X-ray dose profiles using artificial neural networks.

This paper introduces a novel computational method to simulate and predict radiation dose profiles in a water phantom irradiated by X-rays of 6 and 15 MV at different depths and field sizes using Artificial Neural Networks within the error margin required by the code of practice 398 of the International Atomic Energy Agency (IAEA). Our method uses deep-learning Artificial Neural Networks as an alternative to the Monte Carlo methods usually used nowadays. It reproduces the radiation dose profiles for X-rays of 6 and 15 MV data reported in the British Journal of Radiology (Aird, 1996). Even more, our method reproduces data from other sources with acceptable errors. These simulations pave the way to enhance radiotherapy techniques in planning patient doses and calibrating ionizing radiation measurement instruments used in the fight against cancer.

Monte Carlo Calculation of the Energy Spectrum of a 6 MeV Electron Beam using PENetration and Energy Loss of Positrons and Electrons Code.

BACKGROUND: The limited bibliographic existence of research works on the use of Monte Carlo simulation to determine the energy spectra of electron beams compared to the information available regarding photon beams is a scientific task that should be resolved. AIMS: In this work, Monte Carlo simulation was performed through the PENELOPE code of the Sinergy Elekta accelerator head to obtain the spectrum of a 6 MeV electron beam and its characteristic dosimetric parameters. MATERIALS AND METHODS: The central-axis energy spectrum and the percentage depth dose curve of a 6 MeV electron beam of an Elekta Synergy linear accelerator were obtained by using Monte Carlo PENELOPE code v2014. For this, the linear accelerator head geometry, electron applicators, and water phantom were simplified. Subsequently, the interaction process between the electron beam and head components was simulated in a time of 86.4x104 s. RESULTS: From this simulation, the energy spectrum at the linear accelerator exit window and the surface of the phantom was obtained, as well as the associated percentage depth dose curves. The validation of the Monte Carlo simulation was performed by comparing the simulated and the measured percentage depth dose curves via the gamma index criterion. Measured percentage depth- dose was determined by using a Markus electron ionization chamber, type T23343. Characteristic parameters of the beam related with the PDD curves such as the maximum dose depth (R100), 90% dose depth (R90), 90% dose depth or therapeutic range (R85), half dose depth (R50), practical range (Rp), maximum range (Rmax), surface dose (Ds), normalized dose gradient (G0) and photon contamination dose (Dx) were determined. Parameters related with the energy spectrum, namely, the most probable energy of electrons at the surface (Ep,0) and electron average energy (E- 0) were also determined. CONCLUSION: It was demonstrated that PENELOPE is an attractive and accurate tool for the obtaining of dosimetric parameters of a medical linear accelerator since it can reliably reproduce important clinical data such as the energy spectrum, depth dose, and dose profile.

Dosimetry in a mammography phantom using TLD-300 dosimeters.

PURPOSE: The purpose of this study was to evaluate the photon field effective energy (Eeff ) distribution and percentage depth-dose (PDD) within a mammography phantom by the analysis of the CaF2 :Tm (TLD-300) thermoluminescent (TL) glow curve. The experimental procedure involves the use of TLD-300 to determine with single dosimeter exposures both the relative dose and the beam quality. METHODS: TLD-300 chips were exposed to x rays from a GE Senographe 2000D mammography unit at the surface and different depths within a BR12 phantom. X-ray beams were generated with Mo/Mo, Mo/Rh, and Rh/Rh anode/filter combinations and voltages between 25 and 34 kV. Glow curves were deconvoluted into component peaks and the high- to low-temperature ratio (HLTR) was evaluated. The photon field Eeff was obtained from the HLTR values using a calibration curve determined previously. PDD was established from the peak 5 TL signal (TLSP5 ) at depths between 0.0 and 3.5 cm inside the phantom. Taking into account the differences in density and composition between CaF2 :Tm and breast tissue, an energy-dependent correction factor (ß(E)) was applied to TLSP5 . Measurements were compared with radiation transport Monte Carlo (MC) simulations performed with PENELOPE-2008. RESULTS: A typical 5% change in the HLTR from the phantom top surface to 3.5 cm depth was measured, which corresponds to a 2.2 keV increase in photon field Eeff . Values of the ß(E) correction factor were 0.33 and 0.13 for Eeff equal to 15.1 and 22.5 keV, respectively. This strong energy dependence of ß(E) is mostly due to the differences in fluence attenuation between CaF2 and breast tissue. According to PDD measurements, dose decreased to half the surface value at depths between 0.7 and 1.0 cm for Mo/Mo/25 and Rh/Rh/34 beams, respectively. Values of PDD, less than 10% at 3.5 cm depth, would have been overestimated by about 3.5% (a large relative error) if an energy-independent correction factor had been assumed. Mean differences between experiments and MC simulations were 0.8 keV and 1.2% in the determination of Eeff and PDD, respectively. CONCLUSION: The TLD-300 glow curve was used to accurately measure the photon field Eeff and PDD within a mammographic phantom. This work has demonstrated that Eeff and dose can be established simultaneously by using solely TLD-300.

Dosimetria de raios X em mamografia para combinação Mo/Mo utilizando espectrometria Compton / X-ray dosimetry in mammography for Mo/Mo combination utilizing Compton spectrometry

OBJETIVO: Para comparar o benefício da mamografia e o risco de câncer induzido por raios X, devese investigar as doses absorvidas. Nesse sentido, determinaram-se espectros dos raios X de um mamógrafo clínico, para combinação alvo/filtro Mo/Mo, utilizando espectrometria Compton, e avaliou-se a dose glandular média (DGM) em um simulador de mamas de BR-12. MATERIAL E MÉTODO:Um detector de CdTe foi usado para espectrometria dos raios X espalhados a ~ 100° por um cilindrode PMMA, para diferentes profundidades de BR-12 e tensões entre 28 e 35 kV. Após a reconstrução do espectro dos feixes primários, a partir dos medidos, determinou-se a DGM. RESULTADOS:Obtiveram-se camadas semirredutoras de 0,39 a 0,45 mmAl (espectrometricamente) e de 0,38 a0,42 mmAl (com câmara de ionização) para os feixes incidentes na superfície do simulador. A DGMNnormalizada por unidade de kerma no ar incidente, na superfície de BR-12, variou de 0,156 a 0,226.CONCLUSÃO: Os valores de DGMN variaram de 1% a 3%, em relação aos obtidos com câmara. O método empregado é uma boa alternativa para a determinação de DGMN e da distribuição de dose em profundidade em simuladores mamários.

OBJECTIVE: To compare mammography benefit and X-ray induced cancer risk, one should investigate absorbed doses. For this purpose, spectra of primary X-ray beams from a clinical mammographyequipment were determined for Mo/Mo target/filter combination,using Compton spectrometry and average glandular dose (AGD) in a BR-12 breast phantom was evaluated. MATERIAL AND METHOD: A CdTe detector was used for spectrometry of X-ray beams Compton scattered around 100°, by a PMMA cylinder, for different depths inside the BR-12 phantom and voltages between 28 and 35 kV. The reconstruction of the primary beam spectra from the measured ones was followed by the determination of AGD. RESULTS: Half-value layer values determined by spectra resulted 0.39 to 0.45 mmAl, and by ionization chamber, 0.38 to 0.42 mmAl, respectively, for beams incident on the phantom surface. The AGDN normalized per unitary incident air kerma, on the BR-12 surface, ranged from 0.156 to 0.226. CONCLUSION: The percentage deviation of AGDN, relative to the chamber measurements, ranged from 1% to 3%. The utilized method is a good alternative to determineAGDN and depth-dose distributions in breast phantoms.

Simulação computacional de um feixe de fótons de 6 MV em diferentes meios heterogêneos utilizando o código PENELOPE / Computer simulation of a 6 MV photon beam in different heterogeneous media utilizing the PENELOPE code

OBJETIVO: Utilizar o código PENELOPE e desenvolver geometrias onde estão presentes heterogeneidades para simular o comportamento do feixe de fótons nessas condições. MATERIAIS E MÉTODOS: Foram feitas simulações do comportamento da radiação ionizante para o caso homogêneo, apenas água, e para os casos heterogêneos, com diferentes materiais. Consideraram-se geometrias cúbicas para os fantomas e geometrias em forma de paralelepípedos para as heterogeneidades com a seguinte composição: tecido simulador de osso e pulmão, seguindo recomendações da International Commission on Radiological Protection, e titânio, alumínio e prata. Definiram-se, como parâmetros de entrada: a energia e o tipo de partícula da fonte, 6 MV de fótons; a distância fonte-superfície de 100 cm; e o campo de radiação de 10x 10 cm². RESULTADOS: Obtiveram-se curvas de percentual de dose em profundidade para todos os casos. Observou-se que em materiais com densidade eletrônica alta, como a prata, a dose absorvida é maior em relação à dose absorvida no fantoma homogêneo, enquanto no tecido simulador de pulmão a dose é menor. CONCLUSÃO: Os resultados obtidos demonstram a importância de se considerar heterogeneidades nos algoritmos dos sistemas de planejamento usados no cálculo da distribuição de dose nos pacientes, evitando-se sub ou superdosagem dos tecidos próximos às heterogeneidades.

OBJECTIVE: The PENELOPE code was utilized to simulate irradiation geometries where heterogeneities are present and to simulate a photon beam behavior under these conditions. MATERIALS AND METHODS: For the homogeneous case, the ionizing radiation behavior was simulated only with water, and different materials were introduced to simulate heterogeneous conditions. Cubic geometries were utilized for the homogeneous phantoms, and parallelepiped-shaped geometries for the heterogeneities with the following composition: bone and lung tissue simulators, as recommended by the International Commission on Radiological Protection, and titanium, aluminum and silver. Input parameters were defined as follows: energy and type of source, 6 MV photons; source-surface distance=100 cm; and radiation field of 10x 10 cm². RESULTS: Percentage depth-dose curves were obtained for all the cases. As result, it was observed that for high electronic density materials, such as silver, the absorbed dose is higher than the absorbed dose in the homogeneous phantom, and for the lung tissue simulator, it is lower. CONCLUSION: Results clearly demonstrate the relevant role of heterogeneities in the treatment planning system algorithms utilized in the calculation of dose distribution in patients, increasing the accuracy of the dose delivered to the tumor and avoiding unnecessary irradiation of healthy tissues.