Superficial parotid lobe-sparing delineation approach: a better method of dose optimization to protect the parotid gland in intensity-modulated radiotherapy for nasopharyngeal carcinoma.

PURPOSE: We used a superficial parotid lobe-sparing delineation approach for dose optimization with better protection for the parotid glands in intensity-modulated radiotherapy (imrt) for nasopharyngeal carcinoma (npc) patients. METHODS: Compared with traditional contouring of the entire parotid glands as organs at risk (oars) in imrt for npc, we used a superficial parotid lobe-sparing delineation approach of contouring the superficial parotid lobes as oars. Changes in dose to the parotid glands, the targets, and other oars were evaluated. RESULTS: The mean dose to the parotid glands overall decreased by more than 4 Gy in the test plans. Impressively, the mean dose to the superficial parotid lobes in the test plans was not more than 30 Gy, regardless of clinical stage. In T1-3 npc patients, the dose distributions for targets were not significantly different in the control plans and the test plans. However, for some T4 patients, the dose distributions for targets and brainstem in the test plans could not meet clinical requirements. CONCLUSIONS: The superficial parotid lobe-sparing delineation approach can significantly lower the mean dose to the entire parotid and to the superficial parotid lobe in T1-3 npc patients, which would be expected to result in less xerostomia and better quality of life for those patients.

Prognostic model for risk stratification of de novo metastatic nasopharyngeal carcinoma patients treated with chemotherapy followed by locoregional radiotherapy.

BACKGROUND: There is no clinically applicable prognostic model designed for patients with de novo metastatic nasopharyngeal carcinoma (mNPC) treated with chemotherapy followed by locoregional radiotherapy (LRRT). We sought to develop a predictive tool of overall survival for individualized prediction and risk stratification in this heterogeneous patient population. PATIENTS AND METHODS: A total of 244 eligible patients with de novo mNPC, who were treated with platinum-based first-line chemotherapy followed by LRRT, were included in this retrospective study. We divided patients into the training and validation sets based on the date of initial treatment, with 152 patients treated between 2008 and 2013 comprising the training set for model development and 92 patients treated at a later time (2014 to 2015) forming the validation set. We applied Cox proportional hazards model to examine factors associated with overall survival (OS). We developed and subsequently validated a prognostic model to predict OS. We assessed the performance of this prognostic model and stratified patients based on prognostic scores obtained from this proposed model. RESULTS: The median OS of the entire cohort was 60.9 months. C-creative protein, number of metastatic sites, liver metastasis, post-treatment Epstein-Barr virus DNA, and response of metastasis were significantly associated with OS. A prognostic model for individual survival prediction was developed and graphically represented as a nomogram. The model showed favorable discrimination (C-index: 0.759), predictive accuracy [time dependent area under the curve (tAUC) at 5 years: 0.800], and calibration, and was further validated in an independent dataset. A risk stratification derived from the model can stratify these patients into three prognostic subgroups with significantly different survival. CONCLUSION: We developed and validated a prognostic model that exhibited adequate performance in individualized prediction and risk stratification for patients with de novo mNPC treated with chemotherapy followed by LRRT.

An achiral ferromagnetic/chiral antiferromagnetic bilayer system leading to controllable size and density of skyrmions.

Magnetic skyrmions are topologically protected domain structures related to the Dzyaloshinskii-Moriya interaction (DMI). To understand how magnetic skyrmions occur under different circumstances, we propose a model for skyrmion formation in a bilayer system of ferromagnetic/antiferromagnetic (FM/AFM) films, in which the bulk DMI is only present in the AFM film. Micromagnetic simulations reveal that skyrmions are formed in this system due to the competition between the DMI and demagnetization energies. A critical interfacial exchange energy (Ai = 6.5 mJ/m2) is determined, above which the competition occurs at its full extent. More skyrmions are formed with increasing external magnetic field till a critical value above which the external field is too large and thus leading to the annihilation of skyrmions. The spacing between two skyrmions can be as small as 45 nm. Our results may give technological implications for future skyrmion applications.

Skyrmion-skyrmion and skyrmion-edge repulsions in skyrmion-based racetrack memory.

Magnetic skyrmions are promising for building next-generation magnetic memories and spintronic devices due to their stability, small size and the extremely low currents needed to move them. In particular, skyrmion-based racetrack memory is attractive for information technology, where skyrmions are used to store information as data bits instead of traditional domain walls. Here we numerically demonstrate the impacts of skyrmion-skyrmion and skyrmion-edge repulsions on the feasibility of skyrmion-based racetrack memory. The reliable and practicable spacing between consecutive skyrmionic bits on the racetrack as well as the ability to adjust it are investigated. Clogging of skyrmionic bits is found at the end of the racetrack, leading to the reduction of skyrmion size. Further, we demonstrate an effective and simple method to avoid the clogging of skyrmionic bits, which ensures the elimination of skyrmionic bits beyond the reading element. Our results give guidance for the design and development of future skyrmion-based racetrack memory.

Effect of stoichiometry on the magnetocrystalline anisotropy of Fe-Pt and Co-Pt from first-principles calculation.

The effect of stoichiometry on magnetocrystalline anisotropy energy (MAE) of Fe1+xPt1-x and Co1+xPt1-x (-0.5 < x < 0.5) is studied by use of first-principles method. The calculated MAEs show maxima at x = 0 for both fully L10-ordered systems. Compared with that, the MAEs of partially L10-ordered systems reduce but their composition dependences do not change, without shift of the maximum MAE to Fe/Co-rich alloy as found in experiment at room temperature. In the off-stoichiometric alloys, the misoccupied Fe/Co and Pt show large MAEs, which is explained by the enhanced in-plane hybridization between Fe/Co and Pt. The composition dependence of the atom-resolved MAE is governed by the varying number of heterogeneous ligands around the atom. The MAE(T)/MAE(0) is discussed based on spontaneous magnetization and Curie temperature, which suggests that the temperature effect may contribute to the discrepancy between calculation and experiment in the composition dependence of MAE.