ESTRO 36 Abstract Book

S423 ESTRO 36 2017 _______________________________________________________________________________________________

Gesellschaft für Schwerionenforschung (GSI) were used as reference data. Results For all physics lists, the relative dose differences up to the Bragg peak were found to be less than 4% compared to measurements. Beyond the Bragg peak, in the so-called fragmentation tail, differences increased notably, by up to one order of magnitude. However, the absolute dose difference in the fragmentation tail was comparable to the absolute difference before the Bragg peak. The QMD model systematically overestimated whereas the other models underestimated the dose in the fragmentation tail. Overall, deviations to the measurement were less than 2% of the maximum dose for all models, disregarding the dose fall off region due to the steep dose gradient. Partial charge changing cross sections simulated with the BIC, BERT and QBBC models deviated up to 60% from the measurements, INCLXX up to 38% and the QMD model up to 24%. However, the significance on fragmentation in particle therapy is limited by the high energy equal to 630 MeV/u used in the measurements. Conclusion IDDs simulated with Gate/Geant4 agreed well with measurements for all models under investigation, although notable deviations were observed in the fragmentation tail. Measured partial charge changing cross sections could best be reproduced using the QMD model, whereas the BIC model showed considerable discrepancies. Therefore, Gate/Geant4 can be considered a valid dose calculation tool for oxygen ion beams and will further on be used for the development of a pencil beam algorithm for oxygen ions. The QMD model is recommended in order to obtain accurate fragmentation results, which is essential for radiation oncology purposes. PO-0802 Experimental validation of single detector proton radiography with scanning beams C. Chirvase 1 , K. Teo 2 , R. Barlow 1 , E.H. Bentefour 3 1 International Institute for Accelerator Applications, The University of Huddersfield, Huddersfield, United Kingdom 2 University of Pennsylvania, Department of Radiation Oncology, Philadelphia PA, USA 3 Advanced Technology Group, Ion Beam Applications s.a., Louvain-la-Neuve, Belgium Purpose or Objective Proton radiography represents a potential solution to solve the uncertainties of dose delivery in proton therapy. It can be used for in-vivo beam range verification; patient specific Hounsfield unit (HU) to relative stopping power calibration and improving patient set-up. The purpose of this study is to experimentally validate the concept of the energy resolved dose measurement for proton radiography using a single detector with Pencil Beam Scanning (PBS). Material and Methods A 45 layers imaging field with a size of 30 x 30 cm 2 and energies between 226 MeV and 115 MeV is used to deliver a uniform dose. The dose per spot is 4.25 mGy with spot spacing equal to the beam sigma. The imaging field is first delivered on wedge shaped water phantom to produce calibration library of Energy Resolved Dose Functions (ERDF) between 0 cm and 30 cm. Then, the same imaging field is delivered in three different configurations: a stack of solid water in a stairs shape with thicknesses between 1 mm and 10 mm – that determines the accuracy with which the WEPL (water-equivalent path length) can be retrieved, CIRS lung phantom – that illustrates the accuracy on the density of multiple materials and a head phantom – which represents a realistic case of heterogeneous target. As shown in Figure 1, proton radiographs are recorded with a commercial 2D detector (Lynx, IBA-Dosimetry, Schwarzenbruck, Germany) which has an active area of 300 × 300 mm² with an effective resolution of 0.5 mm.

Figure 1. Experimental set-up with an example of proton radiograph imaged at beam energy of 220 MeV. Results In this study we demonstrate the robustness of the energy resolved dose measurement method for single detector proton imaging. It shows the capability to determine the WEPL with sub-millimeter accuracy in a homogeneous target and performs well in heterogeneous target, proving an accuracy better than 2 mm even in most heterogeneous areas of a head phantom. These performances are achieved by using an imaging field with as little as 5 energy layers with spacing up to 10 mm between the layers. Although the optimization of the imaging dose was not a goal of this study, only ~21 mGy per cm 2 is sufficient to obtain the above accuracies. This dose can be further decreased by using a detector with higher sensitivity and by reducing the number of beam spots per layer of the imaging field. Conclusion Proton radiography with single detector using energy resolved dose measurement did show potential for clinical use. Further studies are needed to optimize the imaging dose and the clinical workflow. PO-0803 CloudMC, a Cloud Computing application for fast Monte Carlo treatment verification H. Miras 1 , R. Jiménez 2 , R. Arrans 1 , A. Perales 3 , M. Cortés- Giraldo 3 , A. Ortiz 1 , J. Macías 1 1 Hospital Universitario Virgen Macarena, Medical Physics, Sevilla, Spain 2 Icinetic TIC SL, R&D division, Sevilla, Spain 3 Universidad de Sevilla, Atomic- Molecular and Nuclear Physics Department, Sevilla, Spain Purpose or Objective CloudMC is a cloud-based solution developed for r educing time of Monte Carlo (MC) simulation s through parallelization in multiple virtual computing nodes in the Microsoft’s cloud. This work presents an update for performing MC calculation of complete RT treatments in an easy, fast and cheap way. Material and Methods The application CloudMC, presented in previous works, has been updated with a solution for automatically perform MC treatment verification. CloudMC architecture (figure 1) is divided into two units. The processing unit consists of a web role that hosts the user interface and is responsible of provisioning the computing worker roles pool, where the tasks are distributed and executed, and a reducer worker role that merges the outputs. The storage unit contains the user files, a data base with the users and simulations metadata and a system of message queues to maintain asynchronous communication between the front- end and the back-end of the application.