ESTRO 2020 Abstract Book

S700 ESTRO 2020

.This deviation in the stack method might be due to the uncertainty of the TLD sheet density obtained from the composition, and that in the parallel incidence method might be due to the gap between the slab phantom and the TLD sheet. Another possible factor is that the temperature uniformity of the reading system for the TLD sheet might have a certain slope toward the edge of the sheet. In addition, there might be energy dependence. Conclusion We evaluated the PDD of high-energy electron beams using a new material TLD sheet and confirmed its usefulness. The TLD sheet confirmed that the dose could be accurately evaluated at a depth deeper than the maximum dose depth. However, the build-up area was underestimated. This problem could be solved by improving the reading mechanism. PO-1327 Performances of new beam monitors based on Ultra Fast Silicon Detectors for proton therapy Z. Shakarami 1,2 , M. Donetti 3 , F. Fausti 2 , M. Ferrero 1,2 , S. Giordanengo 2 , O. Hammad Ali 1,2 , M. Mandurrino 2 , O.A. Marti Villarreal 1,2 , F.M. Milian 2,4 , V. Monaco 1,2 , R. Sacchi 1,2 , V. Sola 1,2 , A. Staiano 2 , A. Vignati 1,2 , R. Cirio 1,2 1 Universita Degli Studi di Torino, Physics department, Torino, Italy ; 2 INFN, National Institute of Nuclear Physics, Torino, Italy ; 3 CNAO, National Center of Oncological Adrotherapy, Pavia, Italy ; 4 Universidade Estadual de Santa Cruz, Department of Exact Sciences and technologies, Ilheus, Brazil Purpose or Objective To overcome many limitations of gas detector systems, such as reduced sensitivity and slow charge collection, sensors based on the Ultra Fast Silicon Detectors (UFSDs) technology are being developed. The main advantages of UFSDs are fast charge collection (~1 ns) and excellent time resolution (few tens of ps). A segmented UFSD sensor could allow discriminating and counting single protons up to high fluxes of therapeutic beams (10 8 p/s cm 2 ) and the time resolution could be exploited for measuring the proton beam energy, using time-of-flight (TOF) techniques. Material and Methods Two prototypes of strip detectors with different geometries and doping modalities, to improve radiation hardness, were developed. The sensor design for the first prototype was optimized to provide the possibility to count individual protons up to 10 8 p/cm 2 s, with an active thickness of 50 µm. A dedicated VLSI readout chip has been designed and produced to deal with a single proton signal of nanosecond duration and with 10 8 Hz signal rate on each channel. In the second prototype, UFSD sensors of 70 and 120 µm total thickness are positioned in a telescope configuration to allow the measurement of protons’ TOF (figure 1). To minimize the time-walk effect, the time of arrival of protons is obtained using a constant fraction discriminator algorithm. Through analytical approximation validated with Geant4 simulations, the corresponding beam energies are obtained from TOF values.

Figure1: Two UFSD strip sensors in a telescope for beam energy measurement. Results Both the detectors were tested first in laboratory and then with two different clinical proton beams. Beam flux, pile- up inefficiency, signal-to-noise ratio, accuracy of TOF and mean energy measurements were determined from the analysis of the collected data. Using correction methods, the pile-up effect was mitigated to lower than 2% in therapeutic fluxes. The difference between calculated and nominal energies at the isocenter, for various energies and distances between the two sensors, reading out only one channel per sensor, showed an uncertainty lower than 0.5 MeV. Conclusion This work demonstrates the feasibility of using the UFSD technology, combined with a dedicated read out electronic in the case of the counter prototype, as an option to control the beam flux and position in particle therapy. The preliminary results of the beam energy prototype indicate that the clinical requirements (accuracy in the range measurement within 1 mm) can be achieved. In the next future, multiple channels from each sensor will be read out, to improve the statistics, an optimized readout electronics will be developed, along with a high precision mechanical support.