Abstract
BackgroundA new algorithm for photon dose calculation, Acuros XB, has been recently introduced in the Eclipse, Varian treatment planning system, allowing, similarly to the classic Monte Carlo methods, for accurate modelling of dose deposition in media. Aim of the present study was the assessment of its behaviour in clinical cases.MethodsDatasets from ten breast patients scanned under different breathing conditions (free breathing and deep inspiration) were used to calculate dose plans using the simple two tangential field setting, with Acuros XB (in its versions 10 and 11) and the Anisotropic Analytical Algorithm (AAA) for a 6MV beam. Acuros XB calculations were performed as dose-to-medium distributions. This feature was investigated to appraise the capability of the algorithm to distinguish between different elemental compositions in the human body: lobular vs. adipose tissue in the breast, lower (deep inspiration condition) vs. higher (free breathing condition) densities in the lung.ResultsThe analysis of the two breast structures presenting densities compatible with muscle and with adipose tissue showed an average difference in dose calculation between Acuros XB and AAA of 1.6%, with AAA predicting higher dose than Acuros XB, for the muscle tissue (the lobular breast); while the difference for adipose tissue was negligible. From histograms of the dose difference plans between AAA and Acuros XB (version 10), the dose of the lung portion inside the tangential fields presented an average difference of 0.5% in the free breathing conditions, increasing to 1.5% for the deep inspiration cases, with AAA predicting higher doses than Acuros XB. In lung tissue significant differences are found also between Acuros XB version 10 and 11 for lower density lung.ConclusionsAcuros XB, differently from AAA, is capable to distinguish between the different elemental compositions of the body, and suggests the possibility to further improve the accuracy of the dose plans computed for actual treatment of patients.
Highlights
A new algorithm for photon dose calculation, Acuros XB, has been recently introduced in the Eclipse, Varian treatment planning system, allowing, to the classic Monte Carlo methods, for accurate modelling of dose deposition in media
Data shows a significant dose difference inside the field (Lung_IN) between Analytical Algorithm (AAA) and Acuros XB in the two air filling, being the average variation of 0.5% in the FB case (p < 10-4 with a t-Student test), value that increases to 1.5% in the DIBH case (p < 10-4 with a t-Student test)
Looking at the two Acuros XB versions, negligible difference of 0.2% is shown in the FB case, while an average of 1.3% (p < 10-4 with a t-Student test) is obtained for the lower density case of lung, resulting in higher dose computed by version 11
Summary
A new algorithm for photon dose calculation, Acuros XB, has been recently introduced in the Eclipse, Varian treatment planning system, allowing, to the classic Monte Carlo methods, for accurate modelling of dose deposition in media. It is a fact that most of the photon dose calculation engines have a more or less limited accuracy in predicting dose in low density media than in higher density tissues [5,6,7], especially those algorithms that use heavy approximations in modelling the lateral electron transport (e.g. convolution/superposition methods). To improve dose calculation in heterogeneous tissues, some algorithms implement the possibility to account for the specific elemental composition of the human body. This is typically realised by associating the Hounsfield Units from the CT scans to a mass density and material derived from customised and simplified conversion tables where, for predefined density ranges, specific elemental composition are assigned. In the case of breast treatments, beside the need of properly modelling the lung tissue (with complex composition and very low density at the same time when deep inspiration breathing is considered), inhomogeneities in the region of the target volume should be carefully modelled since the mammary gland has a quite complex structure as well
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
