A simplified model of the source channel of the Leksell Gamma Knife(R)^(R): testing multisource configurations with PENELOPE

A simplification of the source channel geometry of the Leksell Gamma Knife$^{\circledR}$, recently proposed by the authors and checked for a single source configuration (Al-Dweri et al 2004), has been used to calculate the dose distributions along the $x$, $y$ and $z$ axes in a water phantom with a diameter of 160~mm, for different configurations of the Gamma Knife including 201, 150 and 102 unplugged sources. The code PENELOPE (v. 2001) has been used to perform the Monte Carlo simulations. In addition, the output factors for the 14, 8 and 4~mm helmets have been calculated. The results found for the dose profiles show a qualitatively good agreement with previous ones obtained with EGS4 and PENELOPE (v. 2000) codes and with the predictions of GammaPlan$^{\circledR}$. The output factors obtained with our model agree within the statistical uncertainties with those calculated with the same Monte Carlo codes and with those measured with different techniques. Owing to the accuracy of the results obtained and to the reduction in the computational time with respect to full geometry simulations (larger than a factor 15), this simplified model opens the possibility to use Monte Carlo tools for planning purposes in the Gamma Knife$^{\circledR}$.Comment: 13 pages, 8 figures, 5 table

Evaluasi Penangkal Petir Eksternal Dengan Membandingkan Metode Sudut Proteksi, Metode Jala-Jala Dan Bola Bergulir (Studi Kasus Gedung Biro Rektor USU)

Pada penelitian ini melakukan analisa terkait dan  membandingkan  metode sudut proteksi dan metode bola bergulir pada gedung Biro Rektor Universitas Sumatera Utara dengan melakukan evaluasi system penangkal  petireks ternal dengan membandingkan metode sudut proteksi, metode jala-jala dan bola bergulir dan juga penulis akan melakukan perancangan suatu system pengaman terhadap bahaya sambaran petir pada Gedung Biro Rektor Universitas Sumatera Utara. Hasil analisa pada penelitian ini menunjukkan bahwa Gedung biro rektor Universitas Sumatera Utara memiliki daerah sambaran petir sekitar 33.493,23 m2 dengan rata rata sambaran petir ke tanah sekitar 38,63 Sambaran perkilo meter persegi pertahun, efisiensi system proteksi pada gedung sekitar 0,92 dan masuk kedalam tingkat proteksi level 2. Penggunaan metode sudut proteksi  pada Gedung Biro Rektor Universitas Sumatera Utara masih terdapat beberapa ruangan pada sisi kanan dan kiri di lantai 3 dan lantai 4 yang masih berpotensi terkena sambaran petir dengan pemasangan batang penangkap petir ke-1 dengan tinggi 9 meter dan batang penangkap petir ke-2 dengan tinggi 22 meter. Pemasangan dengan metode bola bergulir tidak lagi berpotensi terkena sambaran petir dengan pemasangan 47 Splitzen pada atap gedung. Metode Bola bergulir dapat mengidentifikasi daerah-daerah yang perlu dilindungi, metode bola bergulir dapat diterapkan untuk semua jenis desain bangunan. Hal ini berbeda dari metode sudut proteksi yang terbatas penggunaannya pada evaluas itingkat efektivitas system perlindungan petir yang telah didesain. Metode jala jala merupakan metode yang paling mudah dalam penerapan akan tetapi biaya investasinya cukup mahal

Effects of bone- and air-tissue inhomogeneities on the dose distributions of the Leksell Gamma Knife®^{\circledR} calculated with PENELOPE

Monte Carlo simulation with PENELOPE (v.~2003) is applied to calculate Leksell Gamma Knife$^{\circledR}$ dose distributions for heterogeneous phantoms. The usual spherical water phantom is modified with a spherical bone shell simulating the skull and an air-filled cube simulating the frontal or maxillary sinuses. Different simulations of the 201 source configuration of the Gamma Knife have been carried out with a simplified model of the geometry of the source channel of the Gamma Knife recently tested for both single source and multisource configurations. The dose distributions determined for heterogeneous phantoms including the bone- and/or air-tissue interfaces show non negligible differences with respect to those calculated for a homogeneous one, mainly when the Gamma Knife isocenter approaches the separation surfaces. Our findings confirm an important underdosage ($\sim$10%) nearby the air-tissue interface, in accordance with previous results obtained with PENELOPE code with a procedure different to ours. On the other hand, the presence of the spherical shell simulating the skull produces a few percent underdosage at the isocenter wherever it is situated.Comment: 13 pages, 8 figures, 2 table

PENERAPAN ALGORITMA TABU SEARCH PADA MODEL ACVRP UNTUK MENENTUKAN RUTE PENGANGKUTAN SAMPAH YANG OPTIMAL DI KECAMATAN KALIDONI

Penulisan artikel ini membahas mengenai penerapan Algoritma Tabu Search pada model ACVRP untuk mencari rute pengangkutan sampah yang optimal di Kecamatan Kalidoni. ACVRP merupakan matriks jarak asimetris dimana perjalanan dari tempat i ke j tidak sama dengan perjalanan dari tempat j ke i. Proses algoritma berpindah dari satu solusi ke solusi berikutnya dengan memilih solusi terbaik yang ada pada Tabu List. Hasil penelitian menunjukkan bahwa rute terpendek yang diperoleh dari perhitungan menggunakan Algoritma Tabu yaitu berjarak 17,7 km pada iterasi 1, dengan rute (6 – 4 – 5 – 3 – 2 – 1 – 0) yaitu TPS 6 (Jl. Mayor Zen Mata Merah (Depan SMA N 7)) – TPS 4 (Jl. Arozak (Depan Halte Sekojo)) – TPS 5 (Jl. Arozak (Depan SPBU Sekojo)) – TPS 3 (Jl. Arozak (Depan Perumahan Buana Hijau)) – TPS 2 (Jl. Arozak (Depan Perumahan Kedamaian)) – TPA Sukawinatan

Uncertainty and sensitivity analysis of the effect of the mean energy and FWHM of the initial electron fluence on the Bremsstrahlung photon spectra of linear accelerators

A calculation of the correct dose in radiation therapy requires an accurate description of the radiation source because uncertainties in characterization of the linac photon spectrum are propagated through the dose calculations. Unfortunately, detailed knowledge of the initial electron beam parameters is not readily available, and many researchers adjust the initial electron fluence values by trial-and-error methods. The main goal of this work was to develop a methodology to characterize the fluence of initial electrons before they hit the tungsten target of an Elekta Precise medical linear accelerator. To this end, we used a Monte Carlo technique to analyze the influence of the characteristics of the initial electron beam on the distribution of absorbed dose from a 6 MV linac photon beam in a water phantom. The technique is based on calculations with Software for Uncertainty and Sensitivity Analysis (SUSA) and Monte Carlo simulations with the MCNP5 transport code. The free parameters used in the SUSA calculations were the mean energy and full-width-at-half-maximum (FWHM) of the initial electron distribution. A total of 93 combinations of these parameters gave initial electron fluence configurations. The electron spectra thus obtained were used in a simulation of the electron transport through the target of the linear accelerator, which produced different photon (Bremsstrahlung) spectra. The simulated photon spectra were compared with the 6-MV photon spectrum provided by the linac manufacturer (Elekta). This comparison revealed how the mean energy and FWHM of the initial electron fluence affect the spectrum of the generated photons. This study has made it possible to fine-tune the examined electron beam parameters to obtain the resulted absorbed doses with acceptable accuracy (error < 1%). (C) 2012 Elsevier Ltd. All rights reserved.Juste Vidal, BJ.; Miró Herrero, R.; Verdú Martín, GJ.; Macian, R. (2012). Uncertainty and sensitivity analysis of the effect of the mean energy and FWHM of the initial electron fluence on the Bremsstrahlung photon spectra of linear accelerators. Applied Radiation and Isotopes. 70(7):1267-1271. doi:10.1016/j.apradiso.2012.03.040S1267127170

First multicentre experience of SABR for lymph node and liver oligometastatic disease on the unity MR-Linac

The treatment of oligometastatic disease using MR guidance is an evolving field. Since August 2018 patients are treated on a 1.5 Tesla MR-Linac (MRL). We present current workflows and practice standards from seven institutions for the initial patients treated for lymph node and liver metastases

Difference in performance between 3D and 4D CBCT for lung imaging: a dose and image quality analysis.

The study was to describe and to compare the performance of 3D and 4D CBCT imaging modalities by measuring and analyzing the delivered dose and the image quality. The 3D (Chest) and 4D (Symmetry) CBCT Elekta XVI lung IGRT protocols were analyzed. Dose profiles were measured with TLDs inside a dedicated phantom. The dosimetric indicator cone-beam dose index (CBDI) was evaluated. The image quality analysis was performed by assessing the contrast transfer function (CTF), the noise power spectrum (NPS) and the noise-equivalent quanta (NEQ). Artifacts were also evaluated by simulating irregular breathing variations. The two imaging modalities showed different dose distributions within the phantom. At the center, the 3D CBCT delivered twice the dose of the 4D CBCT. The CTF was strongly reduced by motion compared to static conditions, resulting in a CTF reduction of 85% for the 3D CBCT and 65% for the 4D CBCT. The amplitude of the NPS was two times higher for the 4D CBCT than for the 3D CBCT. In the presence of motion, the NEQ of the 4D CBCT was 50% higher than the 3D CBCT. In the presence of breathing irregularities, the 4D CBCT protocol was mainly affected by view-aliasing artifacts, which were typically cone-beam artifacts, while the 3D CBCT protocol was mainly affected by duplication artifacts. The results showed that the 4D CBCT ensures a reasonable dose and better image quality when mov-ing targets are involved compared to 3D CBCT. Therefore, 4D CBCT is a reliable imaging modality for lung free-breathing radiation therapy

František Bílek (sculptor)

Sculptor František Bílek in front of his villa in Prague-Hradčany on 28 March 1926 during the unveiling of the sculpture Comenius Says Farewell to the Motherland in a segment from the Elekta-Journal Newsreel 1926

Otakar Španiel (sculptor)

Sculptor Otakar Španiel working in his studio on a statue of T. G. Masaryk. Španiel on Bohumil Veselý's balcony. Working on a statue of T. G. Masaryk in 1928, in footage from the documentary Velikáni naší současné kultury (The Luminaries of Our Contemporary Culture, Elekta-journal, 1929). The sculptor in the garden of his villa in Ořechovka, Prague