Few cross section measurements have been performed at the n TOF facility at CERN with the aim of supplying nuclear data for some neutron-induced reactions of importance in Neutron Capture Therapy. In this paper, a brief introduction to the topic will be presented as well as a discussion on the status of the nuclear data available prior to the executions of the experiments

Ogállar, F.

Porras, I.

Praena, J.

Sabaté-Gilarte, M.

Torres-Sánchez, P.

Scientific Open-access Literature Archive and Repository

DOI 10.1393/ncc/i2019-19137-3Colloquia: EuNPC 2018IL NUOVO CIMENTO 42 C (2019) 137Nuclear data program for Neutron Capture Therapyat the n TOF facility at CERNF. Ogállar(1)(2), M. Sabaté-Gilarte(2)(3)(∗), P. Torres-Sánchez(1),I. Porras(1), J. Praena(1), J. M. Quesada(3), T. Wright(4), S. Bennett(4),C. Lederer-Woods(5), S. J. Lonsdale(5), R. Garg(5)and The n TOF Collaboration(1) Dpto. de F́ısica Atómica, Molecular y Nuclear, Universidad de Granada - Granada, Spain(2) European Organization for Nuclear Research (CERN) - Geneva, Switzerland(3) Dpto. de F́ısica Atómica, Molecular y Nuclear, Universidad de Sevilla - Sevilla, Spain(4) Dpt. of Physics and Astronomy, University of Manchester - Manchester, UK(5) Sch. of Physics and Astronomy, University of Edinburgh - Edinburgh, UKreceived 5 February 2019Summary. — Few cross section measurements have been performed at the n TOFfacility at CERN with the aim of supplying nuclear data for some neutron-inducedreactions of importance in Neutron Capture Therapy. In this paper, a brief intro-duction to the topic will be presented as well as a discussion on the status of thenuclear data available prior to the executions of the experiments.1. – Introduction1.1. Neutron Capture Therapy . – NCT is a selective binary experimental radiotherapybased on the neutron irradiation of a tumour previously loaded with a suitable stableisotope. Incoming neutrons induce a high Q-value nuclear reaction in the isotope, causingthe emission of high LET (Linear Energy Transfer) radiation with an energy depositionrange of 5 to 9 μm, which is comparable to the cancerous cell size. As a result of theenergy deposition, the cancer cell is damaged. 10B is the isotope that is normally usedin this radiotherapy, and 10B(n, α)7Li the reaction induced by neutrons reaching thetumour. In the past, patients were taken to nuclear reactors to receive the necessaryneutron irradiation, this posed logistical problems that significantly limited the potentialof this therapy. Nowadays, the development of accelerator-based neutron sources forNCT opens the possibility to implement this therapy in hospitals [1], taking advantageof more versatile and safe neutron beams. This paradigm shift inaugurates a new era(∗) E-mail: marta.sabate.gilarte@cern.chCreative Commons Attribution 4.0 License (http://creativecommons.org/licenses/by/4.0) 12 F. OGÁLLAR et al.for NCT, therefore, many aspects of this therapy must be studied in detail in orderto improve its therapeutic outcome. The use of 33S as a cooperative target to 10B wasproposed in 2008 [2,3]. The most probable neutron-induced reaction channel of this stableisotope is 33S(n, α), presenting important resonances above 10 keV. These resonances canbe used to increase the delivered dose to the tumour loaded with 33S, especially whenusing accelerator based neutron sources, which provide neutrons in the epithermal rangeof energy. Regarding the dosimetry specifications, the International Commission onRadiation Units and Measurements (ICRU) recommends that the delivered dose shouldhave less than 5% deviation from the prescribed dose [4]. Therefore, a good knowledgeof the nuclear reactions involved is required; what will lead to a better control of thereleased dose through more accurate estimation of the therapy safety margins. Moreover,chlorine is present in human body tissue, especially in the brain where it represents afraction of 0.3% in mass. Accordingly, neutron-induced reactions on chlorine may play animportant role. Using Monte Carlo simulations, it was concluded that 35Cl(n, p)35S and35Cl(n, γ)36Cl reactions should be included accurately in NCT dosimetry studies [5, 6],due to their cross section resonances in the epithermal region, the high LET of thereleased proton in the first reaction and the high Q-value of the 35Cl(n, γ)36Cl reaction(approximately 8.58 MeV).In order to improve the dosimetry studies of this therapy and to explore the po-tential of 33S as a cooperative target to 10B, several cross section measurements wereperformed at the neutron time of flight facility (n TOF) at the European Organizationfor Nuclear Research (CERN), since the status of the available nuclear data was notoptimal according to the recommendations of the ICRU.1.2. Neutron Time Of Flight facility at CERN . – n TOF is a spallation neutron sourcebased on a 20 GeV/c proton beam impinging on a lead target [7,8]. n TOF is a uniquefacility in the world due to the state of the art of its detectors, the data acquisition systemand the characteristics of its neutron beam, i.e., high instantaneous flux in a wide energyrange —from few meV to several GeV—, high energy resolution which allows resolvingresonances and low repetition rate of the primary pulsed proton beam. The facility is inoperation since 2001 and features two experimental areas: n TOF-EAR1 [9], located at185 m from the spallation target along the horizontal direction of the incoming protonbeam, and n TOF-EAR2 [10], along the vertical direction at 20 m from the target, whichwas built in 2014. n TOF is mainly dedicated to measure neutron-induced cross sectionsfor nuclear technology, astrophysics, basic nuclear physics and medical physics.2. – Nuclear data status before the n TOF measurementsThe 33S(n, α)30Si cross section data available showed important deficiencies, as dis-cussed in [11], with no experimental data between thermal (25 meV) and 10 keV, andmajor discrepancies at the thermal point. There was only one (n, α) experiment resolvingresonances [12]. An important discrepancy was found between such experiment and thedescription of the most important resonance by means of the unique transmission mea-surement [13]. With respect to the evaluated nuclear data files, only EAF-2010 includesthe resonance, but with a lower average cross section than the one reported in ref. [12].For the 35Cl(n, p)35S reaction, the cross section data showed significant discrepanciesamong existing data sets in both the resonance region and the thermal point, leadingto some complications in the nuclear data evaluation [14], as it is widely discussed inref. [5].NUCLEAR DATA PROGRAM FOR NEUTRON CAPTURE THERAPY AT n TOF 3The reaction 14N(n, p)14C is of great importance in NCT, with the biggest contribu-tion to the energy deposition in brain tissue for neutrons with energies below 50 eV, inabsence of 10B [15]. However, as explained in ref. [5], some discrepancies with potentiallycrucial consequences for NCT were identified in the available nuclear data.The quality of the data available for the 35Cl(n, γ)36Cl reaction in the resonance re-gion limited the accuracy of the cross section determination. This has led to discrepanciesin the cross section evaluations across the major libraries, evidenced in ref. [6]. The onlymeasurement in the resonance region was performed using natural Chlorine [16], and themeasurements of the cross section at the thermal point showed too large discrepanciesfor NCT dosimetry calculations, as shown in ref. [6].3. – Experiments3.1. 33S(n, α)30Si. – The measurement of the cross section was performed at n TOF-EAR1 for the resonance region [17] and at n TOF-EAR2 for neutron energies down to0.01 eV [11]. In both cases, a setup of in-beam gaseous micromegas detectors [18] wasused. Two important results were found: the 1/v behaviour below 10 keV, and a muchhigher area of the resonance at 13.5 keV than the one obtained in ref. [12], in agreementwith the transmission measurement [13]. Fig. 1 (left) shows the combination of thedata obtained in both experiments for the cross section measurement. The potential of33S as a cooperative target for NCT was evaluated in ref. [19] using the new n TOFcross section data, where it can be seen that adding sulfur could be very appropriate fortreating superficial tumors.3.2. 14N(n, p)14C and 35Cl(n, p)35S. – A combination of in-beam micromegas detec-tors and off-beam DSSSD detectors was used in our experimental setup [5] at n TOF-EAR2. With the micromegas detectors collecting most of the statistics, the DSSSDswere used to study any possible anisotropy of the emitted protons in the most importantresonances. The analysis of the data is an ongoing work; preliminary results of the yieldare shown in fig. 1 (right), where cross sections are shown up to 100 keV. Our goal is toextend the neutron energy range up to 500 keV or even 1 MeV. In this experiment, themicromegas setup has proved to be suitable for measuring (n, cp) reaction cross sectionsfor low energy charged particles (approximately 400 keV) in the neutron energy rangewhich extends from thermal up to 100 keV.Fig. 1. – Differential cross sections obtained at n TOF using micromegas detectors: 33S(n, α)30Sireaction (left); preliminary results for the 14N(n, p)14C and 35Cl(n, p)35S reactions (right).4 F. OGÁLLAR et al.3.3. 35Cl(n, γ)36Cl. – In order to measure the 35Cl(n, γ)36Cl cross section, four C6D6liquid scintillators [20], widely used for capture measurements at n TOF, were employedat n TOF-EAR1. The data analysis of this experiment is at an early stage, but some ofthe 35Cl(n, γ)36Cl resonances have been already identified.4. – ConclusionsNCT faces a new era due to the development of accelerator-based NCT facilities.There is room to improve its therapeutic outcome from many different perspectives,such as the investigation of alternative and cooperative isotopes to 10B, or the improve-ment of dosimetric calculations, which requires accurate nuclear data that is not alwaysavailable. For this reason, in recent years, important efforts have been made by then TOF Collaboration seeking to solve this lack of data by conducting experiments aimedto obtain the cross section of those reactions of interest for this therapy. Four reactionshave been studied so far and the data analysis of some of them is a work in progress.The resulting nuclear data will, ideally, allow the NCT community to plan treatmentscapable of increasing the dose delivered to tumours, improving the chances of patientsurvival.∗ ∗ ∗Acknowledgments: this work was supported by the Spanish projects Mineco (FPA2013-47327-C2-1-R, FPA2016-77689-C2-1-R, FPA2011-28770-C03-0, FPA2014-53290-C2-2-P,FIS2015-69941-C2-1-P) ; J. de Andalućıa (P11-FQM-8229, FQM-220, P11-FQM-822);CEI-Biotic Granada (P-BS-64); the Spanish Association Against Cancer (AECC) (GrantNo. PS16163811PORR); the European Research Council ERC-2015-STG Nr.677497; theScience and Technology Facilities Council UK (ST/M006085/1); and the funding agenciesof the participating institutes. Special thanks to the n TOF Collaboration at CERN.REFERENCES[1] KREINER A.J. et al., Rep. Pract. Oncol. Radiother. 21 95-111 (2016).[2] PORRAS I., Phys. Med. Biol. 53 L1 (2008).[3] PORRAS I. et al., Appl. Radiat. Isot. 69 1838-41.3 (2011).[4] ICRU Rep. 46 (1992).[5] PRAENA J. et al., CERN Reports CERN-INTC-2017-039 INTC-P-510 (2017).[6] PORRAS I. et al., CERN Reports CERN-INTC-2018-010 INTC-P-541 (2018).[7] RUBBIA C. et al., CERN/LHC/98-02 (EET) (1998).[8] GUNSING F. et al., Eur. Phys. J. Plus 131:37 (2016).[9] GUERRERO C. et al., Eur. Phys. J. A 49: 27 (2013).[10] WEISS C. et al., NIM A 799 (2015).[11] SABATÉ-GILARTE M. et al., EPJ Web of Conferences 146 08004 (2017).[12] WAGEMANS C. et al., Nucl. Phys. A 469 497-506 (1987).[13] CODDENS G.P. et al., Nucl. Phys. A 469 480-96 (1987).[14] SAYER R.O. et al., Phys. Rev. C 73 044603 (2006).[15] GOORLEY J.T. et al., Med. Phys. 29 145-56 (2002).[16] GUBER K. H. et al., Phys. Rev. C 65 058801 (2002).[17] PRAENA J. et al., Phys. Rev. C 97 064603 (2018).[18] CHARPAK G. et al., Nucl. Instr. Meth. Phys. Res. A 478 26-36 (2002).[19] SABATÉ-GILARTE M. et al., Rad. Prot. Dos. pp. 1-4 (2017).[20] PLAG R. et al., Nucl. Instrum. and Meth. A 496 425-436 (2003).

Nuclear data program for Neutron Capture Therapy at the n TOF facility at CERN

http://eprints.bice.rm.cnr.it/20540/1/ncc11877.pdf

Nuclear data program for Neutron Capture Therapy at the n TOF facility at CERN

Abstract

Similar works

Full text

Available Versions

Scientific Open-access Literature Archive and Repository