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Summary: Rice (Oryza sativa) plants have porous or hollow organs consisting of aerenchyma, which is presumed to function as a low‐resistance diffusion pathway for air to travel from the foliage above the water to submerged organs. However, gas movement in rice plants has yet to be visualized in real time.In this study involving partially submerged rice plants, the leaves emerging from the water were fed nitrogen‐13‐labeled nitrogen ([13N]N2) tracer gas, and the gas movement downward along the leaf blade, leaf sheath, and internode over time was monitored.The [13N]N2 gas arrived at the bottom of the plant within 10 min, which was 20 min earlier than carbon‐11 photoassimilates. The [13N]N2 gas movement was presumably mediated by diffusion along the aerenchyma network from the leaf blade to the root via nodes functioning as junctions, which were detected by X‐ray computed tomography.These findings imply the diffusion of gas along the aerenchyma, which does not consume energy, has enabled plants to adapt to aquatic environments. Additionally, there were no major differences in [13N]N2 gas movement between paddy rice and deepwater rice plants, indicative of a common aeration mechanism in the two varieties, despite the difference in their response to flooding. [ABSTRACT FROM AUTHOR]

We evaluated an estimation ability of shifts of therapeutic carbon-ion beams owing to cavities in a polyethylene target by measuring prompt X-rays emitted from beam trajectories. Carbon-12 beams having the energy of 241.5 MeV u−1 were irradiated on a polyethylene target. The target had a square-prism-shaped cavity in it. The thickness of the cavity was changed from 3.0 to 0.0 cm with 0.3 cm steps. For each setup of the cavity, 7.5 × 1010 carbon ions were irradiated. A pinhole-type X-ray camera was placed beside the target and utilized to acquire the beam images. The beam trajectory and a gap on the trajectory clearly appeared in the acquired images. The actual beam shifts well coincided with the estimated beam shifts from the acquired images. The maximum fluctuation of the estimated shifts was approximately 0.2 cm. It was confirmed that the internal cavity can be imaged and the range can be accurately evaluated. [ABSTRACT FROM AUTHOR]

Purpose: Imaging of the secondary electron bremsstrahlung (SEB) x rays emitted during particle‐ion irradiation is a promising method for beam range estimation. However, the SEB x‐ray images are not directly correlated to the dose images. In addition, limited spatial resolution of the x‐ray camera and low‐count situation may impede correctly estimating the beam range and width in SEB x‐ray images. To overcome these limitations of the SEB x‐ray images measured by the x‐ray camera, a deep learning (DL) approach was proposed in this work to predict the dose images for estimating the range and width of the carbon ion beam on the measured SEB x‐ray images. Methods: To prepare enough data for the DL training efficiently, 10,000 simulated SEB x‐ray and dose image pairs were generated by our in‐house developed model function for different carbon ion beam energies and doses. The proposed DL neural network consists of two U‐nets for SEB x ray to dose image conversion and super resolution. After the network being trained with these simulated x‐ray and dose image pairs, the dose images were predicted from simulated and measured SEB x‐ray testing images for performance evaluation. Results: For the 500 simulated testing images, the average mean squared error (MSE) was 2.5 × 10−5 and average structural similarity index (SSIM) was 0.997 while the error of both beam range and width was within 1 mm FWHM. For the three measured SEB x‐ray images, the MSE was no worse than 5.5 × 10−3 and SSIM was no worse than 0.980 while the error of the beam range and width was 2 mm and 5 mm FWHM, respectively. Conclusions: We have demonstrated the advantages of predicting dose images from not only simulated data but also measured data using our deep learning approach. [ABSTRACT FROM AUTHOR]

Low-energy x-ray imaging of secondary electron bremsstrahlung x-rays emitted during carbon-ion irradiation is a promising method for range estimation and could be used for imaging with almost clinical dose levels of carbon ion. However, the number of counts in images with clinical dose levels is relatively small, making it difficult to obtain precise range estimations. Since improving the sensitivity of the x-ray camera may solve this issue, we developed two new types of x-ray cameras. One uses a 1 mm thick, 40 mm × 40 mm cerium-doped yttrium aluminum perovskite (YA1O3: YAP(Ce)) scintillator plate combined with a 2 inch square flat panel photomultiplier tube (FP-PMT) contained in a 2 cm thick tungsten shield with a pinhole collimator positioned 50 mm from the scintillator; the other uses a 0.5 mm thick, 20 mm × 20 mm YAP(Ce) scintillator plate combined with a 1 inch square position sensitive photomultiplier tube (PSPMT) contained in the same tungsten shield with a pinhole collimator, but with the scintillator positioned closer (30 mm) to the pinhole collimator to obtain a similar field of view. For both cameras, we used a wider angle (∼55°) pinhole collimator to measure the phantom closer to improve sensitivity. Although the 40 mm × 40 mm YAP(Ce) camera had high system spatial resolution, the background count fractions were high and produced a high count area at the center of the images due to the pulse pileup of the signals. With the 20 mm × 20 mm YAP(Ce) camera, we obtained x-ray images with low background counts without a high count area at the image center. By smoothing the measured images, we were able to estimate the ranges even for clinical dose levels. We therefore confirmed that one of our newly developed YAP(Ce) cameras had high sensitivity and is promising for the imaging of secondary electron bremsstrahlung x-rays during irradiation of carbon ions in clinical conditions. [ABSTRACT FROM AUTHOR]

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 BG components 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%. [ABSTRACT FROM AUTHOR]

We studied feasibility of detection of a gap which is located across a beam track by measuring low-energy (63-68 keV) photons generated by beam irradiation. An experiment was performed with the Heavy Ion Medical Accelerator in Chiba (HIMAC). A 12C beam having 290 MeV/u was injected on a target consisting of two acrylic blocks. These two blocks were placed with a 10 mm gap along the beam axis. A detection system consisting of a semiconductor detector, a lead collimator having a slit, and borated polyethylene blocks was placed on a movable stage to detect low-energy photons emitted perpendicularly to the beam axis. The position of the detection system was moved at 2 mm intervals along the beam axis. It was found that the yield of 63-68 keV photons was clearly correlated with the position of the detection system. The position at which the yield curve had the lowest value agreed with the gap position. We also confirmed that the experimental result was well reproduced by a Monte Carlo simulation that includes generation of secondary electron bremsstrahlung. [ABSTRACT FROM AUTHOR]

Purpose: In proton therapy, imaging of proton-induced positrons is a useful method to monitor the proton beam distribution after therapy. Usually, a positron emission tomography (PET) system installed in or near the proton beam treatment room is used for this purpose. However, a PET system is sometimes too large and expensive for this purpose. We developed a small field-of-view (FOV) gamma camera for high-energy gamma photons and used it for monitoring the proton-induced positron distribution. Methods: The gamma camera used 0.85 mm × 0.85 mm × 10 mm Ce:GdAGaO (GAGG) pixels arranged in 20 × 20 matrix to form a scintillator block, which was optically coupled to a 1-inch-square position-sensitive photomultiplier tube (PSPMT). The GAGG detector was encased in a 20-mm thick container and a pinhole collimator was mounted on its front. The gamma camera was set 1.2 m from the 35 cm × 35 cm × 5 cm plastic phantom in the proton therapy treatment room, and proton beams were irradiated to the phantom with two proton energies. Results: The gamma camera had spatial resolution of ~6.7 cm and sensitivity of 3.2 × 10 at 1 m from the collimator surface. For both proton energies, positron distribution in the phantom could be imaged by the gamma camera with 10-min acquisition. The lengths of the range of protons measured from the images were almost identical to the simulation results. Conclusions: These results indicate that the developed high-energy gamma camera is useful for imaging positron distributions in proton therapy. [ABSTRACT FROM AUTHOR]

We describe a new method for estimating the beam range in heavy-ion radiation therapy by measuring the ion beam bremsstrahlung. We experimentally confirm that the secondary electron bremsstrahlung process provides the dominant bremsstrahlung contribution. A Monte Carlo simulation shows that the number of background photons from annihilation gamma rays is about 1% of the bremsstrahlung strength in the low-energy region used in our estimation (63-68 keV). Agreement between the experimental results and the theoretical prediction for the characteristic shape of the bremsstrahlung spectrum validates the effectiveness of our new method in estimating the ion beam range. [ABSTRACT FROM AUTHOR]

Visualizing the dynamics of cesium (Cs) is desirable to understand the impact of radiocesium when accidentally ingested or inhaled by humans. However, visualization of radiocesium in vivo is currently limited to plants. Herein, we describe a method for the production and purification of 127Cs and its use in visualizing Cs dynamics in a living animal. The positron-emitting nuclide 127Cs was produced using the 127I (α, 4n) 127Cs reaction, which was induced by irradiation of sodium iodide with a 4He2+ beam from a cyclotron. We excluded sodium ions by using a material that specifically adsorbs Cs as a purification column and successfully eluted 127Cs by flowing a solution of ammonium sulfate into the column. We injected the purified 127Cs tracer solution into living rats and the dynamics of Cs were visualized using positron emission tomography; the distributional images showed the same tendency as the results of previous studies using disruptive methods. Thus, this method is useful for the non-invasive investigation of radiocesium in a living animal. [ABSTRACT FROM AUTHOR]

Compton cameras can simultaneously detect multi-isotopes; however, when simultaneous imaging is performed, crosstalk artifacts appear on the images obtained using a low-energy window. In conventional single-photon emission computed tomography, a dual energy window (DEW) subtraction method is used to reduce crosstalk. This study aimed to evaluate the effectiveness of employing the DEW technique to reduce crosstalk artifacts in Compton images obtained using low-energy windows. To this end, in this study, we compared reconstructed images obtained using either a photo-peak window or a scatter window by performing image subtraction based on the differences between the two images. Simulation calculations were performed to obtain the list data for the Compton camera using a 171 and a 511 keV point source. In the images reconstructed using these data, crosstalk artifacts were clearly observed in the images obtained using a 171 keV photo-peak energy window. In the images obtained using a scatter window (176–186 keV), only crosstalk artifacts were visible. The DEW method could eliminate the influence of high-energy sources on the images obtained with a photo-peak window, thereby improving quantitative capability. This was also observed when the DEW method was used on experimentally obtained images. [ABSTRACT FROM AUTHOR]