Dosimetric verification of a commercial Monte Carlo treatment planning system (VMC++) for a 9 MeV electron beam

Abstract

The aim of this work was to evaluate the performance of the voxel-based Monte Carlo algorithm implemented in the commercial treatment planning system ONCENTRA MASTERPLAN for a 9 MeV electron beam produced by a linear accelerator Varian Clinac 2100 C/D. In order to realize an experimental verification of the computed data, three different groups of tests were planned. The first set was performed in a water phantom to investigate standard fields, custom inserts, and extended treatment distances. The second one concerned standard field, irregular entrance surface, and oblique incidence in a homogeneous PMMA phantom. The last group involved the introduction of inhomogeneities in a PMMA phantom to simulate high and low density materials such as bone and lung. Measurements in water were performed by means of cylindrical and plane-parallel ionization chambers, whereas measurements in PMMA were carried out by the use of radiochromic films. Point dose values were compared in terms of percentage difference, whereas the gamma index tool was used to perform the comparison between computed and measured dose profiles, considering different tolerances according to the test complexity. In the case of transverse scans, the agreement was searched in the plane formed by the intersection of beam axis and the profile (2D analysis), while for percentage depth dose curves, only the beam axis was explored (1D analysis). An excellent agreement was found for point dose evaluation in water (discrepancies smaller than 2%). Also the comparison between planned and measured dose profiles in homogeneous water and PMMA phantoms showed good results (agreement within 2%-2 mm). Profile evaluation in phantoms with internal inhomogeneities showed a good agreement in the case of "lung" insert, while in tests concerning a small "bone" inhomogeneity, a discrepancy was particularly evidenced in dose values on the beam axis. This is due to the inaccurate geometrical description of the phantom that is linked to the calculation voxel size, a feature over which the user has no control.

Monte Carlo simulation of electron modes of a Siemens Primus linac (8, 12 and 14 MeV)

“…There are various commercially available systems that utilise MC algorithms for dose calculations. Examples of such MC-based treatment planning softwares are MasterPlan, eMC and Eclipse 6 – 8 . However there are other systems for electron treatment planning which may suffer from large uncertainties, especially when they are applied to an inhomogeneous media.…”

“…Examples of such MC-based treatment planning softwares are MasterPlan, eMC and Eclipse. [6][7][8] However there are other systems for electron treatment planning which may suffer from large uncertainties, especially when they are applied to an inhomogeneous media. Such treatment planning systems use different algorithms such as pencil beam algorithm and they have limitations in predicting hot and cold spots in inhomogeneous regions.…”

On the wall perturbation correction for a parallel‐plate NACP‐02 chamber in clinical electron beams

“…Due to the implementation of new Monte Carlo based dose calculation algorithms, 18 there is an increasing interest in validating and commissioning these algorithms, [19][20][21] requiring a better knowledge about the depth dependence of perturbation corrections in electron dosimetry. The presence of an energy and depth dependence of perturbation corrections for parallel-plate chambers in clinical electron dosimetry has been shown in recent years by several authors.…”

Absence of the right forelimb in Corythomantis greeningi Boulenger, 1896: case report

“…Although conventional radiographs, because they are two-dimensional, do not allow the qualitative visualization of images with high magnification (up to 300,000 X) and resolution, nor the observation and recording of three-dimensional images such as scanning electron microscopy -SEM (PICON et al, 2006). Therefore, studies using SEM in bone tissues allow the analysis of the bone architecture, bone neoformation and, in cases of bone repair, its maturation (CRUZ et al, 2007;SCHIAPPARELLI;ZEFIRO;TACCINI, 2009). Given the circumstances of the environ ent where the spe i en w s foun ro o ern u o r i in region of wor s of transposition of the São Francisco River and thereby, the presence of furrows, irregularities and bone protrusions on the surface of the distal epiphysis of the humerus can be observed through SEM, confirming that the case involved thoracic limb amputation after traumatic injury and not ectromelia.…”