ESTRO 38 Abstract book

S1148 ESTRO 38

secondary electrons under irradiation in comparison to a high-Z material like gold. Yet no decrease in functionality that would exclude the hybrid AuFeNPs from implementation could be found so far. Conclusion The limited range of secondary electrons and fast decrease of the DEF with increasing range underlines the importance of developing techniques to deliver the AuNPs not only into the tumor cells but at best in close range to their nucleus to maximize the probability of cell death during irradiation. The results of the simulations will be used to compute the overall dose in a phantom under irradiation. By this we determine optimal conditions for the subsequent in vivo experiments, where cmHsp70.1 conjugated GNPs will be tested in small animals treated with radiotherapy. EP-2081 Real time CyberKnife dosimetry using Radioluminescence imaging A. Spinelli 1 , E. D'Agostino 2 , C. Fiorino 3 , S. Broggi 3 1 San Raffaele Scientific Institute, Experimental Imaging Centre, Milano, Italy ; 2 DoseVue NV, Research and Development, Turnhout, Belgium ; 3 San Raffaele Scientific Institute, Medical Physics, Milano, Italy Purpose or Objective The main objective of this work was the development and the preliminary test of a novel real-time 2D dosimetry approach for CyberKnife quality assurance using radioluminescence imaging (RLI) with a commercial CMOS detector. In particular, the possibility to verify collimators field size was investigated. Radioluminescence light was generated by two flexible and thin scintillators film composed respectively of green-emitting and red emitting A CMOS detector was mounted on a photographic tripod and coupled with a F=1.4, 8 mm C-mount lens (Edmund Optics) facing the scintillator film placed on the patient bed, as shown in figure 1. The scintillator film was placed under a 1 cm slab of PMMA. rare earth phosphors. Material and Methods

München, Institute of Radiation Protection, Munich, Germany ; 3 Helmholtz Zentrum München, Institute of Biological and Medical Imaging, Munich, Germany Purpose or Objective Different cell culture experiments and Monte Carlo simulations already showed that gold nanoparticles (AuNPs) can result in a dose enhancement of radiotherapy. Current in vitro results suggest an increased uptake of AuNPs into Hsp70-positive tumor cells after conjugation of AuNPs with cmHsp70.1 antibody. Before the start of in vivo investigation, the dose enhancement effect of functionalized cmHsp70.1 mAb AuNPs will be simulated. Material and Methods The Geant4-DNA toolkit was used to compute the dose enhancement effects of gold nanoparticles in different cellular compartments after x-ray irradiation. In particular, the amount of energy released by photon interactions will be analyzed after penetration of the x- ray beam through the cell. This energy is released by secondary electrons. Especially Auger-electrons contribute exceedingly to the dose enhancement effect for the tested energy spectra (50kVp, 60kVp, 100kVp). Different nanoparticle sizes (4nm, 10nm, 50nm, 100nm) and distribution patterns were used in the simulations. Simultaneously the same simulations are performed with the same geometry in water without AuNPs. The comparison provides the respective dose enhancement factor (DEF) in distinct areas within a cell. This work provides information about localization and energy deposition of the particle events and also the electron spectrum around the AuNPs. To allow for tracking of the nanoparticles via MRI, we are planning to include an Fe3O4 core at the center of the AuNPs used in experiments. Accordingly, we repeated the same set of simulations replacing the pure AuNPs with hybrid AuFeNPs. Results

The DEF is calculated by dividing the results from simulations containing AuNPs by results from respective simulations without AuNPs. Results of simulations with 10^8 photons shot directly at one AuNP are shown in the first figure. Due to the limited range of Auger-electrons, the DEF is at its maximum in immediate range to the AuNP and decreases with increasing range.

Figure 1 RLI acquisition setup in the CyberKnife treatment room . The CMOS is mounted on a tripod and coupled to a C-mount lens facing the film. Dose measurements were performed using the CyberKnife system (Accuray) switching off the main treatment room light during RLI image acquisition; few led lights around the CyberKnife system were on. The CMOS setting was as follows: gain=22, brightness=50 and exposure time=1/100 sec. A sequence of 120 images was acquired every 1 sec

The second figure shows the comparison between the courses of the DEF for simulations with 1 AuNP and 1 AuFeNP respectively. A decrease in dose enhancement was expected, since iron-oxide is less likely to produce