB) by Monte Carlo simulation. Proton beams having energy of 139 MeV were incident on a water phantom with randomly placed air spheres inside, and 6400 pairs of “proton-beam images” and “a Bragg-peak shift” were prepared and then multiple linear regression analysis was carried out. A good agreement was found between the actual Bragg-peak shifts and predicted values in both the training and test sets. The coefficients of determination of the obtained prediction model were 0.899 for the training set and 0.894 for the test set. Consequently, we found that a prediction model with small variance and high prediction performance could be obtained using the SEB data

A simulation study on reduction of the background component using veto counters for imaging of therapeutic proton beams by measuring secondary electron bremsstrahlung using a parallel-hole collimator

A simulation study on reduction of a background (BG) component for an imaging method of therapeutic proton beams by measuring secondary electron bremsstrahlung (SEB) component was performed using the Monte Carlo method. We simulated the images obtained by measuring the SEB and the BG component using a parallel-hole-type X-ray camera placed close to an irradiation target. We found that reduction of the BG component was possible by utilizing veto counters placed close to the imaging detector of the X-ray camera. The ratio of the BG component to the sum of the SEB and BG components was able to be reduced from 73% to approximately 20%

Periodical Calibration of Ionization Chamber System for 60Co Gamma Ray High Dose Rate at Radiation Processing

国家標準機関である産業技術総合研究所において電離箱式照射線量率計の校正を実施した。これにより高崎量子応用研究所のガンマ線量基準の信頼性を確認した

Simulation evaluation on a compact monitor for gamma-emitting tracers in plant stems

Non-destructive monitoring of radioactivities derived from radioactive tracers at multiple points in plant stems can be used to evaluate the velocity of element transport in living plants. In this study, we calculated absorption-efficiency distributions for several detector geometries to determine appropriate shapes for non-destructive monitoring of radioactivities in the stem. The efficiency distributions were calculated by Monte Carlo simulations, and the flatnesses and spatial resolutions were evaluated. It was found that the placement of four detectors around the stem could limit the percentage of standard deviation to the mean of the pixel values to less than 5%. We could determine a compact detector geometry with the spatial resolution of 1.35 cm using four small detectors. The detection efficiencies were 0.014, 0.0030 and 0.00063 cm at the initial gamma-ray energies of 0.5, 1 and 2 MeV, which is sufficiently applicable to detect 10 kBq/cm of radioactivity

A novel estimation method of water-equivalent thicknesses of secondary particle tracks using secondary electron bremsstrahlung emitted from therapeutic ion beams for attenuation correction

Monitoring methods of therapeutic beams based on the measurement of secondary particles have been proposed and studied worldwide. Since secondary particles are influenced by substances in the human body before they reach detectors, estimation methods of the water-equivalent thickness of the tracks of the secondary particles are required for attenuation correction. In this work, we studied a novel estimation method of the water-equivalent thickness based on the observation of energy distribution of secondary electron bremsstrahlung (SEB) emitted from the trajectories of the therapeutic beams by Monte Carlo simulations. A 12C-ion beam with an energy of 290 MeV/u was injected into a water phantom. The phantom was surrounded by a collimator having a CdTe detector behind the collimator. A distribution of energy deposition due to SEB emission was recorded during beam injection. The simulation was iterated by varying the radius of the phantom. The simulation results were plotted as an R1 vs. R2 scatter plot, where R1 was defined as the ratio of the yield having a deposition energy between 30 and 40 keV to that between 20 and 30 keV, and R2 was defined as the ratio of the yield having a deposition energy between 60 and 70 keV to that between 20 and 30 keV. We found that clusters are formed at different positions on the scatter plot by different radii of the phantom and that the water-equivalent thickness of the secondary particle tracks could be estimated using the R1 vs. R2 plot

Operation of the Electron Accelerator and the Gamma-ray Irradiation Facilities (2017)

平成29年度の高崎研の電子・ガンマ線照射施設の運転状況、電子加速器の修理状況、コバルト60線源の処分状況、付帯設備の老朽化対策・整備状況について概要を報告する