Monte Carlo Simulation Code PENELOPE Research Articles

Performance of a virtual source model for stereotactic radiosurgery with a dynamic micro-multileaf collimator

A virtual source model recently developed for external radiotherapy, which includes two photon sources and two electron sources, is tested for stereotactic radiosurgery with a dynamic micro-multileaf collimator. A MV Elekta Precise linac incorporating a 3Dline L’Arancio dynamic micro-multileaf collimator was considered. The capabilities of the virtual source model have been tested against full simulations performed with the Monte Carlo simulation code PENELOPE, using both PENELOPE itself and the rapid Monte Carlo code DPM. The reference radiation field, as well as small fields of , and , were considered. The dynamic micro-multileaf collimator effect can be included in the virtual source model by reducing the width of the primary photon source by a factor of three. In all cases the virtual source model simulations were in very good agreement with the complete ones including the linac and collimator geometries.

Abstract ID: 79 Virtual source model for stereotactic radiosurgery with a dynamic micro-multileaf collimator

A virtual source model recently developed for external radiotherapy, which includes two photon sources [1] and two electron sources [2] , is tested for stereotactic radiosurgery with a dynamic micro-multileaf collimator. A 6 MV Elekta Precise linac that incorporates a 3Dline L’Arancio dynamic micro-multileaf collimator was considered [3] . The capabilities of the virtual source model have been tested against full simulations performed with the Monte Carlo simulation code PENELOPE using both PENELOPE itself and the rapid Monte Carlo code DPM. The reference 10 cm × 10 cm radiation field as well as small fields of 1.2 cm cm × 1.2 cm, 2.9 cm cm × 2.9 cm and 5.8 cm cm × 5.8 cm were considered. The dynamic micro-multileaf collimator effect can be included in the virtual source model by reducing the width of the photon primary source by a factor 3. In all cases the virtual source model simulations were in very good agreement with the complete ones including the linac and collimator geometries.

Photon beam quality correction factors for the NE2571A and NE2581A thimble ionization chambers using PENELOPE

The beam quality correction factor kQ,Q0 and the perturbation factor pQ for photon beams were calculated for the NE2571A and NE2581A ionization chambers, using the Monte Carlo simulation code PENELOPE. Results are compared to those quoted for the NE2571 and NE2581 chambers in previous works. Both kQ,Q0 and pQ obtained for NE2571A and NE2581A chambers agree with those of their predecessors NE2571 and NE2581 ones.

Coincidence summing corrections for volume samples using the PENELOPE/penEasy Monte Carlo code

The coincidence summing correction factors estimated with penEasy, a steering program for the Monte Carlo simulation code PENELOPE, and with penEasy-eXtended, an in-house modified version of penEasy, are presented and discussed for 152Eu and 134Cs in volume sources. The geometries and experimental data were obtained from an intercomparison study organized by the International Committee for Radionuclide Metrology (ICRM). A significant improvement in the results calculated with PENELOPE/penEasy was obtained when X-rays are included in the 152Eu simulations.

SU-E-T-54: A Methodology for Monte Carlo Simulation Time Reduction in Dose Calculation for Reference Dosimetry

Purpose: To develop and optimize the simulation methodology to calculate the response of ionization chambers over a range of beam qualities commonly used in radiotherapy. The methodology can be used to determine the perturbation and beam quality correction factors for thimble ionizationchambers in high energy photons in a simple way. Methods: The Monte Carlo simulation code PENELOPE was used to simulate the dose in the sensitive volume of the NE2571 ionization chamber placed in a cubic water phantom, at the reference depth, for four different photon beams: 60Co, 4 MV, 6 MV and 10 MV. On a first step simulation, the radiation spectrum that reaches the geometric region of a 6 cm diameter sphere involving the chamber is sampled. Then, in a second simulation, the response of the ionization chamber is simulated using the sampled spectrum and without the cubic water phantom. The results of dose to the sensitive volume of the chamber in the two steps simulation was compared to the dose simulated in a one step simulation with the primary beam incident on the cubic phantom. Results: The dose values obtained without the water phantom, using the pre-sampled spectrum, are similar to the values obtained with those obtained in chamber positioned inside the phantom, with a maximum relative difference of 2.5% for the 10 MV beam. With the pre-sampled spectrum the time required for the simulation was about 30 times lower than for the one step simulation. The best results showed a relative difference of 0.4% for the 6 MV beam. Conclusions: The pre-sampling spectrum methodology proposed presented potential for significant simulation time reduction in dose calculations for reference dosimetry, studies of perturbation factors for thimble ionization chambers and beam quality correction determinations.

Simulation Study of Quantitative X-Ray Fluorescence Analysis of Ore Slurry Using Partial Least-Squares Regression

X-ray fluorescence (XRF) in combination with partial least-squares (PLS) regression was employed to analyze the ore slurry grade. Using the Monte Carlo simulation code PENELOPE, X-ray fluorescence spectra of ore samples were obtained. Good accuracy was achieved when this method was used to analyze elements with concentrations of several percent or above. It was demonstrated that the more the number of X-ray fluorescence spectra used to calibrate, the better the obtained accuracy. In this method detector resolution was found to have little or no effect on the results of quantitative analysis. The effect of the concentration of water was investigated as well, and it was found to have little influence on the results.

Calculation of beam quality correction factors for various thimble ionization chambers using the Monte Carlo code PENELOPE

The beam quality correction factor kQ,Q0 and the perturbation factor pQ, commonly considered in dosimetry with ionization chambers, were calculated for the NE2571 and the Standard Imaging A19 and A12S chambers, using the Monte Carlo simulation code PENELOPE. For the NE2571 chamber, the values of kQ,Q0 obtained are in very good agreement with those found in previous works by Wulff et al. and Muir and Rogers with the code EGSnrc and also with the experimental results summarized in the NCS code of practice. For pQ, a difference of ∼0.4% has been found between our results and those obtained with EGSnrc for 60Co and this difference increases slightly with TPR1020 values. These factors have been calculated also for the A19 and A12S chambers of Standard Imaging. The values of kQ,Q0 show reasonable agreement with those recently calculated by Muir and Rogers and the measurements of McEwen.

Parameters affecting full energy peak efficiency determination during Monte Carlo simulation

Aim of this work is to study the effect of various simulation parameters on the calculation of the full energy peak efficiency of HPGe detectors with the Monte Carlo simulation code PENELOPE.

Bremsstrahlung spectra produced from kilovolt electrons incident on thick targets of Ti, W and Pt

Measurements of x-ray emission spectra generated by 10–20 keV electrons impinging normally on bulk targets of pure elements Ti (Z = 22), W (Z = 74) and Pt (Z = 78) have been performed using an experimental setup developed for studying electron–atom/molecule collisions in our laboratory. Values extracted from the experimental data for bremsstrahlung yield, integrated yield and mean energy of the bremsstrahlung radiation beam for the above collision systems have been compared with the simulation results obtained from the general purpose Monte Carlo simulation code PENELOPE. The comparisons are found to show a satisfactory agreement between them within their statistical uncertainties. Some apparent mismatches are observed for which possible causes and their origins are discussed.

Monte Carlo analysis of the degradation of the spectrum produced by an X-ray tube in conventional radiography

Medical imaging detectors used in diagnostic radiology are very sensitive to the spectra of the X-ray beams used. In this work, we use Monte Carlo simulation to analyse the degradation of various X-ray spectra at different stages of their travel from the X-tube focus to the detector. Special attention is paid to the antiscatter grid that is normally used in diagnostic radiology. For the present study, we have considered various measured spectra corresponding to accelerating voltages of 60, 80, 90 and 125 kV. We have assumed that the X-ray beams are parallel beams going successively through an aluminium filter, the air gap between the focus and the patient, a patient-equivalent water phantom and a parallel cross antiscatter grid. The Monte Carlo simulation code PENELOPE has been used to find out the X-ray spectrum at three planes: the patient, the grid, and the detector entrance. Additional simulations with monoenergetic beams of 30, 40, 55 and 100 keV have been carried out for comparison. We have investigated in detail the dependence of the attenuation of the primary beam with the initial energy, the percentage of the initial X-rays reaching the grid and the ratio of scatter to primary photons reaching the grid. The role played by the grid has been studied in depth. In particular, we have analysed the modification of the incident spectrum that it produces and its efficiency in removing the scattered photons.

Absolute Determination of Characteristic X-Ray Yields with a Wavelength-Dispersive Spectrometer

We describe a method to determine characteristic x-ray yields in absolute units with a wavelength-dispersive spectrometer. The method requires measurement and calculation of the thick-target bremsstrahlung intensity emitted from a reference sample at the photon energy of interest. Bremsstrahlung intensities are calculated by using the general-purpose Monte Carlo simulation code PENELOPE. We discuss the different sources of uncertainty and apply the developed methodology to the determination of absolute x-ray yields emitted from (i) thick samples, (ii) thin films on substrates and (iii) ultra-thin, self-supporting films. We compare measured yields with the predictions of theoretical/analytical calculations and Monte Carlo simulation, and whenever possible, with similar measurements found in the literature.