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The linear accelerators (LINACs) produce high-energy X-rays and electron beams for the treatment of cancer patients. The basis of radiation therapy is based on the interaction between substance and radiation. LINAC as External beam radiotherapy, neutron contamination is produced in electron beams of medical LINAC by the contribution of the primary and the secondary collimators are founded. Consequently, the resulting photoneutrons can easily be scattered and spread into the clinical room. Thus, it is recommended that treatment planning performed should not be ignored in the tumor volume of the patient and areas outside this volume. The contribution of the primary collimator and the secondary collimators to the neutron contamination was found to be approximately 52% and 30%, respectively. This paper’s objective is to determine the neutron dose contamination from different materials in a LINAC. The effects of using different material ratios such as Gadolinium (Gd) and Tungsten (W) in secondary collimators on neutron contamination have been investigated by using Geant4-based Architecture for Medicine-Oriented Simulations (GAMOS) and TALYS 1.95 codes.

Comparison of IMRT and VMAT techniques in thoracic esophageal tumors. IMRT and VMAT plans were created for a total of 10 thorax-located esophagus patients. All plans were compared in terms of HI and CI for PTV; V-5, V-10, V-20 and mean lung dose parameters for total lung; V-30, V-40 and mean heart dose for the heart; and the Dmax for the medulla spinalis. IMRT and VMAT techniques yielded similar results with respect to HI and CI values (p> 0.05). Median mean lung dose was found to be lower in VMAT (11.77 Gy) technique compared to IMRT (12.05 Gy). While the lowest lung median V-5 (67.17%) and V-10 (41.95%) values belonged to IMRT, the V-20 value was achieved with VMAT (17.85%) planning. Median mean heart dose was found the lowest in VMAT (28.81 Gy) and the highest IMRT (29.31 Gy) planning. The lowest heart median V30 value was obtained with IMRT (43.00%) and median V-40 value was obtained with VMAT (18.95%) planning. The median mean medulla spinalis maximum dose was found to be lower with VMAT (41.54 Gy), with no statistically significant difference between them (p= 0.074). VMAT technique was better for reducing cardiovascular and medulla spinalis doses with reduced duration of treatment time and dosimetric uncertainties, while YART technique provides higher PTV control with less low-dose lung volume. Both threatment options have advantages and disadvantages over normal tissue and tumor volume compared to each other, and should be evaluated according to the other clinical conditions of the patient.

We calculated the total energy of a semiconductor quantum dot which is defined by the trench gate method. In our calculation we used a recently developed energy functional called ``orbital-free energy functional". We compared the total energies obtained by Thomas-Fermi approximation, orbital-free energy functional and standard local-density approximation for the square quantum slab geometry. We have seen that this newly developed energy functional is numerically very efficient, superior to the Thomas-Fermi approximation and is in good agreement with the local-density approximation for two different sizes of quantum dot systems., 8 pages, 4 figures

State-selective differential cross sections for single-electron capture processes in very slow collisions of Ar(q+) (q = 4-6) ions with neon (Ne) have been studied experimentally at laboratory impact energies between 0.4 and 4 qeV/amu and scattering angles between 0°and 8°by means of the translational energy-gain spectroscopy technique. The translational energy spectra show that the dominant reaction channels are due to capture into excited states of the projectile product Ar((q-1)+). However, at very low energies, other channels due to transfer excitation processes are found to open at large scattering angles. The energy-gain spectra are interpreted qualitatively in terms of the reaction windows, which are calculated using the single-crossing Landau-Zener model and the extended version of the classical over-the-barrier model. The energy dependence of cross sections for single-electron capture by Ar(q+) (q = 4-8) ions from Ne are also measured and found to be nearly constant with changing impact energy, but increase with an increase in the projectile charge state. The data are also compared with available measurements and theoretical calculations.

High-resolution translational energy-gain spectra for single-electron capture by N3+ ions from H-2, He, Ne, and Ar have been measured experimentally at laboratory impact energies of 6, 9, 12, and 15 keV. For N3+-He and Ne collisions, transfer excitation into the 2s2p(2) state of N2+ is significantly populated, while in N3+-H-2 collisions, transfer excitation into the 2s2p(22)P state dominates at low energies, In N3+-Ar collisions, pure single-electron capture into 3s is selectively populated. In all the collision systems studied here, contributions from processes commencing with a long-lived metastable state of N3+(2s(S-2)2p P-3) are detected. The translational energy-gain spectra are interpreted qualitatively in terms of the reaction windows, which are calculated using the single-crossing Landau-Zener model and the extended version of the classical over-the-barrier model. Total cross sections for single-electron capture for N3+ ions colliding with He and H-2 are also measured and compared with available measurements and theoretical calculations.