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Custidiano E.R.,FaCENA | Valenzuela M.R.,FaCENA | Dumont J.L.,Elekta CMS Software | McDonnell J.,Santa Fe Institute | And 2 more authors.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2011

Monte Carlo simulations were used to study the changes in the incident spectrum when a poly-energetic photon beam passes through a static brass compensator. The simulated photon beam spectrum was evaluated by comparing it against the incident spectra. We also discriminated the changes in the transmitted spectrum produced by each of the microscopic processes. (i.e. Rayleigh scattering, photoelectric effect, Compton scattering, and pair production). The results show that the relevant process in the energy range considered is the Compton Effect, as expected for composite materials of intermediate atomic number and energy range considered. © 2011 Elsevier B.V. All rights reserved. Source

Cashmore J.,University of Birmingham | Golubev S.,Elekta CMS Software | Dumont J.L.,Elekta CMS Software | Sikora M.,University of Bergen | And 2 more authors.
Medical Physics | Year: 2012

Purpose: A linac delivering intensity-modulated radiotherapy (IMRT) can benefit from a flattening filter free (FFF) design which offers higher dose rates and reduced accelerator head scatter than for conventional (flattened) delivery. This reduction in scatter simplifies beam modeling, and combining a Monte Carlo dose engine with a FFF accelerator could potentially increase dose calculation accuracy. The objective of this work was to model a FFF machine using an adapted version of a previously published virtual source model (VSM) for Monte Carlo calculations and to verify its accuracy. Methods: An Elekta Synergy linear accelerator operating at 6 MV has been modified to enable irradiation both with and without the flattening filter (FF). The VSM has been incorporated into a commercially available treatment planning system (Monaco™ v 3.1) as VSM 1.6. Dosimetric data were measured to commission the treatment planning system (TPS) and the VSM adapted to account for the lack of angular differential absorption and general beam hardening. The model was then tested using standard water phantom measurements and also by creating IMRT plans for a range of clinical cases. Results: The results show that the VSM implementation handles the FFF beams very well, with an uncertainty between measurement and calculation of 1 which is comparable to conventional flattened beams. All IMRT beams passed standard quality assurance tests with >95 of all points passing gamma analysis (γ 1) using a 3/3 mm tolerance. Conclusions: The virtual source model for flattened beams was successfully adapted to a flattening filter free beam production. Water phantom and patient specific QA measurements show excellent results, and comparisons of IMRT plans generated in conventional and FFF mode are underway to assess dosimetric uncertainties and possible improvements in dose calculation and delivery. © 2012 American Association of Physicists in Medicine. Source

Teguh D.N.,Erasmus Medical Center | Levendag P.C.,Erasmus Medical Center | Voet P.W.J.,Erasmus Medical Center | Al-Mamgani A.,Erasmus Medical Center | And 8 more authors.
International Journal of Radiation Oncology Biology Physics | Year: 2011

Purpose: To validate and clinically evaluate autocontouring using atlas-based autosegmentation (ABAS) of computed tomography images. Methods and Materials: The data from 10 head-and-neck patients were selected as input for ABAS, and neck levels I-V and 20 organs at risk were manually contoured according to published guidelines. The total contouring times were recorded. Two different ABAS strategies, multiple and single subject, were evaluated, and the similarity of the autocontours with the atlas contours was assessed using Dice coefficients and the mean distances, using the leave-one-out method. For 12 clinically treated patients, 5 experienced observers edited the autosegmented contours. The editing times were recorded. The Dice coefficients and mean distances were calculated among the clinically used contours, autocontours, and edited autocontours. Finally, an expert panel scored all autocontours and the edited autocontours regarding their adequacy relative to the published atlas. Results: The time to autosegment all the structures using ABAS was 7 min/patient. No significant differences were observed in the autosegmentation accuracy for stage N0 and N+ patients. The multisubject atlas performed best, with a Dice coefficient and mean distance of 0.74 and 2 mm, 0.67 and 3 mm, 0.71 and 2 mm, 0.50 and 2 mm, and 0.78 and 2 mm for the salivary glands, neck levels, chewing muscles, swallowing muscles, and spinal cord-brainstem, respectively. The mean Dice coefficient and mean distance of the autocontours vs. The clinical contours was 0.8 and 2.4 mm for the neck levels and salivary glands, respectively. For the autocontours vs. The edited autocontours, the mean Dice coefficient and mean distance was 0.9 and 1.6 mm, respectively. The expert panel scored 100% of the autocontours as a "minor deviation, editable" or better. The expert panel scored 88% of the edited contours as good compared with 83% of the clinical contours. The total editing time was 66 min. Conclusion: Multiple-subject ABAS of computed tomography images proved to be a useful novel tool in the rapid delineation of target and normal tissues. Although editing of the autocontours is inevitable, a substantial time reduction was achieved using editing, instead of manual contouring (180 vs. 66 min). © 2011 Elsevier Inc. Source

Han X.,Elekta CMS Software | Hibbard L.S.,Elekta CMS Software | Willcut V.,Elekta CMS Software
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2010

Deformable image registration is a key enabling technology for adaptive radiation therapy (ART) as it can facilitate structure segmentation as well as dose tracking and accumulation. In this work, we develop an efficient inverse-consistent diffeomorphic registration method applying the log-Euclidean formulation of diffeomorphisms. Unlike existing log-Euclidean deformable registration approaches, the proposed method deforms two images towards each other in a completely symmetric fashion during the registration optimization, which leads to higher efficiency and better accuracy in recovering large deformations. The method is applied for the automatic segmentation of daily CT images in prostate ART. To address difficulties caused by large bladder and rectum content change, we propose further improvements and combine deformable registration with model-based image segmentation. Validation results on real clinical data showed that the proposed method gives highly accurate segmentation of interested structures. © 2010 Springer-Verlag. Source

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