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[en] A 300 MeV electron linac is constructed in 1967 at Tohoku University for advanced research on nuclear physics, radiochemistry and neutron science. A very high beam repetition rate of 300 pps is employed to achieve a duty factor of more than 0.1%. Although substantial parts of the linac sadly collapsed as a result of the Great East Japan earthquake occurred in 2011, the low-energy part of the linac still supplies high-intensity beams. To expand current research activities, the introduction of a versatile accelerator system that employs superconducting radiofrequency (SRF) cavities have been considered. Because the low surface resistance on these SRF cavities decreases the power dissipated to the cavity walls, the beams can be accelerated with a duty factor as high as 100%. However, the SRF cavities, which are manufactured from niobium (Nb), need to be operated at cryogenic temperatures of 2 K with a considerably large cryogenic system. Recently it is pointed out that the large heat load could be greatly lowered by replacing the standard Nb cavities with those coated with high-temperature superconductors. The possibility of developing simple and low-cost SRF accelerators based on conduction cooling with a 4 K refrigerator system is anticipated. (© 2020 Wiley‐VCH GmbH)
[en] This paper deals with a detailed investigation of the effects of various metal oxide nanoparticles on unsteady stagnation point flow of a hybrid base fluid impinging on a flat surface. The ‘single-phase’ nano fluid model,i.e., the Tiwari and Das model, is considered for the study. We consider water and ethylene glycol in 1:1 ratio as the base fluid and four different types of metal oxides, namely, CuO, TiO2, ZnO and MgO as the nanoparticles.Using similarity transformations, the conservation equations are transformed into self-similar ordinary differential equations. Dual and unique similarity solutions are obtained for certain set of values of parameters. The analysis explores many important findings. Dual self-similar solutions exist up to a certain critical value of the decelerating unsteady parameter and the critical value is independent of the type of metal oxide nanoparticles considered. The strongest surface drag force is observed for the nano fluid with CuO nanoparticles, while the weakest is for the nano fluid with MgO nanoparticles. The heat transfer rate is highest for the nano fluid with CuO nanoparticles and lowest for the nano fluid with TiO2 nanoparticles. Also, the boundary layer is thickest for the nano fluid with multiprocessing MgO nanoparticles. (author)
[en] Recently, Fe-based superconductors have shown promising properties of high critical temperature and high upper critical fields, which are prerequisites for applications in high-field magnets. Critical temperature, T, is an important characteristic correlated with crystallographic and electronic structures. By doping with foreign ions in the crystal structure, T can be modified, which however requires significant manpower and resources for materials synthesis and characterizations. In this study, we develop the Gaussian process regression model to predict T of doped Fe-based superconductors based on structural and topological parameters, including the lattice constants, volume, and bonding parameter topological index H. The model is stable and accurate, contributing to fast T estimations.
[en] Motivated by the recent experimental discovery of the high-critical-temperature superconductor LaH (250-260 K at high pressures 170-190 GPa), the influence of H isotope substitution on the phonon spectra, electron-phonon interactions, and thermodynamic properties of superconducting LaHD (x = 0 , 2 , 5 , 8 , 10) at 250 GPa are studied. On the basis of first-principles calculations, it is found that all investigated systems are dynamically stable in a clathrate structure with space group Fmm and exhibit high superconducting critical temperatures T ranging from 169 to 234 K. The dominant role of hydrogen in enhancing T is examined by numerically solving the Eliashberg equations. The estimated critical temperature, superconducting energy gap, specific heat, and thermodynamic critical field demonstrate that the underlying mechanism of superconductivity in lanthanum hydride is conventional electron-phonon coupling, which manifests itself in terms of isotope effect. (© 2020 Wiley‐VCH GmbH)
[en] The EC Directive 2013/59/Euratom states in article 56 that exposures of target volumes in nuclear medicine treatments shall be individually planned and their delivery appropriately verified. The Directive also mentions that medical physics experts should always be appropriately involved in those treatments. Although it is obvious that, in nuclear medicine practice, every nuclear medicine physician and physicist should follow national rules and legislation, the EANM considered it necessary to provide guidance on how to interpret the Directive statements for nuclear medicine treatments. For this purpose, the EANM proposes to distinguish three levels in compliance to the optimization principle in the directive, inspired by the indication of levels in prescribing, recording and reporting of absorbed doses after radiotherapy defined by the International Commission on Radiation Units and Measurements (ICRU): Most nuclear medicine treatments currently applied in Europe are standardized. The minimum requirement for those treatments is ICRU level 1 (“activity-based prescription and patient-averaged dosimetry”), which is defined by administering the activity within 10% of the intended activity, typically according to the package insert or to the respective EANM guidelines, followed by verification of the therapy delivery, if applicable. Non-standardized treatments are essentially those in developmental phase or approved radiopharmaceuticals being used off-label with significantly (> 25% more than in the label) higher activities. These treatments should comply with ICRU level 2 (“activity-based prescription and patient-specific dosimetry”), which implies recording and reporting of the absorbed dose to organs at risk and optionally the absorbed dose to treatment regions. The EANM strongly encourages to foster research that eventually leads to treatment planning according to ICRU level 3 (“dosimetry-guided patient-specific prescription and verification”), whenever possible and relevant. Evidence for superiority of therapy prescription on basis of patient-specific dosimetry has not been obtained. However, the authors believe that a better understanding of therapy dosimetry, i.e. how much and where the energy is delivered, and radiobiology, i.e. radiation-related processes in tissues, are keys to the long-term improvement of our treatments.
[en] To determine whether rectal displacement devices (RDDs) have a prostate-stabilizing effect during prostate external beam radiotherapy (EBRT). A systematic literature search using the PubMed database from January 1, 2000 to December 30th, 2019 was conducted. The effect of RDDs on inter- and intra-fractional prostate displacements was extracted. From 356 articles identified via the PubMed database and hand search, 21 articles were included in the systematic review. There was no randomized study. Twelve studies evaluated the role of the endorectal balloon (ERB) in managing prostate motion. Four studies reported the effect of hydrogel spacer on prostate motion. Four studies examined the effect of the rectal retractor (RR) on intra-fractional prostate motion, and only one study assessed the impact of ProSpare (Nottinghamshire, UK) in reducing prostate motion. Using an ERB significantly reduces intra-fractional prostate motion. This prostate-stabilizing effect of the ERB can translate into reduced planning target volume (PTV) margins and additional rectal dose sparing. Even with an ERB in place, inter-fractional prostate displacements are seen. As a consequence, ERB application does not obviate daily verification; however, this is not a crucial topic because pretreatment imaging is always done nowadays. As compared with ERB, the hydrogel spacer significantly reduces rectal dose and toxicity without influencing prostate immobilization. The RR can increase prostate and rectal inter- and intra-fractional stability without a clear influence on the reduction of rectal toxicity. Finally, it is unclear whether ProSpare is a suitable device reducing prostate motion. Further study will be required to clarify whether the prostate-stabilizing effects of the ERB and RR can result in a safe reduction of PTV margins and further sparing of organs at risks, especially the rectum.
[en] Mediastinal radiotherapy (RT), especially when combined with bleomycin, may result in substantial pulmonary morbidity and mortality. The use of modern RT techniques like intensity-modulated radiotherapy (IMRT) is gaining interest to spare organs at risk. We evaluated 27 patients who underwent RT for Hodgkin’s lymphoma between 2009 and 2013 at our institution. For each patient, three different treatment plans for a 30-Gy involved-field RT (IFRT) were created (anterior-posterior-posterior-anterior setup [APPA], 5‑field IMRT, and 7‑field IMRT) and analyzed concerning their inherent “normal tissue complication probability” (NTCP) for pneumonitis and secondary pulmonary malignancy. The comparison of different radiation techniques showed a significant difference in favor of standard APPA (p < 0.01). The risk of lung toxicity was significantly higher in plans using 7‑field IMRT than in plans using 5‑field IMRT. The absolute juxtaposition showed an increase in risk for radiation pneumonitis of 1% for plans using 5‑field IMRT over APPA according to QUANTEC (Quantitative Analyses of Normal Tissue Effects in the Clinic) parameters (Burman: 0.15%) and 2.6% when using 7‑field IMRT over APPA (Burman: 0.7%) as well as 1.6% when using 7‑field IMRT over 5‑field IMRT (Burman: 0.6%). Further analysis showed an increase in risk for secondary pulmonary malignancies to be statistically significant (p < 0.01); mean induction probability for pulmonary malignoma was 0.1% higher in plans using 5‑field IMRT than APPA and 0.19% higher in plans using 7‑field IMRT than APPA as well as 0.09% higher in plans using 7‑field IMRT than 5‑field IMRT. During a median follow-up period of 65 months (95% confidence interval: 53.8–76.2 months), only one patient developed radiation-induced pneumonitis. No secondary pulmonary malignancies have been detected to date. Radiation-induced lung toxicity is rare after treatment for Hodgkin lymphoma but may be influenced significantly by the RT technique used. In this study, APPA RT plans demonstrated a decrease in potential radiation pneumonitis and pulmonary malignancies. Biological planning using NTCP may have the potential to define personalized RT strategies.
[en] HANARO has been actively utilized since attaining first criticality in 1995. In 2009, the cold neutron source was installed inside the reflector tank. The main utilization fields of HANARO are neutron beam applications, nuclear fuel and material test, radioisotope production, neutron activation analysis and neutron transmutation doping. After the Fukushima accident, HANARO had been requested to evaluate the seismic margin for the reactor’s main components, and the seismic margin assessment led to the reinforcement of HANARO’s wall. In December 2017, HANARO started operating after overcoming many issues for about a 3 year-shutdown. For the period of long-term shutdown, the circumstances surrounding HANARO, such as research reactor regulation and new research reactor construction project, has been drastically changed. To meet the expectations of HANARO to produce world-class science and to respond to the rapidly changing environment, a strategic plan for HANARO was prepared, and 4 missions were re-established. They are 1) advancement of neutron science and technology, 2) not only meeting but also creating the needs of the industry, 3) contributions to the national society issues, and 4) safe and stable operation of the facility. To achieve the missions, all members involved in the HANARO shared their same perception that the stable operation of HANARO is the most important. HANARO is trying hard to give the confidence for its sustainability and excellence through the various activities. (author)
[en] Due to its low fractionation sensitivity, also known as “alpha/beta ratio,” in relation to its surrounding organs at risk, prostate cancer is predestined for hypofractionated radiation schedules assuming an increased therapeutic ratio compared to normofractionated regimens. While moderate hypofractionation (2.2–4 Gy) has been proven to be non-inferior to normal fractionation in several large randomized trials for localized prostate cancer, level I evidence for ultrahypofractionation (>4 Gy) was lacking until recently. An accumulating body of non-randomized evidence has recently been strengthened by the publication of two randomized studies comparing ultrahypofractionation with a normofractionated schedule, i.e., the Scandinavian HYPO-RT trial by Widmark et al. and the first toxicity results of the PACE‑B trial. In this review, we aim to give a brief overview of the current evidence of ultrahypofractionation, make an overall assessment of the level of evidence, and provide recommendations and requirements that should be followed before introducing ultrahypofractionation into routine clinical use.
[en] Currently there is an ever increasing interest in Lu-177 targeted radionuclide therapies, which target neuro-endocrine and prostate tumours. For a patient-specific treatment, an individual dosimetry based on SPECT/CT imaging is necessary. The aim of this study is to introduce a dosimetry method, where dose voxel kernels (DVK) are predicted by a neural network.Kidneys are considered one of the most critical organs in any radionuclide therapy. Hence we chose kidneys of 26 patients, who underwent Lu-177-DOTATOC or PSMA therapy, as target organs for our dosimetric method. First of all, density kernels with a size of voxels were considered, and the corresponding DVKs were calculated by Monte Carlo simulations. These kernels were used to train a neural network (NN), which received a density kernel as input and predicted a DVK at the output. To predict the dose distribution of an entire kidney, the organ had to be partitioned into a large number of density kernels. Afterwards the DVKs were predicted by a trained NN, and employed to reconstruct the whole-organ dose distribution by convolution with the activity distribution. This method was compared to the standard method where the activity distribution is convolved with a DVK based on a homogeneous soft tissue kernel. The number of training kernels amounted to 52,274 density kernels with corresponding MC-derived DVKs. The results serve as proof of principle of the newly proposed method and showed that the NN approach yielded superior results compared to the standard method with no additional computational effort. The NN approach is an accurate and highly competitive dosimetric method to precisely estimate absorbed radiation dose in critical organs like kidneys in clinical routine. To further improve the results, a larger number of DVKs needs to be computed by Monte Carlo simulations. An extension of the method to other organs is easily conceivable.