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Most instruments for measuring radon concentrations in the air should be calibrated using air with known radon concentrations, obtained from a solution of radium. However, safe handling of such a solution of alpha-active elements can be troublesome. Standard gamma-ray sources of low activity are handled more safely and typically used to obtain the absolute detection efficiency of a Ge detector with high accuracy. A new method has been developed to calibrate a radon detector with such sources. A radon exhalation rate for a substance containing a small amount of radium is measured with the radon detector to be calibrated. After this, the vessel containing the radium is sealed so that the radon does not escape from it. The buildup of the activity of 214Bi in it is obtained from gamma-ray measurements and gives the radon exhalation rate on the basis of the activity of the standard sources. From the comparison between the two values of the exhalation rate, the radon detector is calibrated. A plane multiwire-electrode ionization chamber is used as a radon detector, and its detection efficiency is calculated from its geometrical form. The radon exhalation rate computed from the calculated efficiency agrees with that determined from the activity of the standard gamma-ray sources within their specified 6% error. [ABSTRACT FROM AUTHOR]

A continuous measuring system has been developed, which uses a plane multiwire-electrode ionization chamber and obtains radon concentrations by measuring in situ alpha energy spectra due to alpha-active nuclei in the air. The chamber has three rigid plane multiwire electrodes in a box of aluminum plates which have holes for the air to flow freely through them. The concentration measurements do not disturb the distribution of radon in the air. Values of concentration are obtained with good statistical errors because of the use of a large volume for the ionization chamber. The slow rise-time pulses of alpha particles from the chamber are analyzed with a specially designed analog-to-digital converter which is controlled with a microcomputer. The energy spectra have been obtained with a FWHM of about 600 keV. Time variations of radon concentrations have been measured in a room in a ferroconcrete building. [ABSTRACT FROM AUTHOR]

Purpose: The accuracy of the CyberKnife Synchrony Respiratory Tracking System is dependent on the breathing pattern of a patient. Therefore, the tracking error in each patient must be determined. Support vector regression (SVR) can be used to easily identify the tracking error in each patient. This study aimed to develop a system with SVR that can predict tracking error according to a patient's respiratory waveform. Methods: Datasets of the respiratory waveforms of 93 patients were obtained. The feature variables were variation in respiration amplitude, tumor velocity, and phase shift between tumor and the chest wall, and the target variable was tracking error. A learning model was evaluated with tenfold cross-validation. We documented the difference between the predicted and actual tracking errors and assessed the correlation coefficient and coefficient of determination. Results: The average difference and maximum difference between the actual and predicted tracking errors were 0.57 ± 0.63 mm and 2.1 mm, respectively. The correlation coefficient and coefficient of determination were 0.86 and 0.74, respectively. Conclusion: We developed a system for obtaining tracking error by using SVR. The accuracy of such a system is clinically useful. Moreover, the system can easily evaluate tracking error. [ABSTRACT FROM AUTHOR]

Purpose In markerless tumor tracking using X-ray fluoroscopic images for image-guided radiation therapy (IGRT), robustness against mistracking is important. Mistracking is primarily caused by bone structures projected on fluoroscopic images because they generally hide tumor features. We devised a real-time tumor-tracking method. The novelty of this method is to control “importance recognition” in computers, i.e., controlling recognition of image features that are important or unimportant for tumor tracking. This study demonstrates the feasibility of our method using clinical X-ray fluoroscopic images. Methods The strategy of our method was to utilize different positional co-occurrence probabilities in training images for supervised deep learning. A bone digitally reconstructed radiograph (DRR) was randomly overlapped on a soft-tissue DRR to create training images for deep learning, which established positional decorrelation between the bone feature and ground truth, indicating tumor position and shape. As the training of deep learning processed, this decorrelation induced the computer recognition that the bone feature was unimportant for tumor tracking. Moreover, this method was fully optimized for a patient because DRRs were created from patient-specific CT data only, unlike a general medical application of deep learning such as diagnosis that uses a massive amount of patient data. Results The accuracy of lung tumor tracking was within approximately 1 mm although the low-visible tumor and spine were overlapped on X-ray fluoroscopic images. Conclusions Feasibility of robust tumor tracking by our method was demonstrated. This method can be expected as a breakthrough technique that can contribute to the robust and safe implementation of markerless tumor tracking for radiation therapy in future. [ABSTRACT FROM AUTHOR]

Background: Administration of external radiation therapy via proton therapy systems carries a risk of occasional collisions between the patient's body and gantry, which is increased by the snout placed near the patient for better dose distribution. Although treatment planning software (TPS) can simulate controlled collisions, the computed tomography (CT) data used for treatment planning are insufficient given that collisions can occur outside the CT imaging region. Thus, imaging the three‐dimensional (3D) surface outside the CT range and combining the data with those obtained by CT are essential for avoiding collisions. Purpose: To construct a prototype for 3D surface imaging and an end‐to‐end framework for preventing collisions between the patient's body and the gantry. Methods: We obtained 3D surface data using a light sectioning method (LSM). By installing only cameras in front of the CT, we achieved LSM using the CT couch motion and preinstalled patient‐positioning lasers. The camera image contained both sagittal and coronal lines, which are unnecessary for LSM and were removed by deep learning. We combined LSM 3D surface data and original CT data to create synthetic Digital Imaging and Communications in Medicine (DICOM) data. Subsequently, we compared the TPS snout auto‐optimization using the original CT data with the synthetic DICOM data. Results: The mean positional error for LSM of the arms and head was 0.7 ± 0.8 and 0.8 ± 0.8 mm for axial and sagittal imaging, respectively. The TPS snout auto‐optimization indicated that the original CT data would cause collisions; however, the synthetic DICOM data prevented these collisions. Conclusions: The prototype system's acquisition accuracy for 3D surface data was approximately 1 mm, which was sufficient for the collision simulation. The use of a TPS with collision avoidance can help optimize the snout position using synthetic DICOM data. Our proposed method requires no external software for collision simulation and can be integrated into the clinical workflow to improve treatment planning efficiency. [ABSTRACT FROM AUTHOR]

Background: Volumetric modulated arc therapy (VMAT) for locally advanced rectal cancer (LARC) has emerged as a promising technique, but the planning process can be time-consuming and dependent on planner expertise. We aimed to develop a fully automated VMAT planning program for LARC and evaluate its feasibility and efficiency. Methods: A total of 26 LARC patients who received VMAT treatment and the computed tomography (CT) scans were included in this study. Clinical target volumes and organs at risk were contoured by radiation oncologists. The automatic planning program, developed within the Raystation treatment planning system, used scripting capabilities and a Python environment to automate the entire planning process. The automated VMAT plan (auto-VMAT) was created by our automated planning program with the 26 CT scans used in the manual VMAT plan (manual-VMAT) and their regions of interests. Dosimetric parameters and time efficiency were compared between the auto-VMAT and the manual-VMAT created by experienced planners. All results were analyzed using the Wilcoxon signed-rank sum test. Results: The auto-VMAT achieved comparable coverage of the target volume while demonstrating improved dose conformity and uniformity compared with the manual-VMAT. V30 and V40 in the small bowel were significantly lower in the auto-VMAT compared with those in the manual-VMAT (p < 0.001 and < 0.001, respectively); the mean dose of the bladder was also significantly reduced in the auto-VMAT (p < 0.001). Furthermore, auto-VMAT plans were consistently generated with less variability in quality. In terms of efficiency, the auto-VMAT markedly reduced the time required for planning and expedited plan approval, with 93% of cases approved within one day. Conclusion: We developed a fully automatic feasible VMAT plan creation program for LARC. The auto-VMAT maintained target coverage while providing organs at risk dose reduction. The developed program dramatically reduced the time to approval. [ABSTRACT FROM AUTHOR]

Introduction: Despite the development of DOSIRIS™, an eye lens dosimeter, the characteristics of DOSIRIS™ in the area of radiotherapy have not been investigated. The purpose of this study was to evaluate the basic characteristics of the 3‐mm dose equivalent measuring instrument DOSIRIS™ in radiotherapy. Methods: Dose linearity and energy dependence were evaluated for the irradiation system based on the calibration method of the monitor dosimeter. The angle dependence was measured by irradiating from a total of 18 directions. Interdevice variation was repeated three times by simultaneously irradiating five dosimeters. The measurement accuracy was based on the absorbed dose measured by the monitor dosimeter of the radiotherapy equipment. Absorbed doses were converted to 3‐mm dose equivalents and compared with DOSIRIS™ measurements. Results: Dose linearity was evaluated using the determination coefficient (R2) R2 = 0.9998 and 0.9996 at 6 and 10 MV, respectively. For energy dependence, although the therapeutic photons evaluated in this study had higher energies than in the previous studies and had a continuous spectrum, the response was equivalent to 0.2–1.25 MeV, well below the IEC 62387 limits. The maximum error at all angles was 15% (angle of 140°) and the coefficient of variation at all angles was 4.70%, which satisfies the standard of the thermoluminescent dosimeter measuring instrument. Accuracy of measurement was determined in terms of the measurement errors for DOSIRIS™ (3.2% and 4.3% at 6 and 10 MV, respectively,) using the 3‐mm dose equivalent obtained from the theoretical value as a reference. The DOSIRIS™ measurements met the IEC standard which defines the measurement error of ±30% of the irradiance value in IEC 62387. Conclusions: We found that the characteristics of the 3‐mm dose equivalent dosimeter in a high‐energy radiation satisfy the IEC standards and have the same measurement accuracy as diagnostic areas such as Interventional Radiology. [ABSTRACT FROM AUTHOR]

Background: 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.Methods: 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.Results: 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.Conclusions: 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. [ABSTRACT FROM AUTHOR]

The iBNCT project aims to develop "iBNCT001," a demonstration device of the linac-based neutron irradiation facility for boron neutron capture therapy (BNCT) application. iBNCT001 generates an epithermal neutron beam by irradiating 8 MeV protons accelerated by a linac onto a beryllium target. Currently, the linac can drive an average proton current of 2.1 mA. Several experiments were performed using a water phantom to confirm the main physical characteristics of the neutron beam produced at the irradiation position. The measurement results demonstrated that the maximum thermal neutron flux achievable in the phantom volume was approximately 1.36 × 10 9 cm − 2 s − 1 when a normal beam collimator with a 120 mm diameter was used. This neutron beam intensity was sufficient to complete the irradiation within 30 min using the BNCT approach. In addition to normal beam collimators, extended collimators that protrude 100 mm from the wall were developed. By using an extended collimator, it is possible to prevent interference of the patient's body with the wall when irradiating head and neck cancers. The measurement results for the extended collimator demonstrated that irradiation with the collimator could be completed within 1 h when the neutron beam is generated with an average proton current of 2.1 mA. [ABSTRACT FROM AUTHOR]

• For respiratory-gated radiotherapy near end-exhalation and irradiation fields involving the liver dome, components of geometric uncertainties originate from temporospatial diaphragm segment movements. • The displacements in a caudal direction of the diaphragm in dorsal/medial segments are significantly larger than those in ventral/right segments. • Personalized irradiating strategies, including inhalation phases of irradiation and beam angles of incidence, are required to reduce the temporospatial geometric uncertainties. The technique of gating near end-exhalation is commonly adopted to reduce respiration-associated geometric uncertainties for particle beam therapy. However, for irradiation fields involving the liver dome, how diaphragm movements generating liver–lung interface change, alongside geometric uncertainties, remain unspecified. Patients receiving respiratory-gated computed tomography (RGCT) with four-dimensional computed tomography (4DCT) scans during simulation were retrospectively reviewed. Differences (Δ) between RGCT and 4DCT images, including diaphragm displacements and liver–lung interface changes, were investigated to specify geometric uncertainties during early inhalation phases. Craniocaudal displacements (Δy, in sagittal/coronal planes) of diaphragm segments (dorsal/ventral/right lateral/medial), liver area changes (ΔA, in axial planes), and liver extent changes in specific directions of incidence (Δr, in axial planes) were analyzed. Altogether, 162 patients received simulating RGCT and 4DCT scans. In 22 of them, both images involved the liver dome. For most cases during early inhalation phases, the Δy values in the dorsal diaphragm were significantly greater than those in the ventral diaphragm (p < 0.05), the ΔA values were significantly enlarged with inhalation progressing (p < 0.05), and the Δr values in the dorsal direction were significantly larger than those in the ventral direction (p < 0.05). These results suggested that the dorsal diaphragm moves earlier and more in a caudal direction than the ventral diaphragm during early inhalation phases. For respiratory-gated radiotherapy near end-exhalation and irradiation fields involving the liver dome, components of geometric uncertainties are temporospatial, including diaphragm segment movements, inhalation phases of irradiation, and beam angles of incidence. [ABSTRACT FROM AUTHOR]

Purpose: To develop a system for detecting anatomical changes using two‐dimensional (2D) x‐ray images. Methods: Ten patients with head and neck cancer were retrospectively analyzed using 2D x‐ray and cone‐beam computed tomography (CBCT) images. The 2D x‐ray images were acquired daily, whereas the CBCT images were acquired weekly during the treatment period. The developed system imported the 2D x‐ray images obtained on the initial treatment day and on another day, and thereafter converted them into the water equivalent thickness (WET) using the conversion table. The difference between the WET images for the first and other treatment days (ΔWET) was calculated as the quantitative value for anatomical changes and visualized to recognize the anatomical change location. We compared ΔWET and the difference in the lateral neck distance (ΔLND) on the corresponding CBCT images. ΔLND was used as the ground truth for anatomical changes. ΔWET and ΔLND were measured at the first cervical vertebra (C1) and the tumor center (TC). C1 and TC were selected to observe the volume changes in the parotid gland and tumor, respectively. Sensitivity and specificity were calculated to evaluate the performance of the 2D‐WET system. The cut‐off values of WET and LND were set to 2–10 mm. Furthermore, intensity‐modulated proton therapy (IMPT) plans for six patients with rescan CT images were generated. The IMPT plans on the rescan CT images were compared to the original plans on simulation CT using the dosimetric parameters for the target and the organs at risk. Results: The mean differences between ΔWET and ΔLND for C1 and TC were −0.62 ± 1.66 mm and −0.93 ± 1.28 mm (mean ± 1 SD), respectively. ΔWET in the proposed system was in good agreement with ΔLND using the CBCT images. In the sensitivity and specificity results for C1 and TC with cut‐off values from 2 to 10 mm, the sensitivity was >85% for all cut‐off values, while the specificity was >90% at 5–10 mm and <90% at less than 5 mm. The average ΔWET at the time of replanning was 12.8 mm which resulted in maximum dose increase in the spinal cord D1cc by 8.4 Gy, the parotid gland D50 by 26.6 Gy, and the oral cavity D50 by 23.2 Gy. Conclusions: We developed a new system for detecting anatomical changes using 2D x‐ray images. The developed system with ΔWET showed an agreement with ΔLND at C1 and TC with an average difference of less than 1 mm. ΔWET detected anatomical changes with high sensitivity and specificity with a cut‐off value of 5–10 mm. This system can monitor daily anatomical changes without causing high exposure to patients and requiring any inefficient work, and it can be applied to daily online adaptive proton beam therapy and triggered adaptive radiotherapy. [ABSTRACT FROM AUTHOR]

Several studies investigated the changes in diffusion of water molecules in skeletal muscle cells of lifestyle-related-disease patients who performed a hybrid training (HYBT) for six months. They reported that the apparent diffusion coefficient (ADC) and all diffusion eigenvalues (λ 1 , λ 2 , and λ 3) increased after the HYBT, owing to the enlargement of the intramyocellular diffusion space (intracellular space) caused by the muscular hypertrophy. We assumed that the HYBT promoted metabolism of the whole skeletal muscle including lipids, which reduced the amount of intramyocellular lipid (IMCL), and led to a secondary enlargement of the diffusion space in the skeletal muscle cells. However, the IMCL has to be a diffusion limiting factor in order to verify this hypothesis. Until now, there is no report on whether IMCL is a diffusion limiting factor for water molecules. The objective of this study was to examine whether the IMCL is a diffusion limiting factor in skeletal muscle cells. We performed a three-dimensional quantification of the IMCL in triceps surae muscles of lifestyle-related-disease patients and healthy volunteers. In addition, we measured the ADC in the volume of interest (VOI), diffusion anisotropy (FA), and diffusion eigenvalues (λ 1 , λ 2 , and λ 3), and evaluated the correlations between these diffusion parameters and IMCL. The results showed that the amount of IMCL was positively and negatively correlated with the FA and λ 3 , respectively, in lifestyle-related-disease patients. In addition, there was a weak negative correlation between IMCL and ADC, λ 1 , and λ 2. There was no correlation between the amount of IMCL and diffusion parameters of healthy volunteers. Above a certain amount, the IMCL correlates with the diffusion parameters. A higher amount of IMCL leads to smaller diffusion eigenvalues. This result suggested that IMCL possibility of influencing diffusion of water molecules in skeletal muscle cells. However, in order for the influence of IMCL to be reflected in the diffusion eigenvalues, it was needed large amount of IMCL existed, and we thought that the influence was smaller than the influence by the already reported cell membrane. [ABSTRACT FROM AUTHOR]

The effective utilization of various biomolecules for creating a series of mesoporous boehmite (γ‐AlOOH) and gamma‐alumina (γ‐Al2O3) nanosheets with unique hierarchical multilayered structures is demonstrated. The nature and concentration of the biomolecules strongly influence the degree of the crystallinity, the morphology, and the textural properties of the resulting γ‐AlOOH and γ‐Al2O3 nanosheets, allowing for easy tuning. The hierarchical γ‐AlOOH and γ‐Al2O3 multilayered nanosheets synthesized by using biomolecules exhibit enhanced crystallinity, improved particle separation, and well‐defined multilayered structures compared to those obtained without biomolecules. More impressively, these γ‐AlOOH and γ‐Al2O3 nanosheets possess high surface areas up to 425 and 371 m2 g−1, respectively, due to their mesoporous nature and hierarchical multilayered structure. When employed for molybdenum adsorption toward medical radioisotope production, the hierarchical γ‐Al2O3 multilayered nanosheets exhibit Mo adsorption capacities of 33.1–40.8 mg g−1. The Mo adsorption performance of these materials is influenced by the synergistic combination of the crystallinity, the surface area, and the pore volume. It is expected that the proposed biomolecule‐assisted strategy may be expanded for the creation of other 3D mesoporous oxides in the future. Biomolecular influencer: Mesoporous γ‐Al2O3 nanosheets with unique hierarchical multilayered structures have been fabricated in the presence of biomolecules (see figure). They exhibit high molybdenum adsorption capacities up to 40.8 mg g−1. [ABSTRACT FROM AUTHOR]

Purpose Hypo-fractionated proton beam therapy (PBT) is an approach that has been increasingly explored over the past decade. It requires high geometric accuracy for targeting of the PBT beams. However, image-guided PBT is currently commonly performed with kV X-ray images of bony anatomy. A dynamic adaptive passive scattering PBT system using computed tomography-based three-dimensional image guidance was developed, and its effectiveness was then evaluated retrospectively in patients with nonsmall cell lung cancer (NSCLC). Methods The dynamic adaptive PBT system consisted of computed tomography-based image registration and proton dose calculation using a simplified Monte Carlo algorithm, with a range adaptation system that could adjust the range shifter thickness to alter the dose distribution. Three patients were retrospectively analyzed. All plans, which each had a total dose of 60 Gy (relative biological effectiveness; RBE), were generated using two fields (Gantry angles: 270 degree and 180 degree) in a passive scattering method. Three dose distributions were generated for each patient according to the following different registrations: bone registration, tumor registration, and tumor registration with range adaptation. The following dosimetric parameters were compared with the original plan: target dose coverage at D95% for the clinical target volume (CTV), homogeneity of D5% to D95% for the CTV, and dose distributions in normal tissue (Dmax of Spinal cord and V20 Gy of lung). Results For the bone registration method, the average D95% and D5% to D95% for the CTV showed average differences from the original plan of −3.7 ± 4.1 Gy (mean ± 1SD; RBE) and 3.6 ± 3.9 Gy (RBE) respectively. The tumor registration method achieved better coverage than the bone registration method, although the dosimetric parameters for coverage and homogeneity still showed average differences in −2.0 ± 2.3 Gy (RBE) and 1.9 ± 2.2 Gy (RBE) respectively. The range adaptive plan showed comparable coverage and homogeneity [D95%: −1.0 ± 1.3 Gy (RBE) and D5% to D95%: 0.9 ± 1.0 Gy (RBE) on average] to the original plan, as well as demonstrating similar normal tissue sparing. The approach could be completed in less than 10 min, including CT acquisition, image registration, dose recalculation with range optimization, and the operator's visual verification. Conclusions The tumor dose coverage in patients with NSCLC may deteriorate as a result of respiratory or body movement if daily proton range adaptation is not performed. Our approach may provide higher geometric accuracy for localization of the tumor, and the dynamic range adaptation enables us to achieve the planned dose distribution for hypo-fractionated PBT in the lung. [ABSTRACT FROM AUTHOR]

The neutron spectral fluence of an accelerator-based neutron source facility for boron neutron capture therapy (BNCT) based on a proton linac and a beryllium target was evaluated by the unfolding method using a Bonner sphere spectrometer (BSS). A 3 He-proportional-counter-based BSS was used with weak beam during the development of the facility. The measured epithermal neutron spectra were consistent with calculations. The epithermal neutron intensity at the beam port was estimated and the results gave a numerical target for the enhancement of the proton beam intensity and will be used as reference data for measurements performed after the completion of the facility. [ABSTRACT FROM AUTHOR]

• Evaluation of lung tumor 4D motion during breath-holding (BH) using cine CT. • Some cases showed substantial tumor motion in the posterior directions during BH. • Surrogate markers (external marker/diaphragm) did not detect tumor motion. • In 18% of cases, tumor motion during BH was larger than that during free breathing. • Pretreatment evaluation of the tumor motion during BH using cine CT is recommended. This study was performed to evaluate the four-dimensional motion of lung tumors during end-exhalation (EE) breath-holding (BH) using cine computed tomography (CT) and investigate the correlation between tumor and surrogate marker motions. This study included 28 patients who underwent stereotactic body radiation therapy at our institution and were capable of 15–20 s of EE BH within a ±1.5-mm gating window with external markers. During EE BH with cine CT, 21 s of continuous data were acquired using 320-row multislice CT. Displacements in the tumor position during EE BH were assessed in the left–right (LR), anterior–posterior (AP), and superior–inferior (SI) directions. Pearson's correlation coefficient (r) between tumor motions during EE BH and diaphragm/external marker motions was also determined. The mean absolute maximum displacements of the tumor position during EE BH were 1.3 (range: 0.2–4.0), 1.9 (range: 0.3–12.0), and 1.3 (range: 0.1–7.2) mm in the LR, AP, and SI directions, respectively. The displacement of the tumor position in the AP direction was weakly correlated (|r| < 0.4) with the external marker and diaphragm displacements in many cases (proportions of 50% and 46%, respectively). We found some cases showing substantial displacement in lung tumor positions during EE BH, especially in the AP direction. Because these tumor position displacements did not correlate with surrogate markers and were difficult to detect, we recommend pretreatment evaluation of the four-dimensional motions of tumors during BH using cine CT. [ABSTRACT FROM AUTHOR]