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Objective To establish an optimal limiting dose for dose limiting rings placed in the anterior and posterior regions of the neck for reducing head and neck lymphedema under intensity-modulated radiation therapy(IMRT) for early nasopharyngeal carcinoma(NPC) from a dosimetric perspective. Method Fifteen newly diagnosed early-stage nasopharyngeal carcinoma patients who underwent CT localization for radiotherapy at the Cancer Hospital of Guangzhou Medical University from January to September 2022 were included in the study. Each case was designed with five sets of radiotherapy plans. Plan A consisted of conventional unlimited-field plans, while Plans B-E consisted of limited-field plans with dose constraints set at 20, 18, 16, and 14 Gy, respectively, with the remaining parameters consistent with Plan A. The impact on target coverage and organ-at-risk constraints was evaluated through variance analysis and pairwise multiple comparisons using a randomized block design to determine the optimal dose limits. Results The gradient of 16Gy was determined as the optimal dose limiting cutoff point for achieving the balance between target coverage and organ limiting dose. Compared with the conventional plan, The plans with the placement of a cervical anterior and posterior dose limiting ring (16Gy) did not change the target dose coverage (P > 0.05), but only yielded a slight change in the homogeneity index (P < 0.05). It did not cause any changes of the dosage in the inner ear, mandible, and brainstem (all P > 0.05), but lead to statistically significant reductions in the oral cavity, throat, and thyroid (all P < 0.05). It caused a slight increase of the dose in the parotid gland and spinal cord (both P < 0.05), but the increased dose was anyhow within the tolerance range. Conclusion The dosimetric investigation determines an optimal dose limit cutoff point for the cervical anterior and posterior dose limiting rings. It is expected to provide a design method for IMRT plans to reduce head and neck lymphedema after radiotherapy for early NPC. [ABSTRACT FROM AUTHOR]

This paper presents a novel mechanical environmental test method that multi-output random strain responses are replicated instead of acceleration responses. In this work, the positive-definite strain reference spectral matrix and reference kurtoses for multiple control channels are defined first, and then three types of strain random signals including stationary Gaussian, stationary non-Gaussian, and non-stationary are generated. The inverse Fourier transform is used to obtain the stationary Gaussian strain random signals and the stationary non-Gaussian strain signals are obtained by the zero-memory nonlinear transformation. To synthetize non-stationary strain random signals, an amplitude modulation function is introduced with time-varying root mean square values. The correction algorithms are employed to update the drive signals for matching the strain responses compared with corresponding reference values. The simulation and experimental results prove the effectiveness and feasibility of the proposed strain response control procedure. The presented work provides new perspectives to investigate the fatigue behavior and life estimation of structure under controlled strain response environments for vibration fatigue tests. [ABSTRACT FROM AUTHOR]

Shock vibration environments frequently occur and threaten the reliability of products in aerospace engineering. This work deals with the shock response spectra replication control method for multi-shaker vibration test systems. Two synthetic methods for reconstitution of shock response signals with specified shock response spectra are presented. One is the random delay superposition method and the other is the filtering superposition method. The former utilizes a random time delay vector satisfying a normal distribution to simulate a shock response signal with symmetrical attenuated oscillation features while the latter is employed when the measured shock records are available. A time-domain inverse system method is formulated to obtain the multi-input drive signals based on a finite-difference equation. The multi-input multi-output frequency response functions are estimated first and then used to construct the inverse system. The multi-output shock response spectra are calculated by response signals from control sensors. A closed-loop iteration control procedure is provided to correct the drive signals according to the deviations between the responses and corresponding reference values. A numerical simulation and a triaxial vibration test are carried out and the results show the feasibility and effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]