Nova metodologia d’anàlisi de distribucions de dosi per algorismes de càlcul de dosi absorbida en radioteràpia externa que simulen el transport de radiació en medi

Jurado-Bruggeman, Diego
Compartir
Introduction Different types of dose calculation algorithms for external beam radiation therapy with MV photons coexist nowadays. The oldest ones are convolution/superposition (C/S), which consider all media as water of different densities and report doses in water surrounded by water (Dw,w). Subsequently, advanced algorithms are incorporated, which model in detail the transport of radiation in the medium and allow reporting the dose in medium surrounded by medium (Dm,m) or in water surrounded by medium (Dw,m). Advanced algorithms improve accuracy but, unlike C/S algorithms, their dose values are sensitive to the atomic composition of the medium, which requires new considerations in the analysis of dose distributions and plan optimisation. Purpose To propose a methodology for analysing the absorbed dose distributions obtained with algorithms that model radiation transport in medium that allows using the criteria and parameters established internationally for previous algorithms. To study whether the proposed methodology makes it possible to discern whether the altered dose values are due to tissue composition effects or to a sub-optimal plan. Materials and methods The doses of advanced algorithms are expressed in such a way that their values are not sensitive to the atomic composition, which formally entails introducing a new dose quantity that we have named dose in reference-like medium (Dref,m*). Dref,m* is linked to a reference medium, and is defined as the absorbed dose in a voxel of that medium surrounded by a medium with the same composition but with the same radiation transport properties as the original. A methodology was developed to derive Dref,m* distributions by post-processing Dw,m or Dm,m and applying a correction factor (CF) to each voxel depending on its composition. The CFs were obtained within the planning system with two virtual dummies of varying density and composition. A proof of concept was performed for the advanced Acuros XB algorithm and a 6-VM beam, comparing the Dref,m*, Dm,m, Dw,m and Dw,w results of the AAA C/S algorithm in several cases. Finally, the performance of Dref,m* and the other quantities in the optimisation process was evaluated for three representative cases that were optimised over the PTV with the criteria established for Dw,w to achieve the same dose distributions. The differences between quantities in terms of radiation fluence, robustness and complexity were analysed ​
​L'accés als continguts d'aquesta tesi queda condicionat a l'acceptació de les condicions d'ús establertes per la següent llicència Creative Commons: http://creativecommons.org/licenses/by-sa/4.0/