Abstract Book

S928

ESTRO 37

the acoustic signal, a lead block was submerged in water and placed partially or totally in the irradiation field. Electromagnetic shielding was required for all sensitive electronic components due to the presence of strong electromagnetic fields in the treatment rooms.

Figure 1. Scheme of the experimental setup Results

The experimental setup was optimized according to the results of the Monte Carlo and analytical simulations. According to spectral analysis, the optimal frequency range of ultrasonic transducers was found to be around 200 kHz. The bandwidth of transducers had a strong impact on the detectability of the photoacoustic signal. If lead blocks are used to amplify the signal, its size must be chosen so that its resonance frequency matches that of the transducer. Photo and protoacoustic signals were detected with both photon and proton beams and its shape, position and intensity are in the range of the predicted values.

Conclusion Beam profile measurements of FOX gel sheets using the onboard MRI of the MR-Linac were comparable to microDiamond, EBT-3 film, and FOX gel sheets read out optically. Future work will include improving the fabrication of the gel sheets to achieve uniform sheet thickness and acquiring MR images with more averaging. The FOX gel sheets demonstrated their usefulness as an alternative to film and other conventional detector measurements for beam profile analysis using onboard MR imaging in MR-IGRT systems. EP-1734 Photo- and proto- acoustic dose monitoring in radiosurgery and proton beams D. Sanchez-Parcerisa 1 , O. Giza 1 , J. Camacho 2 , V. Sanchez- Tembleque 1 , S. Avery 3 , J. Udias 1 1 Universidad Complutense de Madrid, Departamento de Fisica Atomica- Molecular y Nuclear, Madrid, Spain 2 CSIC, ITEFI, Madrid, Spain 3 University of Pennsylvania, Department of Radiation Oncology, Philadelphia, USA Purpose or Objective This work describes the development of an acoustic sensitive device that can be used for range monitoring and dosimetry of clinical beams. It comprises the optimization, performance and analysis of a set of experimental measurements in radiosurgery and proton beams. Material and Methods The experimental setup consists of several ultrasonic transducers of different resonance frequencies and bandwidths, a combination of preamplifiers and differential amplifiers with filtered outputs and a digital oscilloscope. Simulations of the experimental setup were carried out to study the optimal measurement geometry and choice of transducer. The dose distributions were calculated with Monte Carlo code FLUKA, while the acoustic simulations were performed with analytical wave transport code k-Wave. The temporal profiles of the dose pulses, in the order of µs, were measured with a scintillating crystal coupled with a PMT and used as an input to the acoustic simulation. Measurements were performed in a Cyberknife™ radiosurgery beam and a PBS proton beam. Both small and wide fields were irradiated on a water tank and in some cases, in order to amplify

Figure 2. Measured VS simulated acoustic waves Conclusion Photoacoustic simulation with FLUKA and k-Wave can reproduce the experimental response of acoustic transducers in dose monitoring applications. The proposed setup can detect photoacoustic and protoacoustic signals originating from the penumbral areas of the treated fields and with the relevant image analysis, can be used to monitor the position of the proton Bragg peak with mm accuracy. EP-1735 Pixelated semiconductor detectors for next generation imaging in ion beam radiotherapy M. Martisikova 1,2 , T. Gehrke 1,2,3 , R. Felix Bautista 1,2,3 , C. Amato 1,2 , G. Arico 1,2,3,4 , B. Hartmann 1,2,3,4 , R. Gallas 1,2,3 , M. Reinhart 1,2,3 , T. Gaa 1,2,3 , O. Jäkel 1,2,5 1 German Cancer Research Center DKFZ, Department of Medical Physics, Heidelberg, Germany 2 National Institute for Radiation Oncology NCRO, Heidelberg Institute for Radiation Oncology HIRO- Heidelberg- Germany, Heidelberg, Germany