ESTRO 2021 Abstract Book

S1350

ESTRO 2021

Conclusion The non-reproducibility of the mechanical bending of the iviewGT system complicates its use as a dosimetric detector. However, G(2,1) EP shows good enough results (passing rate > 95%) for the original plans while it is sensitive in both cases a and b (< 90%). The behaviour in case-d is intermediate, indicating an anomalous conformational behaviour with minor dosimetric consequences. Due to the difficulty of identifying these random errors, both a good statistical analysis of the QA results and an adequate quality control of the MLC are necessary. PO-1629 Monte Carlo calculation for metallic and synthetic material modeling in proton therapy J.D. Azcona 1 , B. Aguilar 1 , A. Viñals 1 , P. Cabello 1 , J.M. Delgado 1 , J. Serrano 2 , P. Arce 3 , P. Rato 3 , J.I. Lagares 3 1 Clínica Universidad de Navarra, Radiofísica y Protección Radiológica, Madrid, Spain; 2 Clínica Universidad de Navarra, Oncología Radioterápica, Madrid, Spain; 3 CIEMAT, Unidad de Aplicaciones Médicas, Madrid, Spain Purpose or Objective To ensure the accuracy of dose calculations in proton therapy in the presence of metallic prostheses and synthetic material. Materials and Methods We have treated patients with prosthesis made on a basis of Titanium, Cobalt-Chrome, and with boluses made of ABS resin. We have characterized them by obtaining the WET by measurement and calculations, and to characterize the material by its chemical composition and mass density, as the basis for Monte Carlo dose calculation and proton electromagnetic and nuclear scattering, and cross sections of nuclear reactions. Treatment planning was done on RayStation (RaySearch Laboratories AB) versions 9 and 10. Modelling actual prostheses and synthetic materials can be done in RayStation by using compounds in its database with different chemical composition, then tweaking the mass density to match the actual material WET. We have calculated using a benchmarked Monte Carlo GAMOS/Geant4 dose calculation code the proton scatter and nuclear cross sections for a sample of the actual compound vs. the RayStation model. Mass densities used in both cases were those needed to reproduce best the WET. Calculations were done for a sample of 7 energies between 75 and 225 MeV, spaced every 25 MeV. We have also calculated the influence of the different materials in the treatment dose.