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Metal artifacts cause errors in the exact delineation of implants and dose changes in radiotherapy. In this study, the dose distributiondifferences in the region of interest (ROI) were calculated by deliberately making contouring errors from the real size of model implantsby using both Monaco treatment planning system (TPS) and Geant4 toolkit. In Sec. 2, the computed tomography images were acquired byplacing known uniform cylindrical geometry titanium (Ti6Al4V) and cobalt (CoCrMo) alloys into water phantoms separately. The metalalloys were artificially contoured as 2 mm contracted and expanded from their real dimensions in Monaco TPS. The plans were generatedwith 6 MV photon beams for contouring of three different sizes, real, contracted and expanded, for each metal alloy. In addition, allconfigurations were simulated in Geant4 by using the photon energy spectrum data of the Elekta Synergy linear accelerator. Then, the 3Ddose data obtained from ROIs near the implant in Monaco TPS and Geant4 were analyzed with in-house programs. In Sec. 3, the depthdose values of Geant4 were compatible with TPS calculations and ion chamber measurements. When the alloys were contoured to realdimensions, it was observed that the local isodose values have changed up to 15% in ROI. The mean dose values were found to be higherin contracted and lower in expanded contours. It was observed that ±2 mm error in contouring the implants changed the mean dose up to±8%. In Sec. 4, this study emphasized that a few millimeters of error in contouring different implant materials can have a significant effecton dose distribution in a region close to the implant.

This study presents the radiation absorption properties of fluid dental composite was investigated computationally and experimentally. In the computational part of the study, I and I0 values were obtained for biomaterial by using the Gamos 6.2 simulation program. The results calculated with the GAMOS simulation program were compared with the XCOM data. In addition to (μ) and (μ/ρ) values, half value layer (HVL), tenth value layer (TVL) and mean free path (MFP) quantities were obtained which are important in terms of radiation absorption properties. The simulation results were found to be compatible with XCOM data for this composit biomaterial. The simulation results showed that the Monte Carlo technique can be used as an alternative to calculate the mass absorption coefficients at the requested gamma energy, especially for samples that are physically difficult to produce.Keywords: GAMOS, XCOM, biomaterial, linear attenuation coefficients, Bu çalışma, insan vücudunda doğal veya sentetik malzeme olarak kullanılan akışkan dental kompozitin radyasyon soğurma özelliklerinin Monte Carlo yöntemi kullanılarak hesaplanması ve XCOM sonuçları ile karşılaştırmayı amaçlamaktadır. Lineer soğurma katsayısından elde edilen veriler ile ortalama serbest yol (MFP), yarı değer kalınlığı (HVL) ve onda bir değer kalınlığı (TVL) gibi parametreler de elde edilmiştir. GAMOS 6.2 programı ile gerçekleştirilen simülasyonlarda, disk şeklinde bir soğurucu malzeme üzerine gönderilen noktasal foton kaynak geometrisi kullanılmıştır. 1 keV-20 MeV aralığında otuz altı farklı foton enerjisinde gerçekleştirilmiş ve XCOM verileri ile karşılaştırılmış ve uyumlu bulunmuştur. Bu yöntemin lineer soğurma katsayıları literatürde yer almayan malzeme bileşimleri ve enerji değerleri için alternatif bir hesaplama aracı olarak güvenle kullanılabileceği düşünülmektedir.

Günümüzde, beta yayıcı radyonüklidleri içeren radyoterapi yöntemleri yaygın olarak kullanılmakta ve araştırılmaktadır. Tedavinin başarısı, belirlenen tümör alanına, hesaplanan radyasyonu doğru dozda vermekle ilişkilidir. Bu aşamada kişiye özgü dozun hesaplanması ve doz hesaplama yöntemi önem kazanmaktadır. Bu çalışmada, saf beta yayıcı İtriyum 90 (90Y) noktasal kaynağının, su ve akciğer fantomu içerisindeki radyal doz dağılımı Geant4 tabanlı GAMOS Monte Carlo yöntemi ile hesaplanmıştır. Elde edilen sonuçlar International Committee for Radiological Units (ICRU) de yayınlanan referans dozimetrik veriler ile karşılaştırılmış ve uyumlu olduğu görülmüştür.

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