Battistoni, G.

Giacometti, V.

Marafini, M.

Mirabelli, R.

Patera, V.

Pinci, D.

Sarti, A.

Sciubba, A.

Traini, G.

Journal of Physics : Conference Series

English

Archivio della ricerca- Università di Roma La Sapienza

Journal of Physics: Conference SeriesPAPER • OPEN ACCESSMONDO: A tracker for the characterization of secondary fast andultrafast neutrons emitted in particle therapyTo cite this article: R Mirabelli et al 2018 J. Phys.: Conf. Ser. 956 012013 View the article online for updates and enhancements.This content was downloaded from IP address 151.100.47.233 on 10/03/2018 at 16:051Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distributionof this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.Published under licence by IOP Publishing Ltd1234567890 ‘’“”8th Young Researcher Meeting IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 956 (2018) 012013  doi :10.1088/1742-6596/956/1/012013MONDO: A tracker for the characterization ofsecondary fast and ultrafast neutrons emitted inparticle therapyR Mirabelli1,2, G Battistoni3, V Giacometti2,4, V Patera2,4,5, D Pinci2,A Sarti4,5,6, A Sciubba2,4,5, G Traini1,2, M Marafini2,41 Dipartimento di Fisica, Sapienza Universita` di Roma, Roma, Italy2 INFN Sezione di Roma, Roma, Italy3 INFN Sezione di Milano, Milano, Italy4 Centro Fermi, Museo Storico della Fisica e Centro Studi e Ricerche “E. Fermi”, Roma, Italy5 Dipartimento di Scienze di base e Applicate per l’Ingegneria, Sapienza Universita` di Roma,Roma, Italy6 INFN Sezione Laboratori Nazionali di Frascati, Frascati, ItalyE-mail: riccardo.mirabelli@roma1.infn.itAbstract. In Particle Therapy (PT) accelerated charged particles and light ions are usedfor treating tumors. One of the main limitation to the precision of PT is the emission ofsecondary particles due to the beam interaction with the patient: secondary emitted neutronscan release a significant dose far from the tumor. Therefore, a precise characterization oftheir flux, production energy and angle distribution is eagerly needed in order to improve theTreatment Planning Systems (TPS) codes. The principal aim of the MONDO (MOnitor forNeutron Dose in hadrOntherapy) project is the development of a tracking device optimized forthe detection of fast and ultra-fast secondary neutrons emitted in PT. The detector consists ofa matrix of scintillating square fibres coupled with a CMOS-based readout.Here, we present the characterization of the detector tracker prototype and CMOS-baseddigital SPAD (Single Photon Avalanche Diode) array sensor tested with protons at the BeamTest Facility (Frascati, Italy) and at the Proton Therapy Centre (Trento, Italy), respectively.1. IntroductionNowadays Particle Therapy (PT) is more and more diffused as proven by the number oftreatment centers with light ions (mainly protons and carbon ions) that are continuouslyincreasing. The main advantage of PT, compared to conventional radiation therapy, is its powerin concentrating the dose release in the tumor region preserving the surrounding tissues. Thecharged particles, protons and light ions, release the maximum dose at the end of their path inthe well known Bragg Peak: the position of that peak, as well as its width, depends on beamenergy and on type of particles used. The abundant components of secondary particles (neutraland charged particles) produced by the nuclear fragmentation of the beam (and of the target)and by the de-excitation of the isotopes exited by the beam interaction in the matter, has beenpreviously studied [1-3]: charged particles, prompt photons and photons from β+ annihilation.In general, the additional dose due to charged secondary products and photons is negligiblecompared to the beam one. However, the secondary particles have been carefully characterised21234567890 ‘’“”8th Young Researcher Meeting IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 956 (2018) 012013  doi :10.1088/1742-6596/956/1/012013Figure 1. Schematic representation of a neutron double elastic scattering. Measuring protonstracks, kinetic energies and angles, it is possible to calculate the kinematics and establishdirection and energy of the neutrons.because of their usefulness in beam range monitoring and partially contribute to the effectivedose delivered in treatments. For the neutron component instead the characterization is notcomplete: fluxes and energy spectra in function of the emission angle have been measured forthin target [4] and no efficent tracking detector for neutrons are nowadays available in theenergy range of PT interest. Available measurements are based on the combination of differentexperimental setups, e.g. with an extended range Bonner sphere [5] or on the use of detectorswith long and complex calibrations. Secondary neutron production is one of the main causeof Secondary Malignant Neoplasms (SMN), which develop significantly later (many years) afterthe treatment [6]. Therefore, it is crucial to characterise the secondary neutron production inthe patient and the limit of the application of PT in the treatment of paediatric tumors is inthis context evident.The aim of the MONDO project (MOnitor for Neutron Dose in hadrOntherapy) is to characterisethe secondary neutrons production in PT in order to improve the Monte Carlo and the analyticalmodels at the base of the Treatment Planning System (TPS) [7]. A tracker dedicated to themeasurements of neutrons in the energy range of 20 - 400 MeV will be built. Specifically, Sec. 2presents the detector principle of operation, while some results with electrons and protons beamare reported in Sec. 3 testing a detector prototype.2. The MONDO ProjectIn the MONDO tracker the complete reconstruction of the neutrons quadri-momentum isperformed through the detection of recoiled protons emitted by neutrons Double ElasticScattering (DES) with the interacting material. When two consequent recoiled protons emittedin DES are completely contained in the active area of the detector, the energy and the directionof the incoming neutrons are calculated using the following equation:En =Epcos2θ(1)where Ei (i = n, p) is the neutron/proton kinetic energy and θ is the angle between the recoilproton and the incoming neutron. Fig. 1 shows an example of a DES event.The final design of the detector includes a 10 × 10 × 20 cm3 matrix of scintillating plasticfibers (square cross section, 250 μm side) arranged in orthogonal layers. The active volumeacts both as a target for neutrons and as a detector for secondary emitted protons. The lightproduced by the proton interaction with the fibers is collected with a dedicated system developed31234567890 ‘’“”8th Young Researcher Meeting IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 956 (2018) 012013  doi :10.1088/1742-6596/956/1/012013Figure 2. PENELOPE: a MONDO tracker prototype.in collaboration with Fondazione Bruno Kessler (FBK).The readout consists of a SPAD-array built with the same technology presented in [8], but withsome characteristics optimized for our goal. In particular, the sensor trigger logic is based on adouble threshold logic with a smaller pixel size (250× 125 μm).In order to characterise the fibers and to finalize the construction of the MONDO detector, asmall prototype (called PENELOPE) was built (total dimension: 4× 4× 4.8 cm3). The deviceis shown in Fig. 2.3. Experimental resultsPENELOPE was tested both with electrons and protons; its efficiency and light productionwere characterised. The prototype was readout with three different devices: (1) a commercialHamamatsu H10580 PhotomultiplierTube (PMT), (2) a Multianode H8500C and (3) a spad-netsensor (described in the previous Section).3.1. Test with an electron beamIn May 2016 PENELOPE was tested at the Beam Test Facility (BTF) at the Frascati INFNNational Laboratory. The goal of the test beam was the evaluation of the charged produced bya 450 MeV electron crossing a layer of fiber. In fact, at that energy electrons act like a mip(minimum ionizing particles) thus allowing to study the worst case scenario in energy release andlight production. The Hamamatsu PMT response is presented here. Fig. 3 shows a schematicrepresentation of the experimental setup and the average PMT output signal. The integral ofthe signal corresponds to the total charged produced and 250±50 photoelectrons were measured.Considering that the PMT covers an equivalent area of 30 ± 2 layers, the calculated chargedproduced by a single layer is 7.2± 1.4.41234567890 ‘’“”8th Young Researcher Meeting IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 956 (2018) 012013  doi :10.1088/1742-6596/956/1/012013Figure 3. (Left) Experimental setup at the BTF: the area covered by the PMT is smaller thanthe total area covered by PENELOPE. (Right) Average waveform signal produced by the PMT.[9]HV [V]600 700 800 900 1000 1100Efficiency []00.20.40.60.81Efficiencypixel rowpixel columnFigure 4. (Left) Example of an event with a track, in which 6 pixels in a row are activated.(Right) Efficiency in function of the multianode HV.3.2. Test with a proton beamIn May 2017 PENELOPE was tested at the Proton Therapy Center (PTC) at the TrentoHospital, using protons in the energy range of 70 - 230 MeV, which corresponds to the energyspectra of the recoiled protons produced in DES neutron events. The multianode and spad-netsensor responses are presented here.3.2.1. Multianode readout: efficiency A study of the efficiency in function of the multianodeHigh Voltage (HV) supply was performed. The multianode H8500C has 64 pixel (8× 8, 6 mmside) individually readout covering a total area of ∼ 5 × 5 cm2. The efficiency is calculated asthe number of events with at least 6 pixels in the same row showing a signal (i.e. a proton track)over the total number of events (Fig. 4).The efficiency increases with HV. So we decided to operate our multianode with the maximumHV suggested by the multianode data-sheet.3.2.2. Spad-net sensor: tracks reconstruction An analysis of the proton tracks extracted usingthe spad-net sensor was also performed: the single event maps, obtained counting the number51234567890 ‘’“”8th Young Researcher Meeting IOP PublishingIOP Conf. Series: Journal of Physics: Conf. Series 956 (2018) 012013  doi :10.1088/1742-6596/956/1/012013pixel (x)0 2 4 6 8 10 12 14 16pixel (y)01234567800.511.522.533.544.55pixel rowpixel column# photoelectronpixel columprotonsFigure 5. (Left) Expermental setup at the PTC: the area covered by the spad-net sensor isvery small compared to the total area covered by PENELOPE. (Right) Example of a protontrack reconstruction.of photo-electrons detected from each pixel, were fitted with a linear function to reconstructthe proton direction (Fig. 5). In order to reduce the background noise, pixels with less than 2activated spads were not included in the fit.4. ConclusionThe MONDO project is dedicated to the characterization of secondary neutrons produced duringparticle therapy treatments. The system is based on the detection of double elastic scatteringevents (neutron on scintillating fibres) and the readout requirements are quite stringent.The data colleced at BTF and CPT revealed that a fully digital CMOS approach is suitablefor the MONDO tracker. The prototype shows good characteristics in efficiency, trackreconstruction, light production and collection. A new readout sensor (SBAM: SPAD-BasedAcquisition readout for MONDO experiment) is under development: the new design will matchthe tracker geometry and implement a smart discrimination mechanism specifically tailored tothe proton tracks.AcknowledgmentsWe would like to thank Marco Magi (SBAI Department) for his valuable work in the design andconstruction of the mechanical structure of the detector. The authors also thank the BTF andTIFPA staff for beam-time and helpful support during the data taking.The MONDO project is supported by INFN Gruppo V with a Young Researchers Grant (2015-2016) and by SIR (Scientific Independence of young Researchers) MIUR Founding (2015-2018).References[1] Muraro S et al. 2016 Review Article Front. Oncol. 6[2] Mattei I et al. 2016 Phys. Med. Biol. 62 1438[3] Agodi C et al. 2012 NIM B 23 1-8[4] Gunzert-Marx K et al. 2008 New Journal of Physics 10[5] Mares C et al. 2016 Phys. Med. Biol. 61 4127-4140[6] Newhauser W and Durante M 2009 Phys. Med. Biol. 54 2277-2291[7] Marafini M et al. 2017 Phys. Med. Biol. 62 3299-3312[8] Braga L et al. 2014 IEEE Journal of Solid-State Circuits 49 301[9] Mirabelli R et al. 2017 IEEE Transactions on Nuclear Science Submitted

MONDO: A tracker for the characterization of secondary fast and ultrafast neutrons emitted in particle therapy

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MONDO: A tracker for the characterization of secondary fast and ultrafast neutrons emitted in particle therapy

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